Multifetal

Multifetal refers to pregnancy involving more than one fetus. The most common multifetal gestations are twins; triplets and higher-order multiples occur less frequently. Multifetal pregnancy can result from various combinations of zygosity and placentation and is studied in obstetrics as multifetal gestation or multifetal pregnancy.

Twins can be dizygotic (fraternal), arising from two separate eggs fertilized by two sperm, or monozygotic (identical), arising from a single fertilized egg that splits. Higher-order multiples, such as triplets or quadruplets, may arise from multiple eggs or from splitting of embryos. Chorionicity and amnionicity describe placentation and sac arrangement: monochorionic twins share a placenta, while dichorionic twins have separate placentas; monoamniotic twins share a sac, whereas diamniotic twins have separate amniotic sacs. These features influence risk profiles and management.

Incidence varies by population, maternal age, and use of assisted reproductive technologies. Monozygotic twinning is relatively constant worldwide (about 0.4% of births), while dizygotic twinning rates vary widely (higher in some populations and with certain fertility treatments). ART and older maternal age have contributed to rising rates of multifetal pregnancies in many regions.

Multifetal pregnancies carry higher risks of obstetric complications, including preterm birth, low birth weight, preeclampsia, gestational diabetes, fetal growth restriction, and twin–twin transfusion syndrome in monochorionic pairs. Delivery is often planned earlier than in singleton pregnancies, with cesarean delivery more common in many multifetal cases. Regular prenatal monitoring, ultrasound assessment of chorionicity and growth, and individualized delivery planning are key components of management. In some cases, multifetal pregnancy reduction may be considered to reduce the number of fetuses and associated risks.