US birth rates have plummeted to historic lows, new CDC figures reveal.

Since 2007, fertility rates have plummeted 18 percent in large cities, 16 percent in mid-sized counties, and 12 percent in rural areas.

As expected, the average age that women have their first child continues to climb - now at 24.5 years old in rural counties and 27.5 in metropolitan areas.

The figures fall in line with the steady trend of declining birth rates in the US, which started to sharply downturn after the economic crash in 2008.

But according to Gretchen Livingston, a demographer at Pew Research who specializes in fertility, it’s not clear why that dip hasn’t started to level off now, 10 years later.

Demographers had expected that the sharp dip, which started after the 2008 economic crash, would have leveled off by now. But new CDC figures suggest there is no slow-down in any region

'It's not a great surprise to see declines in rural and urban areas,' Livingstone told DailyMail.com, 'but most experts would have expected that there would have been more of a recovery than we have seen.

'There are some people who syspect that there may still be some kind of economic uncertainty contributing to the low fertility rate.'

The report shows the same gaps between rural, mid-level, and large urban counties.

White women in large cities are still having the fewest babies, and postponing motherhood later and later. In 2017, the average age city-based white women have their first child was 29, up from 27.5 in 2007.

In contrast, black women in rural counties tend to be the youngest mothers, with an average first-time-birth age of 22.7, up from 21 in 2007. Rural Hispanic women are close behind, with motherhood starting at an average age of 23, up from 21.7 in 2007.

In terms of overall fertility rates, Hispanic women still outpace the rest of the country with the amount of kids, followed by black women, then white women.

However, it was Hispanic women that saw the sharpest decline of any race in the last 10 years.

The average age that women have their first child continues to climb - now at 24.5 years old in rural counties and 27.5 in metropolitan areas

In 2017, the average age city-based white women have their first child was 29, up from 27.5 in 2007

In terms of overall fertility rates, Hispanic women still outpace the rest of the country but they have seen the sharpest dip

Today, even despite the drop, birth rates among Hispanic women are generally higher even than other racial groups were 10 years ago.

But the gap has shrunk dramatically.

In 2007, rural Hispanic women had double the amount of kids compared to city-based white women (3,126.5 babies per 1,000 rural Hispanic women compared to 1,820.5 city-based white women).

In 2017, there were 2,320.5 babies born per every 1,000 rural Hispanic women, and 1,575.5 babies per 1,000 city-based white women - which is around 1.4 times higher.

All of those micro-trends, though, do little to change the shape of a significantly straight-lined graph tipping downwards on all fronts.

Prior to 2007, America's birth rate was looking healthy, but swiftly dipped after 2008.

The gradual decline in birth rates mirrors the gradual increase in maternal age.

That does play a role - despite all the technologies making pregnancy possible for older women, things like IVF are more expensive than most can afford, and fertility does still rapidly decline with age, whether a petri dish is involved or not.

However, Livingstone cautions that this trend started way before the economic crash.

'It's important to keep in mind that the postponement of fertility started long, long before the recession.'

These drops also come amid a male fertility crisis, with drops in the quality of semen seen globally and across the US.