What Are My Chances of Having Twins?

Odds of Conceiving Twins Naturally or With Fertility Treatment

identical twin baby boys (3-6 months) lying side by side, portrait, chance of having twins
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What boosts your odds of having twins? Fertility treatments like Clomid, Gonal-F, and Follistim make it more likely you'll conceive multiples, but also, your height, age, and even family history can increase your odds of birthing more than one.

Chances of Having Twins With Fertility Treatments

Fertility treatments that boost ovulation can lead to twins, triplets, or higher order multiples. Conceiving multiples is a possible risk of fertility treatments, one that can be decreased with careful monitoring, single embryo transfer (for IVF treatment), and the lowest possible effective dosage (when treating with gonadotropins.)

You may wonder why conceiving multiples is considered a "risk" and not a possible benefit to fertility treatments. After all, especially if you've been struggling to get pregnant, wouldn't a double or triple blessing be a good thing?

The fact of the matter is that multiple pregnancies come with risks to the mother and babies. Your doctor's goal is for you to conceive and give birth to one healthy baby at a time.

Not all treatments for infertility increase your odds of twins, but most do. Fertility drugs and treatments that may lead to twins include...

Clomid and Femera have the lowest rate of twins, ranging from 5 to 12 percent. The rate of triplets and higher order multiples is under 1 percent. Gonadotropins, whether used with or without IUI treatment, have the highest rate of twins.

According to some studies, up to 30 percent of pregnancies conceived with gonadotropins lead to multiples. Most of these pregnancies are twin pregnancies, but up to 5 percent are triplet or higher order pregnancies.

Contrary to popular belief, IVF treatment is not the main source of triplet and higher order pregnancies.

Data collected by the CDC indicates that the rate of IVF-conceived triplets in 2014 was 1.5 pregnancies (but only 0.9 percent of live births, lower due to pregnancy loss.)

IVF twins are relatively common, with the twin rate highest for women younger than 35, at 12.1 percent per transfer in 2014. The IVF twin rate is lower for women over age 35—9.1 percent for women aged 35 to 37 and 5.3 for women ages 38 to 40—likely due to the overall decreased success rate as a woman ages.

Causes of Twins Besides Fertility Treatments

Fertility treatments are not the only reason for twins. Other factors that increase your chances of getting pregnant with multiples include...

Age

Women over 30 are more likely to conceive twins. This is because the hormone FSH rises as a woman gets older. FSH, or follicle stimulating hormone, is responsible for the development of eggs in the ovaries before they are released.

Higher levels of FSH are needed as a woman ages because the eggs require more stimulation to grow than in a younger woman.

This is somewhat ironic, given that increased FSH is also due to lowering fertility. But sometimes, the follicles overreact to the higher FSH levels, and two or more eggs are released, resulting in a twin pregnancy.

Family History

A family history of identical twins does not make it more likely you'll have multiples. However, if you have fraternal twins (non-identical) in your family, your chances of conceiving twins rise. If there are fraternal twins on both the mother and father's side, your odds for twins goes up even higher.

A history of twins on the female side of the family indicates a higher likelihood of ovulating more than one egg per cycle, and a history of fraternal twins on the male side indicates a higher likelihood of the man producing enough sperm to fertilize more than one egg.

Weight

Women who are obese—with a BMI over 30—are more likely to conceive twins than women with a healthier BMI.

This is an ironic situation since overweight women are also more likely to have difficulty conceiving.

Extra fat leads to increased levels of of estrogen. The higher levels of estrogen can lead to over stimulation of the ovaries. Instead of releasing just one egg at ovulation, the ovaries may release two or more.

Height

Women who are taller than average are more likely to have twins. One study found that women averaging 164.8 cm in height (about 5' 4.8") were more likely to conceive twins than women averaging 161.8 cm (about 5' 3.7").

Why this happens isn't clear, but one theory is that better nutrition (which may lead to more height) is partially behind the increased rate of twins.

Number of Children

Twins are more common in women who have carried many pregnancies and have large families.

Race

African-Americans are more likely to conceive twins than Caucasian women. Asian women are the least likely to conceive twins.

Breastfeeding

Women who conceive while breastfeeding are more likely to conceive twins than women who are not. It's true that breastfeeding can also suppress fertility and prevent pregnancy, specifically during a baby's first six months if the baby is exclusively breastfed.

However, it is possible to get pregnant when breastfeeding—and with twins!

One study found the rate of twins to be 11.4 percent among breastfeeding women, as compared to just 1.1 percent in non-breastfeeding women.

Diet

While research is still ongoing, some studies have found that women who eat a lot of dairy products are more likely to conceive twins. One theory is that the growth hormones given to cows affect the hormone levels in humans.

How Common Are Twin Pregnancies?

According to data collected by the Centers for Disease Control, there were 133,155 twins born in the United States in 2015. That's 33.5 per 1,000 live births, or put another way, about 3.35 percent of live births.

There were 3,871 triplet births, 228 quadruplet births, and 24 quintuplet or higher order births. These numbers include naturally occurring multiples, along with those conceived with fertility treatment.

The rate of multiple births increased and peaked during the 1990s, but has been declining over the past decade. The percentage of triplet and higher order pregnancies has dropped 36 percent since 2004.

Chances of Having Identical Twins

In the general population, identical twin pregnancies occur 0.45 percent of the time, or 1 in 250 births.

While most multiple pregnancies conceived with fertility treatments are fraternal twins, the use of fertility treatment does increase your risk of having identical twins. According to one study, identical twins made up 0.95 percent of the pregnancies conceived with treatment. That's double the general population's risk.

It's unclear why fertility treatment leads to more identical twins. One theory is that the culture embryos are placed in during IVF increases the risk of identical twinning. Another theory is that treatments using gonadotropins lead to the increased risk of identical twins.

A Word From Verywell

Your chances of having twins will depend not just on your use of fertility drugs, but also your family history, race, age, and many other factors. These factors do work together. In other words, a tall woman with a family history of fraternal twins is more likely to conceive twins during fertility treatments than a short woman without any family history of twins.

Your chances of conceiving twins will also be affected by your particular cause of infertility. A young woman with healthier eggs is more likely to conceive twins than a woman over 40, whose egg quality is poor.

The twin and multiple rates also vary from fertility clinic to clinic. Twin rates differ based on how carefully they track ovulation stimulation during fertility drug use and how many embryos they transfer during IVF.

While having twins may sound like the kind of two-for-one deal any couple would love to have after infertility, it really is best to aim for one healthy baby. Your doctor can reduce the odds of multiples with careful monitoring and single-embryo transfer during IVF.

However, if you do conceive twins or more, know that good prenatal care can reduce your risk of complications. There are also many positive benefits to having twins.

Sources:

Assisted Reproductive Technology (ART) Report. National Summary Report: 2014. Center for Disease Control.

Kawachiya S, Bodri D, Shimada N, Kato K, Takehara Y, Kato O. "Blastocyst culture is associated with an elevated incidence of monozygotic twinning after single embryo transfer." Fertility and Sterility. 2011 May;95(6):2140-2. Epub 2011 Jan 7.

Multiples: twins, triplets and beyond. March of Dimes.

Schachter M, Raziel A, Friedler S, Strassburger D, Bern O, Ron-El R. "Monozygotic twinning after assisted reproductive techniques: a phenomenon independent of micromanipulation." Human Reproduction. 2001 Jun;16(6):1264-9.

Steinman G. "Mechanisms of twinning. IV. Sex preference and lactation." Journal of Reproductive Medicine. 2001 Nov;46(11):1003-7.

Steinman G. "Mechanisms of twinning: VII. Effect of diet and heredity on the human twinning rate." Journal of Reproductive Medicine. 2006 May;51(5):405-10.

Steinman G. "Mechanisms of twinning: VIII. Maternal height, insulinlike growth factor and twinning rate." Journal of Reproductive Medicine. 2006 Sep;51(9):694-8.

Steinman G. "Mechanisms of twinning: X. The male factor." Journal of Reproductive Medicine. 2008 Sep;53(9):681-4.

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