A Harvard study has revealed a link between a woman's age and the likelihood of giving birth to multiple children of the same sex.
Siwen Wang, a PhD student in nutritional epidemiology at the Harvard T.H. Chan School of Public Health, began researching the topic after noticing a trend in her own family. Her mother was one of three sisters and a younger brother, while her father had two brothers and no sisters.
'I was wondering whether it's just pure chance or if there was some special biology underlying this phenomenon,' she told the Boston Globe.
Her questions led to a study published July 18 in Science Advances by her and seven others.
The researchers analyzed 146,064 pregnancies from 58,000 US nurses across nearly six decades and discovered that in some families the odds are not so random.
