If you're a tall women who wants kids, you may be more likely to have twins, suggests an obstetrician whose specialty is multiple-birth pregnancies. Now this is strange, indeed. Why would tall women be more likely to have twins?
Gary Steinman, MD, PhD, suspects an insulin-like growth factor. This factor has been tied to height and the propensity to have twins. Dr. Steinman compared the heights of women who had twins (and triplets) with the height-average of U.S. adult females.
Results? The women who had the multiples were, on average, an inch taller. Though this may seem negligible, it's statistically significant enough to have made it into the Sept. 2019 Journal of Reproductive Medicine. Says Dr. Steinman: "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."
Insulin-like growth factor, a protein, stimulates the cells in bone shafts to grow. Short people have much lower levels of this protein. Countries with more tall women have higher rates of twins, when compared to nations with shorter women.
The term "taller" is used in this study, but how tall are we talking? This is more of a comparison feature, than absolute height, because the study shows that the subjects who had the twins or triplets were, on average, 5-5. The U.S. average female height for adults is 5 feet, three and three-quarter inches.
So does this mean that women 5-10 tall have some great chance of giving birth to twins? Of course not. But it would be interesting to investigate the rate of multiple births in women six feet tall, compared to shorter heights.
Dr. Steinman's study did not specifically differentiate between fraternal and identical pairs, other than to note that the majority of the multiple births involved fraternal twins. A previous study by Dr. Steinman showed a link between participants who ate animal products, particularly dairy, and having twins: They are five times as likely to give birth to twins. This is because cows produce insulin-like growth factor (a response to the growth hormones that they are given).
So does this mean that tall women who drink lots of milk are wildly likely to have twins? No. But wouldn't it be interesting to get a study on very tall women who eat lots of dairy, and compare their multiple-birth rate to short participants who avoid dairy?