Being pregnant with more than one baby is exciting and can be a happy event for many couples. However, multiple pregnancy has increased risks for complications. Some of the most common complications are:
- Preterm labor and birth. More than 60 percent of twins and nearly all higher-order multiples are premature (born before 37 weeks). The higher the number of fetuses in the pregnancy, the greater the risk for early birth. Premature babies are born before their bodies and organ systems have completely matured. These babies are often small, with low birth weights (less than 5 pounds), and they may need help breathing, eating, fighting infection and staying warm. Very premature babies, those born before 28 weeks, are especially vulnerable. Many of their organs are not ready for life outside the mother's uterus, and they may be too immature to function well. Multiple birth babies often need care in a neonatal intensive care unit (NICU) after they are born.
- Gestational hypertension. Women with multiple fetuses are two to five times more likely to develop high blood pressure during pregnancy. This condition often develops earlier and is more severe than in pregnancy with one baby. High blood pressure can increase the chance of placental abruption (early detachment of the placenta). High blood pressure during pregnancy is called preeclampsia or toxemia, and it can lead to a deadly complication called eclampsia if it is not treated early and quickly enough.
- Anemia. Anemia is more common in multiple pregnancies than in a single pregnancy.
- Birth defects. Multiple birth babies have a higher risk of congenital abnormalities, including neural tube defects like spina bifida and gastrointestinal and heart abnormalities.
- Miscarriage. A phenomenon called the vanishing twin syndrome, in which more than one fetus is found through testing, but one vanishes (or is miscarried) may occur in a multiple pregnancy. It usually happens during the first trimester, and it may or may not be accompanied by bleeding. The risk of pregnancy loss is increased in later trimesters as well.
- Twin-to-twin transfusion syndrome. Twin-to-twin transfusion syndrome (TTTS) is a condition of the placenta that can develop with identical twins who share a placenta. Blood vessels connect within the placenta and divert blood from one fetus to the other. It occurs in up to 15-20 percent of twins who share a placenta.
In TTTS, blood is shunted from one fetus to the other through blood vessel connections in a shared placenta. Over time, the recipient fetus receives too much blood, which can overload the cardiovascular system and cause too much amniotic fluid to develop. The smaller donor fetus does not get enough blood and has low amounts of amniotic fluid, which can also cause serious problems.
- Abnormal amounts of amniotic fluid. Polyhydramnios (too much fluid) and oligohydramnios (too little fluid) are more common in multiple pregnancies, especially in twins who share a placenta.
- Cesarean delivery. Abnormal fetal positions increase the chances of cesarean birth or c-section.
- Postpartum hemorrhage. The large placental area and over-distended uterus can place a mother at risk for bleeding after delivery when she’s pregnant with multiples.