Using sex to conceive, the chance of having twins or higher multiple births is about 1-2%. With assisted reproduction, including intrauterine insemination (IUI) in the office and in vitro fertilization (IVF) in the lab, the chance of twins, triplets or high order births ranges from 30-50%. That’s quite a big difference!
Twins have fascinated us for eons. They run in families but a twin gene has not been found. More twin babies grow up to be left handed than you’d expect, and identical twins built of the exact same genetic blueprint have similar brain wave patterns and may think the same, but have different fingerprints.
Since records have been kept starting in 1915, our multiple birth rate has been stable at 1-2% throughout most of the last century. IVF arrived in 1978 and is now 33 years old and is now performed over 120,000 times annually. One would expect it to affect our birth rate numbers at some point. Well, the data is in and it has.
The Instant Family
The Centers for Disease Control and Prevention (i.e., CDC) just published the information on twin births over the last 3 decades (1980-2009). Here are the key findings:
- The twin birth rate rose 76% over this time, from 19/1000 births to 33/1000 births.
- In 2009, 1/30 U.S. births was a twin compared to 1/53 babies 30 years ago. Among multiple births reported in 2009, 96% were twins.
- Twin birth rates increased by 100% in women ages 35-39 years and by over 200% in women ages 40 years and older.
- If the twinning rate had not changed, almost 1 million fewer babies would have been born over the last 30 years.
Since only about 1/3 of the rising twin rate can be ascribed to older moms in the study, this leaves the rise of IVF and fertility treatments as the only elephant left in the room.
An Epidemic of Multiples
Although convenient for many couples as the entire family is complete with a single birth event, the twinning epidemic has other implications. Here are some of them that concern the CDC:
- Higher risk to moms health (eclampsia, gestational diabetes)
- Higher rate of premature births
- Less healthy, smaller sized babies (about half of twins)
When I see those twin strollers while walking down the street, I think “chock it up to technology changing the face of humanity yet again.” For the couple pushing those strollers, you will never seen bigger, or more tired, smiles. In the words of Josh Billings: “There are two things in life for which we are never truly prepared: twins.” But there is something to be said for getting the family built in one fell swoop.