Rauch et al. In multivariable analysis, a 10-fold increase in ΣDAP concentrations, which corresponds roughly to a shift from the 15th (29.5 nmol/L) to the 85th percentile (318.0 nmol/L) of the distribution, was asso- ciated with a 0.5-week decrease in gestational age [95% confidence interval (CI): –0.8, –0.1] (Table 2). Associations with ΣDEAP and ΣDMAP concentrations were weaker, but ΣDMAP concentrations were associ- ated with a 0.4-week decrease in gestational length (95% CI: –0.7, 0.0). Birth weight was also inversely associated with ΣDAP concen- trations (–151 g, 95% CI: –287, –16) and ΣDMAP concentrations (–124 g, 95% CI: –245, –2), but not ΣDEAP concentrations. The relationship between ΣDAP concentra- tions and birth weight was attenuated after adjustment for gestational age (–40 g; 95% CI: –146, 65). In race-stratified models, ΣDAP concen- trations were associated with shortened ges- tation in white newborns, but not in black newborns (Table 2). The interaction between ΣDAP concentrations and black race/ethnicity in separate cross-product models was signifi- cant at p = 0.10. In contrast, ΣDAP concen- trations were associated with a larger decrease in birth weight among black newborns than in white newborns, although the interaction was not statistically significant (p = 0.46). Once we adjusted for gestational age, however, we observed a slightly weaker but statistically sig- nificant inverse association between ΣDAP concentrations and birth weight for black newborns, and the interaction for ΣDAP con- centrations and birth weight by race/ethnicity became statistically significant (p = 0.02). We also found a nonsignificant inverse relation- ship between urinary OP metabolite concen- trations and birth weight for gestational age (–0.18 z-score units; 95% CI: –0.41, 0.06). The relationship was stronger among blacks (–0.40; 95% CI: –0.73, –0.08) than whites (–0.02; 95% CI: –0.33, 0.30). In PON1-stratified models, we observed the strongest associations between ΣDAP con- centrations and birth weight and gestational age in the heterozygous groups: PON1192QR and PON1–108CT [see Supplemental Material, Table 1 and Figures 1 and 2 (http://dx.doi. org/10.1289/ehp.1104615)]. Several inter- action terms between PON1 genotypes and ΣDAP concentrations were statistically signifi- cant. Looking at models stratified by race and PON1 status, numbers of observations in many of the categories were too small to produce stable point estimates. However, in almost all cases we observed the strongest associations between DAP metabolites and birth outcomes appearing in the heterozygous groups. We found no evidence for main effects of PON1 genotype on either birth weight or length of gestation (data not shown). Sensitivity analyses. Medical conditions were associated with birth outcomes and DAP urinary concentrations (Table 3). Mothers who had abruptio placenta (n = 9), placenta previa (n = 1), chorioamnionitis (n = 1), pre- eclampsia (n = 15), or pregnancy-induced hypertension (n = 9) had shorter gestations and lower-birth-weight newborns than the rest of the study population (data not shown). These mothers also had higher median DAP urinary concentrations than mothers without the con- ditions (Table 3), although we did not perform formal statistical tests because of small sample sizes. Generally, the magnitude of association between ΣDAP concentrations and gestational age was similar when we excluded observations based on various combinations of the medical conditions. The point estimates for birth weight ranged from –168 g (95% CI: –307, –28) when women with hypertension were excluded to –111 g (CI: –248, 26) when women with placental conditions, chorioamnionitis, or hypertension were all excluded (all estimates reported for sensitivity analyses are adjusted for the same covariates as in the primary analysis, unless otherwise noted). Restricting analyses to full-term births (≥ 37 weeks gestation, n = 282) attenuated the effect estimates for a 10-fold increase in ΣDAP concentrations for both gestational age (–0.2 weeks, 95% CI: –0.4, 0.0) and birth weight (–88 g, 95% CI: –213, 37), but the pat- terns were consistent with our primary results. Stratifying full-term births by race produced results that were similar to those for preterm and term births combined: Associations with birth weight were stronger among black new- borns than white newborns, whereas estimated effects for gestational age were stronger in white newborns than black newborns. We did not find any suggestion of an interaction between child sex and ΣDAP concentrations for either gestational age or birth weight (p > 0.3). Using non-creatinine-standardized ΣDAP concentrations modestly attenuated the observed estimates: In the full group, the gestational age coefficient was –0.3 weeks (95% CI: –0.7, 0.0) and the birth weight coefficient was –100 g (95% CI: –232, 32). Adjusted coefficients in all secondary analy- ses were closer to the without creatinine adjustment, but the pattern with respect to race remained the same (data not shown). Likewise, excluding women with urinary creatinine values < 20 mg/dL (n = 37) did not change the pattern of results (data not shown). Finally, associations obtained when using ΣDAP concentrations from individual spot urine collections were slightly attenuated compared with the average of the 16- and 26-week collections, for both the 16-week (gestational age: β = –0.2 weeks, 95% CI: –0.6, 0.1; birth weight: β = –110g, 95% CI: –221, 1) and 26-week samples (gesta- tional age: β = –0.3 weeks, 95% CI: –0.6, 0.0; birth weight: β = –88g, 95% CI: –208, 33). Table 2. Mean change in gestational length and birth weight associated with a 10-fold increase in average urinary DAP concentrations (nmol/L) among white Length of gestation (weeks)b Birth weight (g)b Birth weight, adjusted for gestational age (g)c p-value pinteractiond p-value pinteractiond p-value pinteractiond and black mothers. OP Metabolitea All mothers (n = 306) Black mothers (n = 93) ΣDAP ΣDEAP ΣDMAP ΣDAP ΣDEAP ΣDMAP ΣDAP ΣDEAP ΣDMAP White mothers (n = 213) 1058 NA, not applicable. Excludes mothers in the “other race” category (n = 15) and with missing covariate information (n = 23). A 10-fold increase in total DAP concentrations (i.e., a 1-unit increase in log10-transformed concentrations) corresponds roughly to an increase from the 15th (29.5 nmol/L) to the 85th percentile (318.0 nmol/L) of the distribution. aMetabolites are log10-transformed and creatinine-standardized. bAdjusted for mother’s age, household income, marital status, parity category, and log10-transformed blood lead and log10-transformed cotinine. Models including black and white mothers are also adjusted for maternal race. cAdditional adjustment for gestational age. dp-Value for race × exposure interaction term from separate cross-product models. ovlume 120 | number 7 | July 2012 • Environmental Health Perspectives β (95% CI) –0.5 (–0.8, –0.1) –0.2 (–0.5, 0.1) –0.4 (–0.7, 0.0) –0.1 (–0.9, 0.6) –0.1 (–0.8, 0.5) 0.0 (–0.7, 0.6) –0.7 (–1.1, –0.3) –0.3 (–0.7, 0.0) –0.6 (–0.9, –0.2) 0.01 0.14 0.03 0.69 0.64 0.97 < 0.01 0.09 < 0.01 0.10 0.47 0.09 β (95% CI) –151 (–287, –16) –65 (–180, 51) –124 (–245, –2) –188 (–395, 19) –162 (–340, 16) –142 (–333, 50) –118 (–296, 60) –39 (–189, 111) –96 (–254, 62) 0.03 0.27 0.05 0.07 0.07 0.15 0.19 0.61 0.23 0.46 0.39 0.46 β (95% CI) –40 (–146, 65) –9 (–99, 80) –38 (–133, 56) –158 (–297, –18) –131 (–251, –11) –139 (–267, –10) 60 (–84, 204) 41 (–78, 160) 49 (–78, 177) 0.45 0.83 0.43 0.03 0.03 0.03 0.41 0.5 0.45 0.02 0.08 0.02