LiveScience reports on a study that shows a link between the height of mothers and the likelihood that they will have twins. The study compared the heights of 149 mothers of twins or triplets to those of average U.S. women and found that the moms of twins and triplets were on average more than an inch taller.
Dr. Gary Steinman, who led the study, explained that taller women have more insulin-like growth factor.
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.
It's this increased sensitivity that influences the rate of twinning. I also found it interesting that countries with higher average heights have higher rates of twinning.