Offspring sex ratio at birth and maternal breast cancer risk: A case-control study and meta-analysis of literature.

To investigate whether offspring sex ratio at birth (SRB) was associated with maternal breast cancer risk, the present case-control study and a meta-analysis of literature were done. A total of 389 female breast cancer patients who had at least one offspring participated in the study. From general population 356 healthy female were selected as a control group. Control subjects were frequency matched with patients according to age and number of offspring. Among control group, 1324 offspring (666 males, 658 females) and within families of the breast cancer patients 1326 offspring (648 males, 678 females) were identified. There was no difference for SRB between breast cancer patients and control subjects (P>0.05). Meta-analysis was performed using 7 eligible studies. There was significant heterogeneity between studies (P<0.05). In overall the SRB was negatively associated with the maternal breast cancer risk (OR=0.95; 95 % CI: 0.92-0.99, P=0.02). Menopausal status of the patients was not associated with offspring SRB (P=0.07). Further researches are needed to determine the possible association between gender of offspring and maternal breast cancer risk.