IVF and multiple pregnancy

People often associate IVF with the potential for getting pregnant with more than one adorable baby. It’s definitely possible to have multiples with fertility treatments that stimulate the ovaries and increase egg production, but IVF can sometimes increase your chances even more.

Why does it happen?

A typical IVF cycle looks like this: first, the ovaries are stimulated by a combination of fertility medications. One or more of the eggs are harvested from the ovarian follicle. The egg is then fertilized in the laboratory, and transferred to the uterine cavity for implantation.

Even one cycle of IVF is expensive. Because of this, many people want to do as much as they can to get pregnant in one cycle. Instead of implanting just one embryo, some choose to do two or more to maximize their chances of conception. Multiple embryo transfers make conception more likely, but the result is a far greater likelihood for a multiple pregnancy than natural conception, or artificial insemination.

How does it happen?

Identical twins or higher order multiples come from an embryo that divides itself in the uterus, and this can happen with any pregnancy, including one aided by fertility treatments. Fraternal twins come from two separate eggs that have been individually fertilized. Most sets of multiples that come from IVF treatments are fraternal because they come from the multiple embryos implanted into the uterus. However, it’s believed that identical twin rates are higher in IVF pregnancies as well, though researchers are still unsure about the exact cause.

What’s the likelihood of multiples?

According to the 2013 ART National Summary Report, the U.S. rate of multiple births for IVF cycles using fresh, nondonor eggs or embryos is about 27%. Most of those births were twins, but about 1% percent of births were triplets or more. In contrast, the rate of U.S. multiples overall is about 3%. So it’s safe to say that multiple embryo transfers increase the likelihood of multiples significantly.

Are there any other factors?

Even if you don’t transfer more than one embryo, that doesn’t mean the chance of having multiples completely disappears. Multiple embryos being transferred increases the risk of fraternal multiples, but there’s still a possibility that a single embryo could split into identical multiples. If you undergo a fertility treatment other than IVF that uses hormone therapies to increase egg production, you might also increase your chances of having multiples.

Sources

Mayo Clinic Staff. “In vitro fertilization (IVF): Overview.” Mayo Clinic. Mayo Clinic, June 16, 2016. Web.
“Avoiding multiple births in IVF.” Resolve. Resolve: The National Infertility Association. Web.
National Center for Chronic Disease Prevention and Health Promotion: Division of Reproductive Health. “2013 Assisted Reproductive Technology National Summary Report.” Center of Disease Control. Web. 2013.