Our study found the magnitude of the association between parental educational level and rate of low birthweight was different in births where the mother was white than in it was for members of other racial groups. In whites, low maternal and paternal educational levels were independently associated with a higher risk of LBW, even after adjustment for available demographic, health services, and maternal factors. In births where the mother was not white, maternal educational level appeared to have little or no effect on risk of LBW. However, low paternal educational level was independently associated with a higher risk of LBW after adjustment for maternal educational level, race, and other demographic and health services variables. The effect of paternal educational level remained significant after adjustment for maternal factors.
An association between SES and health is widely recognized. People of lower SES have worse health status, with higher mortality rates for all causes of death, higher prevalence of chronic diseases, and higher measures of disability . We found that maternal educational level was associated with the risk of LBW in whites, but not in other racial groups. Prior literature has noted that the discrepancy in the risk of adverse pregnancy outcomes between blacks and whites increased at higher levels of education [1, 8]. Also, prior studies have found relatively low rates of adverse pregnancy outcomes in Hispanics despite socioeconomic disadvantage [8, 9]. Our findings suggests that maternal educational level may be less important in influencing the risk of adverse pregnancy outcomes in blacks or Hispanics than it is in whites. Our study contributes the additional finding that paternal educational level is significantly associated with LBW regardless of race.
Other studies in the United States have examined the relationship between paternal characteristics and utilization of prenatal care, LBW, small-for-gestational-age status, and premature delivery. Parker, et al., found that both maternal and paternal educational level were associated with low birthweight and prematurity . D'Ascoli, et al., found that higher paternal educational level was associated with early initiation of prenatal care, even after adjusting for maternal educational level . Another study found that paternal educational level and race were independent risk factors for LBW . Here, the effects of maternal and paternal educational level were similar, and no interactions were found between the two measures. However, the latter two studies did not examine the effects of parental educational level separately by race. Also, in most studies, minority groups other than blacks were not studied.
Though we can only speculate about possible explanations for our findings, doing so may allow us to generate new hypotheses to be tested in future research. One possible explanation of these findings may relate to the variable impact of educational attainment across racial groups and between men and women. For example, the increase in income and social status that typically accompanies advanced educational attainment may be less substantial for nonwhites than whites, particularly among women . If this were the case in our population, there may have been less variability across educational levels, among nonwhite as compared to white women, in financial resources and other protective factors that appear to accompany higher SES. This would tend to minimize the association between educational level and the risk of LBW in nonwhite women. Another possibility is that the mix of social, cultural, and biological factors conferring protective (among Hispanics) or harmful (among African-Americans) effects on birth outcomes among nonwhite women are so influential that the effect of maternal education is rendered negligible.
Our study has a number of important limitations. First, we had to rely on the accuracy and completeness of birth certificate data. In fact, we excluded over 20% of birth certificates due to missing data on parental education, age, or race. Births with missing parental information appear to be significantly different from those with complete information. The fact that there were higher rates of LBW at delivery for births with incomplete data could be due to parents' having less ability or interest in completing the birth certificate form when suffering the stress of having just delivered a LBW infant. Moreover, SES and cultural factors may influence a parent's ability or desire to accurately complete the form, as suggested by the lower educational attainment and greater racial and ethnic diversity seen in the group with incomplete birth certificate data. However, missing paternal information, in the setting of complete maternal information, may be due to the mother's not knowing who the father is, not wishing to list him on the birth certificate, or not knowing him well enough to answer the questions about his race, educational attainment, or age. In any of these cases, one would assume that the mother may not be receiving significant support from the father. We found that missing paternal information was significantly associated with risk of LBW at delivery, even after adjustment for the level of completeness of maternal information. Moreover, the effect of missing paternal information remained significant after adjustment of all available maternal information, even when analyzing each race separately. These findings are consistent with our hypothesis that paternal support plays an important role in the risk of LBW at delivery in all the racial groups we studied.
Second, we used parental educational level as a proxy measure of SES, since it is easily measured and obtained from birth certificates. However, SES is a difficult construct to quantify, and educational level is only one of the many variables that may influence SES. Educational attainment cannot serve as a proxy for teen parents as they have not had a chance to attain higher levels of education. Our results, thus, cannot be generalized to parents under the age of 19. Income, another indication of SES, is not available from Washington state birth certificates. Also, occupational status, although available on Washington state birth certificates, is difficult to classify into meaningful categories for these purposes. The complex interaction between these and other variables in defining one's SES is difficult to quantify for purposes of this type of study, and thus, our use of educational level as a proxy for SES likely does not fully capture this concept. Third, even using 5 years of birth certificate data, we had an inadequate sample size to assess rare outcomes such as infant mortality, and thus had to rely on the intermediate outcome of LBW. Fourth, we cannot infer a causal association between parental educational level and the risk of LBW from these observational data.
Lastly, we conducted this study using only data from the state of Washington – a state which has relatively small proportions of racial minorities as compared to other parts of the U.S. This may have limited our ability to detect significant differences between each of the nonwhite racial groups. For example, though the effect of maternal education on risk of LBW did not vary by race once whites were excluded from the analysis, it is possible that effect modification by race does exist, even in the other racial groups. Not having found evidence of such, we chose to group the other racial categories together to improve our statistical power to detect any effect of parental education on LBW. Analyses looking at each race separately yielded a similar pattern, but did not reach statistical significance, presumably due to low numbers. We do not wish to imply that members of the different racial categories are similar in regards to birth outcomes, SES, or the many cultural factors that can influence both. The grouping simply results from the finding that the magnitude of association between educational level and LBW is similar amongst all racial groups studied other than whites. All analyses using this grouping still adjust for race.
These limitations notwithstanding, we believe our study adds important information about the effect of paternal SES in the risk of LBW in different races. Studies examining maternal SES have focused only on the relationship between the mother and the fetus to explain pregnancy outcomes. The additional independent association seen between paternal educational level and pregnancy outcomes may speak to the importance of looking beyond the maternal-fetal dyad to the world surrounding a pregnancy. For example, family and community support may play an important role in determining pregnancy outcomes. Paternal educational level may be a marker for the father's ability to provide the mother such support during her pregnancy or to shield her from societal stressors. Further studies looking at the balance between societal stressors and support systems available to a mother during pregnancy may not only help explain our findings about paternal educational levels but may also shed light on the discrepancies amongst different racial and ethnic groups.
We conclude that paternal educational level is associated with the risk of LBW regardless of race, but that maternal educational level seems only to be a significant factor in whites. The reason for the different degree of association in whites than in members of other racial groups is not clear and deserves further examination. This study has important implications. First, obtaining information on paternal educational levels may improve our ability to identify groups at highest risk for LBW, in both whites and nonwhites. Identifying these groups may allow the development and implementation of targeted interventions to reduce the risk of such adverse pregnancy outcomes. Second, the assumption that maternal SES strongly relates to pregnancy outcomes may only be true for whites. This relationship may be significantly different for members of other racial groups. Studies looking at risk factors and mechanisms for LBW should conduct race-stratified analyses, or at least should routinely examine the possible interaction between race and education. Studies using national vital statistic data are needed in order to confirm our results in each separate racial category. If confirmed, this racial discrepancy between the relative effect of maternal vs. paternal SES may prove to be an interesting clue to the role of differences in family and community support systems, income, and discrimination in birth outcome disparities. Further studies using data beyond what is available on birth certificates will be needed to better understand these complex relationships.