Chances Of Having Twins Can Be Modified By Diet

An obstetrician well known for his care of and research into multiple-birth pregnancies has found that dietary changes can affect a woman's chances of having twins, and that her overall chance is determined by a combination of diet and heredity. During a series of seven studies, Gary Steinman, MD, PhD, an attending physician at Long Island Jewish (LIJ) Medical Center in New Hyde Park, New York, discovered the following fascinating points.
  • Dr Steinman found that women who become pregnant while breastfeeding are nine times more likely to conceive twins than women who are not breastfeeding at the time of conception.

  • In his most recent study of the mechanisms of twinning prior to the new study, Dr Steinman confirmed that use of in vitro fertilization (IVF) methods increases the incidence of monozygotic twinning -- where the transfer and/or implantation of two embryos results in three infants -- and he proposed that adding more calcium or reducing the chelating agent ethylenediamine tetraacetic acid (EDTA) in the IVF incubation media might decrease the unwanted complication.

  • 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.

  • "The continuing increase in the twinning rate into the 1990s, however, may also be a consequence of the introduction of growth-hormone treatment of cows to enhance their milk and beef production," said Dr Steinman. In the current study, when Dr Steinman compared the twinning rates of women who ate a regular diet, vegetarian diet with dairy, and vegan diet, he found that the vegan women had twins at only one-fifth the rate of women who commonly do not exclude milk from their diets.

  • The twinning rate in the United States has increased significantly since 1975, about the time assisted reproductive technologies (ART) were introduced.

  • The intentional delay of childbearing has also contributed to the increase of multiple-birth pregnancies, since older women are more likely to have twins even without ART.


  • In addition to a dietary influence on IGF levels, there is a genetic link. 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.

  • He also confirmed findings by others that identical twin sets are more often female than male, especially in conjoined twin sets, and that monozygotic twin sets are more likely to miscarry than dizygotic sets.

  • His studies also found evidence through fingerprint analysis that as the number of fetuses in a monozygotic set increases, so does the level of physical diversity among them.

"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. His latest study was published in the May 2006 issue of the Journal of Reproductive Medicine.

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.PregnancyAndBaby.com


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