The number of twin, triplet, and other multiple births has been increasing during the last two decades. As many as 1 of 30 deliveries involves more than one fetus.
The following make women more likely to become pregnant with more than one fetus:
Taking fertility drugs
Using assisted reproductive techniques (such as in vitro fertilization)
Having had a pregnancy with more than one fetus
Being of West African descent
Carrying more than one fetus increases the risk of problems.
Carrying more than one fetus overstretches the uterus, and an overstretched uterus tends to start contracting before the pregnancy reaches full term (preterm labor). As a result, the babies are usually born prematurely and are small. In some cases, the overstretched uterus does not contract well after delivery, causing bleeding in the woman after delivery (postpartum hemorrhage).
Because the fetuses can be in various positions and presentations, vaginal delivery can be complicated. Also, the contraction of the uterus after delivery of the first baby may shear away the placenta of the remaining baby or babies. As a result, the baby or babies that follow the first may have more problems during delivery.
Carrying more than one fetus also increases the risk of problems for the woman. They include
Doctors suspect more than one fetus when the uterus is larger than expected for the length of the pregnancy. Ultrasonography is done to confirm the number of fetuses.
Because problems can result from multiple births, doctors may decide in advance whether to deliver twins vaginally or by cesarean.
If the first twin is in an abnormal position (anything other than head first), cesarean delivery is used. Occasionally, the first twin is delivered vaginally, but a cesarean delivery is considered safer for the second twin. For triplets and other multiple births, a cesarean delivery is usually done.