The association between the multiple birth and breast cancer incidence: an update of a systematic review and meta-analysis from 1983 to 2022

Abstract

Background It has been assumed that perinatal factors such as multiple pregnancies may affect subsequent breast cancer risk in the mother. Considering the inconsistencies in the results of case-control and cohort studies published in the world, this meta-analysis was conducted in order to determine the exact association between multiple pregnancies (twins or more) and the breast cancer incidence. Methods This study was performed as a meta-analysis based on PRISMA guidelines by searching the international databases of PubMed (Medline), Scopus, and Web of Science as well as by screening selected articles based on their subject, abstract and full text. The search time was from January 1983 to November 2022. Then the NOS checklist was used to evaluate the quality of the final selected articles. The indicators considered for the meta-analysis included the odds ratio (OR) and the risk ratio (RR) along with the confidence interval reported in the selected primary studies. The desired analyzes were performed with STATA software version 17 to be reported. Results In this meta-analysis, 19 studies were finally selected for analysis, which fully met the inclusion criteria. Of these, 11 were case-control studies and 8 were cohort ones. Their sample size was 263,956 women (48,696 with breast cancer and 215,260 healthy) and 1,658,378 (63,328 twin or multiple pregnancies and 1,595,050 singleton pregnancies), respectively. After combining the results of cohort and case-control studies, the effect of multiple pregnancies on the breast cancer incidence was equal to 1.01 (95% CI: 0.89–1.14; I2: 44.88%, P: 0.06) and 0.89 (95% CI: 0.83–0.95; I2: 41.73%, P: 0.07), respectively. Conclusion The present meta-analysis results showed, in general, multiple pregnancies were one of the preventive factors of breast cancer.

History of multifetal gestation and long‐term maternal mortality

“…Our finding of reduced risk of all‐cause mortality before age 70 for participants with a history of multifetal gestation was unexpected, as twin pregnancy has not been found to confer either a survival disadvantage or survival benefit in prior studies of cardiovascular mortality, 17,18 and some evidence supports an increased risk of cancer 19–21 . Consistent with our results, two previous studies of cardiovascular morbidity suggest a slight benefit of multifetal gestation: history of twin versus singleton delivery was associated with 15% lower odds of cardiovascular hospitalisation over approximately 11 years of follow‐up in an Israeli cohort 14 ; and among Swedish women without preeclampsia, those with a multifetal pregnancy had 17% lower risk of later compound cardiovascular disease compared to women with a singleton pregnancy 15 .…”

“…The previous studies also focussed largely or entirely on non‐Hispanic White populations, leading to questionable generalisability to the US context, which is characterised by greater racial and ethnic diversity. Finally, all prior studies focussed on cardiovascular outcomes (including mortality), capturing only some of the potential health effects of multifetal gestation, which may additionally include the risk of breast, endometrial, and cervical cancers 19–21 …”