How do sustained birth tears after vaginal birth affect birth tear patterns in a subsequent birth?

Background Tears are common after vaginal birth, and different impact factors are known. However, the impact of tears from a previous birth to the tears of a subsequent birth is unknown. Therefore, we aimed to evaluate the distribution of birth tear patterns according to the sustained tears in a previous birth, in addition to other impact factors. Methods In a retrospective cohort study, we evaluated all women up to parity 4 with subsequent vaginal, singleton births of vertex presentation at ≥37 + 0 gestational weeks between 1/2005 and 12/2016. Their tears were grouped into tear patterns and were analyzed by parity. Tear patterns in the subsequent births were analyzed in association to the patterns of the previous births and impact factors were evaluated. Results We counted 4017 births in 1855 women [P1: 1368 (34.1%), P2: 1730 (43.1%), P3: 741 (18.4%), P4: 178 (4.4%)]. The frequency of tears and episiotomies decreased with higher parity, whereas the frequency of intact perineum increased. Twenty-eight different unique tear patterns were found. We could show that birth tear patterns changed with increasing parity and were associated with sustained tears in a previous birth. In addition, some impact factors on tear patterns could be identified. Conclusion The distribution of the single tear types is in accordance with the current literature. However, it is new that distinct tear patterns are associated to sustained tear patterns of previous births. Furthermore, we demonstrated some weak associations of tear patterns to certain impact factors, such as more episiotomies, low-grade perineal or vaginal tears isolated or in combination with other tears with increasing fetal weight and head circumference in the higher parities, and with a longer duration of the second stage and the pushing phase in lower parities.