Risk factors and population attributable risk percent for lactation mastitis in Chinese women: a systematic review and meta-analysis

Background: Lactation mastitis (LM) is one of the most common breast disorders experienced by postpartum women, affecting approximately 3% to 20% breastfeeding mothers. Although a few researches have studied the risk factors related to LM, there are still some inconsistent problems on this topic and nationally representative evidence is scarce. This study was aimed to determine the well-accepted risk factors for LM in Chinese women. Methods: Six electronic literature databases were searched from their inception to June 1st, 2020. We used RevMan5.3 and Stata14.0 for data analysis. The strength of the association was summarized using odds ratio (OR) with 95% confidence intervals (CI). The population attributable risk (PAR) percent was calculated for significant risk factors. The fail-safe number (Nfs) was used to estimate publication bias and robustness of the current results. Results: Twelve studies involving 6539 participants were included. A total of 18 potential risk factors were eventually evaluated. Significant risk factors for LM included improper breastfeeding posture (OR 2.47, 95%CI 2.09-2.92; PAR 26.51%), improper milking method (OR 6.79, 95%CI 3.45-13.34; PAR 59.14%), repeated milk stasis (OR 6.08, 95%CI 3.75-9.88; PAR 37.42%), little or no cleaning of nipples (OR 2.38, 95%CI 1.88-3.03; PAR 31.28%), abnormal nipple or crater nipple (OR 2.94, 95%CI 1.76-4.91; PAR 33.99%), primipara (OR 1.91, 95%CI 1.26-2.90; PAR 39.06%), history of breast trauma (OR 3.57, 95%CI 2.86-4.46; PAR 13.36%), experience of cesarean section (OR 1.77, 95%CI 1.32-2.38; PAR 28.34%), low educational level (OR 1.85, 95%CI 1.04-3.28, PAR 23.67%), breast massage experience of non-medical personnel (OR 1.90, 95%CI 1.36-2.65, PAR 20.89%), postpartum within 6 months (OR 5.11, 95%CI 2.66-9.82; PAR 65.93%), prone sleeping position (OR 2.53, 95%CI1.51-4.22; PAR 22.72%) and postpartum rest time less than 3 months (OR 4.71, 95%CI 3.92-5.65; PAR 56.95%). There seemed to be good robustness of the pooled results for most of the included risk factors.Conclusion: This study found several important risk factors of LM in Chinese women. In particular, the incidence of LM can be reduced by controlling several modifiable factors such as breastfeeding posture, milking method, milk stasis situation and nipple cleaning condition, etc.