Validation of maternal reported pregnancy and birth characteristics against the Medical Birth Registry of Norway

Abstract

Studies using mothers' self-reported information on birth and pregnancy characteristics are common, but the validity of such data is uncertain. We evaluated questionnaire data from the RHINE III study on reproductive health provided by 715 mothers from Bergen, Norway, about their 1629 births between 1967 and 2010, using the Medical Birth Registry of Norway (MBRN) as gold standard. Validity of dichotomous variables (gender, preterm birth [<37 weeks' gestation], postterm birth [>42 weeks' gestation], induction of labour, forceps delivery, vacuum delivery, caesarean section, were assessed by sensitivity, specificity, positive and negative predictive values (PPV and NPV) and Cohen's kappa. Paired t-test, Pearson's correlation coefficient and Bland-Altman plots were used to validate birthweight, stratified by mother's level of education, parity, birth year and child's asthma status. Child's gender and caesarean section showed high degree of validity (kappa = 0.99, sensitivity and specificity 100%). Instrumental delivery and extremely preterm birth showed good agreement with sensitivity 75-92%. Preterm birth and induction of labour showed moderate agreement. Post-term delivery was poorly reported. The validity appeared to be independent of recall time over 45 years, and of the child's asthma status. Maternally reported birth and pregnancy information is feasible and cheap, showed high validity for important birth and pregnancy parameters, and showed similar risk-associations compared to registry data.

Fig 1. Flowchart for the definition of the study population of mothers in RHINE III.

Fig 2. Paired difference between mothers reported birth weight and birth weight in the MBRN plotted against the number of recall years for the mother in 1464 children with valid data in both data sources.

Fig 3. Bland-Altman plot for birth weight showing the paired difference between mothers reported birth weight and birth weight in the MBRN plotted against the average of the paired birth weights.

The mean difference is plotted as a dashed line. Systematic bias is indicated by the distance between the dashed line and y = 0. Limits of agreement is calculated as mean difference ± 1.96 times the standard deviation of the paired differences, corrected for clustering within mother’s.