There is a significantly increased risk of many pregnancy complications in twins when compared to singletons. These risks are often 4-times or more higher than if you carry a single baby.
One big determinant of possible pregnancy complications is whether the twins share the same placenta or have a separate placenta. Twins that share the same placenta (monochorinionic-diamniotic) are at much higher risk of complications that twins which do not share a placenta (dichorionic-diamniotic).
The most common complications associated with multiples are:
Disabilities in twins are more common, mainly but not entirely due to prematurity and low birthweight complications. Complications are usually 4-times or more higher in twins when compared to singletons.
Cerebral Palsy Rate per 1000 livebirths*
*Western Australia figures
Preterm labor/delivery is defined as delivery before 37 completed weeks of pregnancy. Almost 60% of twins are delivered preterm, while 90% of triplets are preterm. The length of gestation decreases with each additional baby. On average most single pregnancies last 39 weeks, twin pregnancies 36 weeks, triplets 32 weeks, quadruplets 30 weeks, and quintuplets 29 weeks. Higher order pregnancies are almost always preterm. Many times premature labor is a result of preterm premature rupture of the membranes (PPROM). PPROM is rupture of membranes prior to the onset of labor in a patient who is at less than 37 weeks of gestation.
Low Birth Weight:
Low birth weight is less than 5.5 pounds (2,500 grams). Babies born before 32 weeks and weighing less than 3.3 pounds (1,500 grams) have an increased risk of developing complications as newborns. They are at increased risk for having long-term problems such as mental retardation, cerebral palsy, vision loss, and hearing loss.
Intrauterine Growth Restriction (IUGR):
Multiple gestations grow at approximately the same rate as a single pregnancy up to a certain point. The growth rate of twin pregnancies begins to slow at 30 to 32 weeks. Triplet pregnancies begin slowing at 27 to 28 weeks, while quadruplet pregnancies begin slowing at 25 to 26 weeks. IUGR seems to occur because the placenta cannot handle any more growth and because the babies are competing for nutrients. Your doctor will monitor the growth of your babies by ultrasound and by measuring your abdomen.
Preeclampsia, Pregnancy Induced Hypertension (PIH), Toxemia, and high blood pressure are all synonymous terms. Twin pregnancies are twice as likely to be complicated by preeclampsia as single pregnancies. Half of triplet pregnancies develop preeclampsia. Frequent prenatal care increases the chance of detecting and treating preeclampsia. Adequate prenatal care also decreases the chance of a serious problem resulting from preeclampsia for both the babies and mother.
The increased risk for gestational diabetes in a multiple pregnancy appears to be a result of the two placentas increasing the resistance to insulin, increased placental size, and an elevation in placental hormones. The occurrence of gestational diabetes in a multiple pregnancy is still being tested at this time. In one study, an increased risk of gestational diabetes did seem to be apparent, but the doctors involved recommended that further testing be conducted.
Placental abruption is three times more likely to occur in a multiple pregnancy. This may be linked to the fact that there is an increased risk of developing preeclampsia. It most often occurs in the third trimester, but the risk significantly increases once the first baby has been delivered vaginally.