Validity of self-reported number of pregnancies and maternal age at first birth among females attending organized mammographic screening.

Aims: Reproductive history conveys information about potential health risks later in adulthood. This study aimed to examine the validity of self-reported number of pregnancies and maternal age at first birth (AFB) among females attending BreastScreen Norway.

Methods: Participants were identified through the Janus Serum Bank cohort in Norway and were eligible for this cross-sectional validation study if they participated in a health survey issued by BreastScreen Norway between 2006 and 2015. Retrospective self-reported survey information on number of pregnancies and AFB in years was validated against prospectively collected information from the Medical Birth Registry of Norway (MBRN) using the Spearman rank (r_s) and intraclass correlation coefficients (ICC) with 95% confidence intervals (CI).

Results: After exclusions, 51,598 subjects were included in the analysis on number of pregnancies and 46,919 in the analysis on AFB. On average, study subjects were 59-60 years old when completing the health survey and had become first-time mothers roughly 36 years earlier. Survey-based information about number of pregnancies was highly correlated and demonstrated high agreement with the registry data (r_s=0.967, 95% CI 0.964-0.969; ICC=0.884, 95% CI 0.882-0.885). Survey-based information about AFB demonstrated even higher correlation and very high agreement with the registry data (r_s=0.975, 95% CI 0.973-0.976; ICC=0.974, 95% CI 0.974-0.975).

Conclusions: Retrospectively recalled survey-based information about number of pregnancies and AFB was highly accurate when validated against prospectively collected information in the MBRN. These survey-based data are valuable for future epidemiological research, and linkage to the MBRN may not be required when these data are available.