by EBSCO Medical Review Board
(Twins; Triplets; Quadruplets; Quintuplets)


A multiple pregnancy is when a woman is pregnant with two or more fetuses. Twins are the most common type of multiple pregnancy.

Twins in Utero
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Multiple pregnancies happen when:

  • A single egg divides and develops into two or more fetuses (identical)—babies will be same sex and look similar
  • More than one egg is fertilized by a different sperm (fraternal)—babies look different and may be different sexes

If there are three or more fetuses, then they may be identical, fraternal, or both.

Risk Factors

Women over 30 are more likely to have a multiple pregnancy. It is also more common in women with infertility who receive fertility treatments.

Other things that may raise the chances of having a multiple pregnancy are:

  • A previous multiple pregnancy
  • A family history of multiple births
  • More than one previous pregnancy


Symptoms are:

  • More rapid weight gain than expected in the first trimester
  • Severe morning sickness
  • More fetal movement than with a single fetus pregnancy


The number of fetuses can be found with normal prenatal tests. The doctor may suspect twins based on a person's history or symptoms. It can be confirmed with:

  • Ultrasound—can create images of fetuses
  • Fetal heartbeat—more than one heartbeat can be heard
  • Certain blood tests done near the 16th week of pregnancy—will show higher levels with more than one fetus


Regular prenatal visits will help to keep the mother and baby well. Some problems that will be watched for are:

Early Labor

Most multiple births will end before 37 weeks of pregnancy. Babies born preterm have a higher risk for many health problems. Bed rest or medicine may help to delay early birth. Medicine may also be given to help the baby's lungs mature if labor starts before 34 weeks of pregnancy.

Gestational Diabetes

Gestational diabetes is a high level of blood glucose during pregnancy. It can affect both the mother and baby's health. Treatment can help to return blood glucose levels to normal. It may include changes in diet, exercise, and medicine.


Preeclampsia is a fast and dangerous increase in blood pressure during pregnancy. Treatment may include medicine, rest, and delivery of the babies.

Abnormal Fetal Position (Breech or Transverse)

More than one fetus in the uterus raises the chance that one of them will be unable to turn head down. A breech or transverse presentation may require a cesarean delivery.

Twin Twin Transfusion Syndrome (TTTS)

TTTS may happen with identical twins. Fetuses can share a tube to the placenta. If this sharing is unequal, TTTS can develop. One twin gets less blood. The other may end up with too much blood and fluid in the body. It can affect the health of both babies. Fetus growth and heart beat will be closely watched.

Fetal Growth

Multiple fetuses are more likely to have growth issues. Sometimes, one may be much smaller than the other. This can be normal or signal a problem. Growth will be carefully watched.


The risk of c-section is higher with more than one fetus.

Women will also have a higher chance of heavy blood loss after giving birth.


Multiple pregnancy with natural conception cannot be prevented. Fertility treatments can lead to a multiple pregnancy. The care team will work to make sure the number of possible pregnancies is safe.


American Congress of Obstetricians and Gynecologists 

March of Dimes 


Health Canada 

The Society of Obstetricians and Gynaecologists of Canada 


American College of Obstetricians and Gynecologists (ACOG), Society for Maternal-Fetal Medicine. ACOG Practice Bulletin No. 169: Multifetal gestations: twin, triplet, and higher-order multifetal pregnancies. Obstet Gynecol 2016 Oct;128(4):e131, reaffirmed 2016.

Multiple gestation. EBSCO DynaMed website. Available at: Accessed September 14, 2021.

Multiple pregnancy. American College of Obstetricians and Gynecologists website. Available at: Accessed September 14, 2021.

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