Figure 2. Stratified Analysis of Maternal Age and Risk of Cesarean Section.

Adjusted odds ratio for a 5-y increase in maternal age (bars are 95% CIs) stratified by maternal age, year of delivery, week of gestation, and deprivation category. Interactions were statistically significant for year of delivery (p < 0.001), week of gestation (p = 0.002), and deprivation category (p = 0.002) using the likelihood ratio test. Odds ratios are adjusted for maternal age, height, deprivation category, onset of labor, week of gestation, sex, birth weight percentile of infant, and year. The vertical dashed line indicates unity.