The accuracy of using last menstrual period to determine gestational age for first trimester medication abortion: a systematic review

Objective: We sought to evaluate the accuracy of assessing gestational age (GA) prior to first trimester medication abortion using last menstrual period (LMP) compared to ultrasound (U/S).

Study design: We searched Medline, Embase and Cochrane databases through October 2013 for peer-reviewed articles comparing LMP to U/S for GA dating in abortion care. Two teams of investigators independently evaluated data using standard abstraction forms. The US Preventive Services Task Force and Quality Assessment of Diagnostic Accuracy Studies guidelines were used to assess quality.

Results: Of 318 articles identified, 5 met inclusion criteria. Three studies reported that 2.5-11.8% of women were eligible for medication abortion by LMP and ineligible by U/S. The number of women who underestimated GA using LMP compared to U/S ranged from 1.8 to 14.8%, with lower rates found when the sample was limited to a GA <63 days. Most women (90.5-99.1%) knew their LMP, 70.8-90.5% with certainty.

Conclusion: Our results support that LMP can be used to assess GA prior to medication abortion at GA <63 days. Further research looking at patient outcomes and identifying women eligible for medication abortion by LMP but ineligible by U/S is needed to confirm the safety and effectiveness of providing medication abortion using LMP alone to determine GA.