In the United States, the prevalence of third trimester anemia among low-income pregnant women is 29% and has not improved since the 1980s. Although low adherence has been linked to the ineffectiveness of iron supplementation programs, data regarding adherence to supplementation in low-income women are currently lacking. Hence this study was conducted to better understand the factors associated with adherence to the use of iron-containing prenatal multivitamin/mineral supplements among low-income pregnant women. Adherence to supplement use was assessed by pill counts among 244 pregnant women of 867 women who were initially randomized to receive 1 of 3 prenatal supplements. All women received care at a public prenatal clinic. Maternal characteristics associated with adherence were identified using predictive modeling. Women took 74% of supplements as prescribed. Adherence was higher among non-Hispanic white women than among non-Hispanic black women (79% vs. 72%, P

Women of African American, Hispanic, Asian, Pacific Islander, Native American and Alaskan descent constitute 29% of the female population in the United States but they experience health problems disproportionately. Compared with white women as a group, they are in poorer health and use fewer health services. We know from recent studies that the daily use of multivitamins has been associated with lower risk of coronary disease, colon cancer and breast cancer, particularly for alcohol drinkers. In addition, daily multivitamin and multimineral usage by the elderly can reduce the number of days of illness due to infections by 50%. However, supplement use among women tends to be more prevalent among the middle and older age categories; white, well-educated and higher income women; and those residing in the western part of the United States. This examination of the current health disparities and usage patterns indicates that the women who could benefit most from supplements are not typical users. Qualitative data collected on iron and folic acid supplementation programs in developing countries indicate that diverse cultural practices, attitudes and beliefs among vulnerable populations may influence supplement use. However, data in the U.S literature that describe these factors by culture or ethnicity are sparse. If we are to promote dietary supplements to women who are most vulnerable, more research is warranted in the area of health beliefs, attitudes and sociodemographic determinants of supplement use by culture and or ethnicity, particularly among underprivileged groups.

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Adherence to prenatal multivitamin/mineral supplement use is often measured by self-reports or pill counts. Although both measures were shown to overestimate adherence, measurement error is rarely considered. In this study, we examined measurement error in adherence to prenatal supplement use among pregnant women and demonstrated a calibration method to adjust for error. In a validation subsample (n=51) from a larger clinical study of supplementation, adherence was assessed by self-reports, pill counts, and a Medication Event Monitoring System (MEMS) bottle cap that recorded the date and time of each opening of the pill bottle. Mean adherence in the validation sample as measured by the MEMS (the gold standard) was 68%; thus, adherence measured by self-report (77%) and pill count (84%) reflected overestimation. The Pearson correlation coefficients of self-reports and pill counts to MEMS were 0.35 and 0.62, respectively. When adherence was defined as taking >or=75% of the pills prescribed, sensitivity and specificity were greater for pill counts (93 and 52%, respectively) than for self-reports (88 and 44%). The regression coefficient for pill count adherence from a linear regression on MEMS adherence was applied to pill counts from a larger sample (n=244). The adjustment significantly lowered the estimate of adherence from 74 to 64% (P<0.001) in this larger sample. In conclusion, our data show that both self-reports and pill counts overestimate adherence and that linear regression in comparison to an external standard such as MEMS can be used to correct for measurement error in adherence.

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