Gary Steinman, MD, PhD (attending physician at Long Island Jewish (LIJ) Medical Center in New Hyde Park, New York) obstetrician well known for his acre and research into multiple-birth pregnancies found a woman's overall chances of having twins is determined by a combination of diet and heredity.

According to Dr. Steinman, women who consume animal products, specifically dairy, are five times more likely to have twins.

The culprit may be insulin-like growth factor (IGF), a protein that is released from the liver of animals -- including humans -- in response to growth hormone, circulates in the blood and makes its way into the animal's milk.

IGF increases the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing ovulation. Some studies also suggest that IGF may help embryos survive in the early stages of development. The concentration of IGF in the blood is about 13 percent lower in vegan women than in women who consume dairy.

Dr. Steinman's study that is published in the May 2006 issue of the Journal of Reproductive Medicine (available May 20), is the first to show that the chance of having twins is affected by both heredity and environment. Findings that are similar to what has been observed in cows by other researchers.

Read more at Science Daily.