Low birth weight, maternal birth-spacing decisions, and future reproduction - A cost-benefit analysis

The aim of this study is an analysis of the possible adaptive consequences of delivery of low birth weight infants. We attempt to reveal the cost and benefit components of bearing small children, estimate the chance of the in fants' survival, and calculate the mothers' reproductive success. According to life-history theory, under certain circumstances mothers can enhance th eir lifetime fitness by lowering the rate of investment in an infant and/or enhancing the rate of subsequent births. We assume that living in a risky environment and giving birth to a small infant may involve a shift from qua litative to quantitative production of offspring. Given high infant mortali ty rates, parents will have a reproductive interest in producing a relative ly large number of children with a smaller amount of prenatal investment. T his hypothesis was tested among 650 Gypsy and 717 non-Gypsy Hungarian mothe rs. Our study has revealed that 23.8% of the Gypsy mothers had low birth we ight (<2,500 g) children, whose mortality rate is very high. These mothers also had more spontaneous abortions and stillbirths than those with normal weight children. As a possible response to these reproductive failures, the y shortened birth spacing, gaining 2-4 years across their reproductive life span for having additional children. Because of the relatively short interb irth intervals, by the end of their fertility period, Gypsy mothers with on e or two low birth weight infants have significantly more children than the ir ethnic Hungarian counter-parts. They appear to compensate for handicaps associated with low birth weights by having a larger number of closely spac ed children following the birth of one or more infants with a reduced proba bility of survival. The possible alternative explanations are discussed, an d the long-term reproductive benefits are estimated for bath ethnic groups.