African-American infants are at greater risk of being born preterm or low birthweight than are white infants. Maternal age is conventionally considered an important determinant of pregnancy outcome. The black/white differential in infant mortality expands as maternal age increases. Also, the proportion of adverse health and behavioral characteristics related to poor pregnancy outcomes are greater among black women of reproductive age than their white counterparts. The prevalence of these adverse factors increases more rapidly among black women as they age than among white women. Geronimus proposed the weathering hypothesis to explain this phenomenon. The hypothesis posits that social and racial inequality may interact with age to produce growing gaps in health among women of reproductive age that may ultimately affect fetal health. The study explores whether specific demographic and behavioral risk factors vary across African-American and white populations and whether these risk factors contribute to black/white disparity in birthweight. Black and white singleton first births to residents of Michigan aged 15-34 (sample size=54888) were analyzed by linking birth and death certificates. A validation study was conducted that showed that economic characteristics of the areas remained stable over the past ten years. Thus, appropriately the socioeconomic status of maternal residential areas was derived from the 1980 census data.

For blacks, the rates of low birthweight and very low birthweight infants increase as maternal age increases. For whites, the rates were lowest among women in the 20s and greatest among the 15-19 and 30-34. The magnitude of excess rate of low birthweight and very low birthweight among blacks relative to whites increases with maternal age. The rates of smoking during pregnancy among black women increase from their teen though their 30s, while the rates decrease among the white women. The prevalence of smoking is 4.5 times greater among white teens than black teens, but by ages 25-29 the prevalence is higher among the black women. The rates of hypertension during pregnancy are higher among the older women, but the gradient is steeper for the blacks than the whites. Within both whites and blacks, younger mothers tend to live in more impoverished areas than the older mothers. But, within each age category, blacks more often live in socioeconomically disadvantaged areas than whites. For blacks, maternal age is statistically related to low birthweight and very low birthweight, while maternal age is not related to either outcome for whites. Among blacks residing in impoverished areas, the odds of very low birthweight and the odds of low birthweight respectively increase three-fold and four-fold between maternal ages 15 and 34.

The rates of maternal health and behavioral characteristics, that may adversely affect pregnancy outcome, tend to increase with age more rapidly among African-American than white women living in urban areas in Michigan. Maternal age represents both social processes as well as biological or developmental process. Thus, whether older maternal age is a lower or higher risk for adverse pregnancy outcome than younger maternal age depends upon maternal race and socioeconomic status. Furthermore, maternal age is an indicator of distinct health and behavioral attributes in different populations. The study suggests that it may be inappropriate to apply “routine clinical screening protocols that apply demographic risk characteristics uniformly to estimate risk status in pregnancy.” Previous thinking was that racial disparity in low and very birthweight infants and infant mortality was reflective of the risk in the black teen population. However, the findings indicate that the greatest decrease in the racial disparity in birthweight and infant mortality should result when clinical interventions are targeted to socioeconomically disadvantaged primiparous black women in their 20s and 30s.