An array of both medical and personal factors can prevent a woman from trying to become pregnant. For example, a recent miscarriage, new job, or any other significant life event can force some women into holding off on pregnancy. A recent study conducted by the Centers for Disease Control and Prevention has found that U.S. birth rates among women under the age of 30 hit an all-time low in 2013.

Researchers from the CDC’s National Center for Health Statistics gathered data using the Natality Data File from the National Vital Statistics System (NVSS). Information on all births occurring in the U.S. are taken from birth certificates. After the total number of births in the U.S. hit a peak in 2007, these rates have continued to decline in the past six years until hitting a record low last year. A total of 3,932,181 births, down less than one percent from 2012, were recorded among all women in the U.S.

Although the overall number of women giving birth in the U.S. has experienced a historic drop, rates of women over the age of 30 giving birth have actually increased in recent years. On the other hand, birth rates for women under the age of 30 have continued to decline over the past few decades. Birth rates for American teenagers dropped by 10 percent, women between the age of 20 and 24 by three percent, and women between the age of 25 and 29 by one percent from 2012 to 2013.

The rate of cesarean deliveries also declined by around one percent to 32.7 percent of all births in 2013. After rising by nearly 60 percent between 1996 and 2009, rates of C sections in the U.S. have started to level off. “After more than a decade of steady rises, cesarean delivery rates are trending slightly downward; a recent report revealed larger declines for 2009–2013 among women at low risk for cesarean delivery than for all women with cesareans,” the research teams explained.

A rise in women over the age of 30 giving birth coinciding with a drop in preterm births challenges a 2013 study conducted by the Karolinska Institutet that compared pregnancy outcomes among first-time mothers over the age of 30 to those between the age of 25 and 29. Findings revealed that infants born to mothers between the age of 30 and 34 are at an increased risk for preterm birth, impeded growth, and stillbirth compared to mothers under the age of 30.

"We were surprised that the risk for certain outcomes increased at such a relatively early age. For women individually, the risk is small, but for society at large there will be a significant number of 'unnecessary' complications with so many women having children just after 30,” Ulla Waldenström, professor at the Department of Women's and Children's Health at Karolinska Institutet, said in a statement. “It would therefore be advisable to inform both women and men, even at schools, of how important age is to child birth.”

Source: Martin J, Hamilton B, Osterman J. Births in the United States, 2013. NCHS Data Brief. 2014.