More women in their 30s today are having children than women in their 20s, and this trend toward later pregnancies does not seem like it will end anytime soon. On the average, 28 is the age that women have their first child. That's up from 26.4 years of age in 2015, and 26.3 in 2014.

Of course, the reasons for the delay are clear. More women are reaching higher levels of education than ever before, methods of contraception have improved, and extraordinary fertility options – such as in vitro fertilization – have become more common and accessible.

The risks that women take when they delay the decision to give birth are also clear. For one, the actual chances for fertilization decrease with age. One study discovered that among women who received artificial insemination, 74 percent of those under 31 years old were pregnant within a year; the chance decreased to 61 percent of individuals between the ages of 31 to 34, and it dropped again to 54 percent of women aged 35 and above.

Those older women who do conceive do it at an increasing risk of giving birth to children with congenital anomalies. The rate of an embryo having Down syndrome at the 10-week mark of pregnancy is 1 in 1,064 at age 25. The rate increases to 1 in 686 at age 30, and 1 in 240 by the age of 35 years. At age 40, the Down syndrome rate increases further yet to 1 in 53.

What's the science? Researchers believe it has something to do with a process known as chromosomal recombination. That's the system whereby pairs of chromosomes exchange genetic material before separating. As women get older, the recombination process is less regulated, which can result in abnormal chromosome numbers or large chromosomal rearrangements.

As women age, the quality of their eggs decline. As a result, the risk of miscarriage increases. The latest research clocks the risk at about 8.9 percent for women aged 20 to 24, and increases to a sobering 74.7 percent for women over the age of 45.

The exact reasons why the rate of stillbirths increase with older women are unclear, but increase it does. A Canadian study found the rate of stillbirth to be around 1.2 to 2.23 times higher in older women, and British research quantified the rate of stillbirth as 4.7 per 1,000 for women aged 18 to 34, 6.1 per 1,000 between the ages of 35 and 40 years, and 8.1 per 1,000 for women aged 40 and over.

It is not just the child's health that is at risk in an older pregnancy. Women aged 40 and older who give birth are at greater risk of ischemic stroke, hemorrhagic stroke, heart attack, and death from cardiovascular disease, according to research presented at the American Stroke Association's International Stroke Conference in 2016. A study from 2004 just out-and-calculates that the risk of maternal mortality increases with age.

On the plus side, children from older mothers are known to have fewer behavioral, social, and emotional difficulties. One study even notes that these children are likelier to be taller, healthier and better educated. Of course, consult with your physician when weighing all the potential benefits against the risks.