Dichorionic twins are a form of multiple gestation in which each twin has a separate placenta (blood supply) and amniotic sac. Dichorionic twins are usually – but not always – fraternal (non-identical).
Twins represent more than 3% of all U.S. live births, with the majority being dichorionic. Dichorionic twins more commonly occur in the setting of fertility treatments such as IVF, in women of advanced maternal age, and in patients with family history of twin births.
As twins are at increased risk for preterm labor and premature delivery, dichorionic twins are closely monitored throughout pregnancy. Surveillance includes serial assessments of fetal growth patterns and cervical length, as well as regular maternal health evaluations to make sure that the mother is tolerating the pregnancy well. In addition to routine twin anatomy assessment, fetal echocardiography is also recommended in pregnancies conceived using IVF.
Overall, the outlook for a dichorionic twin pregnancy is good; however these pregnancies are at risk for premature delivery. Roughly 50% of twins are born before the 36th week of pregnancy. When no other maternal or fetal complications are present, twin outcomes are related to delivery timing.