Number of parity and the risk of non-Hodgkin lymphomas: a dose–response meta-analysis of observational studies

Abstract

Background: Epidemiological reports have shown that parity is associated with a risk of developing non-Hodgkin lymphomas (NHL). However, the findings have been inconsistent. Methods: We searched the EMBASE and PubMed databases for eligible studies up to 10 March 2016. Category and generalized least square regression models were used to perform data analyses. Results: In total, five cohort and seven case–control studies were identified. Categorical analyses indicated that parity number has little association with NHL and its subtypes. In dose–risk analyses, there were no relationships between parity and NHL risk (pfor association = 0.064; n = 10). The summarized risk ratio (RR) was 0.97 (95% confidence interval (CI): 0.95–1.00; I2 = 57.8%; pheterogeneity = 0.014; Power = 0.79) for each additional live birth increase. Similarly, for B-cell NHL, there was a null association between parity and NHL risk (pfor association = 0.121; n = 5). The combined RR was 0.96 (95% CI = 0.90–1.03; I2 = 63.7%; pheterogeneity = 0.026; Power = 0.71) for each additional live birth. For follicular NHL, there was still a non-significant association identified (pfor association = 0.071; n = 4), the pooled RR was 1.00 (95% CI = 0.95–1.07; I2 = 17.3%; pheterogeneity = 0.305; Power = 0.26) per additional live birth. Conclusions: Our data identified little evidence suggesting that high parity is a protective factor against the development of NHL, including its B-cell and follicular subtypes.