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

Mar 20, 2020Canadian journal of anaesthesia = Journal canadien d'anesthesie

How Severe Obesity or Older Maternal Age Affects Oxytocin-Triggered Uterine Muscle Contractions in the Lab

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Abstract

Myometrial contractility was reduced by 69% in oxytocin-pretreated samples compared to oxytocin-naïve samples in control women.

Oxytocin pre-treatment decreased the motility index of contractions in both control and advanced maternal age groups compared to their oxytocin-naïve counterparts.
In the advanced maternal age group, the reduction in motility index was not statistically significant (P = 0.07).
Myometrial contractility in morbidly obese women did not differ between oxytocin-naïve and oxytocin-pretreated samples.
The motility index was significantly lower in morbidly obese women compared to oxytocin-naïve samples from control women.
These findings suggest that morbid obesity may be associated with intrinsically reduced uterine contractile ability.

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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), AMA (≥ 40 yr; BMI, 20-24.9 kg·m), and MO (≤ 35 yr BMI, ≥ 40 kg·m). Each myometrial strip was either pretreated with oxytocin 10M or left in physiologic salt solution for two hours. This was followed by a dose-response testing to oxytocin (10M to 10M), during which contractile parameters were measured. The primary outcome was motility index (MI, amplitude × frequency) of contractions. -2 -2 -2 -5 -10 -5

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).

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

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