What factors increase the odds of having twins?

conceivingtwins_largeOver the last 30 years, there’s been an increase in the instance of twins. This is primarily because more women are seeking help with getting pregnant. Assistive reproductive technology, things like drugs to increase ovulation and techniques like in vitro fertilization (IVF), increases the risk of having multiple gestations.

Factors that increase the odds of conceiving twins

Age – There’s an increased risk of having twins as women age. The average age at which women get pregnant has increased as more women enter the workforce and start a family a little later. The difficulty of getting pregnant and the percentage of miscarriages also increase as women get older. The number of successful pregnancies in women over 40 isn’t high, but the percentage of those successful pregnancies that result in twins is.

Family history – Twins tend to be more common in some families. There may be an underlying genetic factor that predisposes a woman to release more than one egg at a time, which increases the chance of having twins.

Weight – There has been some consideration that women who are overweight are more likely to have more than one ovulation at a time, which may increase the chance of twins.

Diet – Interestingly, the highest rate of twins in the world is among a particular group in Africa called the Yoruba. One possible reason the twinning rate is so high among the Yoruba is that their diet is rich in a specific kind of yam that contains a phytoestrogen, or plant-like estrogen, that may increase the rate of twinning. In that sense, a woman’s diet may affect the odds of conceiving twins, but I wouldn’t say that any specific diet a woman follows is known to produce twins.

Race – Race may affect the rate of twins. Most statistics show that the lowest rate of twins is in the Asian population, and it’s higher in the Black population. That may be due to dietary factors more than genetics, but it’s hard to say.

All of these factors specifically affect the risk of conceiving fraternal twins. Identical twins occur pretty much at random when an embryo splits after fertilization, so there’s no guaranteed way to increase the odds of having identical twins. That’s is the same across continents, populations and generations.

Jonathan Schaffir is medical director of Obstetrics and Gynecology Outpatient Clinic at The Ohio State University Wexner Medical Center and a professor in the Ohio State College of Medicine.