The effect of morbid obesity or advanced maternal age on oxytocin-induced myometrial contractions: an in vitro study

Abstract

Purpose The purpose of this study was to investigate myometrial contractility induced by oxytocin in women with advanced maternal age (AMA) and morbid obesity (MO). We hypothesized that both oxytocin-pretreated and oxytocin-naïve myometrial tissues from women of AMA and women who are MO would exhibit poor myometrial contractility compared with women that are younger and of normal body mass index (BMI). Methods This prospective in vitro study was conducted using myometrial samples obtained from women undergoing elective Cesarean deliveries. Three groups of patient were studied: control (≤ 35 yr; BMI, 20–24.9 kg·m⁻²), AMA (≥ 40 yr; BMI, 20–24.9 kg·m⁻²), and MO (≤ 35 yr BMI, ≥ 40 kg·m⁻²). Each myometrial strip was either pretreated with oxytocin 10⁻⁵ M or left in physiologic salt solution for two hours. This was followed by a dose-response testing to oxytocin (10⁻¹⁰ M to 10⁻⁵ M), during which contractile parameters were measured. The primary outcome was motility index (MI, amplitude × frequency) of contractions. Results The MI of contractions was reduced in oxytocin-pretreated samples when compared with their oxytocin naïve counterparts in control (estimated difference −69%; 95% confidence interval [CI], −82 to −48; P < 0.001) and AMA groups (estimated difference, −44%; 95% CI, −68 to −2; P = 0.07). The MI of contractions was not different between oxytocin naïve and oxytocin-pretreated samples from MO women (estimated difference, −26%; 95% CI, −63 to 49; P = 0.46); however, it was significantly lower in these groups compared with oxytocin-naïve samples from the control group. Conclusions Oxytocin pre-treatment reduced myometrial contractility in AMA and control group women compared with their oxytocin-naïve counterparts, as a function of the desensitization phenomenon. Attenuated oxytocin-induced myometrial contractility in MO women in both oxytocin-pretreated and oxytocin-naïve samples suggests that these women have intrinsically reduced uterine contractile ability. Trial registration www.clinicaltrials.gov (NCT01865669; registered 28 May, 2013).