Twin birth rates are declining in the US: here’s why

Twin birth rates are declining in the US

Data from the U.S. Centers for Disease Control and Prevention has revealed a decline in twin births, with the largest decline seen in women over the age of 40.

In the US, twins represent about 1 in every 30 births – a rate which had been rising steadily since 1980 as a result of in vitro fertilization gaining popularity after the first IVF baby was born in 1978.

Changing approaches with regards to how many embryos are transferred to the uterus of a patient during IVF could be a reason for the dropping rates. Since 2000, some experts have discouraged multiple embryo transfers in a bid to prevent risky pregnancies. Since 2020, more than 80% of embryo transfer cycles in the US have only used a single embryo.

What’s more, some experts say a reduction in fertility treatment during the coronavirus pandemic could also have caused the reduction in twin rates.

What makes a twin?

A person can be considered a twin if they were formed alongside their sibling in the womb during a single pregnancy.

Many people will have heard about identical and fraternal (non-identical) twins.

Fraternal or non-identical (dizygotic) twins are the most common twin type worldwide and are formed when two separate eggs are fertilized by separate sperm. The fertilized eggs then implant in the uterus, resulting in two babies from the same pregnancy. Non-identical twins can be the same sex, or different sexes (one boy and one girl).

However, identical (monozygotic) twins will always be the same sex, as they are formed when a single fertilized egg splits, creating two embryos that share near-identical genes.

A twin DNA test – also called a zygosity test – is a DNA test that can be used to determine whether multiple children from the same birth (twins, triplets, quadruplets etc.) are identical or non-identical.

Why might you want a twin DNA test?

There are many reasons why you might want to order a Twin DNA Test.

Examples include:

  • It wasn’t clear during pregnancy (in utero) whether the twins were identical or non-identical. Identical twins do not always share the same placenta and sac – it all depends on when the egg splits
  • You want to assess the likelihood of conceiving twins again
  • One sibling has been affected by an illness, and you want to know whether you need to test the other sibling for the same condition
  • You need the information to take part in a study about multiple births
  • You want to buy a Twin DNA Test as a gift for multiple birth parents or their children

Where can I buy a Twin DNA test?

Thanks to advances in modern scientific techniques, it’s never been easier to find out for sure whether twins are identical or not.

Available for just $119, our home Twin DNA Test can be ordered quickly and easily online.

With only cheek swabs required, this non-invasive test can be used on siblings of any age – from newborn babies to grown adults.

The DNA (zygosity) certificate provided on completion of the test can also be used as a unique keepsake for multiple birth parents.

Need to know more about our Twin DNA test? Find the answers to your questions in our Learning Center or email

Twin DNA Test

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