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Multiple pregnancies - Diagnosis
Medical expert of the article
Last reviewed: 06.07.2025
Before the introduction of ultrasound examination into obstetric practice, the diagnosis of multiple pregnancies was often established at a later stage or even during childbirth.
Multiple pregnancy can be suspected in patients whose uterine size exceeds the gestational norm both during vaginal examination (early stages) and during external obstetric examination (late stages). In the second half of pregnancy, it is sometimes possible to palpate many small parts of the fetus and two (or more) large balloting parts (fetal heads). Auscultatory signs of multiple pregnancy are fetal heart tones heard in different parts of the uterus with a difference in heart rate of at least 10 per minute. Fetal cardiac activity in multiple pregnancy can be recorded simultaneously using special cardiac monitors for twins (equipped with two sensors).
Ultrasound examination is considered the basis for diagnosing multiple pregnancies in modern obstetrics. Ultrasound diagnostics of multiple pregnancies is possible starting from the early stages of pregnancy (4–5 weeks) and is based on visualization of several fetal eggs and embryos in the uterine cavity.
To develop the correct tactics for managing pregnancy and childbirth in the case of multiple pregnancies, early (in the first trimester) determination of chorionicity (number of placentas) is of crucial importance.
It is chorionicity (and not zygosity) that determines the course of pregnancy, its outcomes, perinatal morbidity and mortality. Monochorionic multiple pregnancy, observed in 65% of identical twins, has the most unfavorable perinatal complications. Perinatal mortality in monochorionic twins, regardless of zygosity, is 3-4 times higher than in dichorionic twins.
The presence of two separately located placentas, a thick interfetal septum (more than 2 mm) is a reliable criterion for bichorionic twins. When a single "placental mass" is detected, it is necessary to differentiate the "single placenta" (monochorial twins) from two fused (bichorionic twins). The presence of specific ultrasound criteria - Ti λ-signs formed at the base of the interfetal septum, with a high degree of reliability allows us to diagnose mono- or bichorionic twins. Detection of the λ-sign during ultrasound examination at any gestational age indicates a bichorionic type of placentation, the T-sign indicates monochorionicity. It should be taken into account that after 16 weeks of pregnancy, the λ-sign becomes less accessible for research.
In later stages of pregnancy (II–III trimesters), accurate diagnostics of chorionicity is possible only in the presence of two separately located placentas. In the presence of a single placental mass (one placenta or fused placentas), ultrasound often overdiagnoses the monochorionic type of placentation.
It is also necessary, starting from the early stages, to conduct comparative ultrasound fetometry to predict intrauterine growth retardation of the fetus/fetuses in later stages of pregnancy. According to ultrasound fetometry data, in multiple pregnancies, physiological development of both fetuses is distinguished; dissociated (discordant) development of fetuses (difference in body weight of 20% or more); growth retardation of both fetuses.
In addition to fetometry, as in singleton pregnancies, attention should be paid to assessing the structure and maturity of the placenta/placentas, the amount of amniotic fluid in both amniotic fluids. Considering that in multiple pregnancies, a velamentous insertion of the umbilical cord and other anomalies in its development are often observed, it is necessary to examine the sites of umbilical cord departure from the fetal surface of the placenta/placentas.
Particular attention should be paid to the assessment of the anatomy of the fetuses to exclude congenital anomalies and, in the case of monoamniotic twins, to exclude conjoined twins.
Given the ineffectiveness of biochemical prenatal screening in multiple pregnancies (higher levels of alpha-fetoprotein, (3-hCG, placental lactogen, estriol compared to singleton pregnancies), the identification of ultrasound markers of congenital developmental anomalies, including examination of the nuchal translucency in fetuses, is of particular importance. The presence of nuchal edema in one of the fetuses in identical twins should not be considered as an absolute indicator of a high risk of chromosomal pathology, since it can be one of the early echographic signs of a severe form of feto-fetal hemotransfusion (FFT).
One of the important moments for choosing the optimal tactics of delivery in multiple pregnancies is considered to be determining the position and presentation of the fetuses by the end of pregnancy. Most often, both fetuses are in a longitudinal position (80%): cephalic-cephalic, breech-breech, cephalic-breech, breech-cephalic. Less common are the following fetal position options: one in a longitudinal position, the second in a transverse position; both in a transverse position.
To assess the condition of the fetus in multiple pregnancies, generally accepted methods of functional diagnostics are used: cardiotocography, Doppler ultrasound of blood flow in the vessels of the mother-placenta-fetus system.
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