Date of Award

11-2023

Degree Type

Thesis

Degree Name

MS in Epidemiology & Biostatistics

First Advisor

Dr. Sarah Saleem

Second Advisor

Dr. Saleem

Third Advisor

Iqbal Azam,

Department

Community Health Sciences

Abstract

Background: Understanding of labor dynamics is evolving, and several population-based studies have examined the normal labor process in different racial groups. This complexity is compounded by changes in maternal characteristics, and obstetric practices overtime. Additionally, labor induction and augmentation practices involving the use of oxytocin and artificial rupture of membranes influence the process of labor. These evolving dynamics necessitate an understanding of current labor progression patterns, which have been introduced by Friedman’s 50 years back and modified by Zhang’s two decades ago.
Objective: This study aimed to evaluate the labor progression patterns in nulliparous Pakistani women and compare these patterns with the curves developed by Friedman’s and Zhang.
Methodology: This retrospective cohort study was conducted at Aga Khan University hospital. Data was collected using structured proforma from the medical records (years 2021- 2022) of nulliparas, at term, with spontaneous labor onset, cervical dilation of less than 6 cm at admission, and singleton vertex deliveries with no adverse birth outcomes. Our main exposure was spontaneous onset of labor and outcome measures were progressive cervical dilation to construct labor curve, and duration of labor at 50th and 95th percentiles. Statistical analysis was performed using generalized linear mixed method approach with polynomial regression to evaluate predictor variables effect on the cervical dilation. The univariate and multivariable models were constructed. To map impact of progression time for cervical dilation from onset till 10cm, quadratic time variables were generated. A labor curve was plotted using the model estimates. Subgroup analyses were also performed for Syntocinon and epidural use.
Results: The characteristics of our study participants (n=309) demonstrated that 89% were primigravida, and 11% had a history of previous miscarriage. The mean maternal age was 26.1 ± 4.0 years, and BMI was 27.7 ± 4.5 kg/m² at admission for delivery. The mean gestational age at admission for delivery was 38.3 ± 1.1 weeks. In 80% of women, labor was augmented with Syntocinon. The procedure of amniotomy was performed in 63% of vi women. Entonox and epidural were mainly used for labor analgesia. The cumulative labor duration from onset to 10 cm dilation was 5.5 hours with 95th percentile of 10.7 hours. The second stage (from 10cm to delivery) was 35 minutes in half of women and with 95th percentile as two hours. In the multivariable model, significant predictors for labor progression included cervical effacement, fetal station, uterine contractions frequency, and progression time. The average estimated change in cervical dilation was 0.5 centimeter (cm) per hour. Fetal head descent was associated with a 0.8 cm change in cervical dilation (95% CI: 0.7, 0.9) while the correlation with contractions' frequency was 0.2cm (95%CI:0.05,0.4). Cervical effacement proved to be a robust predictor for cervical change, with a particularly pronounced effect observed in cases of a fully or nearly fully effaced cervix (0.5cm). We observed a significant interaction between Syntocinon infusion rate and cervical effacement categories. Syntocinon effect on cervical dilation was different for different categories of cervical effacement, indicating significant effect with partial effacement and insignificant with fully effaced cervix. Our labor curve demonstrated gradual progression without a clear inflection point, akin to Zhang's curve. The subgroup analyses regarding Syntocinon augmentation and epidural analgesia highlighted that labor progression was slower in women who received epidural and Syntocinon. Nevertheless, these findings need cautious and thoughtful interpretation.
Conclusion: Utilizing a population-based curve has provided a statistical framework to comprehend the normal progression range relevant to the women in our study. Our labor curve exhibited a smooth, non-linear pattern reminiscent of Zhang's curve, indicating a slower-than-expected labor process. Cervical effacement, fetal head descent, uterine contractions, and labor progression time emerged as crucial predictors for cervical dilation. Cervical effacement serves as an effect modifier for Syntocinon dose, displaying varying degrees of impact on cervical dilation. Nevertheless, it's imperative not to disregard the effects of Syntocinon and epidural analgesia on labor progression.

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