- The Washington Times - Wednesday, April 19, 2006

Very long or very short intervals between pregnancies are significantly associated with an increased risk of unfavorable childbirth outcomes, international research has found.

In an analysis of 67 studies from 1966 to 2006 — a third of which were conducted in the United States — Colombian researchers determined that intervals shorter than 18 months and longer than 59 months increased the risk for three negative outcomes of delivery: low birth weight, preterm birth and small size for gestational age.

“These data suggest that spacing pregnancies appropriately could help prevent such adverse perinatal outcomes,” the authors of the study, published in this week’s issue of Journal of the American Medical Association, concluded.

“The results of our systematic review could be used by reproductive clinicians around the world to advise women of the benefits of delaying a subsequent pregnancy for approximately two to five years to improve the health of both mother and the next infant,” wrote Dr. Augustin Conde-Agudelo of the Fundacion Santa Fe de Bogota, the study’s lead author.

The studies examined to determine the link between birth spacing and the risk of undesirable birth results included 20 conducted in this country. The other 47 were done in 61 nations in Latin America, Asia, Africa, Europe and Australia. The studies looked at more than 11 million pregnancies around the globe.

By pooling data, the researchers found that an interval of 18 to 23 months between pregnancies was the one “with the lowest risk of preterm birth, low birth weight and small size for gestational age,” or SGA.

Compared with that interval, they said, interpregnancy intervals shorter than six months were associated with a 1.4 times greater risk of premature birth; 1.6 times greater risk of low birth weight; and 1.26 times greater risk of SGA.

Put another way, Dr. Conde-Agudelo said, “For each month that interpregnancy interval was shortened from 18 months, the increased risk for preterm birth, low birth weight and SGA was 1.9 percent, 3.3 percent, and 1.5 percent, respectively.

“On the other hand, the risk for those three adverse perinatal outcomes increased by 0.6 percent, 0.9 percent, and 0.8 percent, respectively, for each month that interpregnancy interval was lengthened from 59 months,” he said.

Researchers focused on about a third of the studies, which specifically examined pregnancy spacing and risk of fetal, perinatal and early neonatal death, or death in the first 30 days of a baby’s life. They found that pregnancy 20 to 40 months after prior delivery was linked to the lowest risk of those three negative outcomes.

Colombian researchers did not reach definitive conclusions as to why short and long intervals between pregnancies harm birth outcomes, but they offered some theories.

They said “maternal nutritional depletion” is a “plausible explanation” for why short periods between pregnancies can mean harmful birthing outcomes, particularly in developing countries. This hypothesis holds that a “close succession of pregnancies and periods of lactation worsen the mother’s nutritional status” because there is not enough time for her to recover physiologically.

As for why risks of adverse perinatal outcomes increase with long intervals between pregnancies, the authors cite research that says a woman’s physiologic reproductive capacities decline after an excessively long interval since the last pregnancy.

In an accompanying editorial, Rachel A. Royce of Research Triangle Institute International in North Carolina points out that “birth spacing” is mentioned as a strategy for reducing child mortality in a United Nations Millennium Declaration.

“But its potential seems underemphasized,” she said, adding, “Interventions that increase birth spacing could positively affect both maternal and child health.”

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