Association of Pre-Pregnancy Body Mass Index and Gestational Weight Gain with Labor Stage
In recent years, the trend of delayed marriage and childbearing has led to an increase in the age of primiparous women. Concurrently, changes in dietary habits have contributed to higher body mass index (BMI) during pregnancy and increased birth weights of newborns. This study aimed to explore the association between pre-pregnancy BMI and gestational weight gain (GWG) with the duration of labor stages and the risk of cesarean section (CS).
The study was conducted as a retrospective analysis of 6786 pregnant women who delivered full-term, cephalic presentation, and single pregnancies at Beijing Obstetrics and Gynecology Hospital from September 1, 2014, to August 31, 2015. Exclusion criteria included age under 18 years, multiparity, and complications during pregnancy such as heart, brain, lung, liver, or kidney diseases, chronic hypertension, gestational diabetes mellitus, preeclampsia, uterine scarring, placenta previa, severe fetal malformations, and stillbirth. Among the included women, 6361 had vaginal deliveries (93.32%), and 425 underwent cesarean section (6.68%).
The study evaluated various indices, including maternal age, height, education level, pre-pregnancy weight, pregnancy weight, weight at birth, gravidity history, gestational age, complications during pregnancy, birth mode, duration of labor, and neonatal data such as childbirth complications and newborn condition. Pre-pregnancy BMI was classified according to World Health Organization (WHO) standards: low weight (BMI <18.5 kg/m²), normal weight (18.5 kg/m² ≤ BMI <24.9 kg/m²), overweight (25.0 kg/m² ≤ BMI <29.9 kg/m²), and obesity (BMI ≥30.0 kg/m²). GWG was categorized into six groups: <10.0 kg, 10.0–14.9 kg, 15.0–19.9 kg, 20.0–24.9 kg, 25.0–29.9 kg, and ≥30.0 kg.
Data were entered into a database using EpiData, with quality control measures including rechecking medical records for missing items, logical errors, and extreme values. Statistical analyses were performed using SPSS version 20. Continuous variables with normal distribution were presented as mean ± standard deviation (SD) and analyzed using one-way ANOVA with post-hoc t-tests. Non-normal continuous variables were presented as median and interquartile range and compared using the rank sum test. Count data were expressed as frequency and percentage and compared using Pearson’s chi-square test or Fisher’s exact test. Binary logistic regression was used to determine odds ratios (ORs), adjusted ORs, and 95% confidence intervals (95% CIs) for CS risk during delivery, adjusting for maternal age, education level, pre-pregnancy BMI, and GWG.
The study found that the duration of labor increased gradually with pre-pregnancy BMI, with significant differences in the first and total stages of labor (P=0.02). Women with a pre-pregnancy BMI ≥30 kg/m² had the longest duration of the first stage of labor, with a median of 630 minutes. No significant differences were found in the second stage of labor among groups (P=0.179). For women with a pre-pregnancy BMI <18.5 kg/m², there were no significant differences in the duration of labor in the first, second, or total stages among different GWG levels. However, for women with a pre-pregnancy BMI of 18.5–24.9 kg/m², the duration of labor increased significantly in the first, second, and total stages with higher GWG (P<0.001, 0.015, and <0.001, respectively). For women with a pre-pregnancy BMI ≥25.0 kg/m², there were no significant differences in the duration of labor among different GWG levels.
The study also calculated the CS risk during labor based on pre-pregnancy BMI and GWG. Multivariate logistic regression analysis showed that higher pre-pregnancy BMI and higher GWG were associated with increased CS risk. For example, women with a pre-pregnancy BMI ≥30 kg/m² had a CS risk 2.60 times higher than those with a normal BMI (95% CI: 1.26–5.39, P=0.010). Similarly, GWG of 25.0–29.9 kg was associated with a 3.69-fold increase in CS risk (95% CI: 2.07–6.57, P<0.001).
The findings suggest that pre-pregnancy BMI and GWG significantly impact labor duration and CS risk. Obesity and excessive weight gain during pregnancy can reduce abdominal muscle contractility, leading to prolonged labor and increased CS risk. Fat accumulation in the pelvic and genital regions can increase resistance within the birth canal, further complicating vaginal delivery. The study highlights the importance of managing pre-pregnancy BMI and GWG to optimize labor outcomes and reduce CS prevalence.
The study also reviewed previous research, noting that obesity and sedentary lifestyles during pregnancy can impair uterine contractions and prolong labor. For instance, a study by Ellekjaer et al. found that the median active labor phase lasted 5.83 hours for women with a normal pre-pregnancy BMI, 6.08 hours for overweight women, and 5.90 hours for obese women, indicating that pre-pregnancy BMI did not significantly affect the active phase of labor. However, the CS rate during the active period was significantly higher in obese women compared to those with a normal BMI.
In conclusion, this study underscores the critical role of pre-pregnancy BMI and GWG in determining labor duration and CS risk. Women with higher pre-pregnancy BMI and excessive GWG are at greater risk of prolonged labor and CS. Therefore, it is essential to promote healthy lifestyles and balanced nutritional diets to control pre-pregnancy weight and manage GWG, thereby improving pregnancy outcomes and reducing CS rates.
doi.org/10.1097/CM9.0000000000000093
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