Can You Increase Your Chance of Having Twins?

Several factors linked to increased rates of twinning

Twins continue to both fascinate and polarize people who either view them as "double the joy" or a bigger handful than anyone should want to take on.

To those who love the idea, the prospect can become so enthralling that they will actively explore ways to increase their chances. While some of the techniques people pursue are based more on urban myth than actual science, there are certain factors that may increase the likelihood of a twin pregnancy.

Twins occur when one fertilized egg separates into two embryos (monozygotic, identical twins), or two eggs are fertilized by different sperms (dizygotic, fraternal twins).

While there is no real way to guarantee that anyone will have twins, it may help to know the factors may tip the scale in your favor. Here are seven you should know about:

1
Your Genes

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Genetics play a large part in determining whether you'll have twins or not. In fact, current research suggests that your chance of having twins is doubled if your mother and sister had twins.

But, interestingly enough, this only applies to fraternal twins. Among families with a history of twins, there are, in fact, few that have had identical (monozygotic) twins.

What this suggests is that genetics somehow play a role in multiple ovulation (also known as hyperovulation), in which more than one egg is released during a menstrual cycle.

2
Your Height or Weight

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A study published in the journal Fertility and Sterility found that mothers with a high BMI (body mass index) were significantly more likely to have fraternal twins than women of normal weight.

In women with a BMI over 30 (the clinical definition of obesity), the incidence of fraternal twins was seen to increase by 30 percent to 60 percent. Increased height was also considered as a risk factor in women who fell in the top 25th percentile.

By contrast, neither weight nor height increased the likelihood of identical twins.

Of course, this doesn't mean that gaining weight will increase your odds of having twins. What it does increase, however, is your risk of miscarriage and gestational diabetes if your BMI crosses the threshold toward obesity.

3
Older Age

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Numerous studies have shown that older mothers are more likely to conceive fraternal twins than their younger counterparts. It is thought the genetic changes that occur with aging can accelerate and alter the way in which a woman ovulates.

According to a review by the American Congress of Obstetricians and Gynecologists, women 35 years or older are more likely to release more than one egg during ovulation.

It's important to note, though, that advanced maternal age poses its own risks for pregnancy including miscarriage, gestational diabetes, and chromosomal abnormalities like Down syndrome.

4
Already Having Twins

Roger Federer two sets of twins
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Once you have had a multiple pregnancy, you are significantly more likely to have twins again. In fact, research suggests that mothers of twins are four times more likely to have twins again than mothers with singletons or those never previously pregnant.

Again, this phenomenon appears linked to genetics and applies only to fraternal twins. A rare exception involves tennis star Roger Federer and his wife Micka who had two sets of identical twins (pictured).

5
A Diet Rich in Yams

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No one is quite sure why, but the Yoruba tribe in Nigeria has the highest rate of twinning in the world. Researchers linked this phenomenon, in part, to a diet rich in cassava (a type of yam). The peel of this vegetable is thought to contain a compound (phytoestrogen) that may promote hyperovulation.

Researchers note, however, that genetics may also contribute. It appears that the propensity for twinning remains high among women who remain in the tribe as opposed to those have moved elsewhere and had children with non-Yoruban men.

6
Fertility Assistance

Woman holding bottle of clomid pills in hand
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Reproductive technologies—including fertility drugs, like Clomid (clomiphene)—have dramatically increased the multiple birth rate in the United States. These work by stimulating ovulation and can sometimes cause the release of multiple eggs in a single cycle (referred to as superovulation).

On average, the rate of twinning in the United States is around three percent overall. In women who take Clomid, that number can increase to around six percent, according to researchers at the Yale University School of Medicine.

In addition, multiple births can result from in vitro fertilization (IVF). In this case, it is not just that multiple embryos may be implanted; the transferred embryos can sometimes divide and lead to monozygotic twins.

7
Discontinuation of the Pill

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It has long been suggested that stopping your birth control pills may cause overstimulation of the ovaries and lead to hyperovulation. It is believed that the sudden termination of the Pill may cause a spike in the production of follicle stimulating hormone (FSH) central to ovulation.

When this happens, the body may over-respond and release multiple eggs at once. Most studies suggest that the effect is only temporary and will normalize in a relatively short period of time.

Studies regarding this side effect have conflicted over the years, with some reporting statistically significant increases in fraternal twins and others showing no association at all.

8
Pure Luck

Mom with twin babies
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Many parents of multiples don't meet any of the criteria for twinning yet find themselves with two babies without even trying. Monozygotic twins are particularly surprising since no one is quite sure what can cause an egg to split after conception. It remains a mystery.

A Word From Verywell

There is really no sure-fire way to improve your odds of twins. At the same time, it's important to remember that the risks and complications associated with a multiple pregnancy can be significant, including preterm birth, low birth weight, preeclampsia, and miscarriage.

Whatever route to parenthood you choose, and whether that takes you to where you wish it would or not, arm yourself with information that sets you up for the healthiest road ahead.

Sources:

American Congress of Obstetricians and Gynecologists. “Multiple Pregnancies.” Washington, D.C.; FAQ188, July 2015.

Hoekstra, C.; Willemsen, G.; van Beijsterveldt, C. et al. “Body composition, smoking, and spontaneous dizygotic twinning.” Fertil Steril. 2010; 93(3):885-93; DOI 10.1016/j.fertnstert.2008.10.012.

Hoekstra, C.; Zhao, Z.; Lambalk, C. et al. “Dizygotic twinning.” 2008; 14(1):37-47; DOI 10.1049/humupd/dmm036.

Legro, R.; Brzyski, R.; Diamond, M. et al. “Letrozole versus clomiphene for infertility in the polycystic ovary syndrome.” N Engl J Med. 2014; 371:119; DOI 10.1056/NEJMoa1313517.

Peek, P. (2011) Twins in African and Diaspora Cultures. Bloomington, Indiana: Indiana University Press.

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