Risk of multiple pregnancy from fertility drugs and assisted reproductive technology

Risks during multiple pregnancy

With each additional fetus a pregnant woman carries, health risks to her and her fetuses increase.1

Health risks in a multiple pregnancy. If 100 women* were pregnant with the following conditions the average number that would experience...

Gestational diabetes is:

Preeclampsia is:

Preterm labor is: Preterm birth is:
One fetus 3 6 15 10
Twins 5–8 10–12 40 50
Triplets 7 25–60 75 92
Quads 10 or more 60 or more 95 or more 95 or more

* A risk for 1 person in 100 is equal to a 1% risk.

Your chances of conceiving a multiple pregnancy

In the general population, less than 3% of births involve twins, triplets, or more. By contrast, your chances of conceiving a multiple pregnancy increase when you use fertility drugs and assisted reproductive technology (ART).

Currently, about 20% of multiple pregnancies occur naturally, while the other 80% are the result of using fertility drugs or assisted reproductive technology.2 The majority of these pregnancies are twins, but there are also more triplets (or more) than in the general population. The incidence of triplets or more can be controlled during in vitro fertilization by reducing the number of embryos transferred, but this is not possible with superovulation. Risks of multiple pregnancies are 5% to 8% with clomiphene and superovulation.3 The risks are even higher with gonadotropins.2

Ovulation stimulation

While clomiphene increases the likelihood of pregnancy with one or two fetuses, gonadotropins increase the risk of conceiving twins or more. Researchers continue to search for a dependable way to use gonadotropins, yet effectively prevent triplet-or-more pregnancies.

Balancing ART treatment success versus the risk of conceiving a multiple pregnancy

The risk of conceiving a multiple pregnancy is directly related to the number of embryos transferred to a woman's uterus. However, the chances of embryo or fetal loss increase as a woman ages from her mid-30s into her 40s. In order for a woman over age 35 to maximize her chances of conceiving with her own eggs and carrying a fetus to term, she typically has more embryos transferred than does a younger woman. This practice, however, increases her risk of conceiving multiple fetuses.

In Britain, law permits no more than 2 embryos transferred per ART procedure. In the United States, there are no legal restrictions on embryo transfer, and multiple birth rates are higher.4

Because of the risks of multiple pregnancy to the babies, the American Society for Reproductive Medicine recommends that women under age 35 have no more than two embryos transferred, women age 35 to 37 have no more than three, women 38 to 40 have no more than four transferred, and women who have had repeated failed cycles or are over age 40 have no more than five embryos transferred.5

Women over 40 have a high rate of embryo loss when using their own eggs. As an alternative, an older woman may choose to use more viable donor eggs.


  1. American Society for Reproductive Medicine (2000). Multiple pregnancy associated with infertility therapy. Practice Committee Report. Birmingham, AL: American Society for Reproductive Medicine.
  2. Burney RO, et al. (2007). Infertility. In JS Berek, ed., Berek & Novak's Gynecology, 14th ed., pp. 1185–1275. Philadelphia: Lippincott Williams and Wilkins.
  3. Speroff L, Fritz MA (2005). Induction of ovulation. In Clinical Gynecologic Endocrinology and Infertility, 7th ed., pp. 1175–1213. Philadelphia: Lippincott Williams and Wilkins.
  4. Al-Inany H (2005). Female infertility, search date April 2004. Online version of BMJ Clinical Evidence. Also available online: http://www.clinicalevidence.com.
  5. American Society for Reproductive Medicine (2006). Guidelines on number of embryos transferred. Fertility and Sterility, 86(4): S51–S52.

Last Updated: March 21, 2008

Author: Bets Davis, MFA & Sandy Jocoy, RN

Medical Review: Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology

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