Changes in autonomic nervous system activity, body weight, and percentage fat mass in the first year postpartum and factors regulating the return to pre-pregnancy weight

BACKGROUND: Many women become obese during pregnancy and the postpartum period. Weight gain and obesity in the general population are often attributed to abnormalities of autonomic nervous system (ANS) activity. The aim of this study was to clarify change in ANS activity, body weight, percentage fat mass (%FM), and body mass index (BMI) and the factors regulating the return to the pre-pregnancy weight in the first year postpartum. METHODS: This study was conducted from 2012 to 2016 at the University Hospital of the Kyoto Prefectural University of Medicine and a nearby obstetrics and gynecology clinic in Japan. Body weight and %FM were measured in 51 women using a dual-frequency body composition measuring device. Heart rate variability and R–R spectral transformation were used as indicators of ANS activity. All parameters were calculated at three postpartum time points. Repeated measure analysis of variance was used for comparisons between measurement times. A multivariable Cox proportional hazards model was conducted to determine factors associated with the return to pre-pregnancy weight. RESULTS: Mean body weight, %FM, and BMI decreased significantly over time after delivery (P < 0.001, P < 0.001, P < 0.001). However, ANS activity did not differ among subjects in the three time points. 25.5 % of subjects had still not returned to their pre-pregnancy body weight by 150–270 days postpartum, and 19.6 % had not by 270–360 days postpartum. Normal-weight obesity (NWO; BMI of 18.5–25 kg/m(2) and %FM of ≥30 %) was observed in several subjects at each measurement. The results of analysis using a multivariable Cox proportional hazards model suggest that ANS activity had no significant correlation with the return to pre-pregnancy weight. CONCLUSIONS: The management of body weight and %FM after delivery is considered important. These findings suggest that ANS activity is not associated with the return to pre-pregnancy weight, albeit that sample size was small.