Very long or short intervals between pregnancies associated with increased poor perinatal outcomes

Chicago – Intervals between pregnancies shorter than 18 months and longer than 59 months are associated with increased risk of low birth weight, preterm birth and small size for gestational age, according to an article in the April 19 issue of JAMA.

Agustin Conde-Agudelo, M.D., M.P.H., from the Fundación Santa Fe de Bogotá, Columbia, and colleagues conducted a meta-analysis on studies published between 1966 and 2006 to examine the association between birth spacing and the risk of adverse perinatal outcomes. The researchers identified 67 articles for this analysis, which adjusted for the mother's age and socioeconomic status and reported birth spacing and perinatal outcomes. These articles included a total of 11,091,659 pregnancies.

Infants born to women with an interval shorter than six months after their last birth had a 40 percent increased risk of preterm birth, a 61 percent increased risk of low birth weight (LBW) and a 26 percent increased risk of small for gestational age (SGA), compared to children of mothers with an interval of 18 to 23 months between pregnancies. Infants of mothers with pregnancy intervals longer than 59 months had a 20 to 43 percent greater risk of these adverse outcomes. For each month that the time between pregnancies was shortened from 18 months, the risk for preterm birth, LBW and SGA increased by 1.9, 3.3 and 1.5 percent, respectively. And for each month that the time between pregnancies was lengthened beyond 59 months, the risk for these outcomes increased by 0.6, 0.9 and 0.8 percent, respectively.

"The effects of birth spacing on perinatal health found in our study, as well as the effects of both short and long intervals on infant, child and maternal health, should furnish a strong motivating force for health personnel to provide family planning," the authors write. "The results of our systematic review could be used by reproductive clinicians around the world to advise women on the benefits of delaying a subsequent pregnancy for approximately two to five years to improve the health of both mother and the next infant."


(JAMA. 2006; 295: 1809 – 1823. Available pre-embargo to media at

Editor's Note: This works was supported by the Office of Population and Reproductive Health, Bureau for Global Health, U.S. Agency for International Development, under the terms of Cooperative Agreements awarded to the CATALYST Consortium.

Editorial: Birth Spacing – The Long and Short of It

"Worldwide, more than four million children die in the first four weeks of life, and 28 percent of these deaths are thought to be due directly to preterm birth," writes Rachel A. Royce, Ph.D., M.P.H., of Research Triangle Institute International, Research Triangle Park, N.C., in an accompanying editorial.

"Although the authors [Conde-Agudelo et al] attempted to account for some of the potential sources of heterogeneity, one important source was not adequately explored--the country where each study was conducted," Dr. Royce writes. "Breastfeeding is an important example of a potential confounder that differs greatly by country. Exclusive breastfeeding for the first six months of life delays the mother's resumption of menstruation."

Dr. Royce notes that short intervals between births are mostly unintended and have been shown to be associated with extremes of age, marital status, menstrual irregularities, ethnicity and lower socioeconomic status. " … improving the proportion of women who breastfeed exclusively for the first six months of their infant's life might lengthen the birth interval while providing better nutrition for the first infant and better health outcomes for both infants," she writes.

Dr. Royce states that long periods of time between pregnancies are harder to explain, but are most likely not chosen and "may result from the end of a partnership, infertility, reproductive losses in the interval, health problems in mother or infant, or economic issues."

"Clinicians should counsel all women to space pregnancies at least 12 months apart, if at all possible," she concludes.

(JAMA. 2006: 295: 1837 – 1838. Available pre-embargo to media at

Last reviewed: By John M. Grohol, Psy.D. on 30 Apr 2016
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