Are you seeing double? Recent CDC study reports on rising rate of twins.

 If you haven’t had twins, chances are someone you know has. According to a recent report from the Centers for Disease Control and Prevention (CDC), one of every 30 babies born in 2009 was a twin. That’s nearly twice the rate of twins that was reported in 1980. The   biggest reason for this growth in twin rates is that more women are  having children later in life. Whether through fertility treatment or  naturally, the incidence of twins rose by 100 percent for women 35 to 39   years of age and by more than 200 percent when women over 40 conceived.Even when conception occurs naturally, women are more likely to have twins in their later reproductive years. That’s because as a woman ages the hormones produced by her brain to  signal her ovaries to produce eggs begin to shift into a higher gear. As   a result, a woman of 40 is at least twice as likely to conceive  twins—if she is still fertile—as she would have been at age 20. The  recent CDC report suggests that at least one-third of the rise in twin  rates may be related to the rise in the average age at which women are  having children.

But there are other factors at work as well. The increase rate of twins may be one of the best examples of how food choices can affect you hormonally. In 2006, a study demonstrated that women who ate two or more servings of non-organic  dairy per day were five times more likely to have twins as women who ate   no dairy at all. Other studies have shown that the growth hormones  given to dairy cows can stimulate a woman’s ovaries to release more eggs   at the time of ovulation. In fact, Britain banned the use of these  growth hormones in their dairy farms. British women are about half as  likely to have twins as women in the U.S.

These dietary influences aside, fertility treatment is the most easily documented factor in the rising rate of twins. More than half of the twins conceived today are through fertility treatment. A common strategy used to help women become pregnant is to increase the   number of eggs that they release; with this treatment comes the risk of  a multiple pregnancy. The use of medications to promote ovulation is   not easily monitored and is often prescribed by non-specialists, such as  gynecologists rather than reproductive endocrinologists (REs), which   specialize in the treatment of infertility. Nonetheless, these basic  fertility therapies are responsible for nearly half of the twin  pregnancies attributed to medical intervention; the remainder of the  twins produced through fertility treatment is the result of IVF (in  vitro fertilization) pregnancies.

In the process of IVF, eggs are  fertilized and allowed to go through their initial stages of  development in the laboratory. That allows REs to select the embryos  that are most likely to implant and become a healthy baby. Since the  process can be expensive, there is a tendency to put back more than one  embryo at a time. In fact, a recent experiment even suggested that when two embryos are transferred together they may interact in a way that improves the chance that they will both thrive. That can not only improve pregnancy rates, but it also increases the  risk of having twins.

As a fertility specialist, I know that many of my patients actually want twins. They are eager to complete their family and they view twins as a way of achieving their goal instead of having one child at a time. In other words, patient preference has also  contributed to the increase in twins. That said, the recent CDC report  did find that the rise in twin pregnancies due to fertility treatment  has leveled off considerably since 2005.

If you wish to minimize your risk of having twins, here’s what you can do:

• Go organic. By  avoiding growth hormones, especially in dairy products, you may  minimize any      dietary boost to your chance of having twins.
• See a specialist. A board-certified reproductive      endocrinologist is a fertility specialist      trained to safely improve your odds of  pregnancy while minimizing your risk of      a multiple pregnancy.
• Consider IVF with ESET. Many patients going through treatment are considering elective single embryo transfer (ESET),      in which just one embryo is transferred during IVF, to reduce their risk      of twins.

Have you had twins? Were you counseled on steps you could take to reduce your risk or was this your goal?

Robert Greene, M.D., FACOG, is a physician at the CNY Fertility Center in central New York and the author of Perfect Hormone Balance for Fertility, Perfect Hormone Balance for Pregnancy, and Happy Baby, Healthy Mom Pregnancy Journal.