Statistically, the number of twins that are being born to women in the United States has dramatically increased in the last thirty years, up nearly eighty percent from 1980 to 2009, according to a new report released by the Centers for Disease Control and Prevention. According to that report, 189 out of 10,000 births were twin births in 1980 but had jumped to 333 out of 10,000 in 2009. The study's lead author, Joyce A. Martin, an epidemiologist at the CDC's National Center for Health Statistics called the sudden leap "troubling".

In general, it is ideal to have single birth pregnancies for a number of health reasons, both for the mother and the infant. While the human body can adapt to handle a multiple fetus pregnancy, it is more taxing and can often cause a number of serious complications. Twins are far more likely to be born prematurely, for instance and in many cases are much smaller than single birth babies. Mothers who are carrying twins are also more likely to need extended hospital stays as are their babies.

The biggest jump in twin birth numbers came with white mothers over the age of thirty. And, the number of women who had twins increased more than 200% once the mother reached the age of forty. Martin explained that in the case of women in their mid thirties and beyond, their eggs are much older and are far less likely to behave like younger eggs, even after they become fertilized. In addition, more women in these age groups are seeking some form of treatment for infertility which also increases their risk of multiples.

In the earlier days of in vitro fertilization and other fertility treatment types, the doctors would implant as many as four to six embryos in hopes of increasing the chances of having one or two make it to full term. But, with enhanced technology these days, doctors are opting to implant only one or two of the fertilized embryos which is meant to cut down on some of the multiple births.

The increase in twins is not universal across the country, the study has noted. In some states, the rate has barely changed at all for any of the ethnic groups while in others, the rates have changed dramatically. African American women, who have historically had the highest rates of twins, are now matched by white women in many of the US states according to the study.