In addition to a dietary influence on IGF levels, there is a genetic link in numerous species of animals, including humans. In cattle, regions of the genetic code that control the rate of twinning have been detected in close proximity to the IGF gene. Researchers have found through large population studies of African American, Caucasian and Asian women that blood IGF levels are greatest among African Americans and lowest in Asians. Some women are just genetically programmed to make more IGF than others. Twinning rates in these demographic groups parallel the IGF levels.
"This study shows for the first time that the chance of having twins is affected by both heredity and environment, or in other words, by both nature and nurture," said Dr. Steinman. These findings are similar to those observed in cows by other researchers, namely that a woman's chance of having twins appears to correlate directly with her blood level of insulin-like growth factor.
"Because multiple gestations are more prone to complications such as premature delivery, congenital defects and pregnancy-induced hypertension in the mother than singleton pregnancies, the findings of this study suggest that women contemplating pregnancy might consider substituting meat and dairy products with other protein sources, especially in countries that allow growth hormone administration to cattle," said Dr. Steinman.
Dr. Steinman has been studying factors that cause or contribute to twinning ever since he delivered a rare set of identical quadruplets in 1997 at LIJ Medical Center. His most recent study published in this month's Journal of Reproductive Medicine on fraternal, or dizygotic, twinning is the seventh in a series. The other six studies, published in
Source:North Shore-Long Island Jewish (LIJ) Health System