Study: New moms should wait at least 18 months before next pregnancy
February 24, 1999
ATLANTA (CNN) -- Spacing your kids 2 1/2 years apart may be ideal for producing healthy, full-term babies, according to a study that found a sound medical basis for what many women are doing already, for altogether different reasons.
A study by the Centers for Disease Control and Prevention found that while having babies too close together can be bad for an infant's health, having them too far apart may be even worse.
Both situations raise the risk that the new baby will be premature or small, which can cause long-term health problems, even death.
The CDC study calculated that waiting 18 to 23 months after giving birth to get pregnant again is best. That works out to about 2 1/2 years between children.
"Somehow the body knows that this interval is good for the health of the infant," said Dr. Bao-Ping Zhu, who directed the study.
"The delivery is like running for the marathon. You don't want to have two deliveries too close together ... otherwise the body will be tired and the birth outcomes are not likely to be good," Zhu said. "On the other hand, you don't want to wait too long, either."
Many parents already space their children a couple of years apart. That way, they won't have two children in diapers and the youngsters will be close enough in age to play together when they get older.
Compared with babies born during the ideal interval, those whose moms became pregnant again within six months had a 30 percent to 40 percent greater chance of producing premature or undersize babies.
Those who waited 10 years for another child were twice as likely to have an unusually small baby and 50 percent more likely to deliver prematurely.
The study was based on 173,205 births in Utah from 1989 to 1996. The results were published in Thursday's New England Journal of Medicine.
Dozens of previous studies have linked short intervals with a higher risk of small and premature infants, although none determined the best interval. The few studies on long- interval births were less consistent in their findings.
Zhu said babies conceived too soon probably have problems because the mother is recovering from vitamin depletion, blood loss and reproductive system damage from the prior birth -- all while stressed by having to care for a newborn.
He theorized that the reason getting pregnant after a long interval is risky is that the body becomes primed for birth during the earlier pregnancy, with the uterus enlarging and blood flow to the womb increasing, but those benefits decline over time.
Dr. Robert A. Knuppel, chairman of obstetrics at Robert Wood Johnson Medical School in New Brunswick, New Jersey, noted that 90 percent of the Utah women were white, so the results may not apply to minority mothers or those with high-risk pregnancies. Zhu agrees, and is conducting a parallel study in Michigan.
The researchers took into account 16 factors that could affect outcomes, such as smoking and drinking, prenatal care and the mother's age, race and education.
However, in an accompanying editorial, Dr. Mark A. Klebanoff of the National Institutes of Health cautioned that the researchers might have missed some other factors that could contribute to the risks of conceiving too soon or too long after delivery.
These include such things as whether the mother had chronic medical problems, planned the pregnancy or had a miscarriage or abortion since the last birth.
Among American women, the average interval between first and second births is about 2 1/2 years, according to Susan Tew, a spokeswoman for the Alan Guttmacher Institute, a reproductive health organization in New York.
The American College of Obstetricians and Gynecologists says that waiting 1 1/2 to two years between births is best.
Telling mothers about this information could help reduce health complications in babies, Knuppel said.
But the reality is that many other factors come into play when planning a family. And, regardless of timing, the odds for a healthy baby are high if the mother stays fit and healthy.
"I think the best time to have another child is when it is right for you, your work situation, your family situation, kids ..." said perinatologist Dr. Chip Hamner. "That can be just as important a decision-maker as any study that gets published."
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