Multiples account for only a small percentage of all births (about 3%), though the multiple birth rate is rising. The rate of multiple births is on the increase for several reasons, including older average age of mothers and the use of reproductive technology.
Multiple pregnancy includes the following:
- Twins — two fetuses
- Triplets—three fetuses
- Quadruplets—four fetuses
- Quintuplets—five fetuses
- Sextuplets—six fetuses
- Septuplets—seven fetuses
There are many factors related to a multiple pregnancy. Naturally occurring factors include the following:
- Heredity. A family history of multiple pregnancy increases chances for twins.
- Older age. Women over 30 have a greater chance of multiple conception as a result of delaying childbearing until later in life. There is a possibility for twin.
- High parity. Having one or more previous pregnancies, especially a multiple pregnancy, increases the chances of having multiples.
- Race. African-American women are more likely to have twins than any other race. Asian and Native Americans have the lowest twinning rates, and Caucasian women, especially those over age 35, have the highest rate of higher-order multiple births (triplets or more).
Other factors that have greatly increased the multiple birth rate in recent years include reproductive technologies, including the following:
- Ovulation-stimulating medications, such as clomiphene citrate and follicle stimulating hormone (FSH) help produce many eggs. If fertilized, this can result in multiple babies.
- Assisted reproductive technologies--in vitro fertilization (IVF) and other techniques often use ovulation-stimulating medications to produce multiple eggs which are then fertilized in the laboratory and returned to the uterus to develop.
How does multiple pregnancy occur?
Multiple pregnancy usually occurs when more than one egg is fertilized and implants in the uterus. This is called fraternal twinning and can produce boys, girls, or a combination of both. Fraternal multiples are siblings conceived at the same time, but have a separate placenta and amniotic sac. Just as siblings often look alike, fraternal multiples may also look very similar.
Identical twinning is when one egg is fertilized and divides into two or more embryos, producing all boys, or all girls. Identical multiples are genetically identical. However, these children have different personalities and are distinct individuals. Identical multiples may have individual placentas and amniotic sacs, but most share a placenta with separate sacs. Rarely do identical twins share one placenta and a single amniotic sac.
Each woman may experience symptoms differently, but these are the most common symptoms of multiple pregnancy:
- Uterus is larger than expected for the dates in pregnancy
- Increased morning sickness
- Increased appetite
- Excessive weight gain, especially in early pregnancy
- Fetal movements felt in different parts of abdomen at same time
How is multiple pregnancy diagnosed?
Diagnosis may be made early in pregnancy, especially if reproductive technologies have been used. In addition to a complete medical history and physical examination, diagnosis may be made by:
- Pregnancy blood testing. Possibly higher levels of human chorionic gonadotrophin (hCG).
- Alpha-fetoprotein. Levels of a protein released by the fetal liver and found in the mother's blood may be high when more than one fetus is making the protein.
- Ultrasound. Use of high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs in order to view internal organs as they function, and to assess blood flow through various vessels. A vaginal transducer is also used, especially in early pregnancy, or an abdominal transducer in later pregnancy.
Being pregnant with more than one baby is exciting, but can have increased risks. The most common complications are:
- Preterm labor and birth. Over 60% 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 5lbs.), and 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 may not be ready for life outside the uterus and may be too immature to function well. Many multiple birth babies will need care in a neonatal intensive care unit (NICU).
- Gestational hypertension. Women with multiple fetuses are more than twice as likely to develop high blood pressure. This condition often develops earlier and is more severe than pregnancy with one baby. It can also increase the chance of placental abruption (early detachment of the placenta).
- Anemia. More than twice as common in multiple pregnancies.
- Birth defects. Twice the risk of congenital (present at birth) abnormalities including neural tube defects (such as spina bifida), gastrointestinal, and heart abnormalities.
- Miscarriage. A phenomenon called the vanishing twin syndrome in which more than one fetus is diagnosed, but vanishes (or is miscarried). Usually occurring in the first trimester, it is more likely in multiple pregnancies. This may or may not be accompanied by bleeding. The risk 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 develops only with identical twins that share a placenta. Blood vessels connect within the placenta and divert blood from one fetus to the other. It occurs in about 15% of twins with a shared placenta. 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. As a result, the smaller donor fetus doesn’t get enough blood and has low amounts of amniotic fluid.
- Abnormal amounts of amniotic fluid. Amniotic fluid abnormalities are more common in multiple pregnancies, especially for twins that share a placenta.
- Cesarean delivery. Abnormal fetal positions increase the chances of cesarean birth.
- Postpartum hemorrhage. The large placental area and over-distended uterus place a mother at risk for bleeding after delivery in many multiple pregnancies.
Management of multiple pregnancy
Specific management for multiple pregnancy will be determined by your physician or midwife based on:
- Your pregnancy, overall health, and medical history
- The number of fetuses
- Your tolerance for specific medications, procedures, or therapies
- Expectations for the course of the pregnancy
- Your opinion or preference
Management of multiple pregnancy may include the following:
- Increased nutrition. Mothers carrying two or more fetuses need more calories, protein, and other nutrients, including iron. Higher weight gain is also recommended for multiple pregnancy. The Institute of Medicine recommends that women carrying twins who have a normal body mass index should gain between 37 and 54 pounds. Those who are overweight should gain 31-50 pounds; and obese women should gain 25-42 pounds.
- More frequent prenatal visits. Multiple pregnancy increases the risk for complications. More frequent visits may help detect complications early enough for effective treatment or management. The mother's nutritional status and weight should also be monitored more closely.
- Referrals. Referral to a maternal-fetal medicine specialist, called a perinatologist, for special testing or ultrasound evaluations, and to coordinate care of complications, may be necessary.
- Increased rest. Some women may also need bedrest--either at home or in the hospital depending on pregnancy complications or the number of fetuses. Higher-order multiple pregnancies often require bedrest beginning in the middle of the second trimester. Preventive bed rest has not been shown to prevent preterm birth in multiple pregnancy.
- Maternal and fetal testing. Testing may be needed to monitor the health of the fetuses, especially if there are pregnancy complications.
- Tocolytic medications. Tocolytic medications may be given, if preterm labor occurs, to help slow or stop contractions. These may be given orally, in an injection, or intravenously. Tocolytic medications often used include magnesium sulfate.
- Corticosteroid medications. Corticosteroid medications may be given to help mature the lungs of the fetus. Lung immaturity is a major problem of premature babies.
- Cervical cerclage. Cerclage (a procedure used to suture the cervical opening) is used for women with an incompetent cervix. This is a condition in which the cervix is physically weak and unable to stay closed during pregnancy. Some women with higher-order multiples may require cerclage in early pregnancy.