Multiple pregnancies are generally considered high-risk pregnancies. They require more frequent visits to the obstetrician (OB) and more medical monitoring through ultrasound assessments. Women with multiple pregnancies have a higher risk of some of the complications of pregnancy. Some of the complications for the mother include:

• Preeclampsia. This condition, also called toxemia of pregnancy, includes elevated protein levels and high blood pressure. It can escalate to the more serious condition of eclampsia, which can include convulsions and coma. Preeclampsia occurs more frequently in multiple pregnancies, affecting up to 45 percent of women carrying triplets.
  
  
• Gestational diabetes.  Multiple fetuses make a woman more susceptible to gestational diabetes, where levels of glucose (blood sugar) and insulin are out of balance. Her levels of insulin are lower, which permit too much glucose to reach the fetuses. Some women require treatments such as injections of insulin during a multiple pregnancy but others can handle the condition with dietary changes and exercise.
  
  
• Uterine and placental abnormalities. Multiple pregnancies are more likely to adversely affect the uterus and placenta. Growth rates in multiple pregnancies slow earlier, sometimes at 26 weeks. The placenta cannot grow anymore, and its lack of growth will affect the further well-being of the fetuses. The fetuses depend on the healthy placenta for oxygen and nutrients. Slowing growth rates are more common with triplets and higher order multiple pregnancies than uncomplicated twin pregnancies. Placental abruption, a premature separation of the placenta from the uterine wall that can result in premature delivery and hemorrhaging, is also more common in multiple pregnancies.
  
  
• Preterm labor and premature birth. Many women begin to experience contractions earlier with a multiple pregnancy. Sometimes preterm labor can be delayed with bed rest and the use of certain drugs to stop contractions. Some steroid medications can help fetal lung development in anticipation of a premature delivery.
  
  Premature birth is the most common complication of multiple pregnancy. The likelihood of premature delivery increases with each additional fetus. For example, in 2004, the average age of delivery of twins was at 35 weeks’ gestation, while the average quintuplets were delivered at 29.7 weeks. More than half of twins are born prematurely (before 37 weeks). Recent studies have indicated that twins conceived by in-vitro fertilization are more likely to be born prematurely than twins conceived through sexual intercourse.
  
  More than 90 percent of higher-order births (triplets and more) are born prematurely. Higher-order multiples are more likely to be born even more prematurely, with more than one-third of triplet births and more than half of quadruplet births occurring at 32 weeks or earlier. Babies born this early face more complications and are less likely to survive.

• Caesarean section (C-section). The majority of multiple pregnancies are delivered via C-section. A surgical incision is made in the mother’s abdomen and uterine wall and the babies are removed. Twins may be delivered vaginally if the first twin is positioned correctly (head-first presentation). But if the twins are positioned differently or are otherwise interlocked, a C-section is recommended. Almost all higher-order multiple pregnancies are delivered via C-section.
  
  
• Miscarriage. Multiple pregnancies are more susceptible to miscarriage, stillbirth or sometimes the early loss of one fetus, called the vanishing twin syndrome. An early examination or ultrasound may detect two or more fetuses. Later exams show that one fetus has disappeared, sometimes with the mother experiencing little or no bleeding or other symptoms of miscarriage. There is usually no danger and the remaining fetus develops normally.
  
  
• Twin-to-twin transfusion. Identical twins sometimes have a condition called twin-to-twin transfusion syndrome. This occurs when a defect in the shared placenta allows blood from one twin to transfuse to the other. The first twin becomes anemic and the twins will no longer grow at the same rate. The syndrome ranges in severity, depending on when in pregnancy it develops. The most severe cases can cause death of one or both twins.
  
  
• Conjoined twins. In rare cases, the egg division that forms identical twins is incomplete. Twins may develop joined at the head, back or abdomen in a condition called conjoined twins. Many pregnancies of conjoined twins miscarry. In severe cases, a doctor may recommend termination of the pregnancy. When they are born, conjoined twins have numerous complications, especially if they share some organs. Sometimes surgery can be performed to separate them, with varying degrees of success.
  
  
• Infant health complications. Twins and other babies from multiple pregnancies face numerous complications. Most are associated with premature birth and low birth weight. Low birth weight is defined as less than 5.5 pounds (2.5 kilograms). According to the National Center for Health Statistics, low birth weights occur in more than half of twin births and more than 90 percent of higher-order multiple births. These babies are also subject to other problems associated with premature birth, including vision problems, hearing loss, cardiovascular problems, cerebral palsy and mental retardation.

The lungs of premature infants may be less developed and are commonly affected by respiratory distress syndrome (also called RDS or hyaline membrane disease). Fetal lung development is not complete until about 35 weeks’ gestation because a substance called surfactant, which helps expand the lungs, is not fully present. Some infants born prematurely may have trouble breathing on their own. Medication and respirators help many infants, but some still die from RDS.