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:
If there are three or more fetuses, then they may be identical, fraternal, or both.
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:
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:
Regular prenatal visits will help to keep the mother and baby well. Some problems that will be watched for are:
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 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.
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.
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.
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
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: https://www.dynamed.com/condition/multiple-gestation. Accessed September 14, 2021.
Multiple pregnancy. American College of Obstetricians and Gynecologists website. Available at:
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Accessed September 14, 2021.
Last reviewed July 2021 by EBSCO Medical Review Board Mary-Beth Seymour, RN