Taller women are more likely to have twins.
Researchers from New York's Long Island Jewish Medical Center, USA, compared the heights of 129 women who gave birth to twins or triplets with the average height of women in the United States and found women with multiple-birth pregnancies averaged more than an inch taller.
The researchers said that the reason seemed to be an insulin-like growth factor, which has been positively linked to both height and twinning. Insulin-like growth factor is a protein that is released from the liver in response to growth hormone. 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 appeared to govern the rate of spontaneous twinning.
Previous studies have demonstrated that shorter people have significantly lower levels of this protein and that countries with taller women have higher rates of twinning compared to countries with shorter women. In a previous study, it was found that women who consume animal products, specifically dairy, were five times more likely to have twins. Cows, like humans, produce insulin-like growth factor in response to growth hormones and release it into the blood, and the protein makes its way into their milk.
Journal of Reproductive Medicine,
September 2006
September 2006