The high number of multiple pregnancies is a concern because women who are expecting more than one baby are at increased risk of certain pregnancy complications, including premature birth.
Multiple Births: Twins, Triplets, and Beyond
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When a woman is carrying one baby, it is called a singleton pregnancy. When She is carrying two or more babies it is called multiple births. In the past 2 decades, the rate of multiple births in the United States jumped dramatically. The rate of twin births increased by 70 percent between 1980 and 2004, and the rate of higher-order multiples (triplets or more) increased four-fold between 1980 and 1998 . However, the rapid rise in multiple birth rates may be ending. In 2005 and 2006, the rate of twin births remained stable .
The rate of higher-order multiple births has declined 21 percent since its peak in 1998 . Today, more than 3 percent of babies in this country are born in sets of two, three or more; about 95 percent of these multiple births are twins. The high number of multiple pregnancies is a concern because women who are expecting more than one baby are at increased risk of certain pregnancy complications, including premature birth . Premature babies are at risk of serious health problems during the newborn period, as well as lasting disabilities and death. Some of the complications associated with multiple pregnancy can be minimized or prevented when they are diagnosed early. There are a number of steps a pregnant woman and her health care provider can take to help improve the chances that her babies will be born healthy.
About one-third of the increase in multiple pregnancies is due to the fact that more women over age 30 are having babies. Women in this age group are more likely than younger women to conceive multiples. The remainder of the increase is due to the use of fertility treatments, including fertility-stimulating drugs and assisted reproductive technologies (ART), such as in vitro fertilization (IVF). In IVF, eggs are removed from the mother, fertilized in a laboratory dish and then transferred to the uterus. About 44 percent of ART pregnancies result in twins, and about 5 percent in triplets or more. Doctors now monitor fertility treatments carefully so that women have fewer, but healthier, babies. This involves limiting the number of embryos transferred during IVF.
In 2006, the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology issued updated guidelines on the best number of embryos to transfer, depending on a woman’s age and other factors . For example, the guidelines recommend that doctors transfer no more than two embryos for women under age 35, and consider transferring only one embryo for women in this age group who are considered most likely to become pregnant. Doctors monitor women taking certain fertility drugs with ultrasound. If ultrasound shows that a large number of eggs could be released during a treatment cycle, the doctor can stop the treatment and counsel the woman accordingly. The following factors can increase the chances that a woman will conceive multiples:
•Age over 30 years
•A personal or family history of fraternal (non-identical) twins
•Obesity or taller-than-average height
•African-American race (African-American women are more likely to have fraternal twins than caucasian women, and Asian women are the least likely to have fraternal twins)
Although previous generations often were surprised by a multiple birth, today most parents-to-be learn the news fairly early. A routine first-trimester ultrasound can detect most multiples. (Sometimes a twin pregnancy that is identified very early is later found to have only one fetus. This is called “vanishing twin syndrome,” and its cause is not well understood. The surviving twin generally is not harmed.) Other factors can alert a health care provider that a woman may be expecting twins or more. These include: •Rapid weight gain during the first trimester
•The uterus being larger than expected
•Severe pregnancy-related nausea and vomiting (morning sickness) •More than one heartbeat heard by a provider using a hand-held ultrasound device (Doppler) •More fetal movement than the woman experienced in a previous singleton pregnancy •Abnormal results on maternal blood screening done around 16 weeks of pregnancy to screen for certain birth defects A health care provider who suspects a multiple pregnancy most likely recommends that the woman have an ultrasound to find out for sure.
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 . 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. Low birth weight (LBW): More than half of twins and almost all higher-order multiples are born with low birth weight (less than 5½ pounds or 2,500 grams). LBW can result from premature birth and/or poor fetal growth. Both are common in multiple pregnancies.
Twin-twin transfusion syndrome (TTTS): About 10 percent of identical twins who share a placenta develop this complication. 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. 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 edema.
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. 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.
Women who are expecting multiples generally need to visit their health care providers more frequently than women expecting one baby. These extra visits can help prevent, detect and treat the complications that develop more often in a multiple pregnancy. Health care providers may recommend twice-monthly visits during the second trimester and weekly (or more frequent) visits during the third trimester. During the third trimester, the provider may recommend tests of fetal well-being. These include.
Eating right and gaining the recommended amount of weight reduces the risk of having a premature or LBW baby in singleton, as well as multiple, gestations. A healthy weight gain is especially important if a woman is pregnant with multiples because they have a higher risk of premature birth and LBW than singletons.
The chance of a cesarean birth is higher in twin than in singleton births. However, a pregnant woman has a good chance of having a normal vaginal delivery if both babies are in a head-down position and there are no other complications. When a woman is carrying three or more babies, a cesarean birth usually is recommended because it is safer for the babies.