Overview of Multiple Pregnancy
A multiple pregnancy is a pregnancy involving more than one fetus. Twins, triplets, and quadruplets are multiple pregnancies. The largest multiple pregnancy on record led to the birth of nine offspring.
Twins are the most common type of multiple pregnancy. But worldwide, the incidence of multiple pregnancies of all types - twins, triplets, quadruplets, quinteplets, sextets, and more - is increasing as advanced types of infertility treatment become more common.
In the United States, the number of twin births has risen more than 50% over the last 2 decades since the advent of IVF (in vitro fertilization) in 1978, from about 68,000 to approximately 104,000 in 1997. The incidence of higher-order multiple pregnancies (triplets or greater) has increased 100-fold. Births of single individuals (singletons) rose only 6% in that same time period. The trend is evident in other countries as well. In Sweden, for example, the incidence of twin deliveries has increased nearly 80% over the last 20 years.
The increase of multiple births is age related. According to the National Center for Health Statistics, over the last 20 years, multiple pregnancies in the United States have increased 400% among women in their 30s and 1000% 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 who has not been able to conceive is suddenly faced with the challenge of two, three, four, or more possible new babies? One of the features of IVF 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 shows that about 45% of all IVF newborns are born as multiple birth babies.
About 5% of infertility treatment involves IVF or other forms of assisted reproductive technology. The use of hormones to stimulate superovulation, coupled with insemination, is a more common method of infertility treatment. Superovulation 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% of the increased frequency of multiple births can be explained by IVF and another 33% by the use of ovarian stimulation.