It’s well known that fertility treatments like Clomid (clomiphene), Gonal-F (follitropin alfa), and Follistim (follitropin beta) make it more likely you’ll conceive multiples. But other factors like your height, age, diet, and family history can also increase (or decrease) your risk of conceiving more than one baby at a time. Learn more about what increases the likelihood of having twins.
How Common Are Twins?
According to the Centers for Disease Control and Prevention (CDC) birth statistics, there were 120,291 infants born in twin deliveries in the United States in 2019. That’s 32.1 twins per 1,000 live births, or put another way, about 3.21% of live births. There were 3,136 triplet births and just 150 quadruplet and higher-order births during the same year. These numbers include naturally occurring multiples, along with those conceived with fertility treatment. In the general population, identical twin pregnancies occur 0.45% of the time or 1 in 250 births. The rates are double that if you use fertility treatments, so getting fertility assistance definitely increases the odds of having twins. While most multiple pregnancies conceived with fertility treatments are fraternal twins, the use of fertility treatment also increases your risk of having identical twins.
Factors That Increase the Odds of Twins
Most people know that using fertility treatments increases the incidence of twins. However, fertility treatments are not the only cause of increased incidences of twins and higher-order pregnancies. Here’s an overview of the other factors that increase your chances of getting pregnant with multiples.
Age
People over 30, and particularly those over age 35, are more likely to conceive twins. This is because the level of follicle-stimulating hormone (FSH) rises as birthing parents get older. FSH is responsible for the development of eggs in the ovaries before they are released. As people age, they require higher levels of FSH because their eggs require more stimulation to grow than before. Sometimes, the follicles overreact to higher FSH levels and two or more eggs are released and fertilized, resulting in a multiple pregnancy.
Family History
A family history of identical twins does not necessarily make you more likely to have multiples, although the offspring of male identical twins may be more likely to have their own identical twins. However, if you have fraternal twins (non-identical) in your family, your chances of conceiving twins rise. If there are fraternal twins on both parents’ or egg or sperm donor’s sides, your odds for twins go up even higher.
Weight
People with a higher weight are more likely to conceive twins than people with a lower weight. Extra body fat typically leads to increased levels of estrogen, and higher levels of estrogen can lead to overstimulation of the ovaries. Instead of releasing just one egg at ovulation, the ovaries may release two or more. While the odds of twins may increase, other factors associated with being overweight can make it generally more difficult to conceive.
Height
People who are taller than average are more likely to have twins. One study found that people averaging 164.8 cm in height (about 5'4.8") were more likely to conceive twins than people 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.
Diet
The specific foods you eat or don’t eat may also impact your chances of having twins. While research is still ongoing, some studies have found that people who eat a lot of dairy products are more likely to conceive twins. One study found that vegans were significantly less likely to have twins than those that consumed dairy, with vegans having multiple births just 20% as often. According to the study authors, “Diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation.” Another study found an association between eating yams and a higher twin rate. Similar to the impact of consuming dairy, it’s theorized that yams also may stimulate multiple ovulation.
Breastfeeding
People who conceive while breastfeeding are more likely to have twins than people who are not breastfeeding. 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!
Other Factors
Twins are more common in people who have carried many pregnancies and have large families. Meanwhile, Black people also are more likely to conceive twins than white people, while Asian people are less likely to conceive twins.
Why Fertility Treatments Increase Rates of Twinning
One of the primary reasons for the increasing rate of multiple births is the expanded use of fertility treatments. In fact, according to the CDC, over 30% of twins and 75% of triplet and higher order multiple births are now attributed to using fertility treatments.
Fraternal Twinning Due to Fertility Treatments
Fraternal twins are more common with fertility treatments because increased ovulation is often stimulated as part of these treatments. This results in a higher incidence of two or more ovum being released and fertilized in one cycle, resulting in fraternal twins. Additionally, during in vitro fertilization (IVF), more than one embryo is often implanted, which also can result in twins or higher-order multiples.
Identical Twinning Due to Fertility Treatments
According to one study, identical twins made up 0.95% of the pregnancies conceived with fertility treatment. That’s double the general population’s risk. Researchers do not yet understand why using fertility treatment leads to more identical twins. One theory is that the culture embryos are placed in during the IVF process increases the incidence of identical twinning. Another theory is that treatments using gonadotropins (medications that stimulate ovulation) lead to the increased risk of identical twins.
What Are the Odds of Having Twins?
Fertility treatments that boost ovulation can lead to twins, triplets, or higher-order multiples. Conceiving multiples is a potential risk of fertility treatments and one that can possibly be reduced with careful monitoring and targeted treatment such as single embryo transfer with IVF treatment or using the lowest possible effective dosage when treating with gonadotropins.Not all treatments for infertility increase your odds of conceiving twins, but most do. Here are some of the treatments that may lead to twins.
Clomid (clomiphene) Femera (letrozole) Gonadotropins (also known as injectables) like Gonal-F and Follistim IUI treatment, when used along with fertility drugs IVF treatment
According to some studies, up to 30% of pregnancies conceived with gonadotropins lead to multiples. Most of these pregnancies are twin pregnancies, but up to 5% 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% of pregnancies (but only 0.9% of live births due to pregnancy loss). IVF twins are relatively common, with the twin rate highest for people younger than 35 at 12.1% per transfer in 2014. The IVF twin rate is lower for people over age 35 at 9.1% for people aged 35 to 37 and 5.3% for people ages 38 to 40, likely due to the overall decreased success rate as the gestational parent ages.
What Are the Odds of Triplets or Quadruples?
Anyone trying to conceive will find their chances of having higher-order multiples much lower than twins or singleton births. Without fertility treatments, the odds of conceiving triplets spontaneously is around 1 in 1,800. For quadruplets, the odds are estimated to be around 1 in 729,000. With fertility treatments, the chances of a higher-order pregnancy rise substantially. In 2019, for example, the rate for triplet and higher-order multiples was 87.7 per 100,000 births (0.877 per 1,000 births). Just over three-quarters of triplets and higher-order multiples are estimated to be the result of fertility treatments.
A Word From Verywell
Your chances of having twins will depend not just on whether you undergo fertility treatment to conceive but also on your family history, race, age, and many other factors. These factors are also cumulative. In other words, a tall person with a family history of fraternal twins is more likely to conceive twins during fertility treatments than a short person without any family history of twins. 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 routinely transfer during IVF. While having twins may sound like the kind of two-for-one deal any couple would love to have after experiencing infertility, it really is typically 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. There was an error. Please try again.
