What May Increase Your Chances of Having Twins?

Babies that come in pairs—twins—continue to fascinate people. So it's no surprise that people wonder (for all different reasons) what they can do to increase their chances of having a twin pregnancy.

It's interesting that parents of twins often relay common factors that they believed increased their likelihood of conceiving two babies. Of course, most of these are not scientifically proven but rooted more in tradition or personal experience. Still, there is some biological basis for a couple of the factors, like genetics and the mother's age.

1
Your Genes

Twin baby sister and brother
Twin baby sister and brother. Getty Images/Sue Barr

Do twins run in your family? If you have a mother, brother, sister, uncle, or long-lost cousin with multiples, you may wonder if you'll have them too. According to current research on the genetics of twinning, the risk of having fraternal twins is about twice for women whose mother or sister had fraternal twins. 

Sometimes your chance of having twins is influenced by your genes. However, only fraternal (dizygotic) twins are influenced by heredity, and then only in some cases. If your mother or maternal grandmother was or had fraternal twins, you might have inherited a gene for hyperovulation (meaning releasing more than one egg during ovulation).

It's important to understand that there is no connection between genes and identical  (monozygotic) twins—this is considered a random event in which the fertilized egg splits into two (or more) embryos that are genetically identical (the DNA is the same). This is why boy/girl twins can never be identical—they are always fraternal.

 

2
Your Height or Weight

One study in Fertility and Sterility found that mothers with an increased BMI (Body Mass Index) were significantly more likely to have fraternal (dizygotic) twins, as compared to mothers with identical (monozygotic) twins. The research also showed that women of above-average height were also more likely to have fraternal twins.

The link between increased height and/or weight and having fraternal twins has also been reported in other studies when the control group was mothers with a singleton pregnancy, as opposed to identical twins in the above study.

Of course, this does not mean that women who are tall or heavy will have twins. There are plenty of moms of twins who are not overweight and/or short. Likewise, there are plenty of larger moms who have singletons.

Rather, the research identified that maternal BMI and height are factors that potentially increase a woman's chance of having dizygotic twins. This is particularly interesting because obesity rates have trended upwards in the United States, and so have the number of fraternal twins -- so the study fits or make sense, so to speak. 

3
Your Age

Older mothers are more likely to conceive twins than their younger counterparts. It's thought that the body accelerates ovulation as the biological clock starts ticking faster. According to the American College of Obstetrics and Gynecology, women who are 35 years of age or older are more likely to release more than one egg during ovulation. In other words, they are more likely than younger women to conceive multiples.

It's important to note though that advanced maternal age poses its own risks for pregnancy (in both singletons and multiples). Older mothers have a higher rate of miscarriage and are more likely to experience problems like gestational diabetes during their pregnancy. In addition, their babies are at higher risk for chromosomal abnormalities, like ​Down syndrome

4
Have More Twins

Once you have had a multiple pregnancy, you are significantly more likely to conceive and deliver twins again. In fact, research suggests that mothers of twins are four times more likely to have twins again than a woman who has never been pregnant, or who only had a singleton.

The reason behind this has to do with genetics and only applies to fraternal twins and women not undergoing fertility treatments. If a woman has fraternal twins, she likely releases more than one egg each cycle (this is called hyperovulation or superovulation). So, if she is likely to hyper-ovulate, she also has an increased chance of having twins again.

 

5
A Diet Rich in Yams

No one is quite sure why, but the Yoruba tribe in Nigeria has the highest rate of twinning in the world. Researchers found that the diet in this area was rich in cassava, a type of yam or sweet potato. The peel of this vegetable is thought to contain a chemical (a phytoestrogen) that causes hyperovulation.

Of course, there could be other factors that contribute to why twinning is so high in Nigeria, like the maternal history of having twins. Still, the role of diet is quite interesting. In fact, when the people of the tribe moved from the countryside to the city (and their diets changed—less yams), the rates of twinning declined. 

6
Fertility Assistance

Reproductive technology has dramatically increased the multiple birth rate. Fertility drugs that stimulate ovulation can lead to multiple pregnancies, as more than one egg is released from the ovaries. That being said, fertility drugs like Clomid would only increase a woman's chance of conceiving fraternal twins, due to the release of two eggs during ovulation, not one. According to the American Society for Reproductive Medicine, of those women who achieve pregnancy with Clomid, about 5 to 12 percent have twins.

In addition, multiples can result from in vitro fertilization. It's not just that multiple embryos are implanted in the mother, but there is also a chance that monozygotic twins (identical twins) may result if the transferred embryo splits.

7
Increased Parity

The more kids you have, the more likely you are to conceive twins in a subsequent pregnancy—this is termed increased parity. That being said, no one knows the magic limit that triggers a multiple pregnancy.

8
Conceive While Breastfeeding

Most people think that you can't get pregnant while breastfeeding because the process of lactating keeps a woman from ovulating. However, plenty of mothers of twins will disagree with that idea.

In fact, some research has supported the theory that the chance of twins or multiples is increased if a woman conceives while breastfeeding. One study claimed that women who become pregnant while breastfeeding are nine times more likely to conceive twins than women who are not breastfeeding at the time of conception.

The author of the study suggested that a depletion of calcium levels in the nursing mother could be the culprit, although it's still wholly unclear. 

9
Just Get Lucky!

Many parents of multiples don't meet any of the classic criteria, yet find themselves doubly blessed. Monozygotic twins are particularly mysterious—no one is exactly certain what causes an egg to split after conception, producing identical twins.

The bottom line is that there truly isn't a lot an individual can do to influence their chances of having twins—sometimes it is simply fate.

A Word From Verywell

While wishing for multiple births is an exciting prospect for some women, keep in mind that there are risks and complications associated with a multiple pregnancy, such as preeclampsia and prematurity.

Also, it's important to note that the majority of above factors are merely observations linked with increased odds of twinning. Please talk with your doctor if you have worries, questions, or simply thoughts about conceiving multiples.

Sources:

Akinboro A, Azeez MA, Bakare AA. Frequency of twinning in southwest NigeriaIndian J Hum Genet. 2008 May-Aug;14(2):41-47.

American College of Obstetrics and Gynecologists. (July 2015). Frequently Asked Questions: Multiple Pregnancy.

Hoekstra C et al. Dizygotic twinningHum Reprod Update. 2008 Jan-Feb;14(1):37-47

Hoekstra C, Willemsen G, van Beijsterveldt CE, Lambalk CB, Montgomery GW, Boomsma DI. Body composition, smoking, and spontaneous dizygotic twinningFertil Steril 2010 Feb;93(3):885-93.

Online Mendelian Inheritance in Man (OMIM): An Online Catalog of Human Genes and Genetic Disorders. (June 2016). Twinning, Dyzygotic.

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