Pregnancy Test Use and Timing of Pregnancy Detection in a Prospective Cohort of Pregnancy Planners.

OBJECTIVE: To identify determinants of selected pregnancy testing behaviors among pregnancy planners and to elucidate the relationship between pregnancy testing and detection. METHODS: In PRESTO (Pregnancy Study Online), a North American prepregnancy cohort study of pregnancy planners (2018-2024), participants reported day-specific information about pregnancy testing spanning 4 days before day of expected menstruation through 4 days after. We used generalized linear models to estimate the association between maternal attributes and pregnancy testing behavior, characterized as the timing of the first test and testing frequency. We used quantile regression to estimate the timing of pregnancy detection among participants who conceived by maternal characteristics and pregnancy testing behavior. We estimated the adjusted risk of having a negative test result and the probability of detecting a very early pregnancy loss by the timing of the pregnancy test. RESULTS: We analyzed data from 20,458 pregnancy tests across 6,569 unique participants. Of the participants, 40.7% of reported they engaged in very early testing, defined as testing more than 4 days before their expected period. We observed a range of pregnancy testing intensity, with some participants testing only once and others testing every day. Among participants who detected pregnancy, very early testers were more than 5 times more likely to have a negative test result before a positive test result than those who waited until the day of expected period to test (adjusted risk ratio [aRR[ 5.89; 95% CI, 4.73-7.33). Very early testers were more than 3 times more likely to have an initial positive test result followed by a negative test result, likely reflecting increased detection of very early pregnancy losses (aRR 3.80; 95% CI, 2.12-6.80). CONCLUSION: Patterns in home pregnancy testing varied widely among pregnancy planners. Early initiation of pregnancy testing was associated with slightly earlier pregnancy detection, but also a marked increase in risk of negative test results and detection of very early pregnancy losses.