These Are All the Special Names for Multiple Births (2024)

How Common Are Twin Births?

According to the U.S. National Vital Statistics Report, there are approximately 31.2sets of twinsborn for every 1,000 live births. This number represents a drop in the number of twin births overall, but it's in line with the fact that singleton birth rates also have declined.

Initially, the number of twin births in the U.S. began rising in the early 1980s, but by 2014, they started to decline again. Since then, twin birth rateshave fallen by an average of 2% between 2014 and 2019 and fell by as much as 7% between 2019 and 2020.

Between 2019 and 2020 the number dropped 3%. But the number of twins born from 2020 to 2021 showed a slight increase of 2%. Researchers note that this small increase occurred among older people who are more likely to use infertility treatment.

Trends in High-Order Multiple Births

The rate of twin births and high-order births began to climb in the 1980s, especially among non-Hispanic white people aged 25 and over, because of the use of fertility drugs and assisted reproduction techniques. While the rate of twin births increased by more than 50%, the rate of triplet and higher-order multiples increased by over 400%.

That rate peaked for triplets and higher multiples from 1998 to 2004 and has since been dropping, again in the same demographic group associated with the rise. This is due to a change in assisted reproduction treatments, especially the transfer of fewer embryos. The rates are still three times what they were in the early 1980s, but have been declining.

New practice guidelines have likely influenced the number of multiples being born in the country each year. Having multiples not only increases the risks of mortality but also long-term morbidity continues to be far higher for triplets and higher-order multiples than for singletons.

Multiple Birth Variations

Multiple births can occur naturally, surprising many parents-to-be, especially if there have been no multiples in their family previously. They may also be a predicted possible outcome of efforts made to get pregnant. Here's a closer look at these variations.

Identical

Every month, those assigned female at birth release an egg from an ovary (ovulation), which can then be fertilized by a sperm to form an embryo and, eventually, a developing fetus. If one embryo happens to split into two or more embryos,identical twins (or more) may result. Due to the splitting of the embryo, identical twins share the same DNA. This is why they are always the same sex.

Fraternal

On the other hand, some people release more than one egg during ovulation—they "hyperovulate," so to speak. Experts aren't quite sure why some people hyperovulate and others don't, but there's believed to be a genetic component to it. In addition, age plays a role, as people older than 35 are more likely to release more than one egg during each menstrual cycle.

If a person releases two or more eggs during ovulation, each may be fertilized by a different sperm, forming unique embryos. In this case, twins would be fraternal, not identical; they can be of different sexes or the same sex. Similarly, two (or more) embryos may be formed through assisted reproduction techniques and then transferred to the uterus.

Interestingly, sometimes a combination of the above processes occurs. For example, a personcould hyperovulate, releasing multiple eggs during the middle of their menstrual cycle. These eggs are each fertilized by a sperm, and then one or more of these embryo splits. In this instance, they could have multiple births (such asquadruplets) with two of the babies being fraternal twins and two being identical.