Ultrasound diagnostics and disease markers
Ultrasound examination with fetometry and placentometry is initiated from the 18th–20th week of gestation. The frequency of examinations depends on the clinical picture: in an uncomplicated course, ultrasound is repeated every 2–3 weeks, and in severe forms, every 1–3 days.
Early echographic signs include:
- Placental thickening (0.5–1.0 cm greater than normal for the current gestational age).
- Enlargement of the liver and spleen.
- Polyhydramnios.
- Dilation of the umbilical vein (diameter exceeding 10 mm).
The edematous form of the disease is most clearly diagnosed by ultrasound. In severe hydrops, placentomegaly (thickness reaching 6.0–8.0 cm), hepatosplenomegaly, ascites, and polyhydramnios are detected. Additionally, cardiomegaly, pericardial and pleural effusion (hydrothorax), subcutaneous edema (of the head, trunk, and extremities), and increased echogenicity of the intestine due to edema of its wall are visualized.
Doppler ultrasound: non-invasive standard
A decrease in hemoglobin levels and blood viscosity in HDF leads to the development of a hyperdynamic circulatory state in the fetus with an increased cardiac output.
The leading method for detecting anemia has become the assessment of peak systolic velocity (PSV) in the middle cerebral artery (MCA). There is an inverse relationship between blood flow velocity and hemoglobin levels: the more severe the anemia, the higher the velocity. This method has become a full-fledged alternative to invasive interventions.
Management depends on the identified zone (expressed as multiples of the median, MoM):
- Zone C (< 1.29 MoM): Fetus is healthy. Control ultrasound is scheduled in 1–2 weeks.
- Zone B (1.29–1.5 MoM): Mild anemia. Follow-up in 5–10 days (taking into account medical history).
- Zone A (≥ 1.5 MoM): Moderate or severe anemia. If gestational age is under 32 weeks (and fetal weight is under 2000 g), intrauterine blood transfusion is indicated. After 32 weeks, the issue of delivery is addressed.
Amniocentesis and Liley's scale
In this condition, the fetal kidneys excrete bilirubin into the amniotic fluid. Assessment of the optical density of bilirubin (ODB) in the amniotic fluid helps estimate the severity of hyperbilirubinemia.
Indications for amniocentesis include: burdened medical history (loss of children due to HDF or previous exchange transfusion), antibody titer from 1:16, and the presence of ultrasound markers of the pathology.
The study is performed using a spectrophotometer starting from the 24th week. Results are evaluated according to Liley's scale:
- Zone 1 and 2A: Fetus is healthy, Rh-negative, or out of danger. Repeat analysis in 4 weeks.
- Zone 2B: Follow-up is required in 1–2 weeks.
- Zone 2C: Diagnostic cordocentesis is indicated.
- Zone 3: Critical condition. Before 32 weeks, cordocentesis and blood transfusion are performed; after 32 weeks, delivery is indicated.
Note: Today, amniocentesis is gradually losing relevance, giving way to MCA Doppler ultrasound.
Cordocentesis
Umbilical cord puncture is the most accurate diagnostic method, allowing direct analysis of fetal blood. The procedure is performed starting from the 18th week.
Indications for the procedure:
- ODB values in zones 2C or 3 according to Liley's scale.
- Presence of echographic signs of HDF.
- Blood flow velocity in the MCA in Zone A (≥ 1.5 MoM).
During cordocentesis, the fetal blood type and Rh factor, levels of hemoglobin, hematocrit, and bilirubin are determined, and an indirect Coombs test is performed.
Briefly: answers to topical questions
What are the clinical forms of hemolytic disease of the fetus and newborn?
Three main clinical forms of hemolytic disease of the fetus and newborn are distinguished. Depending on the frequency of occurrence, the following variants of the disease are noted:
- Icteric form — occurs most frequently (88% of cases).
- Anemic form (hemolytic anemia without jaundice and hydrops) — is the mildest form (10% of cases), manifested at birth by skin pallor and a decreased hemoglobin level.
- Edematous form — the most severe form (2% of cases), characterized by pronounced placentomegaly, hepatosplenomegaly, ascites, or generalized edema, as well as polyhydramnios.
Which classes of maternal antibodies cross the placenta and cause hemolysis of fetal red blood cells?
Maternal antibodies of class G (IgG) cross the placenta and cause hemolysis of fetal red blood cells. This is the only class of immunoglobulins capable of crossing the placental barrier. During a subsequent pregnancy with an Rh-positive fetus in an Rh-sensitized mother, class G immunoglobulins have already accumulated. Crossing into the fetal bloodstream, these pre-existing antibodies bind to D-antigens, causing agglutination and subsequent hemolysis of fetal red blood cells.
When and with what medications is specific prevention of Rh-sensitization carried out?
Specific prevention of Rh-sensitization is carried out in an Rh-negative pregnant woman in the absence of anti-Rh antibodies by intramuscular administration of anti-Rh Rho[D] human immunoglobulin. Routine antenatal prophylaxis is performed at 28 weeks of pregnancy; if routine prophylaxis is missed, administration is indicated after 28 weeks. Immunoglobulin is also administered before delivery and immediately after delivery.
Additional administration of anti-Rh immunoglobulin is indicated for invasive procedures: amniocentesis, cordocentesis, chorionic villus sampling, or placental biopsy. Patients with Rh-negative blood in the absence of Rh antibodies are administered immunoglobulin after termination of pregnancy at any gestational age. In partial hydatidiform mole, patients with Rh-negative blood without sensitization require the administration of anti-Rh immunoglobulin.
To memorize the triad of early ultrasound signs, use the "PMS" rule: Placenta (thickening), Multiple amniotic fluid / Polyhydramnios, Spleen and liver (enlargement).
Class and exam questions
Why does the blood flow velocity in the MCA increase in fetal anemia?
A decrease in hemoglobin levels leads to a reduction in blood viscosity. This triggers a hyperdynamic circulatory state: cardiac output increases, and blood flow velocity in the vessels rises.
When is it appropriate to start ultrasound monitoring in rhesus conflict?
Ultrasound examination with fetometry and placentometry starts from the 18th–20th week, since specific markers of the disease are usually not visualized before this gestational age.
In which cases is intrauterine blood transfusion indicated?
The procedure is performed for severe anemia (Zone A by Doppler or Zone 3 by Liley's scale) at a gestational age of up to 32 weeks, if the fetal weight is less than 2000 grams.
What else to study on this topic
- Pathogenesis of hyperdynamic circulation development in the fetus
- Technique and risks of diagnostic cordocentesis
- Features of interpreting the indirect Coombs test
- Algorithm for intrauterine blood transfusion
- Spectrophotometry of amniotic fluid: physical principles of the method
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