Table 1.
Baseline Characteristics (Age-Standardized) of Parous Women in the Black Women's Health Study, According to Duration of Lactation, 1995–2011
| Characteristic | Duration of Lactation, monthsa |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0 (None) (n = 714) |
<3 (n = 528) |
3–5 (n = 536) |
6–11 (n = 918) |
≥12 (n = 451) |
||||||
| Mean (SD) | % | Mean (SD) | % | Mean (SD) | % | Mean (SD) | % | Mean (SD) | % | |
| Age at first birth, years | 31.1 (4.6) | 31.0 (4.3) | 30.9 (4.3) | 31.1 (4.2) | 30.8 (4.3) | |||||
| Prepregnancy body mass indexb | 27.5 (6.8) | 27.5 (7.0) | 26.2 (5.6) | 25.2 (5.0) | 25.4 (5.0) | |||||
| >16 years of education | 27 | 26 | 34 | 37 | 50 | |||||
| Western diet (highest quintile) | 21 | 18 | 16 | 16 | 11 | |||||
| ≥35 pounds (≥15.8 kg) of gestational weight gain | 24 | 29 | 27 | 32 | 30 | |||||
| ≥3 hours/week of vigorous exercise | 24 | 27 | 28 | 31 | 37 | |||||
| Preterm birth | 18 | 16 | 14 | 14 | 11 | |||||
| ≥1 additional births | 24 | 31 | 36 | 43 | 47 | |||||
| ≥6 months’ mean lactation duration for additional births | 13 | 14 | 23 | 57 | 72 | |||||
Abbreviation: SD, standard deviation.
a Median year of first birth in each category of lactation: no lactation, 2001; <3 months, 1999; 3–5 months, 1999; 6–11 months, 1999; ≥12 months, 2001.
b Weight (kg)/height (m)2.