Birth Intervals, Gestational Age, and Low Birth Weight: Are the Relationships Confounded?

Abstract

A member of the US National Research Councils Committee on Population analyzed data on 2234 postpartum and postabortion patients at 2 Mexican Social Security Institute (IMSS) hospitals in Aguascalientes and Queretaro Mexico during October-November 1986 and March-April 1988 to determine whether or not gestational age confounds the relationship between birth intervals and low birth weight. Birth intervals and low birth weight were significantly associated both when gesttional age was and was not controlled (e.g. including gestational age odds ratio [OR] = 1.9 for 0-12 months and 1.65 for 13-21 months and excluding gestational age OR = 1.8 and 1.51 respectively; p < .05). Thus a short birth interval alone increased the likelihood of low birth weight a major predictor of neonatal mortality. Even though the researcher did not have data on maternal nutritional status the association between short intervals may keep mothers from replenishing nutritional reserves expended by the previous pregnancy and lactation. The researcher also controlled for other factors including mothers age height prepregnancy weight outcome of preceding pregnancy number of live births and education. These findings suggest that promotion of family planning use especially among women with adverse last pregnancy outcome would likely result in longer birth intervals thereby reducing the number of low birth weight infants. Prenatal care promotion among women with previous adverse pregnancy outcomes would further contribute to the reduction of low birth weight infants. Previous research at IMSS showed that every US dollar spent on family planning services reduced other health-related expenses by $9. Further increasing birth intervals would decrease pregnancies thereby reducing the demand for IMSS health services.