31) and 30.2 versus 29.4 .26 Mobility rates by mother’s occupation were 16.2, 16.7, 23.3, 23.5, and 26.2 for Nutlin (3a) chemical information managerial, farming/other, service, unemployed, and technical/sales, respectively.29 Area-level SES indicators for mother’s residence were evaluated by several studies, generally indicating higher mobility for lower income areas, but not in all studies. The Index of Multiple Deprivation and Townsend deprivation scores were used to assess overall arealevel SES for the community of delivery, finding that movers were more likely to live in areas with higher deprivation than non-movers (P-value <0.01).32 Those living in disadvantaged areas, as defined by child poverty, were 15 (2?9 ) more likely to move than those in advantaged areas.35 Some studies found contradictory results. In Norway, no difference in mobility was observed for mothers in neighborhoods above and below mean income levels, perhaps owing to less of an income gradient in that country.38 Another study categorized mothers' census tracts at conception into SES levels based on the percentage of persons living below census-defined poverty levels.29 In this study, mobility rates were 24.6, 20.0, 24.7, and 8.8 for the high, mid-high, mid-low, and low SES levels, respectively, indicating higher mobility for wealthier communities. Prenatal Care Earlier or no prenatal care was associated with lower mobility in several studies. Those with no prenatal care were 18 (8?0 ) more likely to move than those with prenatal care.35 In the same study, those who entered care in the second or third trimester had mobility rates only 3 (-0.7?4 ) higher than those who received care in the first trimester. In other work, 12.4, 24.9, and 40 of mothers moved for those who received their first prenatal care in months 1?, 4?, and 7 or later, respectively.27 Those with prenatal care in the first-tothird month had a mobility rate of 12 compared with 21 for those beginning care later in pregnancy.31 Parity Table 4 presents mobility rates by parity (i.e., number of previous births). The highest mobility generally was observed in the group with the fewest previous pregnancies but not in all studies.33,34 This study differs from others presented in Table 4 in that all pregnancies resulted in birth defects. In another study, movers were more likely to have a parity of 0 than non-movers.38 Tunstall et al.35 examined a related issue of how many children were present in the household during the pregnancy. Mothers with no children were 2.38 (2.06?.75) times more likely to move than those with 2 children, and those with one child were 1.26 (1.07?.49) times more likely to move than those with 2 children. Supplementary Table 3 shows an analogous figure for cases and controls from case-control studies.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptJ Expo Sci Environ Epidemiol. Author manuscript; available in PMC 2013 January 11.Bell and BelangerPageHealth status Case-control studies of birth defects generally found mobility rates for cases to be slightly higher, but similar to, those for controls (Supplementary Figure 2).