It is easiest to determine chorionicity and amnionicity in the first trimester.The twin birth rate is increasing in the United States. Finding the placental sites of umbilical cord insertion are important because marginal and velamentous insertions increase risk 5. The number of fetuses and their chorionicity and amnionicity must be determined, as well as monitoring for complications and anomalies. The role of ultrasound is crucial adequate in the monitoring of the pregnancy and planning for delivery. Radiographic features Ultrasound assessment of multi-fetal pregnancies Conjoined twins occur only in monoamniotic pregnancies. Monoamniotic twin pregnancies share the one amniotic sac and are prone to entangled cords, as well as all the monochorionic complications (since you cannot be dichorionic-monoamniotic). twin reversed arterial perfusion sequence ( TRAPS)Īmniotic fluid discordance is the most reliable predictor of poorer outcome.twin anemia polycythemia sequence ( TAPS).Monochorionic twin pregnancies share the one placenta and are therefore prone to hemodynamic complications such as: mono-mono: often >50% perinatal mortalityĭespite monochorionic twins amounting to ~20% of twin pregnancies, they account for ~30% of pregnancy-related complications, when all causes are taken into consideration 6.The risk of complications depends on the chorionicity, with the prognosis worst for mono-mono and best for di-di: This is primarily due to a much higher incidence of premature labor and all the sequelae thereof. 1-2 weeks results in monochorionic-monoamniotic twins (mono-mono) (MCMA):Īll twin pregnancies have higher fetal and neonatal mortality with overall rates of fetal mortality being 3-6 times that of a singleton pregnancy and neonatal mortality 7 times that of single pregnancies.4-8 days ( blastocyst) results in monochorionic-diamniotic twins (mono-di) (MCDA):.1-4 days ( morula) results in dichorionic-diamniotic twins (di-di) (DCDA):.

Nigerian 1 in 25 in Nigeria to 1 in 155 in Japan) 4Īlso known as identical twins are due to fertilisation of a single ovum that then separates into two. Unlike dizygotic pregnancy, monozygotic pregnancies do not have maternal age, family history, or ethnic predisposition. The time at which this separation occurs determines the chorionicity and amnionicity of the pregnancy. in vitro fertilisation (IVF): particularly use of ovulation induction agents.This feature alone cannot be used to distinguish dizygotic from monozygotic pregnancies as approximately 20% of monozygotic pregnancies will also be dichorionic-diamniotic (resulting in ~80% of all twin pregnancies being dichorionic-diamniotic). The most reliable sign of dizygosity on ultrasound is documentation of different sex fetuses. ClassificationĪ twin pregnancy can be broadly categorized into:Īlso known as fraternal twins resulting from independent fertilization of two ova, and always result in dichorionic - diamniotic pregnancies. Multifetal pregnancies account for ~1% of all pregnancies but are seen in much higher numbers in populations where in vitro fertilisation (IVF) is a common practice.

Twin due date calculator