Fetal Biometry in Early Pregnancy

Fetal biometry has been used routinely in the second trimester for the past 40 years for the evaluation of gestational age, fetal weight and fetal anomalies. Its importance in the first trimester is even greater, as it allows for more accurate pregnancy dating, earlier detection of fetal anomalies and multiple gestations, and identifies pregnancies at increased risk for aneuploidy. The gestational sac and yolk sac are early pregnancy structures that can offer information related to the health of the pregnancy. The crown-rump length measurement in the first trimester is the most accurate predictor for pregnancy dating. Nuchal translucency measurement has become integral in the evaluation of increased aneuploidy risk, and is routinely offered with serum markers as a screening option. Evaluation of the nasal bone is useful as a secondary marker in screening for aneuploidy, especially with regard to trisomy 21. Other biometric measurements routinely used later in pregnancy may be utilized in the first trimester in certain scenarios. Fetal biometry in the first trimester is an important tool for evaluation of the health of a pregnancy. Clinicians should be aware of normal and abnormal development to enhance their counseling and management of normal and complicated pregnancies.