Overview of Multiple Pregnancy

A multiple pregnancy is a pregnancy involving more than one fetus. Twins, triplets, and quadruplets are multiple pregnancies.

Twins are the most common type of multiple pregnancy. Worldwide, the incidence of multiple pregnancies of all types—twins, triplets, quadruplets, quinteplets, sextets, and more—is increasing as advanced infertility treatments become more common.

In the United States, the number of twin births has risen substantially since the advent of IVF (in vitro fertilization) in 1978. The incidence of higher-order multiple pregnancies (triplets or greater) also has increased significantly. Births of single individuals (singletons) rose only modestly over the same time period. The trend is evident in other countries as well.

The increase of multiple births is age related. According to the National Center for Health Statistics, over the last 35 years, multiple pregnancies in the United States have increased 400 percent among women in their 30s and 1000 percent in women in their 40s. This trend is due in part to the fact that older women are less able to get pregnant naturally and are more likely to undergo infertility treatment.

Multiple Pregnancy and Infertility Treatment

How is it that a couple previously unable to conceive is suddenly faced with the challenge of two, three, four, or more new babies? One of the features of IVF—one that makes it such a successful infertility treatment—is that it usually involves implanting more than one embryo to increase the chance of a viable pregnancy.

Because there are multiple embryos, the chance of a multiple pregnancy increases. IVF babies are 20 times more likely to be born as multiple birth babies; one study showed that about 45 percent of all IVF newborns are born as multiple birth babies.

Only about 5 percent of infertility treatments involves IVF or another form of assisted reproductive technology. The use of hormones to stimulate superovulation, coupled with insemination, is a more common method of infertility treatment.

This method involves using gonadotropin (a hormone) to induce ovulation of more than one ovum. The more ova that are available to be fertilized, the greater the chance that a multiple pregnancy will result.

Because it is a more commonly used, and because it is so potent, superovulation accounts for as many, if not more, multiple births than IVF. Researchers estimate that 33 percent of the increased frequency of multiple births can be explained by IVF and another 33 percent by the use of ovarian stimulation.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 31 Oct 2000

Last Modified: 01 Oct 2015