There are two types of twin pregnancy: fraternal and identical. Fraternal twins come from two separate eggs, whereas identical twins come from one egg splitting in two.

Twin pregnancies account for around 3% of all births in the United States. About 70% of those are cases of fraternal, or dizygotic, twins.

People can have more intense pregnancy symptoms with twins. Complications are also more common in twin pregnancies. However, in many cases, people can still have a vaginal delivery.

This article discusses the types, symptoms, and diagnosis of twin pregnancies. We also explore how maternity care and delivery differ when someone has twins.

There are several ways of classifying twin pregnancies. These include:

  • Monozygotic vs. dizygotic: Monozygotic twins arise from the same zygote, the medical term for a fertilized egg. The zygote splits into two, creating genetically identical twins. Dizygotic twins come from two separate eggs and are not identical — they are no more genetically similar than other siblings.
  • Dichorionic vs. monochorionic: “Chorion” refers to the placenta. Some twins share a placenta, while others do not. Twins that share one placenta are monochorionic, while those that have separate placentas are dichorionic.
  • Monoamniotic vs. diamniotic: These terms describe whether twin fetuses share an amniotic sac or have an individual sac.

The type of twin pregnancy can influence the risk of complications.

A twin pregnancy causes the body to produce higher levels of pregnancy hormones, particularly human chorionic gonadotropin (HCG). This may intensify early pregnancy symptoms.

Some potential signs of a twin pregnancy include:

  • weight gain, especially in early pregnancy
  • increased appetite
  • increased morning sickness
  • more intense symptoms than previous pregnancies or singleton pregnancies
  • feeling distinct fetal movements in different parts of the stomach

An ultrasound can usually diagnose a twin pregnancy. However, ultrasound is not perfect. Rarely, a sonographer may not see a second fetus, especially in early pregnancy.

Blood tests can also help diagnose a twin pregnancy. HCG levels may be higher than usual in early pregnancy if someone has twins.

A second trimester ultrasound can usually determine the sex by looking at the genitals of each developing fetus, but only if they are well-positioned for the ultrasound. Ultrasound sex determination is also sometimes inaccurate.

Twin pregnancies increase the risk of pregnancy and delivery complications. Some common complications include:

  • Early delivery: More than half of twins are born preterm, which is sooner than 37 weeks. It is the most common complication of twin pregnancies. It can occur because the fetuses have less space to grow or because the placenta has developed unusually.
  • Preeclampsia: This condition causes a sudden rise in blood pressure, along with other symptoms. It is a medical emergency and can require early delivery.
  • Gestational diabetes: This pregnancy-related form of diabetes can cause complications for the pregnant person and the fetus. This can include fetuses growing dangerously large and early birth.
  • Vanishing twin syndrome: This happens when one twin dies in the uterus and the body partially or fully absorbs it. On scans, this gives the appearance of one twin vanishing. According to a 2021 article, vanishing twin syndrome occurs in 36% of all twin pregnancies.
  • Stillbirth: Sometimes, one twin dies during the pregnancy, resulting in the stillbirth of one fetus and live birth of the other.

While there is a higher chance for complications in twin pregnancies, several have treatments that can reduce the risk they pose. For example, people with gestational diabetes can take medications and make dietary or lifestyle changes to control the condition.

There are some differences in care for people with twin pregnancies compared to those with single pregnancies. People who are expecting twins may need to:

  • have more frequent prenatal visits
  • have more ultrasounds to check the position of the fetuses
  • eat more calories to nourish both fetuses
  • take steps to reduce the risk of complications, such as following a special diet or getting the right amount of exercise
  • practice exercises to strengthen their core muscles and spine to carry the extra weight
  • receive additional care for any complications, such as medications

A doctor can advise on the best diet and exercise for each case. A person’s calorie needs will vary depending on their circumstances. Overall, individuals should aim to maintain 150 minutes of low-impact exercise per week when pregnant with twins, unless otherwise instructed by a doctor.

From the second trimester, ultrasounds may be as often as every 4–6 weeks. If there are any problems, ultrasounds may become more frequent, and a person may have to undergo further testing.

There are several ways delivering twins can be different from the birth of one baby. These include:

Early or induced birth

Just over half of all twins are born early. This can happen naturally, or a doctor may recommend inducing labor on a specific day if there are benefits to doing this. For example, if allowing the pregnancy to continue poses a risk, they may recommend induction.

An induced delivery may improve long-term outcomes in high-risk cases. However, it may require the babies to stay in a neonatal intensive care unit in the short term. Some twins may also have complications, such as low birth weight. Induced labor may also result in a longer hospital stay.

If a doctor recommends induction, a person may need a specialized delivery team. Giving birth in the hospital with access to emergency care will also be safer than a birth center or home delivery.

Delivery method

A twin birth does not necessarily mean that the delivery method has to change. A 2021 article emphasizes that vaginal delivery is possible — and advisable — in cases where both fetuses are head-down and there are no other safety concerns.

An older 2013 study compared outcomes between cesarean deliveries and vaginal deliveries in twin pregnancies, and there were no significant differences between the two groups.

Cesarean delivery is a major surgery involving removing babies from the uterus by an incision along the abdomen. Cesarean deliveries have longer recovery times and a higher risk of complications than vaginal delivery.

Cesarean deliveries are extremely valuable for reducing the risk of problems and as an emergency procedure. Otherwise, they might not be necessary for twin births where both fetuses are head-down.

An opinion article in the Medical Journal of Australia notes that elective cesarean deliveries for twins have increased in recent years but that the reasons for this trend are unclear. People should decide by speaking with their doctor and considering the benefits and risks of each method.

Giving birth to twins can feel both exciting and overwhelming. Twin pregnancies are mostly similar to other pregnancies, but they can involve more circulating hormones, extra weight gain, and a higher risk of some complications. The type of twin pregnancy can influence this, as well as someone’s overall health status.

Many people with twins can safely give birth vaginally if they choose to. It is important for individuals to discuss the delivery method with an obstetrician to make an informed decision.