Clinical diagnostics
The development of multiple pregnancy can be suspected by characteristic clinical signs. The main one is enlargement of the uterus, where its dimensions significantly exceed the gestational norm. This discrepancy is detected both in early stages during vaginal examination and in later stages during external obstetric examination.
In the second half of pregnancy, palpation becomes informative: the physician palpates many small fetal parts and two (or more) large balloting parts corresponding to the fetal heads. Upon auscultation, fetal heart tones are clearly heard in different parts of the uterus.
Ultrasound examination (US)
Ultrasound is the absolute foundation for diagnosing multiple pregnancy in modern obstetrics. The method is based on visualizing multiple gestational sacs and embryos within the uterine cavity. Such diagnosis is possible from the earliest stages—as early as 4–5 weeks.
Starting from the early stages of a multiple pregnancy, a thorough assessment of fetal anatomy must be performed. The purpose of this examination is to rule out congenital malformations and identify markers of chromosomal pathology.
Determination of chorionicity and its significance
Early determination of chorionicity (number of placentas) in the first trimester is critical for establishing pregnancy and delivery management. It is important to remember that it is chorionicity, not zygosity, that determines the course of pregnancy, outcomes, as well as perinatal morbidity and mortality.
The most unfavorable in terms of perinatal complications is monochorionic multiple pregnancy. It occurs in 65% of monozygotic twin cases, with perinatal mortality being 3 to 4 times higher than that in dichorionic twins.
Ultrasound criteria of chorionicity
Reliable ultrasound criteria for a dichorionic twin pregnancy include two separately located placentas and a thick inter-fetal partition (greater than 2 mm). However, if a single placental mass is detected on ultrasound, differential diagnosis is necessary between a truly single placenta (monochorionic twins) and two fused placentas (dichorionic twins).
For this purpose, specific ultrasound markers formed at the base of the inter-fetal partition are used:
- λ-sign (lambda sign): identification of this sign at any gestational age reliably indicates a dichorionic type of placentation. Important limitation: starting from the 15th–16th week of pregnancy, the λ-sign becomes less accessible for ultrasound examination.
- T-sign: reliably indicates monochorionicity.
Late diagnosis and prevention of iatrogenic multiple pregnancy
At later stages (in the II–III trimesters), accurate diagnosis of chorionicity is possible exclusively when two separately located placentas are visualized. If accurate establishment of chorionicity is impossible (due to late presentation of the patient), the pregnancy must be managed as monochorionic.
Special attention is required for the prevention of iatrogenic multiple pregnancy, which results from the use of assisted reproductive technologies (ART). The essence of prevention lies in limiting the number of transferred embryos, specifically—transferring only one embryo (single embryo transfer).
Briefly: answers to topical questions
What specific complications are characteristic exclusively of monochorionic multiple pregnancies?
Specific complications of monochorionic multiple pregnancy include:
- Twin-to-twin transfusion syndrome (TTTS), associated with arteriovenous anastomoses in a monochorionic placenta.
- Reversed arterial perfusion sequence—a complication unique to monochorionic twins, associated with umbilical artery-to-artery anastomoses.
- Selective fetal growth restriction (sIUGR).
- Twin anemia-polycythemia sequence (TAPS).
- Discordant fetal growth.
What biochemical blood markers are investigated during first-trimester prenatal screening in twin pregnancies?
During first-trimester prenatal screening in twin pregnancies, two main biochemical markers are examined in blood serum.
Biochemical screening includes:
- Pregnancy-associated plasma protein A (PAPP-A).
- Free beta-hCG subunit.
These indicators are used for subsequent software calculation of the individual risk of having children with chromosomal disorders.
To memorize ultrasound markers: Lambda (λ) visually has two slopes diverging to the sides—this indicates TWO placentas (dichorionic twins). The letter T has one continuous horizontal line—this is ONE placenta (monochorionic twins).
Class and exam questions
At what gestational age does ultrasound confirm a multiple pregnancy?
Ultrasound examination allows visualization of multiple gestational sacs and embryos in the uterine cavity from the early stages—starting at 4–5 weeks of gestation.
Which is more important for predicting the course of pregnancy: chorionicity or zygosity?
Chorionicity (the number of placentas) is of decisive importance. It is chorionicity, rather than zygosity, that determines the course of pregnancy, outcomes, perinatal morbidity, and mortality.
How should a patient be managed if the type of placentation remains undetermined due to late presentation?
If it is impossible to accurately determine chorionicity in the II–III trimesters, obstetric tactics mandate managing the pregnancy as monochorionic due to the high risks of complications.
What is the prevention of iatrogenic multiple pregnancy?
Iatrogenic multiple pregnancy occurs as a result of using assisted reproductive technologies (ART). Prevention consists of limiting the number of transferred embryos—the practice of transferring only one embryo (single embryo transfer).
What else to study on this topic
- Differential diagnosis of a single placental mass on ultrasound
- Perinatal complications and outcomes in monochorionic twins
- Ultrasound markers of chromosomal pathology in multiple pregnancy
- Assessment of fetal anatomy in early gestation
- Impact of assisted reproductive technologies (ART) on the incidence of multiple pregnancy
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