Amniotic fluid volume anomalies (polyhydramnios, oligohydramnios): clinical guidelines

List of Abbreviations

Terms and Definitions

See Section 1.1.

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Amniotic fluid (AF) volume anomalies include its increase – polyhydramnios and decrease – oligohydramnios (extreme form: complete absence of amniotic fluid – anhydramnios) (1). Assessment of AF is an indicator reflecting fetal well-being (2).

A reliable assessment that allows rapid, accurate, non-invasive, and real-time measurement of AF volume is ultrasound examination (ultrasound) (3)

The amount of AF should be evaluated either subjectively, defining it as "normal" or "abnormal" (decreased or increased), or semiquantitatively, by measuring the maximum vertical pocket (MVP) of amniotic fluid or the amniotic fluid index (AFI) (4). An abnormal amount of AF may indicate a complicated pregnancy, or a pregnancy that is in the “at-risk” pregnancy zone (5).

Traditionally, oligohydramnios is defined as an AFI ≤ 5 cm or MVP ≤ 2 cm (1,6), whereas polyhydramnios is defined as an AFI ≥ 25 cm or MVP ≥ 8 cm (1,7,8);

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

Amniotic fluid (AF) is the fluid surrounding the fetus. Early in pregnancy, AF is largely a product of maternal serum and resembles plasma due to hydrostatic and osmotic pressure. After 8 weeks of gestation, the fetal kidneys begin to function and produce urine, which becomes a key component of AF after 23–25 weeks (9). Amniotic fluid has a weakly alkaline or neutral reaction. During normal pregnancy, the amniotic fluid volume changes as follows: 6 weeks – 5 mL; 10 weeks – 30 mL; 16 weeks – 180 mL; 20 weeks – 350 mL; 22 weeks – 650 mL; 28 weeks – 950 mL; 30 weeks – 900 mL; 40 weeks – 750 mL (6,10). Alterations in fetal homeostasis affect the volume of fetal urine production, swallowing, and fluid secretion by the lungs; in this regard, the AF volume indirectly reflects the fetal condition. The daily volume of urine excreted by the fetus is approximately 30% of its body weight (11). The rate of fetal urination decreases in conditions associated with placental dysfunction (e.g., preeclampsia, fetal growth restriction) and increases in conditions associated with heart failure (e.g., fetal anemia, supraventricular tachycardia, twin-to-twin transfusion syndrome) (12). The intensity of fetal swallowing increases as pregnancy progresses, reaching a maximum by the 3rd trimester. Impairments of swallowing are observed in fetuses with neurological anomalies, such as anencephaly, as well as with esophageal and duodenal obstruction (13). The fetal lungs actively secrete fluid; approximately 50% of this fluid (170 mL/day) is swallowed, and the remainder enters the amniotic cavity, which serves as the basis for fetal lung maturity testing (14). Fetal urination and swallowing, lung fluid secretion, and intramembranous absorption (exchange between AF and the fetal bloodstream) make the greatest contributions to the AF volume; the integration and balance between fluid influx and efflux via these pathways determine the final AF volume (15). The total amount of AF does not change significantly from day to day, yet a complete turnover occurs daily. In the 3rd trimester, within 24 hours, amniotic fluid turnover reaches a volume of 1000 mL (16). Maternal pathologies also affect fetal homeostasis. Thus, severe dehydration increases blood osmolarity. Similarly, maternal hyperglycemia can lead to increased fetal diuresis and polyhydramnios (17).

The role of the amnion in controlling the volume of amniotic fluid, specifically its function in absorbing fluid from the uterine cavity, continues to be studied. The fetal membranes represent a multilayered membrane with a through-transport system, including a network of intercellular channels between amniocytes, the porous structure of their basement layer, the reticular structure of the compact layer, clefts among cytotrophoblast cells, a permeable matrix, and finally, maternal microvessels in the decidua (6,10). Morphological or functional impairments of the fetal membranes caused by various exo- or endogenous factors (infections, hormonal imbalance, extragenital maternal pathology, substance abuse) can lead to amniotic fluid volume abnormalities.

Moderate polyhydramnios is most often idiopathic; the two most common pathological causes of polyhydramnios are maternal diabetes mellitus and congenital fetal anomalies. Additionally, other causes include congenital infection and alloimmunization (see Table 1) (18).

Table 1

*Association with polyhydramnios is characteristic of large sizes (≥5 cm) (19).

An abnormal amniotic fluid volume, especially in combination with other ultrasound markers, may be associated with chromosomal abnormalities, copy number variations (numerical and structural chromosomal aberrations, including at the submicroscopic level - microdeletion syndromes), and monogenic disorders (20,21).

The frequency of chromosomal abnormalities in apparently isolated idiopathic polyhydramnios is 2.1%, and the cumulative frequency of monogenic disorders reaches 5.6% (22).

^[1] Bartter syndrome is a rare genetic mutation involving a defect in the loop of Henle, inherited in an autosomal recessive manner; the primary link in the pathogenesis is the loss of the kidneys' ability to retain potassium.

1.3 Epidemiology of the Disease or Condition

Polyhydramnios occurs in 1-2% of all pregnancies and is frequently an incidental finding in asymptomatic women (23,24). In term pregnancies, the prevalence of idiopathic polyhydramnios is 0.3% (25). Two types of polyhydramnios are distinguished: acute and chronic polyhydramnios, which differ in the rate of amniotic fluid accumulation. Therefore, assessing the amniotic fluid volume dynamically throughout pregnancy is of great importance.

If the etiology of excessive amniotic fluid volume is not determined, polyhydramnios is termed "idiopathic"; it accounts for approximately 60-70% of polyhydramnios cases in published studies and is diagnosed in about 1% of pregnancies (26). Oligohydramnios complicates 4.4% of all term pregnancies, whereas in preterm gestation the frequency of oligohydramnios is less than 1% (27).

Amniotic fluid volume abnormalities, both oligohydramnios and polyhydramnios, are associated with adverse perinatal outcomes. Specifically, a study examining pregnancy outcomes in women with oligohydramnios (AFI ≤5 cm) compared to women with AFI >5 cm revealed that oligohydramnios was more frequently associated with: labor induction (42 vs. 18%), stillbirth (1.4 vs. 0.3%), fetal distress (48 vs. 39%), a higher rate of neonatal intensive care unit admission (7 vs. 2%), meconium aspiration (1 vs. 0.01%), and neonatal mortality (5 vs. 0.3%) (28). In a similar study evaluating adverse outcomes of idiopathic polyhydramnios, an increased rate of obstetric complications (such as preterm birth, fetal malpresentation, various fetal developmental anomalies) and a 2- to 5-fold increase in perinatal mortality were reported (29). It is worth noting that polyhydramnios increases perinatal mortality to a lesser extent than oligohydramnios (30).

1.4 Features of Coding the Disease or Condition

O40 – Polyhydramnios

O41 – Other disorders of amniotic fluid and membranes

O41.0 – Oligohydramnios (oligohydramnios without mention of rupture of membranes)

O41.8 – Other specified disorders of amniotic fluid and membranes

O41.9 – Disorder of amniotic fluid and membranes, unspecified

1.5 Classification of the disease or condition

Table No. 1 (1,31)

Mild polyhydramnios accounts for approximately 65-70% of all cases, moderate for 20%, and severe for <15% (31). The likelihood of a congenital fetal anomaly is significantly higher with a greater degree of polyhydramnios (32).

Table No. 2

Classification of oligohydramnios severity (33)

1.6 Clinical presentation of the disease or condition

Pregnant women diagnosed with polyhydramnios or oligohydramnios most often have no specific symptoms and do not present with complaints (34,35). Polyhydramnios may be suspected due to a discrepancy between the fundal height and the gestational age, but more frequently, as with oligohydramnios, it is an incidental finding discovered during an ultrasound performed for other indications (36).

In marked polyhydramnios (see Table 2), patients may complain of dyspnea, a feeling of tightness in the abdomen, and lower extremity edema (34), as well as varicosities of the lower extremities and vulva, and rarely oliguria (due to ureteral compression).

Polyhydramnios, especially in combination with fetal malpresentation, preterm birth (PTB), or preterm premature rupture of membranes (PPROM), can lead to umbilical cord prolapse and/or prolapse of small fetal parts (37). In the postpartum period, polyhydramnios carries higher risks of postpartum hemorrhage (PPH) due to uterine overdistention by the excessive amniotic fluid volume (38).

As previously noted, polyhydramnios is most often detected in the third trimester of pregnancy and less frequently at 18-22 weeks of gestation; idiopathic polyhydramnios is most commonly found at 31-36 weeks (36). No association has been reported between idiopathic polyhydramnios and preterm birth. There is evidence that mild polyhydramnios occurs in the majority of cases (approximately 80% overall and 90% in term pregnancies; for details, see Table No. 3) (25).

Table No. 3

* Probability of antenatal verification (diagnosis)

** Probability of postnatal diagnosis (when not detected prenatally)

The risk of fetal/neonatal developmental anomalies logically correlates with the severity of polyhydramnios. The risk of identifying developmental anomalies in a newborn that were not diagnosed antenatally is 10% in severe polyhydramnios, whereas in mild and moderate polyhydramnios their frequency is only 1% and 2%, respectively (Table 2). This fact highlights the complexity of ultrasound diagnostics in severe polyhydramnios.

It is important to note that idiopathic polyhydramnios is a diagnosis of exclusion (!), and the etiology of increased amniotic fluid volume not identified during pregnancy may become apparent after delivery. Determining the causes of polyhydramnios will depend on its severity, the presence of structural anomalies, and gestational age. First of all, in cases of polyhydramnios, a detailed fetal ultrasound is necessary to rule out developmental anomalies (39). It is important to assess fetal size and growth rate, since idiopathic polyhydramnios may be associated with macrosomia, whereas fetal growth restriction associated with polyhydramnios carries a high risk of genetic abnormalities, most commonly trisomy 13 or 18 (40, 41).

The diagnosis of oligohydramnios in the second trimester is more often associated with fetal developmental anomalies, whereas in the third trimester it is of unclear etiology in the majority of cases (in a study by Shipp, idiopathic oligohydramnios in the second trimester accounted for only 4% of cases, whereas in the third trimester it occurred in 52%) (42). In cases of oligohydramnios diagnosed in the second trimester, pulmonary hypoplasia is the most significant predictor of fetal mortality; the mortality rate from second-trimester oligohydramnios can reach up to 90%, with an 87% incidence of pulmonary hypoplasia. The most severe degree of pulmonary hypoplasia occurs with oligohydramnios developing before or between 16–24 weeks of gestation, when the terminal bronchioles and respiratory divisions of the fetal lung develop. A low AFI in the second and early third trimesters also increases the likelihood of limb contractures and congenital defects due to compression syndrome (43).

2. Diagnostics, medical indications and contraindications for diagnostic methods

Comment: Ultrasound is a safe diagnostic method during pregnancy; nevertheless, it should be performed only for medical indications, following the ALARA ("as low as reasonably achievable") concept to reduce the total thermal index applied to the fetus (44).

Comment: It is important to assess fetal growth, as idiopathic polyhydramnios may be associated with macrosomia, whereas fetal growth restriction associated with polyhydramnios carries a high risk of fetal genetic abnormalities, including the most common trisomies of chromosomes 18 and 21 (39–41).

Comment: Indications for prenatal CMA/NGS are described in the clinical guidelines "Application of High-Throughput Sequencing and Molecular Karyotyping on Microarrays in the Prenatal Period" (45).

The diagnosis of oligohydramnios in the second trimester is more often associated with fetal anomalies, whereas in the third trimester it is of unclear etiology in the majority of cases (in a study by Shipp, idiopathic oligohydramnios in the second trimester accounted for only 4% of cases, whereas in the third trimester it occurred in 52%) (42). In cases of oligohydramnios diagnosed in the second trimester, pulmonary hypoplasia is the most significant predictor of fetal mortality; the mortality rate from second-trimester oligohydramnios can reach up to 90%, with an 87% incidence of pulmonary hypoplasia. The most severe degree of pulmonary hypoplasia occurs with oligohydramnios developing before or during 16–24 weeks of gestation, when the terminal sacs of the fetal lung develop. A low AFI in the second and early third trimesters also increases the likelihood of limb contractures and congenital defects due to compression syndrome (42).

2.1 Complaints and Anamnesis

See Section 1.6

2.2 Physical Examination

Comment: PPROM accounts for more than 37% of oligohydramnios cases diagnosed in the second and third trimesters (42).

^[1] The algorithm for performing a speculum examination, as well as the tests used to diagnose amniotic fluid leakage, are described in the Russian Society of Obstetricians and Gynecologists (RUOG) clinical guidelines "Preterm Birth".

2.3 Laboratory Diagnostics

• When fetal hydrops is detected, it is recommended, if not previously performed, to determine the mother's ABO blood group and Rh factor, as well as to clarify the family obstetric and hereditary history (18, 70, 103).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: Congenital infections such as parvovirus, cytomegalovirus, or syphilis can lead to polyhydramnios under various pathological conditions, including fetal anemia or cardiac dysfunction. Congenital infection may manifest with additional ultrasound signs such as non-immune fetal hydrops (NIFH), hepatomegaly, splenomegaly, and/or placentomegaly.

• In cases of polyhydramnios associated with NIFH or additional ultrasound signs of intrauterine infection, it is recommended to perform Doppler ultrasound of the fetal middle cerebral artery peak systolic velocity (MCA PSV) to detect fetal anemia (1, 8, 18).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

• For patients whose personal/family history suggests a hereditary condition, it is recommended to undergo genetic counseling for further evaluation (e.g., in hereditary forms of anemia leading to NIFH and polyhydramnios) (50).

• It is recommended to perform further evaluation of a pregnant woman with polyhydramnios to rule out diabetes (51).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: Maternal diabetes is the cause of polyhydramnios in 8–25% of cases. In diabetes, it is hypothesized that maternal hyperglycemia leads to fetal hyperglycemia followed by osmotic diuresis into the amniotic fluid. This hypothesis is supported by the observation that glucose concentration in the amniotic fluid frequently correlates with amniotic fluid volume (52). There is no evidence supporting the benefit of repeat GDM screening; however, it can be considered if polyhydramnios is detected in the third trimester and/or more than 1 month has passed since the diabetes screening (53).

Alloimmunization^[1] can lead to fetal anemia, fetal hydrops, and polyhydramnios.

^[1] Alloimmunization, or the formation of maternal antibodies, can lead to varying degrees of transplacental passage of these antibodies into the fetal bloodstream. Depending on the degree of antigenicity, as well as the quantity and type of antibodies involved, this transplacental passage can lead to hemolytic disease of the fetus and newborn (101).

2.4 Instrumental Diagnostics

The methodology for performing a semiquantitative assessment of amniotic fluid volume with MVP determination includes the following features (1,8):

• holding the ultrasound transducer perpendicular to the maternal position;

• determining clear boundaries of the upper and lower edges of the fluid pocket;

• measuring the maximum free pocket of amniotic fluid with a width of more than 1 cm;

• using color Doppler mapping to establish the absence of the umbilical cord when its absence is in doubt.

AFI is calculated by summing the values of four vertical amniotic fluid pockets, one in each quadrant of the uterus (8)

Polyhydramnios in singleton pregnancies is defined as an MVP ≥8 cm or an AFI ≥25 cm (54).

Comment: In cases of oligohydramnios, measuring MVP when assessing amniotic fluid volume appears more appropriate, as the use of AFI increases the frequency of oligohydramnios diagnosis and the rate of labor induction without improving perinatal outcomes (55). Studies comparing ultrasound results with dye-dilution amniotic fluid volume measurement have shown that MVP may be more effective for detecting oligohydramnios, and AFI for detecting polyhydramnios (8,56). When determining AFI, the threshold value is typically considered to be 24 cm or 25 cm, depending on whether the 95th or 97th percentile is chosen (7). In research studies, a value of ≥25 cm is usually chosen as the threshold for polyhydramnios (24). A study by Odibo et al noted that the use of AFI leads to overdiagnosis of oligohydramnios; it is quite possible that the use of MVP may lead to overdiagnosis of polyhydramnios, but further studies on optimal diagnostic methods for polyhydramnios are needed (57). The likelihood of a fetal anomaly is significantly higher with more severe polyhydramnios (58, 70).

LoR CGoE 4Level of Recommendation C (Grade of Evidence - 4).

Comment: Severe polyhydramnios and oligohydramnios first detected in early pregnancy should raise high concern regarding the possible causes (18,58) of this phenomenon; in such cases, it is extremely important to study the family history and perform a detailed ultrasound examination (18). When congenital malformations or chromosomal abnormalities of the fetus are suspected, assessment of the prognosis for fetal life and development, genetic counseling, and invasive prenatal diagnosis or cell-free DNA screening are indicated. The clinical decision is made based on the results of a medical concilium, depending on the gestational age and the prognosis for fetal life. When a chorioangioma is identified, its size should be evaluated. Small chorioangiomas are relatively common and rarely cause pregnancy complications, but large (greater than 5 cm) chorioangiomas are associated with the development of non-immune hydrops fetalis and polyhydramnios (19,59). The clinical decision is made based on the results of a medical concilium, depending on the gestational age and the prognosis for fetal life.

Comment: in the vast majority of cases, signs of non-immune hydrops fetalis precede the manifestation of polyhydramnios associated with fetal anemia, although a number of studies show the reverse sequence of events (61).

^[1] Read more (99)

2.5 Other Procedures

• When a fetal congenital malformation is detected in combination with oligohydramnios or polyhydramnios, it is recommended to assess the prognosis for fetal life and development, provide medical genetic counseling, and perform invasive prenatal diagnosis (1,8)

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: in cases of isolated oligohydramnios in the absence of ultrasound signs of fetal anomalies, the risk of genetic abnormalities is equal to the general population baseline.

Amniocentesis is recommended for oligohydramnios combined with fetal congenital malformations (102)

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: Chromosomal microarray analysis (CMA) is preferred as a laboratory method, allowing the detection of not only quantitative but also other structural karyotype abnormalities (62,64). If patients refuse amniocentesis (or it is not feasible due to technical difficulties), cell-free DNA screening can be offered (63). If no fetal anomalies are found (in cases of isolated oligohydramnios), the risk of genetic abnormalities is equal to the general population baseline.

Currently, there are no data confirming the efficacy of diagnostic amniocentesis in mild or moderate isolated polyhydramnios (65). However, performing it using CMA is advisable in the presence of severe polyhydramnios, as data show an increase in the frequency of congenital (see table No. 2) and chromosomal anomalies with increasing severity of polyhydramnios (65).

^[1] Myotonic dystrophy is the most common hereditary form of muscular dystrophy in adults; the disease is characterized by a progressive clinical course, autosomal dominant inheritance, and multisystem involvement (skeletal muscles, myocardium, endocrine system, visual organs, etc.) (2019, Clinical Neurology, Myotonic Dystrophy: Genetics and Polymorphism of Clinical Manifestations).

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

Mild and moderate oligohydramnios and polyhydramnios do not require treatment (34).

Possible options for correcting severe oligohydramnios and polyhydramnios are invasive procedures—amnioinfusion and amnioreduction, respectively.

3.1. Pharmacotherapy

Comment: Oral hydration with one to two liters of water can be an alternative to amnioinfusion for temporarily increasing AFI for up to 48 hours, especially in hypovolemic patients. This approach is simpler and safer than intravenous fluid administration or amnioinfusion. Water hydration appears to reduce maternal plasma osmolality and sodium concentration, potentially improving uteroplacental perfusion.

Comment: It is known that #indometacin, a drug recommended for acute tocolysis^[1], reduces fetal urine output (73). However, it has been shown that preterm infants born to mothers who received #indometacin (in utero) experienced decreased urine output and increased serum creatinine concentrations, which in some cases persisted for several weeks (71,74). Furthermore, studies indicate that treatment with #indometacin is associated with an increased risk of other neonatal morbidities, including intraventricular hemorrhage, periventricular leukomalacia, and necrotizing enterocolitis (72,75).

Comment: Administration is possible only by decision of the medical commission and upon obtaining the patient's informed consent for off-label use of the drug. The optimal dose is unknown; Moise suggested 25 mg every 6 hours per os, under close monitoring. Ultrasound assessment of the amniotic fluid index (AFI) should be performed once or twice a week. If oligohydramnios develops, #indometacin should be discontinued immediately, while monitoring of the AFI continues. Additionally, fetal echocardiography should be considered within the first 24 hours; signs of significant constriction of the ductus arteriosus or the appearance of tricuspid regurgitation require immediate discontinuation of #indometacin (77).

3.2. Other treatment

Amnioinfusion is a procedure in which complex sodium chloride or sodium lactate solution [Potassium chloride + Calcium chloride + Sodium chloride + Sodium lactate]** is injected into the uterine cavity to replace amniotic fluid. This procedure may be performed for the purpose of: prophylactic treatment of oligohydramnios, correction of fetal heart rate abnormalities (predominantly decelerations) due to umbilical cord compression during labor, as well as correction of PPROM manifestations at a gestational age of 26 weeks or more (78–80).

Comments: Amnioinfusion may be considered in cases of anhydramnios after weighing the potential benefits and risks to improve the fetal condition and/or as a one-time intervention to improve visualization during fetal ultrasound for a more reliable assessment of fetal anatomy (80). Amnioinfusion only temporarily increases the volume of amniotic fluid and is purely symptomatic therapy.

Severe oligohydramnios or anhydramnios in the 2nd trimester is associated with high mortality due to the development of fetal pulmonary hypoplasia. Several studies have shown that gestational age at the time of membrane rupture (15–28 weeks of gestation), latency period (the duration between membrane rupture and birth), and amniotic fluid index (AFI less than 1–5 cm) can influence the development of pulmonary hypoplasia (85). Nevertheless, amnioinfusion in idiopathic oligohydramnios and in the setting of PPROM may have a positive effect and somewhat reduce mortality from postnatal pulmonary hypoplasia, as well as the risk of orthopedic complications. However, in fetuses with oliguria/anuria resulting from primary renal disease, postnatal dialysis and possibly kidney transplantation will be required in any case.

Comments: the cause of severe polyhydramnios leading to maternal respiratory failure is in most cases congenital fetal malformations (87,86). On average, from 1.5 to 3 liters of amniotic fluid can be removed per procedure (88). However, polyhydramnios usually recurs after amnioreduction, which limits the effectiveness of this procedure. Therefore, subsequent AFI monitoring is indicated every one to three weeks (34,89).

3.3. Delivery

• In isolated idiopathic oligohydramnios with intact membranes, it is recommended to consider delivery at 36/0–37/6 weeks of gestation or at the time of diagnosis at a later gestational age to improve perinatal outcomes (18, 70, 90, 101).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: the optimal timing of delivery in idiopathic oligohydramnios remains controversial (18, 70, 91, 101).

• In mild idiopathic polyhydramnios, preinduction/induction of labor is not recommended prior to 39 weeks of gestation (90).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

Comment: There is no evidence indicating that induction of labor or preterm birth is associated with improved perinatal outcomes in the setting of mild idiopathic polyhydramnios (93,94).

• In moderate and severe polyhydramnios, amnioreduction may be recommended prior to delivery to increase the likelihood of vaginal delivery and reduce the risk of postpartum hemorrhage (95).

LoR CGoE 4Level of Recommendation C (Grade of Evidence - 4).

Comment: amnioreduction does not contribute to the prolongation of pregnancy; on the contrary, intrauterine interventions, in particular amnioreduction per se, are risk factors for complications such as PPROM and preterm birth (88).

• In severe polyhydramnios, delivery is recommended in level 3 hospitals due to the high risk of prenatally undiagnosed congenital fetal malformations (18, 70).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

^[1] Algorithm and indications for acute tocolysis are described in the RROCOG clinical guidelines "Preterm Birth"

4. Medical Rehabilitation and Sanatorium-Resort Treatment

Not applicable.

5. Prevention and Dispensary Observation

• In oligohydramnios, it is recommended to measure the maximum vertical pocket (MVP) and perform cardiotocography (CTG) weekly, as well as fetal biometry every 2 weeks (96).

LeveL of Recommendation BGrade of Evidence 2LeveL of Recommendation B (Grade of Evidence - 2).

Comment: dynamic monitoring reduces the incidence of unexplained stillbirth.

• In moderate and severe polyhydramnios, it is recommended to perform an ultrasound examination (transabdominal ultrasound of the uterus and appendages) every 1–3 weeks to monitor the AFI and assess cervical length (70).

LoR CGoE 4Level of Recommendation C (Grade of Evidence - 4).

• At the second stage, it is recommended for all pregnant women to undergo ultrasound screening at 19–21 weeks of gestation to exclude ultrasound markers of chromosomal abnormalities and congenital malformations, and to recalculate risk using software (98).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

• In accordance with the Clinical Guidelines "Normal Pregnancy" (2023), to exclude fetal aneuploidy, the patient may be additionally offered DNA screening after 10 weeks of gestation (64).

GCP CLEL 5Level of Evidence C (Level of Likelihood of Evidence - 5).

6. Organization of Medical Care

Both oligohydramnios and polyhydramnios are common conditions that can have serious consequences for pregnancy outcomes. Healthcare providers caring for pregnant women in antenatal care (obstetrician-gynecologists, midwives, ultrasound diagnostics physicians) must be aware of the parameters requiring dynamic monitoring and possess skills in performing and/or interpreting ultrasound examinations.

The interdisciplinary medical team providing care to the pregnant woman should include all necessary specialists providing care to her and the newborn, including neonatologist-intensivists. Delivery should take place in a level 2–3 obstetric healthcare facility. In severe cases, delivery must take place exclusively in level 3 institutions due to the high risk of admission of the infant to the neonatal intensive care unit and the high probability of detecting developmental anomalies.

A clear interdisciplinary approach to assessing the fetal condition and managing safe delivery leads to a reduction in perinatal complications and improved outcomes (99).

7. Additional Information

Not applicable.

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

Authors

1. Khodzhayeva Zulfiya Sagdullayevna – MD, Professor, Deputy Director for Scientific Work, Institute of Obstetrics, National Medical Research Center for Obstetrics, Gynecology and Perinatology Named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

2. Ksenia A. Gorina – Research Fellow, 1st Obstetric Department of Pregnancy Pathology, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

3. Roman V. Kapustin – Doctor of Medical Sciences, Head of the Department of Obstetrics and Perinatology, Research Institute of Obstetrics, Gynecology and Reproductology named after D.O. Ott (Saint Petersburg). No conflict of interest

4. Tamara A. Yarygina – Candidate of Medical Sciences, Head of the Ultrasound Diagnostics Department, Moscow Regional Research Institute of Obstetrics and Gynecology (MONIIAG) named after Academician V.I. Krasnopolsky (Moscow). No conflict of interest.

5. Vladislav V. Kovalev – Doctor of Medical Sciences, Professor, Head of the Department of Obstetrics and Gynecology, Ural Institute of Healthcare Management named after A.B. Blokhin (Yekaterinburg). No conflict of interest

6. Elena V. Kudryavtseva – Doctor of Medical Sciences, Associate Professor, Head of the Central Research Laboratory, Ural State Medical University of the Russian Ministry of Health; Professor of the Department of Obstetrics and Gynecology, Ural Institute of Healthcare Management named after A.B. Blokhin (Yekaterinburg). No conflict of interest

7. Elena N. Alekseenkova – Junior Research Fellow, Department of Obstetrics and Perinatology, Research Institute of Obstetrics, Gynecology and Reproductology named after D.O. Ott (Saint Petersburg). No conflict of interest.

8. Igor I. Baranov – Doctor of Medical Sciences, Professor, Head of the Department of Scientific and Educational Programs, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

9. Anna S. Bolshakova – Geneticist at the Institute of Reproductive Genetics, Candidate of Medical Sciences National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest

10. Dolgushina Natalia Vitalievna – MD, Professor, Deputy Director – Head of the Department for Organization of Scientific Activities, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

11. Natalia E. Kan – Doctor of Medical Sciences, Professor, Deputy Director for Research, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

12. Natalia I. Klimenchenko – Candidate of Medical Sciences, Associate Professor, Senior Research Fellow, 1st Obstetric Department of Pregnancy Pathology, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

13. Klimov Vladimir Anatolievich – PhD, Head of the Medical Care Organization and Information Service, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

14. Elizaveta M. Limonova – PhD student, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

15. Kamilla T. Muminova – Candidate of Medical Sciences, Research Fellow, 1st Obstetric Department of Pregnancy Pathology, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

16. Anastasia V. Nikolaeva – PhD, Chief Physician, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

17. Serov Vladimir Nikolaevich – Academician of the RAS, MD, Professor, Honored Scientist of the RF, President of the Russian Society of Obstetricians and Gynecologists, Chief Researcher, National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I. Kulakov of the Russian Ministry of Health (Moscow). No conflict of interest.

18. Kholin Aleksey Mikhailovich – Candidate of Medical Sciences, Head of the Telemedicine Department at the V.I. Kulakov National Medical Research Center for Obstetrics, Gynecology and Perinatology of the Russian Ministry of Health (Moscow). No conflict of interest.

19. Roman G. Shmakov – Doctor of Medical Sciences, Professor of the Russian Academy of Sciences, Director of MONIIAG (Moscow), Chief Freelance Specialist in Obstetrics of the Russian Ministry of Health. No conflict of interest.

Appendix A2. Methodology for Developing Clinical Guidelines

Target audience for these clinical guidelines:

1. obstetrician-gynecologists

2. students; residents, PhD students, obstetrician-gynecologists

3. lecturers, researchers

Table 1. Level of Evidence (LoE) grading scale for diagnostic methods (diagnostic interventions)

Table 2. Scale for assessing levels of reliable evidence (LRE) for prevention, treatment, and rehabilitation methods (preventive, therapeutic, rehabilitation interventions)

Table 3. Grade of Recommendation (GoR) scale for prevention, diagnostic, treatment, and rehabilitation methods (preventive, diagnostic, therapeutic, and rehabilitative interventions)

Appendix A3. Reference Materials

• Federal Law No. 323-FZ "On the Fundamentals of Protecting Citizens' Health in the Russian Federation" dated November 21, 2011.

• Order of the Ministry of Health of the Russian Federation No. 203n dated May 10, 2017 "On Approval of Criteria for Assessing the Quality of Medical Care".

• Order of the Ministry of Health and Social Development No. 1687n dated December 27, 2011 "On Medical Criteria of Birth, Form of the Birth Document and Procedure for its Issuance" (registered with the Ministry of Justice of the Russian Federation on March 15, 2012, No. 23490).

• Order of the Russian Ministry of Health No. 1130n dated October 20, 2020, "On Approval of the Procedure for Providing Medical Care in the Profile of 'Obstetrics and Gynecology'" (Registered with the Ministry of Justice of Russia on November 12, 2020, No. 60869)

• Order of the Russian Ministry of Health No. 804n dated October 13, 2017 (as amended on April 16, 2019) "On Approval of the Nomenclature of Medical Services"

• ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan, 2022

• ISUOG Practice Guidelines: performance of third-trimester obstetric ultrasound scan, 2024

• ISUOG Basic Training Assessing the Placenta & Amniotic Fluid in Singleton & Twin Pregnancies

• SMFM Consult Series #46: Evaluation and management of polyhydramnios, 2018

• ROAG Clinical Guidelines «Preterm labor», 2024

Appendix A3.1. Assessment of amniotic fluid volume (1).

AFI may be preferable when evaluating polyhydramnios, whereas SDP may be more accurate when evaluating oligohydramnios.

Amniotic fluid volume should be assessed either subjectively, described as "normal" or "abnormal" (decreased or increased), or semi-quantitatively by measuring SDP or AFI.

To assess SDP, the deepest vertical pocket of amniotic fluid free of fetal parts and umbilical cord loops is measured.

It would be good to insert an image here from our ultrasound archive with arrows and pointers

SDP ≤ 2 cm or AFI ≤ 5 cm is evaluated as decreased amniotic fluid volume (oligohydramnios), SDP > 2 cm and < 8 cm as normal amniotic fluid volume, and SDP ≥ 8 cm or AFI ≥ 25 cm as increased amniotic fluid volume (polyhydramnios).

Detailed ultrasound examination in severe polyhydramnios should include the following parameters (18):

- fetometry

- fetal echocardiography

- assessment of fetal motor activity to evaluate neurological status

- assessment of fetal hand and foot positioning to rule out arthrogryposis^[1]

- assessment of the presence and size of the fetal stomach to rule out tracheoesophageal fistula or esophageal atresia

- assessment of fetal facial and palatal anatomy

- assessment of fetal neck position and anatomy to rule out mass lesions

- assessment of fetal kidneys to evaluate pelviureteric junction obstruction

- assessment of the lower spine and pelvic region to confirm/rule out sacrococcygeal teratoma

- detection/exclusion of signs of fetal hydrops

- examination of the placental bed for the presence/absence of large chorioangiomas

- Doppler assessment of fetal MCA-PSV to detect/rule out anemia

Example 1: clinical case of severe polyhydramnios due to duodenal obstruction in the fetus in the 3rd trimester of pregnancy.

SDP 10.7 cm. AFI 37.7 cm.

Detailed ultrasound examination in oligohydramnios should include the following parameters (8):

- fetometry to detect fetal growth restriction^[2]

- Doppler ultrasound

- assessment of the placenta

- assessment of the umbilical cord insertion site and the number of umbilical cord vessels

- assessment of fetal ultrasound anatomy to rule out congenital malformations, specifically:

- Kidneys (presence, size, position, appearance (echogenicity, cysts, urinary tract dilation))

- Urinary bladder (size and shape)

- assessment of fetal sex (posterior urethral valves are found exclusively in male fetuses, who also have a higher incidence of renal dysplasia and agenesis)

- Second-trimester markers indicating aneuploidy (echogenic intracardiac focus, choroid plexus cysts, single umbilical artery, urinary tract dilation, shortening of the humerus and femur bones, echogenic bowel, increased nuchal fold, hypoplasia or absence of the nasal bone (100).

Example 2: clinical case of oligohydramnios in the 2nd trimester of pregnancy with early severe fetal growth restriction and ultrasound markers of chromosomal abnormalities: echogenic foci in the cardiac ventricles, echogenic bowel

Only two free pockets of amniotic fluid are identified

SDP 1.9 cm. AFI 3.8 cm.

^[1] Arthrogryposis is a severe congenital musculoskeletal disorder characterized by contractures of two or more joints of the lower and/or upper extremities, typically associated with muscle hypoplasia or atrophy (2020, Current Pediatrics, Distal arthrogryposis in a newborn: a clinical case).

^[2] ROAG Clinical Guidelines «Insufficient fetal growth requiring maternal medical care (fetal growth restriction)»

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Amniotic fluid (AF) is the fluid that surrounds the fetus in the uterus. Initially, it consists mainly of water with electrolytes. However, as pregnancy progresses, it contains more molecules (including proteins, carbohydrates, lipids, and urea). During the first trimester of pregnancy, the main component of amniotic fluid is fluid transferred from the mother across the placenta (plasma, nutrients, and growth factors). In the second half of pregnancy, the baby is the primary source and produces AF independently through urination. As the baby develops and produces more urine, the AF volume peaks at approximately 32–34 weeks of gestation. After 36 weeks of gestation, i.e., almost at term, the volume naturally decreases.

Amniotic fluid (AF) supports a vast number of functions aimed at protecting and ensuring the normal development of the fetus. Amniotic fluid allows the baby to move freely, thereby contributing to the development of the musculoskeletal system (muscles and bones); prevents umbilical cord compression, thereby facilitating the normal supply of nutrition and oxygen from the mother; keeps the baby warm and maintains a constant temperature and humidity. Swallowing AF helps the fetus develop its gastrointestinal tract; the fetus also inhales and exhales the fluid, which stimulates lung development; and it acts as a barrier against intrauterine infection. AF contains fetal cells, and its analysis allows for the diagnosis of genetic abnormalities (a procedure known as amniocentesis).

What are polyhydramnios and oligohydramnios?

Polyhydramnios means the presence of an excessive amount of AF or amniotic fluid in the amniotic sac. This is a fairly common condition affecting about 1–4% of all pregnancies. It occurs in the 2nd and 3rd trimesters and is associated with increased perinatal morbidity and mortality. It is usually diagnosed incidentally during a routine ultrasound during pregnancy (most often during the 2nd or 3rd trimester screenings).

Oligohydramnios means that, relative to gestational age, the level of AF surrounding the fetus (baby) is low.

How can one tell/find out if there is polyhydramnios or oligohydramnios?

Using ultrasound, doctors can reliably assess the volume of AF by calculating the amniotic fluid index (using the "four-quadrant method" – the uterus is divided into four imaginary quadrants, and the resulting measurements (the vertical length of each fluid pocket) are summed up) or by measuring the deepest vertical pocket. As a rule, an AF index of less than 5–6 cm is considered below normal. Oligohydramnios also includes cases where the maximum vertical pocket is less than 2 cm. If the vertical pocket is greater than 8 cm and the index is greater than 20 cm, this is defined as polyhydramnios.

What can cause polyhydramnios and oligohydramnios?

The causes of polyhydramnios are numerous and varied, most commonly associated with: gestational diabetes mellitus, fetal hydrops, congenital malformations or genetic abnormalities of the fetus (mainly trisomy 21, 18, and 13), rhesus isoimmunization, infections (toxoplasmosis, CMV, rubella, parvovirus, syphilis), maternal metabolic disorders (such as hypercalcemia), and other rare fetal or maternal conditions (such as Bartter syndrome, etc.). In a large percentage of cases, the cause of polyhydramnios cannot be identified, in which case it is called idiopathic.

The leading cause of oligohydramnios is rupture of membranes, but renal dysfunction or urinary tract obstruction can also be the source of the problem. Oligohydramnios may be a sign of placental dysfunction; very rarely (less than 1% of cases), the cause may be idiopathic (unknown).

What is the prognosis for polyhydramnios and oligohydramnios?

The prognosis for mild idiopathic polyhydramnios is generally favorable. When the cause of polyhydramnios is identified, the prognosis largely depends on the underlying cause and the degree of severity.

Since amniotic fluid is the baby's life support system, oligohydramnios is a serious condition, as all vital functions and protective actions of the amniotic fluid are diminished. There are several complications arising from oligohydramnios, which vary depending on its cause and severity, as well as the time of onset. The earlier in pregnancy oligohydramnios occurs, the worse the prognosis resulting from the underlying cause. Isolated idiopathic oligohydramnios in the third trimester usually has a good prognosis. Some of the risks associated with oligohydramnios include infectious complications (rupture of membranes), preterm birth (rupture of membranes, fetal growth restriction), and malpresentation (due to restricted movement).

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

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