Kate Middleton’s fourth pregnancy could be risky.

There are rumors that the Duke and Duchess of Cambridge are expecting another baby. If true, Middleton’s fourth pregnancy could be risky due to her age.

The royal mom of three is already 37 years old and women who are pregnant at age 35 or older are referred to as “advanced maternal age.” They may be advised to have labor induction or C-Section at 39 weeks solely because of their age.

At this age, certain genetic risks are more common like the embryo having a Down Syndrome, which happens when there’s an extra copy of Chromosome 21. The rate of having a baby with this condition increases with the mother’s age and this has been observed in large studies of women and in studies with embryos conceived with IVF.

The risk of miscarriage also climbs with age from nine percent among 22 years old, 18 percent among women in their 30s, 20 percent at age 35 and 40 percent at age 40. Older women also have higher risks of stillbirth.

It might help that this isn’t Middleton’s first pregnancy. According to Keyna Bracken, a doctor in Hamilton with a special interest in obstetrics and women’s health, the risks are greater in women who are pregnant with their first child like Middleton’s sister-in-law Meghan Markle.

“A first pregnancy in an older woman can be harder on the body,” Bracken said, adding “simply because it hasn’t done this before.”

“Poor egg quality can also result in more genetic disorders, like Down syndrome and trisomy 18, and more miscarriages,” she added.

Although advanced maternal age pregnancy includes risks, this is not that uncommon. There has been a dramatic increase in the number of women having babies at age 35 and older. In the U.S., the figure started to increase in the mid-1970s and has continually steadily risen over time. In 2016, 15 percent of birthing moms were 35 and older, 11 percent in 2002 and eight percent in 1990.

Just recently, Middleton said that she was “feeling broody” after meeting a cute baby. However, according to Nicola Harrison, the royal mom of three’s statement was more of humor and compliment, and not about family planning.

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Kate Middleton takes part in preparations for a Commonwealth Big Lunch at St Luke's Community Centre on March 22, 2018 in London. Getty Images/Paul Edwards