Taller women are more likely to have twins, and a protein called insulin-like growth factor (IGF) may be the reason why. That's the conclusion of a study by Dr. Gary Steinman of Long Island Jewish Medical Center in New Hyde Park, New York. Steinman is an obstetrician specializing in multiple births.
In his study, Steinman compared the heights of 129 women who gave birth to twins or triplets with the average height of women in the United States.
He found that the multiple-birth mothers were an average of 65 inches tall, compared with the average female height of 6334 inches.
IGF—released from the liver in response to growth hormone-has a number of effects in the body, including stimulating the growth of cells in the shaft of long bones.
Steinman noted that IGF also increases the sensitivity of ovaries to follicle-stimulating hormone, thereby boosting ovulation. Some previous studies have suggested that IGF may help embryos survive the early stages of development.
Countries with taller women tend to have higher rates of twins than countries with shorter women. Research has also found that shorter people have lower levels of IGF.
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