The percentage of U.S. women with babies is the lowest it has ever been since we started tracking the statistic in 1909, a new report from the CDC reveals. While the absolute number of babies is still growing, as is the U.S. population — the CDC projects that it will increase from 319 million to 400 million by the year 2051 — this means that a smaller proportion of women ages 15-49 is driving the growth.In some ways, this is a good thing. As The Atlantic points out , global population growth is unsustainable at current rates, and the decline in the overall fertility rate in the U.S. is thanks largely to a precipitous drop in the teen birthrate: It's down 42% since just 2007 . (Thanks, more effective birth control and pregnancy-prevention education !)The fertility rate among all women under 30 is decreasing, too, although more slowly. Data suggests that millennials are putting off or opting out of having kids in part due to the outrageous cost of raising one: In 2014, the U.S. Department of Agriculture projected that it would cost a middle-income couple $245,000 to raise a child to the age of 18. It's no wonder that this price tag would encourage prospective parents to wait to procreate later in their careers than their parents did.Interestingly, the birthrate among women 30 to 44 is going up, thanks to reproductive technology such as IVF. "The good news is that infertility treatment has allowed women to extend the age of child-birthing, going along with a lot of trends we are seeing in increasing age of marriage, increasing education levels, and increasing labor force participation," Donna Strobino, PhD, a Johns Hopkins University professor of population, family, and reproductive health noted to ABC News. "The bad news is the complications associated with aging that have to do with an increase in chronic diseases as women age, increase in pregnancy-induced complications, and increase in complications for the fetus and newborn."We're heartened that teens are accessing more pregnancy prevention resources and that older women are increasingly able to pursue their reproductive goals. As reproductive technology continues to develop, hopefully so will our ability to prevent and treat complications of older women's pregnancies — as well as care for all kids more cost-effectively. Next up on our dream list: better options for people after they have kids, through paid leave and subsidized childcare. A future parent can dream, right?