At age 45, Tracy Slater, an American expat writer living in Osaka, Japan, resigned herself to the fact that she might never be a mother. After a few years of failed fertility treatments and two miscarriages, she and her husband continued trying to have a baby — but shifted their focus to Slater’s husband’s dying father.

So when Slater developed what they assumed was a stomach bug, they figured she had picked it up at the hospital while visiting him. But it turned out she was seven weeks pregnant. “They already saw a heartbeat,” Slater says. “And I’d been drinking one or two glasses of wine a night, and a cup of coffee everyday.” In addition to drinking alcohol and caffeine — not advised for women trying to conceive — Slater was also overwhelmingly stressed over the prospect of losing her beloved father-in-law.

In other words, she was not in ideal fertile conditions — and yet, she had become pregnant with her daughter. “I still have dreams they made a mistake. I still can’t believe I carried to term this healthy child,” says Slater, author of “The Good Shufu.”

While Slater’s outcome is certainly not the norm, and one she attributes to good luck, it’s increasingly common to see women in their 40s have successful pregnancies — through IVF, egg freezing, donor eggs or more rarely, as in Slater’s case, natural conception.

According to the Centers for Disease Control and Prevention, pregnancies among women in their 40s has increased by about 2 percent per year since 2000. In 2014, there were 10.6 pregnancies per 1,000 women in this age group.

[See: The Fertility Preservation Diet: How to Eat if You Want to Get Pregnant.]

Risks to the Baby and Mother

Pregnancies in the fourth decade of life (and beyond) are lumped into the “high-risk” category.

There are two types of risks: fetal problems related to an older egg and obstetrical problems related to being an older mother, explains Dr. Richard Paulson, chair of reproductive medicine at the University of Southern California. Women’s fertility naturally declines between ages 35 and 45, with a steep decline between 40 and 45. Women who delay pregnancy may have frozen their younger eggs for later use or used donor eggs to get pregnant. Otherwise, older eggs pose a higher risk of chromosomal abnormalities, namely trisomy 21 or Down syndrome, Paulson says.

According to the American Congress of Obstetricians and Gynecologists, a 33-year-old woman has a 1 in 208 risk of having a baby with Down syndrome, which rises to a 1 in 19 risk for a 43-year-old woman.

Chromosomal abnormalities can also make women more prone to miscarriages, Paulson adds.

In addition to risks to the baby, pregnant women in their 40s are at higher risk of their own health problems, including hypertension and pre-gestational diabetes. “Pregnancy is a stress on the metabolic system,” says Dr. Mary Norton, a reproductive endocrinologist at the University of California-San Francisco and president of the Society for Maternal-Fetal Medicine. “For a woman destined to get diabetes later in life, it will often show up in pregnancy. We recommend they get tested [for diabetes] right after pregnancy.”

And certainly, women who already have preclinical diabetes or an underlying condition like low-grade hypertension are most at risk for difficult pregnancies, adds Dr. Mark Sauer, chief of reproductive endocrinology and infertility at Columbia University Medical Center. “It’s often very hard to impress upon them how accelerated and severe it can be once they’re pregnant.”

Especially in the third trimester, when a woman’s heart is working extra hard, Sauer adds, cardiovascular events — such as stroke, heart attack, preeclampsia and even death — can occur. This tends to happen if there are other underlying conditions at play, including pulmonary hypertension, valve disease, chronic asthma, thyroid disease or epilepsy. Even being overweight is a risk factor for a difficult pregnancy.

[See: How to Cope With Gestational Diabetes.]

Preventing Problems Via a Healthy Lifestyle

“If you know you have some underlying issues, and if you have the ability to get into a more optimal self, your pregnancy may benefit,” Sauer says, adding that pregnant women — of any age, but especially older women — should follow basic health recommendations, including maintaining a healthy diet, normal body weight and active lifestyle. “People between the ages of 30 and 45 are probably in their busiest years of work life, so it can be hard for them to find an extra hour for exercise every day,” Sauer says.

Sandy Robertson, 57, author of “You Can Get Pregnant Over 40, Naturally,” had been through several years of infertility treatments and a few miscarriages when, at age 45, she resigned herself to not having children. But then she felt a “universal backlash,” she recalls. “I would run into all these people in their 40s who were pregnant — no matter where I went. My radar was up, maybe, but I thought, ‘You know, I bet I can do this,'” she says.

First, she took care of her body. “I would eat broccoli for breakfast. I had [around] 11 servings of vegetables a day. I cut back on the amount of exercise I did. I did meditation,” she continues. “And lo and behold, I got pregnant on my own.”

Robertson was 45 years old when she got pregnant, so she was closely monitored. “The whole pregnancy was completely normal,” she recalls, adding that she was automatically referred to a perinatologist, a specialist in high-risk pregnancies, and also underwent amniocentesis to test for chromosomal abnormalities in the fetus.

[See: The Best and Worst Exercises for Pregnant Women.]

Delivery Challenges

In the end, Robertson had a “fairly run of the mill” vaginal delivery at 39 weeks, she says, adding that doctors encouraged early delivery to avoid the deterioration of the placenta, which is more prone to happen in older women. The placenta feeds the baby nutrients and oxygen throughout the pregnancy, so if it begins to deteriorate, the risks of prematurity and stillbirth increase.

Women in their 40s who have had previous successful pregnancies generally have better pregnancies than those having their first baby, and that goes for delivery, too. Older women are typically more likely to undergo a C-section, according to CDC data: The rate for women over 40 is 41 percent, almost double the 21-percent rate for women ages 20 to 24. That’s because older uteruses may not contract as well, and it’s harder to dilate the cervix — especially for first-time mothers. “I think [the high C-section rate] is partly because doctors and patients are more anxious,” Norton says.

Slater had an emergency C-section after 48 hours of contractions, followed by eight hours of induced labor without pain medications. “The baby was fine, but they weren’t sure I had the energy to push her out, so they did a C-section,” she says.

More from U.S. News

10 Weird Mind and Body Changes That Are Totally Normal During Pregnancy

How to Cope With Gestational Diabetes

The Fertility Preservation Diet: How to Eat if You Want to Get Pregnant

Navigating a Safe Pregnancy in Your 40s originally appeared on usnews.com