Validation of long-term recall of pregnancy-related weight in the Life-course Experiences And Pregnancy (LEAP) study.

BACKGROUND: Pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) are determinants of maternal and child health. However, many studies of these factors rely on error-prone self-reported measures.

METHODS: Using data from Life-course Experiences And Pregnancy (LEAP), a US-based cohort, we assessed the validity of pre-pregnancy BMI and GWG recalled on average 8 years postpartum against medical record data treated as alloyed gold standard ("true") values. We calculated probabilities of being classified into a self-reported pre-pregnancy BMI or GWG category conditional on one's true category (analogous to sensitivities and specificities), and probabilities of truly being in each pre-pregnancy BMI or GWG category conditional on one's self-reported category (analogous to positive and negative predictive values).

RESULTS: There was a tendency toward under-reporting pre-pregnancy BMI. Self-report misclassified 32% (95% CI: 19%, 48%) of those in LEAP with truly overweight and 13% (5%, 27%) with obesity into a lower BMI category. Self-report correctly predicted the truth for 72% (55%, 84%) with self-reported overweight to 100% (90%, 100%) with self-reported obesity. For GWG, both under- and over-reporting were common; self-report misclassified 32% (15%, 55%) with truly low GWG as having moderate GWG and 50% (28%, 72%) with truly high GWG as moderate or low GWG. Self-report correctly predicted the truth for 45% (25%, 67%) with self-reported high GWG to 85% (76%, 91%) with self-reported moderate GWG. Misclassification of BMI and GWG varied across maternal characteristics.

CONCLUSIONS: Findings can be used in quantitative bias analyses to estimate bias-adjusted associations with pre-pregnancy BMI and GWG.