How can drinking milk affect my pregnancy?

The dairy industry’s marketing mantra of “three-a-day” could take on a whole new meaning in light of a 2006 study in the Journal of Reproductive Medicine, which links milk consumption with multiple births. Study author Gary Steinman, MD, PhD, of the Long Island Jewish Medical Center, compared the twinning rates of vegan mothers with the general population of mothers and found the latter to be five times more likely to give birth to twins. Of 1,042 vegan women, only four had experienced multiple births—about 0.4 percent—compared with nearly 2 percent of the general population of mothers. And when Dr. Steinman had 66 women with a history of multiple births rate their dairy consumption on a scale of one to four (one being none, four being a lot of milk), the moms of multiples averaged about a three.

Dr. Steinman speculates that the increased tendency to twin among milk-drinking moms can be attributed to the growth hormones that commonly have been given to cows in the United States since the 1990s—when the rate of multiple births began to rise significantly. Does the data support his hypothesis? Perhaps, though additional factors, such as more women giving birth later in life, likely play a role as well.