A discrepancy between gestational age estimated by last menstrual period and biparietal diameter may indicate an increased risk of fetal death and adverse pregnancy outcome

Objective To determine if the discrepancy between gestational age estimated by last menstrual period and by biparietal diameter (GA_LMP− GA_BPD) is associated with adverse pregnancy outcome.
Design Population-based follow up study.
Population Singleton pregnancies were studied when a reliable date of last menstrual period and biparietal diameter measured between 12 and 22 weeks of gestation was available (   n = 16,469  ).
Methods Logistic regression analysis and Kaplan-Meier survival analysis were used to analyse the association between GA_LMP− GA_BPD and adverse pregnancy outcome.
Main outcome measures Adverse outcome was defined as abortion after 12 weeks of gestation, stillbirth or postnatal death within one year of birth, delivery < 37 weeks of gestation, a birthweight < 2500 g or a sex-specific birthweight lower than 22% below the expected.
Results The risk of death was more than doubled if GA_LMP− GA_BPD of ≥ 8 days was compared with GA_LMP− GA_BPD of < 8 days (OR 2.2; 95% CI 1.6–3.1). The risk of death was a factor of 6.1 higher if GA_LMP− GA_BPD of ≥ 8 days was combined with increased (> 2 × multiple of median) maternal alphafetoprotein measured in the 2nd trimester.
Conclusions A discrepancy between GA_LMP and GA_BPD generally reflects the precision of the two methods used to predict term pregnancy. However, a positive discrepancy of more than seven days, particularly with high maternal alpha-fetoprotein, might indicate intrauterine growth retardation and an increased risk of adverse perinatal outcome.