12 Things You Didn't Know About Multiple Births

Did you know that multiple births are happening more often now than in the past? It's probably because two factors that increase the odds of having multiples—fertility treatments and getting pregnant after 30 years old—are becoming more widespread. So how common are multiple births, and what you can expect throughout the nine-month gestation? Keep reading to learn more about having twins, triplets, and larger numbers of multiples.

1. Twins are the most common type of multiple pregnancy.

According to the Centers for Disease Control and Prevention (CDC), twins occur in 32.1 per 1,000 live births. Women give birth to triplets or higher multiples in 87.7 out of every 100,000 live births. And while more multiples are born now than in past decades, the number is slowly starting to decline—maybe because it's becoming less common to get fertility treatments involving the transfer of multiple embryos, according to The New York Times.

2. Identical twins share all the same genetic material, but fraternal twins don't.

Fraternal (dizygotic) twins happen when two separate eggs are fertilized by two separate sperm, and they implant in the womb at the same time. They share the same amount of genetic material as other siblings.

On the other hand, identical (monozygotic) twins develop from a single fertilized egg, which is more rare. They might share a placenta or amniotic sac, and they have the same DNA. That said, because of environmental factors like their position in the womb, identical twins won't look 100 percent alike, according to the American Academy of Pediatrics.

3. There are medical terms for multiple births.

Most people know that "twins" means two babies and "triplets" means three babies. But what if you're expecting more than that? Here's the proper terminology:

• Quadruplets is for four babies
• Quintuplets is for five babies
• Sextuplets is for six babies
• Septuplets is for seven babies
• Octuplets is for eight babies
• Nonuplets is for nine babies

4. Multiple births have a variety of causes.

Factors that increase the likelihood of pregnancy with multiples include maternal age greater than 30 (hormonal changes might cause the release of more than one egg at ovulation), a history of multiples in your family, and a previous pregnancy with multiples. Fertility drugs and assisted reproductive technologies, such as in vitro fertilization, also raise the odds because they often produce more than one egg.

5. Most multiple births occur in the Northeast.

Studies say that the highest incidence of twins happens in Connecticut, Massachusetts, New Jersey, and the District of Columbia. This might be because women in these locations tend to have babies later in life, and they're more likely to use fertility treatments. In contrast, New Mexico has the lowest twin birth rate.

6. The largest multiple birth happened in 2021.

In May 2021, news broke that a 25-year-old Malian woman gave birth to nine babies (nonuplets), even though she was expecting seven. She ended up breaking a world record for multiple births. Previously, the record for most children delivered in a single birth to survive was held by American Nadya Suleman (known as Octomom by the media), who gave birth to eight kids in 2009.

7. Multiple pregnancies are often considered "high risk."

Multiple pregnancies come with an increased risk of preterm labor, uneven growth, high blood pressure, preeclampsia (a condition characterized by high blood pressure and protein in the urine), diabetes, and other "high-risk" pregnancy conditions. But don't worry: Your doctor will carefully monitor your pregnancy, and they'll often recommend regular ultrasounds and check-up appointments.

8. Multiples are usually delivered 37 weeks or earlier.

Why? If a women is pregnant with multiples, an earlier due date decreases the risk of stillbirth or other complications. And you don't need to worry about a drawn-out delivery: the average time between twins is 17 minutes.

9. You're more likely to have a C-section with multiples.

Most multiple pregnancies end in C-section—especially if you're having triplets or more. That said, you could be a candidate for vaginal delivery if you're having twins, and they're both positioned with their head down. Your doctor might also consider natural birth if Baby A (the one closest to your cervix) is head down, and Baby B is breech, as long as they're about the same size. And sometimes one twin is born vaginally and the other is born via C-section; this is most common if Baby B shows signs of distress.

10. Multiples socialize with each other in the womb.

Here's an endearing fact about multiple births: A 2010 study published in PLOS one detailed research involving five pairs of twins. After studying them with ultrasound technology, experts determined that the twins were physically contacting each other. "We conclude that performance of movements towards the co-twin is not accidental: already starting from the 14th week of gestation twin foetuses execute movements specifically aimed at the co-twin," the study says.

11. Mothers of twins are more likely to be tall and eat dairy.

Take a 2006 study, which was published in the Journal of Reproductive Medicine and conducted by Gary Steinman, M.D., PhD, an attending physician at Long Island Jewish (LIJ) Medical Center. The study involved 129 women who had twins or triplets, and it found that the average mother of multiples was 5'5". In contrast, the national average height for women is 5'3.75".

A separate 2006 study by Dr. Steinman, also published in the Journal of Reproductive Medicine, concluded that women who consume animal products (specifically dairy) were five times more likely to have a multiple birth compared with vegans.

12. Multiples can get absorbed in the womb.

This might seem gruesome, but "Vanishing Twin Syndrome" actually occurs in up to 30 percent of multifetal pregnancies. It happens when one baby stops developing, and it's usually absorbed back into the uterus. Most cases occur before the doctor even hears a fetal heartbeat.