Relationship between serum apelin -36 with mother's anthropometric indices at 18-24 months postpartum: a nested case- control study

The presence of apelin in hypothalamus indicates the potential role of this hormone in the balance of energy and food intake. According to apelin’s protective role on obesity, this study was performed with aim to investigate the relationship between serum apelin-36 with mother's anthropometric indices at 18-24 months postpartum.

In this nested case-control study, serum apelin-36 levels of 42 pregnant women was measured during 28-32 weeks of gestation and the first 24 hours after delivery using ELISA in 2014-2016. After delivery, the participants were divided in to two subgroups based on mode of delivery; vaginal delivery group and cesarean section group. Anthropometric indices were measured two times; third trimester of pregnancy and then 18-24 months after delivery. Data were analyzed by SPSS software (version 21) and independent t and paired t-test, Chi-square, regression, and Pearson correlation test. P<0.05 was considered significant.

Mean of serum apelin-36 level after vaginal delivery had a nearly significant reduction compared with third trimester of pregnancy (P=0.05). Serum level of apelin-36 after cesarean delivery had negative significant relationship with BMI (P = 0.007, r = -0.57) and waist circumference (P = 0.003, r = -0.62) at postpartum follow-up. Linear regression analysis revealed that serum apelin-36 after caesarian delivery was a significant independent predictors of BMI at postpartum follow-up (P< 0.01). Apelin-36 had no significant relationship with anthropometric parameters in vaginal delivery group (P> 0.05). There was no significant difference in mean of anthropometric indices between two groups including: total pregnancy weight gain (P = 0.51), third trimester BMI (P = 0.11), BMI (P = 0.19), waist circumference (P = 0.21), systolic (P = 0.22) and diastolic blood pressure (P = 0.34), weight retention (P = 0.37) at postpartum follow-up.

Maternal serum apelin-36 level had negative significant relationship with maternal body mass index and waist circumference in cesarean section group. However, this mechanism is not completely known.