Study links taller women with multiple births

Couple curious to know the factor behind the birth of twins now can go through a US study which revealed that the taller women are more likely to give birth to twins.

Gary Steinman, an obstetrician at New York's Long Island Jewish Medical Center, who specializes in multiple-birth pregnancies, compared the heights of 129 women who delivered twins or triplets with the average height of women in US and discovered women with multiple-birth pregnancies averaged more than an inch taller.

According to Steinman, the suspected culprit is insulin-like growth factor (IGF), which has been positively linked to both height and multiple births. "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 Steinman.

Steinman, whose study is being published in the September issue of the Journal of Reproductive Medicine, said the insulin-like growth factor is a protein that is released from the liver in response to growth hormone. It multiplies the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing ovulation. Some studies also suggest that this factor may help embryos survive in the early stages of development.

Among its many effects in the body, IGF stimulates cells in the shaft of long bones to grow. Previous studies have demonstrated that people with short stature have significantly lower levels of IGF. Countries with taller women have higher rates of twinning compared to countries with shorter women.

"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," Steinman said in a statement.

After studying the compared data, Steinman discovered that of 129 surveyed women 105 had twins and 24 had triplets and they averaged 5 feet 5 inches tall, more than an inch taller than the U.S. average for adult females of about 5 feet 3 ½ inches.

Earlier studies have revealed that shorter women have remarkably lower levels of IGF and that countries with taller women have higher rates of multiple births compared to countries with shorter women.

In an earlier study in his series on the mechanisms of twinning, Steinman observed that women who consume animal products, specifically dairy, were five times more likely to bear twins. Cows, like humans, produce this protein in response to growth hormones and release it into the blood and the protein makes its way into their milk.

Steinman has been invited to speak about IGF and twinning at the three-day workshop "Milk, Hormones and Human Health," to be held next month from 23rd to 25th in Boston. The workshop is sponsored by the Harvard Center for Cancer Prevention at the Harvard School of Public Health and the McGill University Centre for Cancer Prevention.