In its first year, the pandemic lowered the twin birthrate in the United States, a report from the Centers for Disease Control and Prevention suggests.
When researchers analyzed birth records from 2019 and 2020, when the pandemic began, they found a decrease in all births. But the drop in the number of twin births in the United States outpaced those of single children; while the number of single births declined 3 percent, twin births fell 7 percent.
The biggest changes took place in November and December 2020, when the twin birthrate logged 10 and 14 percent declines, respectively.
From 2019 to 2020, although the decline was small for women under 30, it rose to 5 percent for those ages 30 to 39 and 11 percent for those 40 and older. In December 2020 alone, women 40 and older saw their twin birthrate fall 35 percent from a year before.
Researchers attribute the change to a dramatic decline in fertility treatments at the beginning of the pandemic. The use of assistive reproductive technology such as in vitro fertilization is associated with a higher number of multiple births. But in March 2020, the American Society for Reproductive Medicine (ASRM) recommended that new cycles of IVF, embryo transfers and other fertility treatments be suspended.
Although ASRM rescinded its recommendation in late April 2020, the CDC researchers note that the late 2020 twin birth declines coincided with what would have been the due dates of those receiving fertility treatments.
The number of twin births dropped for all races, but the decline was highest among Hispanic women. Hispanic women are less likely to receive infertility treatments than others, and the researchers write that the disparity might also be due to other factors.
Overall, the CDC counted 112,437 twin births in the United States in 2020, at a rate of about 31 twin births per 1,000 live births.
