What can increase my chances of having twins?
Fraternal twins are conceived when two eggs are fertilized by different sperm cells in the same menstrual cycle. They are twice as common as identical twins, which are conceived when one egg is fertilized by one sperm cell. The fertilized egg splits into two, forming two embryos in the uterus.
Fertility treatments raise your chances of having both fraternal and identical twins, but there are several other factors, like your age, race, and family history, that can increase your probability of having twins:
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Heredity: If you're a twin, or if there are twins in your family, you're slightly more likely to have a set yourself.
Age: The older you are, the higher your chances of having fraternal twins or higher order multiples. One theory is women age 35 or older produce more follicle-stimulating hormone (FSH) than younger women. FSH is also the hormone that causes an egg to mature in preparation for ovulation each month, and women with extra FSH may release more than one egg in a single cycle. So older women are statistically less likely to get pregnant, but they're more likely to have twins if they do.
History of twins: Once you have a set of fraternal twins, you're twice as likely to have another set in future pregnancies.
Number of pregnancies: The more pregnancies you've had, the greater your chances of having twins.
Race: Twins are more common than average among white and African American people and less common among Hispanic and Asian people.
Body type: Fraternal twins are more common in large and tall women than in small women.
Which fertility treatments affect my chances of twins?
Certain treatments for infertility may increase the likelihood you'll become pregnant with twins, triplets, and higher-order multiples because they boost ovulation.
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For example, gonadotropins are injectable fertility medications that stimulate your ovaries to produce multiple eggs during ovulation. If more eggs are released, that increases the likelihood that more than one egg will become fertilized, hence a multiple pregnancy.
Using assisted reproductive technology (ART), such as IVF, boosts your chances of having twins, but you can prevent a multiple pregnancy by asking your doctor to transfer only one embryo at a time.
According to preliminary 2019 national data, the percentage of IVF treatments that resulted in twin births after all embryo transfers are as follows:
- 7.3 percent in women younger than 35
- 6.9 percent in women age 35 to 37
- 6.8 percent in women age 38 to 40
- 5.1 percent in women age 41 to 42
- 5.9 percent in women age 43 and above
Fertility treatments aren't an easy way to boost your chances of having twins, though. They tend to be very expensive and aren't always covered by health insurance. For instance, the average cost of an IVF cycle is $10,000 to $15,000. And fertility treatments are generally reserved for people who have been diagnosed with infertility.
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How common are twins and multiples?
There were approximately 120,291 twin births out of 3.7 million births in the U.S. in 2019, with around 32 sets of twins per 1,000 births. This was a 2 percent decline from 2018 and a 5 percent decline from 2014.
Meanwhile, there were about 88 sets of triplets and higher-order multiples per 100,000 births – a 6 percent decline from 2017.
Although the twin birth rate rose by 76 percent between 1980 and 2009, it declined 4 percent between 2014 and 2018 – the lowest rate in more than a decade. For women age 30 to 34, the twin birth rate declined by 10 percent; 12 percent for women age 35 to 39; and 23 percent for women age 40 and over.
It's possible that the birth rate for twins has slowed down because fertility treatments have improved. For example, with in vitro fertilizations (IVF), doctors would usually transfer multiple embryos into the uterus at once to increase the chances of having one successful pregnancy. This also raises the likelihood of twins, but now doctors are transferring just one or, rarely, two embryos at a time to reduce high-risk pregnancies.
That's because women who have a multiple pregnancy (carrying more than one baby) are at a higher risk for complications, including preterm birth, low birth weight, preeclampsia (high blood pressure), gestational diabetes, and a cesarean birth.
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Although the birth rate for triplets and higher-order multiples had quadrupled between 1980 and 1998, it declined by 6 percent in 2019 and was down 55 percent from the peak in 1998.
The number of triplet and multiple births was 3,286, which is the lowest number reported since 1990. It's also less than half of 7,663 – the highest number of triplet and higher-order multiple births ever reported in 2003.
Similar to twin births, the slowdown in triplet and higher-order multiple births is likely due to the improvements in fertility treatments. About 20 years ago, fertility specialists would transfer four embryos routinely for women of all ages, but now women are getting, on average, half as many embryos transferred at one time.
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