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Glenn D. Braunstein, M.D.

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Why Women, Men Shouldn't Tarry on Parenthood

Posted: 01/ 3/2012 11:18 am

You and the spouse of your dreams have good jobs, good incomes and a lovely home in a good neighborhood. It has a garage built to hold a van and slew of tricycles, bicycles and boogie boards. Behind it sits a yard big enough for a swing set and maybe even a safely fenced swimming pool. Your framed degrees are tucked away in a closet, but your education has served you well both financially, socially and in your grasp of the world.

At last, the time is right to have a baby. But the longer you've waited, the more uncooperative your body may be. One of the saddest complications of delaying a family is involuntary childlessness.

It's possible you've forgotten about that biological clock thing, a concept pushed further into the background in the past few years with technological advances in infertility treatments and news reports of women as late as their 50s and 60s giving birth.

But the truth is, it begins to get more difficult to get pregnant when a woman hits age 30; by 35, her fertility takes a dive; and by 40, it plummets. It takes longer to get pregnant and pregnancy takes on additional risks. Recent research shows that men, too, have their own version of a biological clock.

And we must remember that each pregnancy involves more than one human organism. Babies born to older mothers are more likely to have a number of congenital disorders and are at higher risk for premature birth, which itself carries a host of potential lifelong health consequences.

The Biology of Older Mothers -- And Fathers, Too

The number of germ cells, which become eggs, reaches a peak of six to seven million by 20 weeks of fetal development. This number is reduced to one to two million at birth; 300,000 at puberty; and almost zero at the time of menopause. Between the ages of 35 to 37, the rate of egg loss accelerates, and if the woman smokes the decline is even faster. Also, as women get older, their eggs become increasingly likely to be genetically abnormal. Nature helps ensure that those abnormal eggs are less likely to be fertilized, develop, implant in the uterus and grow to full term. It's not impossible to become pregnant and carry the baby to term into the fifth decade of life, but census numbers show just how rare it is. Of the 4.13 million births in the United States in 2009, about a third of them were to women older than 30; and nearly half a million were born to women 35 to 39. Women aged 40 to 44 delivered just more than 100,000 babies. Fewer than 8,000 babies were born to women older than 45. And those numbers include women who had borne children previously. It's more difficult for older first-time mothers to conceive and to carry a child to term.

The probability of conceiving a child during any one monthly cycle declines with age so that the likelihood of getting pregnant for women ages 19 to 26 is twice as high as for women 35 to 39. And as the father ages, the odds of conceiving within a year drop each year after he reaches the age of 30, falling considerably after his 40th birthday.

Complications for Mother and Baby

One study done in California looked at almost all women who delivered a baby at age 40 or older in 1992 and 1993. Results were published in 1999. Researchers examined a database of hospital records that captured more than 98 percent of births, though not home births, for example, or births in military hospitals. Of more than a million births during that span, some 2 percent, or 24,032, were to women 40 and older. The older women who were having their first baby were more than twice as likely to have a cesarean delivery than a control group of younger women; babies born to the older first-time mothers were smaller by more than five ounces; and rates of complications, including gestational diabetes, fetal growth restriction and problems with the baby receiving enough oxygen (birth asphyxia) were higher in older moms and their infants.

In 2007, researchers looked at records of more than eight million births to women ages 30 to 54. The risks increased in tandem with age. They included prolonged labor, excessive bleeding, breech presentation, cesarean delivery and premature birth.

The risk of bearing a child with a chromosomal defect increases with age. According to the March of Dimes, the risk of a baby with Down syndrome, the most common of such defects, is: 1 in 1,250 at age 25; 1 in 1,000 at age 30; 1 in 400 at age 35; 1 in 100 at age 40; 1 in 30 at age 45; and 1 in 10 at age 49.

Carrying the baby to term becomes more difficult as a woman gets older. Some 10 percent of pregnancies end in miscarriage among women in their 20s; by 35 to 39, the rate rises to 20 percent; at 40 to 44, the rate is 35 percent; and half of all pregnancies among women 45 and older end in miscarriage. And the age of the father, new research has found, is part of the equation. In a study looking at the age of both the mother and father researchers found that the already increased risk of miscarriage in women older than 35 goes up even further if the father is older than 40.

Babies at Higher Risk

Besides higher risks of congenital problems and problems associated with premature birth, babies born to older mothers develop in a fetal environment that seems to predispose them to type 1 diabetes. We don't know why, but researchers speculate that maturation of the immune system in the fetus may be influenced by the mother's age. Type 2 diabetes, the kind once called "adult-onset" diabetes but now seen at younger and younger ages, is more common among children born to older mothers. The risk, though, takes on a U-shaped curve, being higher among teen mothers, dropping through the 20s and early 30s before rising again.

It's not just mom's age that can make a difference. Researchers have found that babies born to men older than 40 have a greater risk of autism than those born to younger fathers. And those children score a few points lower on IQ tests, as well as tests of concentration, memory and reasoning -- at least through age seven.

When an older mom is pregnant with twins -- more likely in cases where assisted reproductive technology such as IVF are used -- her babies fare better than twins born to younger mothers. That could be because the twins conceived through technological methods are more likely to be fraternal. Identical twins have a higher risk of poor outcomes than do fraternal twins. Also, older women having twins are more likely to have begun prenatal care earlier, including pre-conception counseling.

When reading about older women getting pregnant and delivering babies, don't overlook the fine print. Those women older than 45 often are not giving birth to babies genetically related to themselves. Researchers asked 400 Israeli undergraduate students questions about age-related fertility, and found most were unrealistic. The students overestimated the ease of getting pregnant at all ages. And only 11 percent of the students understood that genetic motherhood, or having a child with a woman's own egg, is almost impossible after the age of 45, unless she's frozen her own eggs at a younger age.

Advantages of Delayed Parenthood

It takes time to build a career while searching for our most suitable mate. All of the discussion so far has been biology and medicine. But I know that if people made life decisions based solely on science, no one would smoke, everyone would eat their vegetables and exercise daily and dentists wouldn't have to remind us to floss. Social science shows us that delaying parenthood results in a more stable family environment, higher income and better living conditions. From an economic and career perspective, it makes sense for both men and women to be on sure footing before embarking on such an important and life-altering journey.

No one can advise a couple on the best time for them to have a baby. I only urge couples to make their decisions with a complete understanding of the science of conception and childbirth and an awareness of the difficulties they may face if they delay too long. A blood test, anti-Mullerian hormone, which reflects the status of a woman's eggs and a discussion with a reproductive endocrinologist, may be helpful to assess a couple's probability of conceiving a child either naturally or through assisted reproductive technology.