How Rare Are Twins?

Imagine this – you find out you're pregnant, head to your first-trimester ultrasound, and the technician says, "Congratulations, you are having twins!" You may burst into happy tears or become anxious, because well, having twin children may not have been what you expected. Mothers can give birth to either identical twins (when a single fertilized egg splits into two), or fraternal twins (two separate eggs being fertilized at the same time), according to the National Human Genome Research Institute.

Whether you love the idea of twins or not, your chances of giving birth to twins — identical or fraternal — is influenced by numerous factors, including age, weight, and genetics (via Better Health Channel). For instance, the odds of having fraternal twins is higher if you're a fraternal twin or if you have twins in the family, explained Healthline. Age also plays a factor and women over the age of 35 have an increased chance of naturally conceiving twins (via MayoClinic). Experts suggest this is due to women having a higher likelihood of releasing more than one egg at a time at this age, as well as reproductive technology.

The chance of having twins can vary

So what are your chances of having twins? According to Baby Center, in 2019 there were 32 sets of twins per 1,000 births. And this may be because of improved fertility treatments. In fact, a woman's chance of having twins can increase if she's also undergoing in-vitro fertilization (IVF) treatment. For women younger than 35 and undergoing IVF, there was a little over a 7% chance of conceiving twins. For women between 35 and 40, there was a 6.8% to 6.9% chance of twins. For women 41 to 42, the odds were 5.1% and for those 43 and older the chances rose slightly again to 5.9%.

But are there additional risks for having twins? According to Johns Hopkins Medicine, having twins can increase certain risks of complications, including anemia, and gestational hypertension. Another very common occurrence is preterm labor, which accounts for over 60% of twin births. That means a majority of these babies will be born before 37 weeks. The risk of birth defects, like congenital defects, also increases. But fortunately, your medical team should be able to help monitor your wellness along the way and mitigate risks wherever possible.