Purpose Pregnancies ending before gestational week 12 are common but not notified to the Medical Birth Registry of Norway. Our goal was to develop an algorithm that more completely detects and dates pregnancy outcomes by using diagnostic codes from primary and secondary care registries to complement information from the birth registry. Methods We used nationwide linked registry data between 2008 and 2018 in a hierarchical manner: We developed an algorithm to arrive at unique pregnancy outcomes, considering codes within 56 days as the same event. To infer gestational age of pregnancy outcomes before gestational week 12, we used the median gestational week of pregnancy markers (45 ICD-10 codes and 9 ICPC-2 codes). When no pregnancy markers were available, we assigned outcome-specific gestational age estimates. The performance of the algorithm was assessed by blinded clinicians. Results Using only the medical birth registry, we identified 649,703 pregnancies, including 1,369 (0.2%) miscarriages and 3,058 (0.5%) elective terminations. With the new algorithm, we detected 859,449 pregnancies, including 642,712 live-births (74.8%), 112,257 miscarriages (13.1%), 94,664 elective terminations (11.0%), 6,429 ectopic pregnancies (0.7%), 2,564 stillbirths (0.3%), and 823 molar pregnancies (0.1%). The median gestational age was 10 +0 weeks (IQR 10 +0-11 +3) for miscarriages and 8 +0 weeks (IQR 8 +0-9 +6) for elective terminations. Gestational age could be inferred using pregnancy markers for 66.3% of miscarriages and 47.2% of elective terminations. Conclusion The pregnancy algorithm improved the detection and dating of early non-live pregnancy outcomes that would have gone unnoticed if relying solely on the medical birth registry information.

Objective: To quantify the association between prenatal exposure to selective serotonin (SSRI) and serotonin-norepinephrine (SNRI) reuptake inhibitor antidepressants and ADHD in offspring, with quantification of exposure misclassification bias. Design: Norwegian Mother, Father and Child Cohort Study (MoBa), linked to national health registries. Setting: Norway. Population: 6395 children born to women who self-reported depression/anxiety in pregnancy and were either medicated with SSRI/SNRI in pregnancy (n=818) or non-medicated (n=5228), or did not report depression/anxiety but used antidepressants six months prior to pregnancy (discontinuers, n=349). Main outcome measure: Diagnosis of ADHD or redeemed prescription for ADHD medication in children, and mother-reported symptoms of ADHD at child age five years. Results: When the hazard was averaged over the duration of the study’s follow-up, there was no difference in ADHD risk between ever in-utero SSRI/SNRI-exposed children and comparators (weighted Hazard Ratio (wHR): 1.07, 95% Confidence Interval (CI): 0.76-1.51, vs. non-medicated; wHR: 1.53, 95% CI: 0.77-3.07, vs. discontinuers). Underestimation of effects due to exposure misclassification was modest. At early childhood, the risk for ADHD was lower with prenatal SSRI/SNRI exposure compared with non-medicated, and so were ADHD symptoms (weighted β: -0.23, 95% CI: -0.39, -0.08); this risk became elevated at child age 7-9 years (wHR: 1.93, 95% CI: 1.22-3.05). Maternal depression/anxiety prior to pregnancy was independently associated with child ADHD. Conclusion: Prenatal SSRI/SNRI exposure is unlikely to considerably increase the risk of child ADHD beyond that posed by the underlying psychiatric illness. The elevated risk at child age 7-9 years needs to be further elucidated.