Does a discrepancy between gestational age determined by biparietal diameter and last menstrual period sometimes signify early intrauterine growth retardation?

Objective To assess the association between gestational age estimated from the last menstrual. period. (GA(LMP)) or from the biparietal diameter (GA(B PD)), and the subsequent birthweight for gestational age: Design Population-based followup study. Setting Of 21,936 pregnancies conta ined in the ultrasound database, 16,387 singleton pregnancies with a reliab le last menstrual period date and an ultrasound examination between 12 and 22 weeks of gestation were included. Main outcome measures Correlation between: 1. birthweight deviation (birthw eight-expected weight for gestation); 2. birthweight; and 3. pregnancy leng th and (GA(LMP)-GA(BPD)). Relative risk of birthweight < 2500 g and low bir thweight for gestation (> 22% below normal weight) related to Eve levels of discrepancy between (GA(LMP)-GA(BPD)). Results (GA(LMP)-GA(BPD)) was not associated with deviation of birthweight related to GA(BPD). However the risk of low birthweight (< 2500) and low bi rthweight for gestational age was significantly increased when (GA(LMP)-GA( BPD)) was > 7 days. Conclusion A biparietal diameter smaller than expected from the last menstr ual period date is mainly a problem of an error related to estimated time o f ovulation, At the same time the relative risk: of a low birthweight infan t is slightly increased.