The U.S. fertility rate plunged to its lowest point in four decades last year while birth rates also declined for almost all women under 40. Both the birth rate—which is the number of births per thousand women—and the fertility rate—a lifetime average forecast— fell in 2017, according to new figures from the Center for Disease Control and Prevention’s National Center for Health Statistics. Donna Strobino of John Hopkins University said the change came down to women delaying having a baby for the benefit of their professional lives. “Women are becoming more educated, they are in the workforce, they are pursuing their careers,” said Strobino. “And in the absence of policies that really help women who are working to really take some time off post-partum, you are probably going to see a continuation of this delay.” While births decreased among younger women in the U.S. last year, the rate rose in women aged between 40 and 44.