Table 3.

Eight-Year Weight Gain in Relation to Lactation History in the Black Women's Health Study, 1995–2011

	No. of Women	Unadjusted Mean Weight Gain, kg	Unadjusted Mean Difference in Weight Gain, kg	Multivariable Mean Difference in Weight Gain, kga	95% Confidence Interval	P for Trend
Total
Never lactation	560	7.91	0 (Referent)	0 (Referent)
Ever lactation	1,973	7.91	0.00	0.44	−0.41, 1.29
Lactation duration, months						0.31
<3	436	8.32	0.41	0.35	−0.75, 1.46
3–5	425	8.48	0.57	0.90	−0.23, 2.02
6–11	759	7.69	−0.22	0.36	−0.64, 1.35
≥12	353	7.17	−0.74	0.11	−1.12, 1.33
Age <30 years at time of birthb
Never lactation	176	10.50	0 (Referent)	0 (Referent)
Ever lactation	635	9.06	−1.44	−1.16	−2.82, 0.49
Lactation duration, months						0.08
<3	141	9.58	−0.92	−1.12	−3.24, 1.01
3–5	144	10.20	−0.30	−0.02	−2.13, 2.10
6–11	239	8.53	−1.97	−1.69	−3.62, 0.24
≥12	111	8.03	−2.47	−1.94	−4.31, 0.44
Age ≥30 years at time of birthb
Never lactation	384	6.72	0 (Referent)	0 (Referent)
Ever lactation	1,338	7.36	0.64	1.14	0.15, 2.14
Lactation duration, months						0.09
<3	295	7.71	0.99	1.01	−0.28, 2.30
3–5	281	7.60	0.88	1.30	−0.03, 2.62
6–11	520	7.31	0.59	1.22	0.06, 2.38
≥12	242	6.78	0.06	0.97	−0.46, .40
Prepregnancy BMIc <30d
Never lactation	407	8.75	0 (Referent)	0 (Referent)
Ever lactation	1,598	7.82	−0.93	−0.59	−1.49, 0.32
Lactation duration, months						0.03
<3	314	8.22	−0.53	−0.49	−1.68, 0.71
3–5	343	8.78	0.03	0.27	−0.90, 1.44
6–11	645	7.61	−1.14	−0.76	−1.79, 0.27
≥12	296	6.72	−2.03	−1.53	−2.78, −0.27
Prepregnancy BMI ≥30d
Never lactation	150	5.50	0 (Referent)	0 (Referent)
Ever lactation	370	8.24	2.74	3.25	1.03, 5.46
Lactation duration, months						<0.01
<3	120	8.49	2.99	2.60	−0.11, 5.31
3–5	82	7.22	1.72	2.37	−0.71, 5.45
6–11	112	8.09	2.59	3.77	0.92, 6.61
≥12	56	9.49	3.99	5.76	2.04, 9.48

Abbreviation: BMI, body mass index.

^a Adjusted for age, gestational weight gain, preterm birth, vigorous physical activity, dietary pattern, years of education, number of additional births during follow-up, and mean duration of lactation for the additional births during follow-up.

^b P for interaction with age at time of birth = 0.42.

^c Weight (kg)/height (m)². Data on prepregnancy BMI were missing for 8 women.

^d P for interaction with prepregnancy BMI < 0.01.