Estimation of Perineal Length in First and Second Stage of Labor Among South Indian Women and Its Association With Perineal Tears—A Prospective Observational Study

ABSTRACT Aim To estimate average perineal length during first and second stages of labor and its association with composite perineal tears. Methods A prospective observational study was conducted at a tertiary institute in Southern India. Perineal length was measured using a sterile flexible tape; an episiotomy was made when the perineum appeared stretched and thinned out. Composite tears and obstetric anal sphincter injuries (OASI) were detected clinically. Incidence of tears and their association with perineal length was analyzed using a chi‐squared test and log binomial regression was used to estimate adjusted relative risk (aRR). We used receiver operating characteristic curve to find the optimal cut off for predicting the occurrence of composite tears. Results We recruited 553 women. The mean perineal length was 3.5 ± 0.5 cm and 4.5 ± 0.5 cm in the first and second stages of labor, respectively. The incidence of composite perineal tear and obstetric anal sphincter injuries (OSAIS) were 7.6% and 0.54%, respectively. OASIS was 2.5% in women who underwent instrumental delivery, and a shorter perineum (< 3 cm) involved the anal sphincter ( p = 0.01) during instrumental delivery. A perineal length of ≤ 3.2 cm in the first stage was independently associated with composite perineal tears (aRR = 2.5) after adjusting for birth weight, duration of the second‐stage labor, and mode of delivery. Conclusion Mean perineal length at the first stage was 3.5 cm and increased by a centimeter during the second stage. Perineal length of ≤ 3.2 cm in the first stage significantly increases the risk of composite perineal tears.