Symphysis-fundus height is the traditional initial measure of fetal growth that is monitored in all pregnancies. For many reasons, including poor interobserver reliability, it is a poor technique for detecting a fetus that is small for gestational age. Mongelli and Gardosi correlated clinical symphysis-fundus height measurements with ultrasonic scan measurements to assess maternal and fetal variables that influence the clinical height assessment. The goal of the study was to provide data to improve the usefulness of symphysis-fundus height measurement in detecting a fetus of inappropriate size for gestational age.
Women who attended the antenatal clinics of a medical center in the United Kingdom were recruited for the study. The 325 women who participated all had uncomplicated singleton pregnancies dated by ultrasonography performed before 20 weeks of gestation. Two trained observers performed repeated symphysis-fundus height measurements during these pregnancies using standardized techniques. The data gathered on participants included maternal height and weight at presentation, age, ethnic group, parity and smoking history. Fetal sex was also entered into the analysis.
Contrary to conventional teaching, the symphysis-fundus height was linearly related to gestational age. The flattening of the curve close to term that is usually described was not found. At 40 weeks of gestation, the mean symphysis-fundus height measured 38 cm. The strongest predictor of fundal height was gestational age. The only other variables that showed significant correlation were initial maternal weight, parity and sex of the infant. The authors developed a formula based on these variables to more accurately predict expected fundal height for gestation. At each assessment, they recommend use of the following formula to estimate the expected fundal height to better identify a fetus of inappropriate size for gestational age.
Expected fundal height (cm) = 37.1 + 0.119 × (gestational age in days − 280) + 0.074 × (initial weight in kg −66.5) + 1.01 × (zero, if nulliparous; one, if parous) + 0.91 × (zero, if female fetus; one, if male fetus).