Multiple gestations, including twin, triplet, and higher-order pregnancies, require specialized ultrasound evaluation to determine chorionicity (number of placentas) and amnionicity (number of amniotic sacs), factors that have major implications for pregnancy risks and management. On ultrasound, determining chorionicity is best done in the first trimester by assessing the number of gestational sacs, yolk sacs, and the appearance of any intertwin membranes. The presence or absence of a thin echogenic lambda sign indicates dichorionic diamniotic pregnancy, while a simple thin membrane indicates monochorionic diamniotic pregnancy. Multiple gestations carry increased risk of complications including preeclampsia, gestational diabetes, preterm birth, and fetal growth restriction, necessitating more frequent ultrasound surveillance and careful monitoring for twin-specific complications.
Sonography Term