Distribution of covariates among hairdressers, nail technicians and non-cosmetologists, National Birth Defects Prevention Study, 1997–2011
| Covariate | Hairdressers (n=196)* | Nail technicians (n=61) | Non-cosmetologists (n=42 810) |
| n (%)†‡ | n (%)†‡ | n (%)†‡ | |
| Study site | |||
| Arkansas | 28 (14.3) | NR | 5649 (13.2) |
| California | 8 (4.1) | 8 (13.1) | 5141 (12.0) |
| Georgia | 30 (15.3) | 8 (13.1) | 4760 (11.1) |
| Iowa | 13 (6.6) | 5 (8.2) | 4197 (9.8) |
| Massachusetts | 41 (20.9) | 10 (16.4) | 5258 (12.3) |
| New Jersey | 15 (7.7) | 9 (14.8) | 2184 (5.1) |
| New York | 16 (8.2) | 4 (6.6) | 3092 (7.2) |
| North Carolina | 18 (9.2) | NR | 3356 (7.8) |
| Texas | 13 (6.6) | 6 (9.8) | 4740 (11.1) |
| Utah | 14 (7.1) | 9 (14.8) | 4433 (10.4) |
| Smoking status in early pregnancy | |||
| No | 150 (76.5) | 54 (88.5) | 34 118 (80.4) |
| Any | 46 (23.5) | 7 (11.5) | 8310 (19.6) |
| Age at delivery | |||
| Years (mean, SD) | 29.1 (5.6) | 28.9 (4.6) | 27.7 (6.2) |
| <35 years | 159 (81.1) | 56 (91.8) | 36 445 (85.1) |
| >35 years | 37 (18.9) | 5 (8.2) | 6365 (14.9) |
| Prepregnancy body mass index | |||
| Underweight | 5 (2.6) | 5 (8.2) | 2223 (5.4) |
| Normal weight | 98 (50.8) | 32 (52.5) | 21 119 (51.6) |
| Overweight | 52 (26.9) | 16 (26.2) | 9356 (22.9) |
| Obesity | 38 (19.7) | 8 (13.1) | 8195 (20.0) |
| Education level at delivery | |||
| No high school degree | 12 (6.1) | 3 (4.9) | 7364 (17.4) |
| High school degree | 51 (26.0) | 16 (26.2) | 10 679 (25.2) |
| Some college | 123 (62.8) | 31 (50.8) | 11 378 (26.9) |
| College degree or higher | 10 (5.1) | 11 (18.0) | 12 897 (30.5) |
| Maternal race/ethnicity | |||
| Non-Hispanic white | 133 (67.9) | 38 (62.3) | 25 061 (58.6) |
| Non-Hispanic black | 28 (14.3) | NR | 4414 (10.3) |
| Hispanic | 26 (13.3) | 8 (13.1) | 10 454 (24.4) |
| Asian/Pacific Islander | 4 (2.0) | 11 (18.0) | 1210 (2.8) |
| Other | 5 (2.6) | NR | 1664 (3.9) |
*Excluding hairdressers with indirect nail product exposure.
†Estimates shown as n (%) except where indicated otherwise (ie, age in years).
‡Frequencies may not add up to sample totals where there are missing values (<5% missing for all variables in each exposure category).
NR, not reportable based on n<3.