Fertility Versus Age

Laurie and Dennis McGrath of Minneapolis didn’t think they’d have any problems having a baby. They were both 39 in 2003 when Laurie got pregnant. But then she miscarried at eight weeks.

Two subsequent pregnancies also ended in miscarriages, and the McGraths decided to adopt. “I’d had no idea that at my age, it’s fairly common to miscarry,” Laurie McGrath says. “I’d never even taken it into consideration. I just thought, you get pregnant, you have a healthy baby, that’s it.”

But that’s not how it works for many couples, especially if they’ve waited past their early 30s to have children. Biology doesn’t care whether you’ve met the right someone yet or wanted to reach a career milestone first. Fertility declines in women and men as they age, increasing the odds of not being able to conceive, carry a pregnancy to term, or deliver a healthy baby. For every couple you know beating the odds and having babies in their mid-40s, there’s another that isn’t.

A Steep Decline for Women

Each month when a woman ovulates, there’s a window of 12 to 24 hours to fertilize the egg; she may get pregnant from having sex a few days before or up to a day after ovulation, because sperm can survive in the uterus for a day or two. The likelihood of a woman conceiving in her early 20s is 25 percent in any month when she’s sexually active and not using contraceptives; after that, it drops to 15 percent in her early 30s and 10 percent by her late 30s.

That drop in fertility for women is due to a decline in the number and quality of their eggs. Women are born with all of the eggs they’ll ever have. The supply is depleted, several hundred at a time, during each menstrual cycle.

“Maybe she loses 10 percent each year out to about age 37, then that loss seems to accelerate” says Dr. Theodore Nagel, an associate professor of obstetrics and gynecology at the University of Minnesota who treats couples for infertility at the university-affiliated Reproductive Medicine Center in Minneapolis. Cell division also goes wrong more often starting in the 30s, Nagel says, causing miscarriage or resulting in a problem such as Down syndrome.

For men, fertility starts to decline in their 30s as well, though not as dramatically. Low sperm count or poor sperm movement (motility) or shape (morphology) can lower the chances of fatherhood, but the cause may be genetic, a case of blocked ducts or blood vessels, infection or injury, or a varicose vein in the scrotum (varicocele) that raises testicular temperature, killing sperm. Infertility can be traced to problems like those 20 to 40 percent of the time. But age can be a factor, too, and being older does increase the chances of passing on genetic problems.

“Achondroplasia [dwarfism] is one that seems to have shown up more commonly as dads get older,” Nagel says. “That’s a genetic change that occurs in the sperm and shows up in the offspring, even though the dad does not have it himself.”

Trouble Can Be Hard to Pinpoint

Doctors typically define infertility as the inability to become pregnant after trying for one year, and they advise couples to seek help at that point, no matter their age. That’s what Jocelyn and Steven Abbott (not their real names; they asked to remain anonymous) of St. Paul did in 2003, when she was 36.

“We only really tried for a year, but I just figured with my age, I didn’t want to try for four years and then start going [for treatments],” Jocelyn says.