embryos in petri dishIn 1971, about 1.8 percent of all babies born in the United States were multiple births - twins, triplets, or more (higher-order births). By 2011, the multiple-birth rate had climbed to 3.5 percent. The popularity of medically assisted conceptions had risen, too, as treatments became more socially accepted, insurance companies started picking up the tab, and the success rate improved promisingly.

For couples willing to tackle the challenge of medically assisted conception, more than one child at a time may seem like a multitude of blessings but multiple births, even of twins, is risky business. Women carrying multiple babies run the increased risk of pregnancy complications and so do their babies. Some of the main concerns include premature birth, cerebral palsy, and delays or complications of development as a child matures.

In the early days of in vitro fertilization (IVF), it was standard practice to implant more than one embryo at a time so as to increase the chance that one of them would develop into a full-term, healthy baby. This practice often produced multiple births.

As IVF treatments have improved over time, it is becoming more likely that a carefully selected single embryo will be implanted, eliminating all risk of multiple births. The most desirable outcome of IVF - the birth of a singleton child - is easier on both mother and child.

There are other assisted reproductive treatments besides IVF, however, and multiple births are still common when these treatments are used. Two such procedures include drugs such as clomiphene citrate and injectable hormones.

From 1998 to 2011, the rate of triplets and higher-order births jumped from 36 percent to 45 percent when fertility drugs are used. During this same timeline, the rate of multiple births resulting from IVF dropped almost as dramatically, from 48 percent to 32 percent (a 29-percent decrease).

Fertility drugs are preferred by many couples because they are less expensive, more likely to be covered by medical insurance, and easier to use, amongst other reasons.

Fertility-enhancing hormones (gonadotropins) can can be injected in the home without the need for medical personnel to administer it. Clomiphene citrate is taken orally, in pill form. For either drug, the objective is to stimulate the ovaries into producing multiple eggs per menstrual cycle. There is little, if any, control over how many eggs will be produced or fertilized.

In vitro fertilization (IVF) requires a closely monitored schedule and very close contact with one’s team of fertility specialists. Embryo selection and implantation is an increasingly exacting process. The success rate for producing one child at a time is growing as the technologies and procedures involved are perfected.

Source: Kulkami, Aniket D, et al. “Fertility Treatments and Multiple Births in the United States.” New England Journal of Medicine. Massachusetts Medical Society. Dec 5, 2013. Web. Dec 11, 2013.