Invited commentary: an assessment of maternal intergenerational factors in pregnancy outcome.

Two articles in this issue (1,2) address an important but often-overlooked area of investigation: maternal intergenerational factors in reproductive problems, or "...those factors, conditions, exposures, and environments experienced by one generation that relate to the health, growth, and development of the next generation" (3, p. 27). Coutinho et al. (1) linked infants' birth certificates to mothers' birth certificates in Illinois. They found a consistent decreasing trend in the proportion of infants with low birth weight (<2,500 g) by maternal birth weight for both whites and African Americans and, conversely, an increasing trend for mean infant birth weight. However, at some of the lowest levels of mother's birth weight, the proportions of infant low birth weight were not the highest, nor were infant mean birth weights the lowest. This pattern, in which the lowest-birth-weight mothers did not have the smallest infants, has been seen by other investigators (4-6). One possible explanation is that these mothers had been preterm but healthy and had not been in utero long enough to achieve their genetic potential for prenatal growth. Coutinho et al.'s finding that mother's birth weight was more strongly associated with infant birth weight than was paternal birth weight (1) also sheds light on the relative contributions of genes and environment to low birth weight. In general, it appears, as Coutinho et al. also show, that maternal growth factors—birth weight and adult stature—have stronger relations with fetal growth than do paternal growth factors (7-9).