What Are the Chances of Having Twins?

Certain factors may increase your chance of carrying twins. Experts explain what you need to know about conceiving multiples.

There are a couple of standard questions sonographers expect from parents at their first ultrasound: can you see a heartbeat and how many are there? 

Although having twins might be considered rare, finding out you’re carrying two or more babies can be a big adjustment for any family. That’s why many parents are curious to find out what’s going on in the womb as soon as possible.

So, what are the chances of having twins and is there anything you can do to influence that? Experts share what you need to know about becoming pregnant with twins.

twin babies

Ellen Linder / Getty Images

How Common Are Twin Pregnancies?

It’s possible that you already know one or two sets of twins in your own life, but only about 3% of live births in the United States result in twins. And of all multiple births, twins—as opposed to other sets like triplets or quadruplets—accommodate for 97%. This means producing twins is uncommon but certainly possible. 

Different Types of Twins

While there are different types of twins, the main two categories are fraternal (dizygotic) and identical (monozygotic). Of those, fraternal twins (unidentical) are exceedingly more common, accounting for 70% of all twin pregnancies.

Fraternal twins

Fraternal twins form when two separate eggs are fertilized by different sperm. “In fraternal twins, you can have a boy and a girl, and since they are not identically genetically the same, these twins will not necessarily look alike,” explains Carolina Bibbo, MD, director for the Comprehensive Centre for Multiples at Brigham and Women’s Hospital.

Identical twins

Identical twins occur when one fertilized egg splits into two embryos. They “will share the same genetic information and will be either boys or girls because they come from the same embryo,” says Dr. Bibbo. 

Signs of a Twin Pregnancy

Some signs of carrying twins in early pregnancy may include:

What Increases the Odds of Having Twins?

Contrary to the imagination of scientific screenwriters, there isn’t much you can do to control your chances of having twins. But while the cause of identical twins is generally unknown, certain factors have been found to increase the chances of having fraternal twins.  

  • Fertility treatments. There's a higher chance of having twins through ovulation-inducing infertility drugs, like those used in in vitro fertilization (IVF). Almost one-third of all U.S. twin infants can be attributed to fertility treatments.
  • Age. Those who are over 35 are more likely to conceive twins. “For pregnancies conceived without fertility assistance or medications, the chance of having fraternal (nonidentical) twins is higher in older women as there is an increased chance of releasing more than one egg during ovulation compared to younger women,” says Robin Kalish, MD, FACOG, director of clinical maternal-fetal medicine at NewYork-Presbyterian/Weill Cornell Medicine. 
  • Family history. Those who have a family history of fraternal twins on the mother’s side have a slightly increased chance of carrying twins themselves.
  • Personal history. You're more likely to conceive twins if you’ve already carried them in a previous pregnancy.
  • Race. Carrying twins is more common among Black people, as statistics show they have higher rates of twin births than any other ethnicity or race in the U.S.
  • Genetic factors. Some genetic factors play a role, including hyperovulation, a biological phenomenon where more than one egg is released during the menstrual cycle. “As a result, two eggs may be released in a single menstrual cycle that can then get fertilized by two separate sperm, leading to fraternal twins, says Dr. Kalish.

How Do Fertility Treatments Raise the Chances of Having Twins?

The chance of having twins is significantly increased when undergoing assisted conception via fertility treatments. “Fertility medications can stimulate the ovaries, causing more than one egg to release in a given month,” says Dr. Kalish. “If undergoing in vitro fertilization, transferring more than one embryo into the uterus increases the chance of having twins."

Not all infertility treatments 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

Chances of having twins with clomid

Clomid (clomiphene), a pill taken by mouth to induce ovulation, causes twin pregnancies between 5% and 12% of the time. That's fewer than one in 10 pregnancies. Your odds of conceiving triplets (or more) on Clomid is even lower: less than 1% (less than one in 100 pregnancies).

If you're hoping to take Clomid for twins, know that there is no guarantee. Twins are considered a possible risk of taking this drug, rather than the goal. Most reproductive endocrinologists will try to avoid pregnancies with multiples, because of the associated risks.

Also, most twins conceived with Clomid will not be identical. During clinical trials looking at twin pregnancies, one in five were identical twins and 80% of the twin pregnancies were fraternal twins (not identical). Clomid increases your odds of conceiving twins because your ovaries may ovulate more than one egg. Identical twins come from one egg— not two.

Myths About Twin Pregnancies

You may have heard that bed rest is encouraged for patients carrying twins. However, it isn’t recommended for an uncomplicated twin gestation. “Bed rest can actually increase the risk of blood clots. It can also worsen the physical condition for pregnant people with significant muscle mass loss which will make it difficult to later care for two babies. Furthermore, prolonged bed rest could lead to depression," says Dr. Bibbo.


Other myths not to pay close attention to include theories that certain sexual positions increase your chances of having twins and that twins will always be born via Cesarean section. Both are simply not true, according to Dr. Kalish.


Also, despite popular belief, twins do not skip a generation.

Risks of Twin Pregnancies

While expecting twins can be exciting, they carry higher risks than single-fetus pregnancies. “As a result of these high-risk concerns, twins need more monitoring throughout the pregnancy,” says Dr. Kalish.

Dr. Bibbo agrees, and is adamant that no one should be “trying to have twins" because of the higher risk of complications. Some of those include:

  • Preterm labor or delivery
  • Babies born with low birth weight
  • Hypertensive disorders
  • Gestational diabetes
  • Anemia
  • Fetal growth restriction
  • Congenital anomalies
  • Placenta issues
  • Twin-to-twin transfusion syndrome, a rare condition where unequal amounts of the placenta’s blood is supplied to each twin, meaning they can grow at different rates

While these risks may sound scary, twins are usually watched carefully throughout the pregnancy. People carrying multiple babies typically have more frequent prenatal visits. It's important to find a medical team you feel comfortable with and supported by when having any pregnancy, especially one with multiples.

What About Triplets, Quadruples, and More?

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. Just over three-quarters of triplets and higher-order multiples are estimated to be the result of fertility treatments.

Key Takeaways

There may be certain factors that increase the probability of having twins, but it’s never a guarantee. Once it’s established that you’ve conceived more than one baby, you’ll be closely monitored throughout your pregnancy to ensure the best possible outcome for you and your babies.

Additional reporting by Rachel Gurevich, RN.

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Sources
Parents uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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