An obstetrician known for his focus and research on multiple pregnancies found that dietary changes can affect a woman’s chances of having twins, and that the overall chances are determined by a combination of diet and heredity.
By comparing the twin rates of vegan women who do not eat animal products with women who eat animal products, Dr. Gary Steinman, staff physician at the Long Island Jewish Medical Center in New Hyde Park, New York, found that women products, especially dairy products, are five times more likely to have twins. The study was published in the May 20, 2006 issue of the Journal of Reproductive Medicine.
The Lancet published Dr. Steinman’s commentary on the effects of diet on twins in its May 6 issue.
The culprit could be insulin-like growth factor (IGF), a protein that is secreted from the liver of animals — including humans — in response to growth hormone, circulates in the blood, and passes into milk. IGF increases the sensitivity of the ovaries to follicle-stimulating hormone, increasing ovulation. Some studies suggest that IGF may help embryos survive the early stages of development. The concentration of IGF in the blood of vegan women is approximately 13% lower than that of women who consume dairy products.
The twin rate in the US has risen substantially since 1975, about the time assisted reproductive technology (ART) was introduced. Intentional postponing of pregnancy has also played a role in the increase in multiple pregnancies, as a woman’s chances of having twins increase with age even without ART.
“The continued rise in twins in 1990, however, could also be a consequence of the introduction of growth hormone into cows to improve performance,” says Dr. Steinman.
In the current study, when Dr. Steinman compared the twin rates of women who eat normally, vegetarians who consume milk, and vegans, he found that vegans give birth to twins five times less often than women who do not exclude milk from their diet.
In addition to the effect of nutrition on IGF levels, there is a genetic link in many animal species, including humans. In cattle, the parts of the genetic code responsible for the birth of twins are close to the IGF gene. Researchers conducted a large-scale study of African-American, white, and Asian women and found that IGF levels were highest in African-American women and lowest in Asian women. Some women are genetically predisposed to produce more IGF than others. In these demographics, the twin score graph parallels the FMI level graph. “This study shows for the first time that the chance of having twins is determined by both heredity and the environment, or, in other words, nature and nutrition,” says Dr. Steinman. These results are similar to those observed by other researchers in cows, namely: the chance of giving birth to twins directly correlates with the level of insulin-like growth factor in the woman’s blood.
“Because multiple pregnancies are more prone to complications such as preterm birth, birth defects, and maternal hypertension than singleton pregnancies, the results of this study suggest that women considering pregnancy should consider replacing meat and dairy products with other sources of protein, especially in countries where growth hormones are allowed to be administered to animals,” says Dr. Steinman.
Dr. Steinman has been studying twin birth factors since he adopted four identical twins in 1997 at the Long Island EMC. His recent study, published this month in the Journal of Reproductive Medicine, on fraternal twins, is the seventh in a series. The remaining six, published in the same journal, focus on identical or identical twins. A summary of some of the results is given below.
Previous Research
Dr. Steinman found that women who become pregnant while breastfeeding are nine times more likely to conceive twins than those who do not breastfeed at the time of conception. He also confirmed studies by other scientists showing that identical twins are more common among girls than among boys, especially among conjoined twins, and that identical twins are more likely to miscarry than fraternal twins.
Dr. Steinman, using fingerprinting, found evidence that as the number of identical fetuses increases, their physical differences also increase. In a recent study on the mechanisms of twin birth, Dr. Steinman confirmed that the use of in vitro fertilization (IVF) increases the chance of having identical twins: implanting two embryos gives birth to three babies, he also suggested that an increase in calcium or a decrease in the amount of a chelating agent – ethylenediaminetetraacetic acid (EDTA) in IVF environment can reduce the risk of unwanted complications.