What is a multiple pregnancy?

A multiple pregnancy is a pregnancy where you’re carrying more than one baby at a time. If you’re carrying two babies, they are called twins. Three babies that are carried during one pregnancy are called triplets. You can also carry more than three babies at one time (high-order multiples). There are typically more risks linked to a multiple pregnancy than a singleton (carrying only one baby) pregnancy.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

How do multiple pregnancies happen?

There are two main ways that a multiple pregnancy can happen:

One fertilized egg (ovum) splits before it implants in the uterine lining.
Two or more separate eggs are fertilized by different sperm at the same time.

These two different types of multiple pregnancy result in either identical or fraternal siblings. The difference between identical and fraternal babies goes back to how the multiple pregnancy happens.

Identical twins or triplets happen when a single egg is fertilized and then later splits. These newly divided embryos are identical. Children that are identical multiples will look like each other and be the same sex.

Fraternal multiples develop from separate eggs that are fertilized by a different sperm. Because these are different eggs and different sperm, the genetic material is varied. These children won’t look identical and can be different sexes from each other.

In a pregnancy with triplets or more, your babies could be all identical, all fraternal or a mixture of both. This can happen if your body releases multiple eggs and more than one is fertilized. In a case where you have both identical and fraternal multiples, more than one egg was fertilized and then at least one of those eggs also split after fertilization.

Are identical twins or triplets always the same sex?

Because identical twins or triplets share genetic material, they are always the same sex. The sex of a baby is determined by the particular sperm cell that fertilizes the egg at conception. There are two kinds of sperm cells — those carrying an X chromosome or Y chromosome. The mother’s egg carries an X chromosome. If a sperm cell carrying an X chromosome fertilizes the egg, it will make a XX combination (female). If the sperm cell is carrying a Y chromosome, you end up with an XY pairing (male).

Identical multiples start as one egg and then split, so whatever chromosome combination is present at fertilization is the sex of all multiples.

What increases the chance of a multiple pregnancy?

There are several factors that can increase the risk of a multiple birth. You might be at a higher risk of getting pregnant with more than one baby at a time if you:

Are older (women in their 30s are at a higher risk of multiples because the body starts to release multiple eggs at one time when you get older).
Are a twin yourself or have twins in your family.
Are using fertility drugs.

You might also be at a higher risk of a multiple pregnancy if you are taller than average or have a higher body weight.

Another risk factor for a multiple pregnancy is genetic. There is an increased possibility of a multiple pregnancy if you are a multiple yourself, or if multiples run in your family. This heredity trait is generally passed down through the maternal (mother’s) side of the family.

The use of fertility drugs can be another reason you might have a multiple birth. Treatments for infertility can increase your risk of a multiple pregnancy because procedures, like in vitro fertilization (IVF), often involve transferring more than one fertilized egg into your uterus. Your provider usually transfers more than one egg at a time to increase the odds of a successful pregnancy.

How common are multiple births?

Multiple births have become more common in recent years because more people are using fertility drugs and procedures, such as IVF, to help conceive a baby.

What are the signs of a multiple pregnancy?

The only way to know if you’re pregnant with more than one baby during your pregnancy is through an ultrasound exam with your healthcare provider. During this test, your provider can look at images of the inside of your uterus and confirm how many babies are in there.

You might experience more intense symptoms during a multiple pregnancy than with a single pregnancy. These can include:

Severe nausea and vomiting (morning sickness).
Rapid weight gain in the first trimester of pregnancy.
Sore or very tender breasts.
High human chorionic gonadotrophin (hCG) levels — this hormone is made during pregnancy and is what a pregnancy test picks up.
High amounts of the protein alpha-fetoprotein in your blood.

Apart from an ultrasound, your provider might suspect multiples if there’s more than one heartbeat detected during a fetal Doppler scan.

What complications are linked to multiple births?

Anyone can experience complications during pregnancy — regardless of how many babies you’re carrying. However, most healthcare providers consider multiple pregnancies higher risk than single pregnancies. This doesn’t mean that every woman who carries more than one baby during a pregnancy is going to have problems. If you’re pregnant with multiples, your provider will want to watch you for possible complications that can happen when you carry more than one baby at once. Your provider will talk to you about each risk factor and frequently check with you to make sure you aren’t experiencing anything concerning.

Possible complications include:

Premature labor and birth: The most common complication of multiple births is premature labor. If you’re pregnant for multiples, you are more likely to go into premature labor (before 37 weeks) than a woman carrying only one baby. The goal for many moms of multiples is to complete 37 weeks. This is considered term in a twin pregnancy and reaching this week of gestation increases the chance the babies will be born healthy and at a good weight. Babies that are born prematurely are at risk of another complication of multiple births — low birth weight.
Preeclampsia or gestational hypertension (high blood pressure): High blood pressure is called hypertension. During pregnancy, your healthcare provider will watch your blood pressure carefully to make sure you don’t develop gestational hypertension (high blood pressure during pregnancy). This can lead to a dangerous condition called preeclampsia. Complications related to high blood pressure happen at twice the rate in women carrying multiples compared to women pregnant with only one baby. This complication also tends to happen earlier in pregnancy and be more severe in multiple pregnancies than single pregnancies.
Gestational diabetes: You can develop diabetes during pregnancy. This happens because of the increased amount of hormones from the placenta. The size of the placenta can also be a factor in this condition. If you have two placentas, there’s an increased resistance to insulin.
Placenta abruption: This condition happens when the placenta detaches (separates) from the wall of your uterus before delivery. This is an emergency situation. Placenta abruption is more common in women who are carrying multiples.
Fetal growth restriction: This condition can also be called intrauterine growth restriction (IUGR) or small for gestational age (SGA). This condition happens when one or more of your babies is not growing at the proper rate. This condition might cause the babies to be born prematurely or at a low birth-weight. Nearly half of pregnancies with more than one baby have this problem.

Fraternal twins always have two placentas. The risks of pregnancies with fraternal twins are similar to those of pregnancies with only one baby. However, the number of possible risks are increased when compared to pregnancies with one baby.

Identical twins may have one placenta (70% of the cases) or two placentas (30% of the cases). The risks of identical twins with two placentas are similar to those listed above for fraternal twins. Identical twins with one placenta (called monochorionic) have risks that are unique to them. In 5 to 15% of the cases, they may develop a condition called twin-twin-transfusion-syndrome (TTTS). This is the consequence of vascular communications at the placenta level between the twins. Due to these communications, the twins may share their blood. When this happens — if nothing is done — there is a 90% risk that the twins will die in-utero. In-utero procedures are performed to decrease the fetal death risk for the twins.

Another complication that can happen in identical twins with one placenta is called twin-anemia-polycythemia sequence (TAPS). This is due to blood that goes from one twin to the co-twin because of vascular communications at the placental level. In this condition, one twin becomes anemic (low red-blood cells), whereas the co-twin becomes polycythemic (too many red-blood cells). Several treatments/interventions are performed when this happens.

A third condition that can occur in identical twins with one placenta is called” selective IUGR”. One twin grows well, whereas the co-twin does not experience much growth.

Another condition typical of identical twins is called twin-reversed-arterial-perfusion syndrome. In this condition, the heart of one twin pumps blood for the circulation of both twins. One twin does not have the heart and will not survive following birth. The outcome of the twin with the normal heart varies. Fortunately, this syndrome is rare (1 in 20,000 to 40,000) and it is amenable to in-utero procedures.

Identical twins with one placenta may also be in the same sac. They are called monochorionic (one placenta)-monoamniotic (one gestational sac). This pregnancy occurs in 1% of multiple gestations and it’s associated with an increased risk for one or both twins.

Your healthcare provider will diagnose the above conditions with an ultrasound.

Am I more likely to have a C-section delivery if I’m carrying multiples?

A cesarean section is a procedure used to deliver a baby through an incision (cut) in the abdomen. This type of delivery might be used for a variety of reasons, but it’s fairly common in multiple births. Your chance of having a C-section for a multiple birth is higher than if you were pregnant for only one baby. However, even in single births, a C-section can sometimes be the safest option for delivery.

Often, the babies aren’t in the right position for birth — head down. A C-section can also happen if you have a complication during pregnancy that means a vaginal birth isn’t the safest option for you or your babies. Your healthcare provider will monitor you leading up to your due date and talk to you about the best option for delivery.

What can I do to stay healthy during a multiple pregnancy?

Eating nutritious foods, getting enough rest, and visiting the doctor regularly are important steps for any pregnant woman to take toward a healthy pregnancy. These steps are especially important during multiple pregnancies.

If you’re expecting multiples, you have additional dietary needs to meet. Getting enough protein and enough hydration (fluids) is important. You’ll also need to make sure you get enough extra calories for the developing fetuses. One rule of thumb is to eat an extra 300 calories a day per baby. That means that if you’re pregnant with twins, you will need to add 600 calories to your daily diet. Talk to your healthcare provider about your diet and the specific amounts you’ll need for a healthy pregnancy.

Moms of multiples might also experience the typical discomforts of pregnancy more intensely. It’s important to take good care of yourself and get plenty of rest to help ease the stresses of pregnancy.

In some cases, you might want to find a healthcare provider who has experience with multiple births. Specialized healthcare can help ensure that you and your babies are receiving the best care available. The need for frequent, intensive prenatal care is very important in a multiple pregnancy. Talk to your family doctor or OBGYN about their recommendations for specialists.

Can I be active and exercise during a multiple pregnancy?

Exercise and activity is an important part of any pregnancy. In most cases, you can absolutely exercise during a multiple pregnancy. Low-impact exercises are a great way to stay in shape and maintain your health throughout pregnancy. Some low-impact exercises to try during a multiple pregnancy can include:

Swimming.
Walking.
Prenatal yoga.

Even though activity is wonderful during pregnancy, you should talk to your healthcare provider about the best activities for you. Some more strenuous activities might not be a good idea during a multiple pregnancy, including: