Accuracy of self-assessment of gestational duration among people seeking abortion

Mifepristone, used together with misoprostol, is approved by the United States Food and Drug Administration for medication abortion through 10 weeks' gestation. Although in-person ultrasound is frequently used to establish medication abortion eligibility, previous research demonstrates that people seeking abortion early in pregnancy can accurately self-assess gestational duration using the date of their last menstrual period.

In this study, we establish the screening performance of a broader set of questions for self-assessment of gestational duration among a sample of people seeking abortion at a wide range of gestations.

We surveyed patients seeking abortion at 7 facilities before ultrasound and compared self-assessments of gestational duration using 11 pregnancy dating questions with measurements on ultrasound. For individual pregnancy dating questions and combined questions, we established screening performance focusing on metrics of diagnostic accuracy, defined as the area under the receiver operating characteristic curve, sensitivity (or the proportion of ineligible participants who correctly screened as ineligible for medication abortion), and proportion of false negatives (ie, the proportion of all participants who erroneously screened as eligible for medication abortion). We tested for differences in sensitivity across individual and combined questions using McNemar's test, and for differences in accuracy using the area under the receiver operating curve and Sidak adjusted P values.

One-quarter (25%) of 1089 participants had a gestational duration of >70 days on ultrasound. Using the date of last menstrual period alone demonstrated 83.5% sensitivity (95% confidence interval, 78.4-87.9) in identifying participants with gestational durations of >70 days on ultrasound, with an area under the receiver operating characteristic curve of 0.82 (95% confidence interval, 0.79-0.85) and a proportion of false negatives of 4.0%. A composite measure of responses to questions on number of weeks pregnant, date of last menstrual period, and date they got pregnant demonstrated 89.1% sensitivity (95% confidence interval, 84.7-92.6) and an area under the receiver operating curve of 0.86 (95% confidence interval, 0.83-0.88), with 2.7% of false negatives. A simpler question set focused on being >10 weeks or >2 months pregnant or having missed 2 or more periods had comparable sensitivity (90.7%; 95% confidence interval, 86.6-93.9) and proportion of false negatives (2.3%), but with a slightly lower area under the receiver operating curve (0.82; 95% confidence interval, 0.79-0.84).

In a sample representative of people seeking abortion nationally, broadening the screening questions for assessing gestational duration beyond the date of the last menstrual period resulted in improved accuracy and sensitivity of self-assessment at the 70-day threshold for medication abortion. Ultrasound assessment for medication abortion may not be necessary, especially when requiring ultrasound could increase COVID-19 risk or healthcare costs, restrict access, or limit patient choice.