The rate at which women in their 30s and 40s are having kids is increasing in the United States, according to the Centers for Disease Control and Prevention’s (CDC) latest data from 2012. This sits alongside flattening or outright declines among all other age groups, some of which hit their lowest rates since the middle of the 20th century.
The CDC data doesn’t surprise many demographers and social scientists, as the cohort of women delaying childbirth until they’ve established a career has been growing for the last several years. Dr. Edward McCabe, chief medical officer for the March of Dimes, agreed that the trend makes sense given recent prior data.
“If we just look at our anecdotal experience with women who are friends and colleagues, we know a lot of women are delaying birth until later in life," McCabe told HealthDay.
In contrast with rising birth rates among women in their 30s and 40s, the rates of preterm births, teen births, and nonmarital births all declined in 2012. These trends are likely marked by the increased awareness, and decreased stigma, of contraception — combined with the growing trend to start a family later in life, which is something McCabe wants to monitor given the increased health risks of childbirth later in life.
"It's something we want to follow," he said. "It's important for women to know the risks for certain birth defects and risks for preterm birth may increase with age. It's important for women to be knowledgeable about those risks, to the extent they plan their pregnancies and get a pre-conception health assessment so they go into a pregnancy as healthy as possible."
Women peak in fertility in their early 20s, with a considerable drop taking place after the age of 35. Numerous health risks are associated with increased maternal age, many of which are characterized by genetic complications due to the egg’s inability to fully divide. Down syndrome is the most common disorder seen in later age pregnancies. Other complications pertain mostly to maternal health, as the risk of infertility or loss of pregnancy rises with age. Out of 1,000 live births to 33-year-old mothers, five babies will have abnormal chromosomes, according to the University of Maryland Medical Center. At age 40, that rate rises to 25 out of 1,000.
Of note in the CDC’s preliminary report was the teen birth rate, which fell to a historic low in 2012. The number of births to teenagers 15 to 19 years old dropped seven percent to about 305,000 — the fewest since the end of WWII. The number is nearly a third of what it was in 2001 and less than half of the all-time peak in 1970.
"Last year there was some discussion that more teenagers are using birth control, and more were using more than one form of birth control," McCabe said. "People were attributing that message getting out to teenagers as being important in this decrease."
A similar message had apparently reached women regarding preterm births, he added, as the cohort of women who gave birth before the full 40 weeks had fallen for the sixth consecutive year, down to 11.54 percent of all births. The low birthweight rate also declined in 2012, to 7.9 percent.
"Certainly some women need to deliver early for their health and their baby's health, but otherwise they really should wait until 39 weeks," he said. "We now know that even in early term – 37 and 38 weeks – the outcome is very different than full term at 39 and 40 weeks. The mortality rate is higher."
And despite the rate of Caesarean section births remaining unchanged in 2012 — roughly one-third of all births occurring via C-section — report co-author Joyce Martin said the data could be optimistic given recent trends.
"If you consider that the rate had been going up steadily prior to the last couple of years,” said Martin, who works as a statistician at the CDC's National Center for Health Statistics, “then this is an improvement if you're looking for a decline in cesarean delivery.”