Ultrasound Ultrasound most reliable method for assessing fetal growth in the first trimester of pregnancy, measurement of the crown-rump length on ultrasound is the most precise method of dating earlier ultrasounds are almost always more accurate than late ultrasounds never change the estimated gestational age based on an ultrasound obtained late in the pregnancy ultrasound is the next best step in management in patient's with abnormal AFP, β-hCG, inhibin, unconjugated estriol levels cases where you are unsure of fetal presentation cases of painless vaginal bleeding and fetal bradycardia (vasa previa) any case where you suspect placenta previa (painless vaginal bleeding, no fetal bradycardia) Fetal stress test used to assess fetal well-being most common cause of abnormal fetal stress test is fetal sleep cycle Fundal Height Least invasive If 2 cm deviation from normal during weeks 18-36, repeat measurement and/or ultrasound Timeline Location of Fundus 12 weeks Pubic symphis 16 weeks Midway from symphysis to umbilicus 20 weeks Umbilicus 20-36 weeks Height from pubic symphysis in cm correlates with weeks of gestation Early Pregnancy Fetal Parameters Useful in early pregnancy gestational sac crown-rump length Late Pregnancy Fetal Parameters Four measurement requirement due to wide deviation in normal for each One of the most effective ways of evaluating gestational age Includes cerebellar diameter (HC) biparietal diameter of skull (BPD) abdominal circumference (AC) femur length (FL)