Senior Researcher Department of Chronic Diseases & Centre for Fertility and Health, Norwegian Institute of Public Health Oslo, Norway
Background: Studies of medication safety in early pregnancy should consider whether the exposed have a differential risk of induced abortion which could bias risk estimates. Characteristics of attention-deficit/hyperactivity disorder (ADHD) might lead to more unplanned pregnancies and induced abortions.
Objectives: To determine if young women with ADHD have higher rates of pregnancy and induced abortion than their peers without ADHD.
Methods: We identified females aged 15-30 living in Norway in 2010-2020. We defined ADHD as having filled two or more prescriptions for ADHD medication at any time from 2004-2020. Pregnancies, including spontaneous and induced abortions, and births were identified from the Medical Birth Registry and registers of primary and specialist healthcare. We used Poisson regression to estimate risk ratios (RRs) and 95% confidence intervals (CIs) for any pregnancy or induced abortion comparing individuals with and without ADHD, overall and stratified by age (15-19, 20-25, and 26-30 years), adjusting for the woman’s birth year and country of birth. We additionally estimated the proportion of pregnancies that resulted in an induced abortion at each age. Among individuals with ADHD who had a pregnancy, we estimated the RR for induced abortion according to whether they redeemed a prescription for ADHD medication in the 90 days before the estimated conception versus earlier.
Results: Our study population included 937,791 women born in 1979-2005, of whom 3.1% had ADHD. ADHD was associated with a higher probability of pregnancy at ages 15-19 (RR 2.3, 95% CI 2.2-2.5) and 20-25 (RR 1.5, 1.5-1.6), and with a lower probability at ages 26-30 (RR 0.8, 0.7-0.8). However, ADHD was associated with a higher likelihood of induced abortion in all examined age groups: RRs 2.2 (2.0-2.3), 1.7 (1.6-1.8), 1.8 (1.7-1.9), respectively. Individuals with ADHD were as likely as peers without ADHD to have an induced abortion if they became pregnant before age 22, and more likely if they became pregnant at later ages (28% versus 10% at age 30). Among those with ADHD who had a pregnancy, the risk of induced abortion was higher for those on active treatment, RR 1.2 (1.1-1.3) overall.
Conclusions: Young women with ADHD are at increased risk of experiencing an induced abortion, at younger ages due to having more pregnancies than peers and, at older ages due to more often choosing to have an abortion if they become pregnant. This suggests that there is potential to improve contraceptive use and reduce rates of unplanned pregnancies among women with ADHD. The differences in the risk of induced abortion between women with and without ADHD, and among those with recent or past medication use suggests a potential selection bias in safety studies of ADHD medication during pregnancy that should be accounted for.
