(CNN) -- Actress Halle Berry has joined a growing group of celebrity and real-life moms who are getting pregnant after 40. Berry recently announced she is carrying her second child at the age of 46.
While birth rates for almost all other age groups are at historic lows, according to a 2012 report from the National Center for Health Statistics, the rate for women in their late 30s and early 40s is on the rise.
By 40, a woman's reproductive chance is less than 5% per cycle, so a natural pregnancy is rare. And pregnant women in their 40s face increased risks for several health issues, including gestational diabetes, high blood pressure, breast cancer and miscarriages.
But Dr. Petra M. Casey said those risks vary significantly from patient to patient.
"Underlying health is a huge factor in the outcome of pregnancy," she said.
Casey, an associate professor of obstetrics and gynecology at the Mayo Clinic, gave birth to her two children at age 38 and at 41. "I don't, unfortunately, look anything like Halle Berry," she joked.
"Some women are incredibly healthy at 40; some are sick at 20," she said. "That all makes a huge difference in the challenges they may face in being pregnant."
Berry looks healthy and has less body fat than most Americans. She also makes a great salary, so she can afford to pay for good medical care. All of those elements are factors in her favor. But one factor she can't change is the age of her eggs.
"Aging eggs cannot be helped and are a risk factor for anyone her age," Casey said.
Doctors have several tests available to see whether the child will have any kind of chromosomal problem that could come with aging eggs.
"In terms of risk with women who are a little bit older and the potential genetic problems the baby may have, we pay closer attention to that for sure," said Dr. George Macones, chairman of the department of obstetrics and gynecology at Washington University in St. Louis. "If someone is healthy, though, and doesn't have medical problems other than the genetic issues, there shouldn't be a lot to worry about."
Macones has seen a significant increase in the number of older patients he sees. "I believe my oldest patient was 54. She was incredibly fit as a competitive athlete and everything went fantastic with her pregnancy and birth," he said.
Dr. Carla Roberts, a reproductive endocrinology and infertility specialist and the chief of service at Emory University Hospital Midtown in Atlanta, said she is always mindful about the age of her patients.
"I tell any patient over the age of 40 that they need to be as proactive as possible through their pregnancy. We screen them for diabetes and high blood pressure, test for lipids and HDL and LDL, blood sugars and run EKGs to monitor how the heart is. We want a mammogram that is up to date and want a talk with a genetics counselor. It's a multidisciplinary team effort to talk about risks and how best to proceed."
Any woman who is borderline for a disease such as hypertension that might not otherwise have developed until her 60s could be more at risk, due to the huge influx of hormones that comes with being pregnant, Roberts said.
"It could hasten the development of disease, and no matter how good you are with your diet, there is always increased weight that often comes with pregnancy," Roberts said. "An extra 10 to 15 pounds after pregnancy increases the risk of heart disease and hypertension. High levels of estrogen and progesterone can lead to increased blood pressure and worsen cholesterol levels. So these are all elements we watch carefully."
But, as Casey reminded us, "Halle Berry has probably never been called average, not by a long shot" -- so she should be in good shape.