A researcher who specializes in multiple-birth pregnancies has confirmed that taller women are more likely to have twins.
Taller women have more of an insulin-like growth factor that has been linked to height and to the rate of twins in previous work. Dr. Gary Steinman, an obstetrician at Long Island Jewish Medical Center, compared heights of 125 women who had twins and 24 who had triplets to the average height of U.S. women.
Those who birthed two or more children were on average more than an inch taller.
The study was published in the September issue of the Journal of Reproductive Medicine.
Insulin-like growth factor (IGF) is a protein released by the liver in response to growth hormones. It increases the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing ovulation.
"Any circumstance that affects the amount of available insulin-like growth factor so as to modify the sensitivity of the ovary to follicle-stimulating hormone appears to govern the rate of spontaneous twinning," said Dr. Steinman.
IGF also stimulates cells in the shaft of long bones to grow. Previous studies have found shorter people have lower levels of IGF. Other studies suggest IGF might help embryos survive in the early stages of development.
Countries with taller women have higher rates of twinning, according to a statement released by Steinman.
In a previous study, Steinman found that women who consume animal products, specifically dairy, are five times more likely to have twins. Cows, like humans, produce IGF in response to growth hormone and release it into the blood, and the IGF makes its way into their milk.