No Link Is Found Between Age and Pregnancy Success
Healthy women who delay childbearing until after age 34 are no less likely than younger women to have a successful pregnancy, according to a new study that runs counter to conventional notions that a mother’s age is linked to certain infant disabilities and death.
The study found that babies born to older women are no more likely than others to face premature delivery, growth retardation or serious distress at birth--even though those women are at greater risk of manageable complications during pregnancy.
The study, published today in the New England Journal of Medicine, did not examine the risk of miscarriage or genetic defects. Those problems are known to increase with a woman’s age, just as fertility is known to decline.
“(The study) shows that if you are getting good prenatal care and you’re in good health, there’s absolutely no reason why you can’t enjoy a safe and successful pregnancy,” said Dr. Robert Resnik of UC San Diego, who wrote an editorial accompanying the article.
Questions about the risks of delayed childbearing have become increasingly pressing in recent years as contraception has made it possible for more and more American women to postpone their first pregnancy, often to accommodate educations and careers.
Between 1970 and 1986, the rate of first births among women age 30 to 39 more than doubled. It rose by 50% for women age 40 to 44. According to the researchers, surveys indicate those trends are likely to continue.
The new study, by researchers at Mt. Sinai School of Medicine in New York City, involved 3,917 women, mostly age 20 to 39, who gave birth for the first time. All were private patients, mostly healthy and well-educated, at Mt. Sinai Hospital. Three percent were 40 and over.
The researchers found that those who were 30 to 34, or 35 and up, were no more likely to have a preterm delivery; nor were their babies more likely to be small for gestational age, have low scores on so-called Apgar tests or die in the womb or shortly after birth.
(Smallness for gestational age can indicate problems in the fetus’s development in the uterus, such as intrauterine growth retardation. Apgar tests gauge a baby’s well-being at birth, measured by heart rate, respiration, muscle tone and response to stimuli.)
The researchers did find that women over age 34 were slightly more likely than others to have a so-called low birth weight baby. Such babies, born at less than 5 1/2 pounds, are more likely than others to die in the first year of life.
They also found that those women were significantly more likely to encounter complications during pregnancy, such as pregnancy-related hypertension and diabetes. Physicians say such complications can usually be detected and treated.
Women over 29 were also more likely than younger women to have Cesarean sections and infants admitted to the newborn intensive care unit. The researchers could not explain that finding but suggested that it reflected “more conservative treatment of older . . . women.”
“The study suggests that although older women (having their first child) have higher rates of complications of pregnancy and delivery, their risk of poor neonatal outcome is not appreciably increased,” the researchers concluded.
Past studies have produced conflicting results. The new research, which Resnik described as the best yet, examined not simply birth certificates but patient records. The records revealed underlying medical conditions that could affect a woman’s chances of success.
Such conditions, more common in older women, did indeed account for complications in pregnancy and delivery. But when the researchers controlled for those conditions, they found that age in itself did not increase a woman’s risk of an unsuccessful pregnancy.
The fact that medical problems are more common in older women and are responsible for complications in pregnancy may explain many people’s perception that age alone puts a woman at risk of an unsuccessful pregnancy.
The researchers as well as Resnik hastened to point out that older women still encounter difficulties in having children. Fertility declines with age, making conception more difficult. Miscarriages and chromosomal abnormalities are much more common.
For example, 20-year-old women have a 1 in 1,667 chance of giving birth to a child with Down’s syndrome, a form of congenital mental retardation. The risk rises to 1 in 952 at age 30, 1 in 378 at age 35, 1 in 106 at age 40, and 1 in 30 at age 45.
It is now possible to screen a fetus for genetic defects, and to terminate the pregnancy if necessary. New technology also makes it possible to monitor older women for complications of pregnancy and, in most cases, to take steps to protect the fetus. For example, in the case of pregnancy-induced hypertension, physicians sometimes deliver the baby early to take both the mother and infant out of danger.
“I think some of the technologies have made the whole trip safer for the fetus,” said Dr. Edward Quilligan, professor of obstetrics and gynecology at UC Irvine. “Some of the fetuses 20 years ago that went to term and got into difficulties would (now) be picked up in advance.”
The researchers emphasized that the women they studied were not necessarily representative of the population at large. They were predominantly white, married, college educated and nonsmoking.
“These are private-pay patients and we cannot generalize to clinic patients,” said Mary Louise Skovron, a co-author of the paper. “. . . But to the extent that urban women are delaying childbearing for employment or education reasons, they would be included in this group.”
