What increases the odds of having twins?

Over the past 30 years, there’s been an increase in the instance of twins, with 3.1% of births being twins in 2021, compared with 1.9% in 1980. This is primarily because more people are seeking help with getting pregnant. Fertility treatments, including drugs to increase ovulation and techniques like in vitro fertilization (IVF), increase the risk of having multiple babies.

But there are other factors that could play a role.

Factors believed to increase the odds of conceiving twins

Age – There’s an increased risk of having twins as people age. The average age of childbirth has increased, with younger people starting families a little later than previous generations. The difficulty of getting pregnant and the percentage of miscarriages also increase age. While it’s difficult to have a successful pregnancy at age 40, a high percentage of successful pregnancies at that age results in twins.

Family history – Twins tend to be more common in some families, and it’s linked to the parent whose body releases the egg. There may be an underlying genetic factor that predisposes someone to release more than one egg at a time, which increases the chance of having twins.

Weight – There has been some consideration that people who are overweight are more likely to release more than one egg at a time, which may increase the chance of twins. Height may play a factor, in that overweight is usually measured by body mass index, which is calculated on the basis of weight distribution over height.

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, diet may affect the odds of conceiving twins, but I wouldn’t say that any specific diet is known to produce twins. While some ask whether dairy products or folic acid supplements play a role, neither has been shown to increase the odds of having twins. Likewise, so-called “fertility foods” with many seeds, such as pomegranates, rice and figs, will not increase fertility.

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 possibility 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. Those odds are the same across continents, populations and generations.