It could be that the new generation of millennial women is delaying having children even longer than the women who came before them, as prime childbearing years are also critical years for advancing in a career. A recent study shows that the marital pay gap that springs up after a first child is born typically does not close if the birth happens between age 25 and 35. 
 
 Shannon Hettinger, a 32-year-old from Washington, D.C., said she definitely wanted children. She grew up in a large family in a small town in Pennsylvania and almost all her high school friends are married with children. But she moved to Washington, and spent her 20s deciding on a career. Now that she has one she loves — she works in residential real estate sales — she is not going to stop until she gets established. That means not having children for a while. 
 
 “I just want to build my book of business and see where I can go from here,” she said. “My whole focus is career growth. That’s my No. 1 priority.” 
 
 “Once I achieve a certain level of success,” she added, “then I’ll start thinking about a family.” 
 
 Ivy Gray-Klein, 26, who lives in Philadelphia and works at the University of Pennsylvania School of Design, said she was open to having children but cannot imagine doing so until she is 30 or 35. She wants to feel settled in her own life first. Now she has three roommates, is paying down her student loans and is working to build a little bit of savings. 
 
 “I’m just really trying to get myself to a place that is solid,” she said by phone. “Having a child right now would be so destabilizing. Children just seem like such an enormous financial undertaking.” 
 
 The country has had declines before. The longest period of continuous decline on record was from 1958 to 1968, according to Brady E. Hamilton, a statistician and demographer with the National Center for Health Statistics. The United States has been tracking the number of births and birthrates since about 1910. 
 
 The most recent decline has been deepest for minorities. The fertility rate among Hispanic women dropped more than 27 percent between 2007 and 2016, the most recent year of data by race. The rate for whites has dropped about 4 percent, for blacks about 11 percent and for Asians about 5 percent. ||||| U.S. Births Dip To 30-Year Low; Fertility Rate Sinks Further Below Replacement Level 
 
 Enlarge this image toggle caption AGF/UIG via Getty Images AGF/UIG via Getty Images 
 
 Updated at 8:48 p.m. ET 
 
 The birthrate fell for nearly every group of women of reproductive age in the U.S. in 2017, reflecting a sharp drop that saw the fewest newborns since 1987, according to a new report by the Centers for Disease Control and Prevention. 
 
 There were 3,853,472 births in the U.S. in 2017 — "down 2 percent from 2016 and the lowest number in 30 years," the CDC said. 
 
 The general fertility rate sank to a record low of 60.2 births per 1,000 women between the ages of 15 and 44 — a 3 percent drop from 2016, the CDC said in its tally of provisional data for the year. 
 
 The results put the U.S. further away from a viable replacement rate – the standard for a generation being able to replicate its numbers. 
 
 "The rate has generally been below replacement since 1971," according to the report from CDC's National Center for Health Statistics. 
 
 The CDC calculates a "total fertility rate" by estimating how many babies a hypothetical group of 1,000 women would likely have over their lifetime. That measure now stands at 1,764.5 births per 1,000 women — a 3 percent drop from 2016. The replacement rate is 2,100 births per 1,000 women. 
 
 "The decline in the rate from 2016 to 2017 was the largest single-year decline since 2010," the CDC said. 
 
 The 2017 numbers also represent a 10-year fall from 2007, when the U.S. finally broke its post-World War baby boom record, with more than 4.3 million births. 
 
 Historically, the number of babies born in the U.S. has gradually risen since a sharp decline in the early 1970s. But that growth has been inconsistent, and over the same time frame, the birthrate has shown a general decline. The numbers are often subject to spikes and sudden dips, driven in large part by the country's economy, generational size and other factors. 
 
 The numbers seem to correspond with what the Census Bureau and others have been predicting for years: America's population growth will increasingly depend on immigrants, after decades in which the U.S. enjoyed a relatively high fertility rate when compared with that of other developed countries. 
 
 As The Associated Press reports, the U.S. birthrate is "still above countries such as Spain, Greece, Japan and Italy, but the gap appears to be closing." 
 
 Broken out by age, the 2017 birthrate fell for teenagers by 7 percent, to 18.8 births per 1,000, a record low. That figure is for women from 15 to 19 years old. For that same group, the birthrate has fallen by 55 percent since 2007 and by 70 percent since the most recent peak in 1991, the CDC said. 
 
 Women in their 40s were the only group to see a higher birthrate last year. Between the ages of 40 and 44, there were 11.6 births per 1,000 women, up 2 percent from 2016, according to the CDC's provisional data. 
 
 Birthrates fell by 4 percent both for women from 20 to 24 years old and for women of ages 25 to 29. 
 
 For women in their 30s — a group that had recently seen years of rising birthrates — the rate fell slightly in 2017. The drop included a 2 percent fall among women in their early 30s, a group that still maintained the highest birthrate of any age group, at 100.3 births per 1,000 women. 
 
 For the third year in a row, both the preterm birthrate and the low birth weight rate rose. The CDC said that the 9.93 percent rise in preterm births was due to late preterm births and that the early preterm rate had not changed from 2016's 2.75 percent. 
 
 Low birth weight — defined as newborns that weigh less than 5 pounds, 8 ounces — rose slightly above the highest level previously recorded, with 2017's 8.27 percent topping 2006's 8.26 percent. 
 
 The overall cesarean delivery rate nudged upward in 2017, rising to 32 percent from 31.9 percent – still below the all-time high of 32.9 percent in 2009. 
 
 The CDC also tallied births by race and cultural data (but it doesn't yet have the data to compare those figures to the overall populations). 
 
 Here's how some of the 2017 numbers were reported:
– Although you wouldn't know it from the constant barrage of pregnant celebrity pics on social media, the fertility rate in the US—the number of births per 1,000 women ages 15 to 44—fell to 60 last year, its lowest level since the government started tracking the figure in 1909, reports NPR. Per the Centers for Disease Control and Prevention, the birth rate is down in nearly every age group tracked. The 3,853,472 births in the US last year represent a 3% drop from 2016, the largest single-year decline since 2010 and the fewest babies born in one year since 1978. A country’s fertility rate is an important measure of its sustainability, reports the New York Times. Too many births put a strain on education and housing. Too few births, and over time the labor pool declines, which in turn tightens resources. In the US, the decline has not yet led to a drop in overall population, because it has been offset to some degree by immigrants. The decline is a bit surprising because in 2017 there were about 7% more women in their prime childbearing years of 20 to 39. One group that ran against the trend was older women. The birth rate among women age 40 to 44 was up 2% over the previous year. In fact, almost one in five births were to women 35 or older. Although it’s difficult to say for certain what's causing the decline, several factors may be at work, including economic uncertainty stemming from the economic downturn in 2007, reports LiveScience. In addition, women have been waiting longer to have children, and millennial women appear to be waiting even longer than previous generations as they build their careers. One happy finding: Births in the 15 to 19 age group were down 7%, down 55% since 2007, and down 70% from a high in 1991, a trend one statistician called "phenomenal."