Accuracy of gestational dating by last menstrual period in period tracking application users

Period tracking applications (apps) are becoming an increasingly common tool used to predict cycles and plan or prevent pregnancy. We sought to evaluate if app users' pregnancy dating by last menstrual period (LMP) and dating by ultrasound were more congruent than those who did not use apps.

We conducted a secondary analysis of data collected from the LMP-SURE study in the United States, which surveyed participants without prior ultrasound from abortion clinics in Alaska, Hawai'i, Idaho and Utah about date and certainty of LMP and use of period tracking apps. We obtained subsequent ultrasound dating by chart review. We compared agreement between LMP and ultrasound dating between those who did and did not use period-tracking apps.

Of the 1025 participants that started the survey, 730 had complete data including ultrasound dating and period tracking app use. Of those, 288 (39.5%) used a period tracking app. App users were more likely to be certain or fairly certain of LMP (279 (96.9%) vs 352 (79.6%) of non-app users, p<0.001). Of those who tracked their periods with an app, 163 (56.6%) had a gestational duration by LMP within 5 days of their gestational duration by ultrasound compared with 191 (43.2%) of non-app users (p<0.001).

Participants who used period tracking apps were significantly more likely than those who did not use apps to report an LMP-based gestational duration that was within 5 days of their gestational duration by ultrasound.