ABSTRACT
<p><b>OBJECTIVE</b>To explore the effect of pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) on the onset time of lactation (OL).</p><p><b>METHODS</b>In this longitudinal study, 751 healthy single pregnant women were selected from three hospitals in Chengdu as subjects of baseline survey during March and September 2013 and were followed before and after delivery, respectively. Finally, data from a total of 473 pregnant women were analyzed. Data on pre-pregnancy weight, delivery mode, birth weight of neonate, information of lactation and maternal demographic characteristics were collected through questionnaire and medical records. Height and weight at the last week before delivery were measured and GWG were calculated. After controlling the potential confounders, a serial of multi-factor ordinal logistic regression models were performed to test the associations between pre-pregnancy BMI, GWG and OL.</p><p><b>RESULTS</b>The proportions of OL at the < 1, 1-, 24-, 48- and ≥ 72 h groups were 16.3%, 37.0%, 17.5%, 18.6% and 10.6%, respectively. When compared to women with normal weight, the ORs for prolonged OL were 2.85 (1.91-4.27) and 3.42 (1.69-6.90) among pre-pregnant underweight and overweight/obese women, respectively. When compared to women with normal weight and adequate GWG, pre-pregnant underweight women with adequate and excessive GWG showed greater odds of prolonged OL (OR = 2.34, 95% CI: 1.31-4.18; OR = 3.42, 95% CI: 1.67-7.00), respectively. Pre-pregnant overweight/obese women with excessive GWG had increased the odds of prolonged OL (OR = 3.10, 95% CI: 1.15-8.37).</p><p><b>CONCLUSION</b>Pre-pregnant BMI appeared an independently factor, associated with OL while GWG might have an effect on OL, when pre-pregnant BMI was considered.</p>