Today, more twins are being born than ever before. In 1980, twins were born only once in about every 55 births. Now, twins are born once in about every 31 births. This increase is mostly because of fertility treatments. A healthy twin pregnancy can be similar to a pregnancy with one baby. However, twin pregnancies can pose risks to the mother and babies. Special care may be needed during pregnancy. Parents may need extra help once the babies are born.
This pamphlet explains
How Twins Occur
Usually, a woman releases one egg during ovulation. Fertilization occurs when one sperm joins with one egg. Sometimes, a woman releases two eggs, both of which can be fertilized by different sperm. When this occurs, it produces fraternal twins. These twins are no more alike than siblings born at different times. These twins can be boys, girls, or one of each. Each baby has its own placenta and amniotic sac.
Once fertilization occurs, the fertilized egg moves down one of the fallopian tubes to the uterus. There, it attaches to grow during pregnancy. During this process, identical twins can form. Identical twins are less common than fraternal twins. They occur when one fertilized egg splits and develops into two embryos. Identical twins may share a placenta or have separate placentas, but each baby usually has its own amniotic sac. Identical twins are the same sex and have the same blood type, hair color, and eye color. They usually look very much alike.
Causes of Twin Pregnancy
Having twins runs in some families. The most important factor, however, is age. Women older than 30 years are more likely to have twins than are younger women. One reason is that women in their 30s—especially those in their late 30s—often release more than one egg during a menstrual cycle. When this happens, the chances of a twin pregnancy increase.
Women who take fertility drugs or use in vitro fertilization have a greater chance of having fraternal twins. Fertility drugs can cause more than one egg to be released. This can result in a multiple pregnancy. During in vitro fertilization, the egg is fertilized by a sperm in a lab. A doctor then places the embryo inside the uterus. If more than one embryo is transferred, twins, triplets, or even more can result. Identical twins also may result if the fertilized egg splits after transfer and develops into two embryos.
A twin pregnancy usually is diagnosed during a routine ultrasound exam performed in the first trimester of pregnancy. You or your health care provider may suspect that you are carrying twins if you have more severe signs and symptoms of pregnancy, such as severe morning sickness or breast tenderness. You also may gain weight more quickly.
You will need special prenatal care with twins. You may need to change your diet and exercise routines. You will see your health care provider more often, and you may need special tests.
When pregnant with twins, your body must nourish the babies and meet your energy needs as well. You should gain more weight when carrying twins than if you were having only one baby. Women at a normal weight before pregnancy should plan to gain 37–54 pounds. This weight should be gained gradually. In the first half of pregnancy, you should gain about 1 pound per week. In the second half, you should aim for a little more than 1 pound per week. If you are underweight, you may need to gain more. If you are overweight, you may need to gain less. Your health care provider will talk to you about the right amount of weight to gain.
To gain weight in a healthy way, you should eat an extra 400–600 calories a day. These calories should come from healthy foods to meet your body’s nutritional needs. Some women with twins may have more nausea and vomiting, which may make getting the right amount of calories difficult. It may be easier to eat smaller, more frequent meals.
All pregnant women need to get extra amounts of iron (27 milligrams a day) and folic acid (0.4–0.6 milligrams a day) to prevent anemia. Taking a prenatal multivitamin supplement will ensure you are getting these recommended amounts.
Staying active during pregnancy is important for your health. Talk to your health care provider about the type and level of exercise that is right for you. You may need to avoid strenuous exercise. Walking and swimming are usually good choices.
Monitoring a Twin Pregnancy
You will visit your health care provider more frequently if you are carrying twins. Your provider will monitor the health of your babies during your pregnancy with exams and special tests. Some tests are routine. Others may be done only when a problem is suspected. You may have some or all of these tests, depending on the status of your pregnancy:
The risk of certain complications is higher in a twin pregnancy. Sometimes, problems that occur in a twin pregnancy are genetic or the result of the mother’s age. Some of these problems may be prevented with early detection and care.
The most common complication is preterm labor and preterm birth. Preterm labor is labor that starts before the end of 37 weeks of pregnancy. It can result in preterm birth. More than one half of all twins are born preterm.
Preterm babies—including those considered “late preterm” (born between week 34 and week 37 of pregnancy)—often have problems breathing and eating. They often have to stay in the hospital nursery longer than usual. Very preterm babies can die or have severe mental or physical problems, even with the best of care. Problems also can occur as the babies grow and develop.
Some of these problems may be prevented if preterm labor is found early enough. It is important to know the signs and symptoms of preterm labor (see box). If you have preterm labor, you may be given a corticosteroid. This drug can help the babies’ lungs mature. In some cases, a drug called a tocolytic may be given to slow down or stop your contractions. Tocolytics can sometimes help postpone delivery for up to several days. These extra days can allow time for the corticosteroid to work. Tocolytics may cause heart and lung problems in women pregnant with twins. For this reason, these drugs are used with caution in twin pregnancies.
Preeclampsia is a disorder that occurs only during pregnancy. It usually starts after the 20th week of pregnancy. With twins, preeclampsia can start earlier and be more severe.
Preeclampsia can lead to serious problems for both the woman and babies. In the woman, it causes high blood pressure that can be severe. The kidneys and liver may fail. In rare cases, stroke can occur. The twins are at risk of growth problems and problems with the placenta. Preeclampsia that worsens and causes seizures in the woman is called eclampsia. The only cure for preeclampsia is delivery of the babies, which may result in preterm birth.
Women carrying twins have a higher risk of gestational diabetes. Women with gestational diabetes have an increased risk of preeclampsia and of developing diabetes later in life. Babies born to women with this condition may have breathing problems or low blood sugar levels. You may be referred to a specialist to help manage this condition.
Twins are more likely to be smaller than single babies. Ultrasound often is used throughout pregnancy to check the growth of each baby.
Twins are called discordant if one is much smaller than the other. Discordant twins are more likely to have problems during pregnancy and after birth. Identical twins may be discordant because of problems with the placenta or twin–twin transfusion syndrome (TTTS).
TTTS can develop when identical twins share a placenta. It occurs when the blood flow between the twins becomes unbalanced. One twin will have too little blood. The other twin will have too much blood. This condition can pose serious problems for both babies. If the condition is not treated, both babies can die.
TTTS can be treated during pregnancy by withdrawing some of the extra fluid with a needle or with surgery on the placenta. Sometimes, the twins may need to be delivered early.
Birth defects occur twice as often in twin pregnancies because each baby is at risk of having a birth defect. The risk of birth defects also increases with the mother’s age.
Your health care provider may do special tests to find out if your baby has certain birth defects. These tests include chorionic villus sampling (CVS) and amniocentesis. Before having one of these tests, you should know that
In addition, these tests are more technically difficult to perform in twins. To reduce the risk of complications, only experienced health care providers should perform these tests in twin pregnancies.
The chance of needing a cesarean delivery is higher with twins. In some cases, twins can be delivered by vaginal birth. How your babies are born depends on the following factors:
Twins usually can be born vaginally if they both are in the head-down position. A vaginal birth also may be possible when the lower twin is in the head-down position but the higher twin is not. Once the first twin is born, the other twin can sometimes be turned headfirst or delivered with feet or buttocks first. When this cannot be done, the second twin is delivered by cesarean birth. When the lower twin is not in the head-down position, both twins often are delivered by cesarean birth.
Caring for Your Newborn Twins
Caring for twins can be stressful. This is especially true if they are born preterm. Get as much rest as you can before and after the babies arrive. Arrange to get help from family, friends, and neighbors, especially in the beginning. Accept help when it is offered. Make sure to take time for you and your partner as a couple. Be as prepared as you can by learning about some of the challenges that may lie ahead.
Two babies mean double the feedings and diaper changes. This physical work can take a toll on you. You may feel overwhelmed or even sad sometimes. The “baby blues” are very common after pregnancy. These feelings usually go away after a week or two. Having twins might make you more prone to postpartum depression. If you feel sad for longer than 2 weeks or if your symptoms are severe, let your health care provider know.
Many women wonder if they can breastfeed more than one baby. It may be more difficult to breastfeed twins—especially if they were born preterm—but it can be done. Mother’s milk is the best food for any infant. It has the right amount of all the nutrients the babies need and adapts as your babies’ needs change. When you breastfeed, your milk supply will increase to meet the amount needed by your babies. You will need to eat healthy foods and drink plenty of liquids. If your babies are premature, you can pump and store your milk until they are strong enough to feed from the breast.
You can give your twins the best possible start by taking good care of yourself. Learn the warning signs of problems and talk to your health care provider about your questions and concerns.
It also is helpful to talk with others who have twins. There are organizations and support groups that provide services for parents of twins. Ask your health care provider to recommend one. There also are books you can read and web sites you can visit to learn more.
Amniocentesis: A procedure in which a needle is used to withdraw and test a small amount of amniotic fluid and cells from the sac surrounding the fetus.
Amniotic Fluid: Water in the sac surrounding the fetus in the mother’s uterus.
Amniotic Sac: A fluid-filled sac in the woman’s uterus where the fetus develops.
Anemia: Abnormally low levels of blood or red blood cells in the bloodstream. Most cases are caused by iron deficiency, or lack of iron.
Biophysical Profile (BPP): An assessment by ultrasound of fetal breathing, fetal body movement, fetal muscle tone, and the amount of amniotic fluid. May include fetal heart rate. Sometimes the profile includes only the nonstress test and an estimate of the amniotic fluid.
Cervix: The opening of the uterus at the top of the vagina.
Cesarean Delivery: Delivery of a baby through incisions made in the mother’s abdomen and uterus.
Chorionic Villus Sampling (CVS): A procedure in which a small sample of cells is taken from the placenta and tested.
Corticosteroid: A hormone given to help fetal lungs mature, for arthritis, or for other medical conditions.
Discordant: A large difference in the size of fetuses in a multiple pregnancy.
Eclampsia: Seizures occurring in pregnancy and linked to high blood pressure.
Embryo: The developing fertilized egg up to 8 completed weeks of pregnancy.
Fallopian Tubes: Tubes through which an egg travels from the ovary to the uterus.
Fertilization: Joining of the egg and sperm.
Fraternal Twins: Twins that have developed from more than one fertilized egg; they are not genetically identical and each has its own placenta and amniotic sac.
Gestational Diabetes: Diabetes that arises during pregnancy.
Identical Twins: Twins that have developed from a single fertilized egg; they are usually genetically identical and may or may not share the same placenta and amniotic sac.
In Vitro Fertilization: A procedure in which an egg is removed from a woman’s ovary, fertilized in a dish in a laboratory with the man’s sperm, and then transferred to the woman’s uterus to achieve a pregnancy.
Nonstress Test (NST): A test in which changes in the fetal heart rate are recorded using an electronic fetal monitor.
Ovulation: The release of an egg from one of the ovaries.
Placenta: Tissue that provides nourishment to and takes waste away from the fetus.
Postpartum Depression: Intense feelings of sadness, anxiety, or despair after childbirth that interfere with a new mother’s ability to function and that do not go away after 2 weeks.
Preeclampsia: A condition of pregnancy in which there is high blood pressure and protein in the urine.
Prenatal Care: A program of care for a pregnant woman before the birth of her baby.
Preterm: Born before 37 weeks of pregnancy.
Stroke: A sudden interruption of blood flow to all or part of the brain, caused by blockage or bursting of a blood vessel in the brain and often resulting in loss of consciousness and temporary or permanent paralysis.
Tocolytic: A drug used to slow contractions of the uterus.
Trimester: Any of the three 3-month periods into which pregnancy is divided.
Twin–Twin Transfusion Syndrome (TTTS): A condition of identical twin fetuses when the blood passes from one twin to the other through a shared placenta.
Ultrasound: A test that uses sound waves to examine the fetus.
Uterus: A muscular organ located in the female pelvis that contains and nourishes the developing fetus during pregnancy.