Objective: To estimate the risk of adverse outcomes in women whose first day of the last menstrual period (LMP) was unreliable.
Methods: Among 20,244 singleton pregnancies with measurements of biparietal diameter between 12 and 22 weeks' gestation, LMP was registered as unreliable in 3775 (18.6%) and reliable in 16,469 (81.4%). Adverse outcomes were defined as spontaneous or missed abortions after 12 weeks' gestation, stillbirth or postnatal death within 1 year, preterm birth, birth weight less than 2500 g, and low birth weight (LBW) for gestation (lower than 22% below sex-specific expected weight). Logistic regression analysis and Kaplan-Meier survival analysis were used to analyze the risk of adverse outcomes.
Results: The risk of death was doubled in pregnant women with unreliable LMPs compared with those with reliable LMPs (odds ratio [OR] 2.0; 95% confidence interval [CI] 1.5, 2.6). This risk was highest with respect to stillbirth (OR 2.7; 95% CI 1.7, 4.3). The risks of preterm birth, LBW, and LBW for gestation were also significantly increased (ORs 1.5, 1.4, and 1.2; 95% CIs 1.3, 1.7; 1.2, 1.6; and 1. 0, 1.4, respectively).
Conclusion: An unreliable LMP is associated with increased risk of adverse outcomes, especially fetal death.