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Discrepancy Rate and Associated Factors of Gestational Age Determination by Last Menstrual Period Compared with First-Trimester Ultrasound in Certain Menstrual Period Pregnant Women

Objective: To assess discrepancy rate and associated factors of gestational age (GA) determination by last menstrual period (LMP) compared with first-trimester ultrasound in certain menstrual period pregnant women.0

Materials and Methods: The present study was a cross-sectional study that was conducted at Srinagarind Hospital, Khon Kaen University, Thailand between May 2020 and January 2021. Participants were singleton pregnant women who reported certain LMP dates. GA was estimated using Naegele’s rule and crown-rump length (CRL) measurement. Differences of GA more than five days at GA of 8 or fewer⁶/⁷ weeks and more than seven days at GA of nine⁰/⁷ to twelve⁶/⁷ weeks were considered discrepant. Factors associated with discrepancy were determined by calculating an odds ratio (OR) with a 95% confidence interval (CI).

Results: Of the 220 participants, 67 had discrepant GA obtained from LMP and CRL measures, accounting for a rate of 30.5% (95% CI 24.4% to 36.9%). Factors associated with increased risk of discrepant GA consisted of low household income (adjusted OR 2.76; 95% CI 1.43 to 5.31) and long intervals of the menstrual cycle (adjusted OR 3.85; 95% CI 1.85 to 8.02).

Conclusion: Approximately one-third of participants in the present study had a discrepancy of LMP and early ultrasound-based GA measures. Factors influencing the risk of discrepant GA between these two methods included household income and interval of menstruation.

Keywords: Gestational age; Last menstrual period; First-trimester ultrasound; Discrepancy