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What complications occur more frequently in a multiple pregnancy?

Women who are expecting more than one baby are at increased risk of a number of pregnancy complications. The more babies a woman is carrying at once, the greater her risk. Common complications include:

Premature birth: About 60 percent of twins, more than 90 percent of triplets, and virtually all quadruplets and higher-order multiples are born premature (1). The length of pregnancy decreases with each additional baby. On average, most singleton pregnancies last 39 weeks; for twins, 35 weeks; for triplets, 32 weeks; and for quadruplets, 29 weeks (1).

Low birthweight (LBW): More than half of twins and almost all higher-order multiples are born with low birthweight (less than 5½ pounds or 2,500 grams) (1). LBW can result from premature birth and/or poor fetal growth. Both are common in multiple pregnancies.

LBW babies, especially those born before about 32 weeks gestation and/or weighing less than 3 1/3 pounds (1,500 grams), are at increased risk of health problems in the newborn period as well as lasting disabilities, such as intellectual disabilities, cerebral palsy, and vision and hearing loss. While advances in caring for very small infants has brightened the outlook for these tiny babies, chances remain slim that all infants in a set of sextuplets or more will survive and thrive.

Twin-twin transfusion syndrome (TTTS): About 10 percent of identical twins who share a placenta develop this complication (6, 7). TTTS occurs when a connection between the two babies' blood vessels in the placenta causes one baby to get too much blood flow and the other too little. Until recently, severe cases often resulted in the loss of both babies.

TTTS now can be treated with laser surgery to seal off the connection between the babies' blood vessels. It also can be treated with serial (repeated) amniocentesis to drain off excess fluid. Removing the excess fluid appears to improve blood flow in the placenta and reduces the risk of preterm labor. Both procedures can greatly improve the outlook for the babies.

However, recent studies suggest that laser surgery may save more babies and cause fewer neurological problems (such as cerebral palsy) in survivors than amniocentesis (6, 8). For example, a European study found a 76 percent survival rate for at least one fetus after laser surgery compared to 56 percent for serial amniocentesis (8). Another advantage of laser surgery is that only one treatment is needed, while amniocentesis generally must be repeated more than once.

Preeclampsia: Women expecting twins are more than twice as likely as women with a singleton pregnancy to develop this complication, characterized by high blood pressure, protein in the urine and generalized swelling (edema) (9). Severe cases can be dangerous for mother and baby. In some cases, the baby must be delivered early to prevent serious complications.

Gestational diabetes: Women carrying multiples are at increased risk of this pregnancy-related form of diabetes (high blood sugar) (9). This condition can cause the baby to grow especially large, increasing the risk of injuries to mother and baby during vaginal birth. Babies born to women with gestational diabetes also may have breathing and other problems during the newborn period.

Early diagnosis and management of these complications can help protect mother and babies.

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