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 o f gestation was available (n = 16,469). Methods Logistic regression analysis and Kaplan-Meier survival analysis wer e used to analyse the association between GA(LMP) - GA(BPD), and adverse pr egnancy outcome. Main outcome measures Adverse outcome was defined as abortion after 12 week s of gestation, stillbirth or postnatal death within one year of birth, del ivery < 37 weeks of gestation, a birthweight < 2500 g or a sex-specific bir thweight lower than 22% below the expected. Results The risk of death was more than doubled if GA(LMP) - GA(BPD) of gre ater than or equal to 8 days was compared with GA(LMP) - GA(BPD) of < 8 day s (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 greater than or equal to 8 days was combined with inc reased (> 2 x multiple of median) maternal alpha fetoprotein measured in th e 2nd trimester. Conclusions A discrepancy between GA(LMP) - GA(BPD) generally reflects the precision of the two methods used to predict term pregnancy. However, a pos itive discrepancy of more than seven days, particularly with high maternal alpha-fetoprotein, might indicate intrauterine growth retardation and an in creased risk of adverse perinatal outcome.