BACKGROUND: Studies of birth weight associations with ovarian and endometrial cancer risks are limited with inconsistent results, and none has evaluated associations by histologic subtype. We utilized prospectively collected birth weight information to investigate the association with risk of ovarian and endometrial cancers overall and by histologic subtype.

METHODS: 162,559 girls, born from 1930 to 1989, from the Copenhagen School Health Records Register (CSHRR) were followed prospectively via linkage with the Danish health registers. Ovarian (n=666) and endometrial (n=694) cancers were identified from 1978 to 2014. Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI).

RESULTS: Women with lower (2.0-3.25 vs. 3.26-3.75kg) and higher (3.75-5.5 vs. 3.26-3.75kg) birth weights had increased risks of ovarian cancer overall [HR (95% CI): 1.27 (1.06-1.52); 1.51 (1.21-1.87), respectively] and serous ovarian cancers [1.54 (1.19-1.98); 1.98 (1.47-2.67), respectively]. A decreased risk of Type II endometrial tumors was suggested per kilogram increase in birth weight [HR (95% CI): 0.63 (0.40-1.00)].

CONCLUSIONS: Our results suggest that both lower and higher birth weights were associated with increased ovarian cancer risk and associations were particularly strong for serous ovarian cancer, the most common subtype. Birth weight was not associated with most types of endometrial cancer.