RESUMEN
OBJECTIVE: To develop a chart for risk of small-for-gestational-age (SGA) at birth depending on deviations in symphysis-fundus (SF) height values for gestational age during pregnancy weeks 24-42. DESIGN: Registry-based population cohort study. SETTING: Antenatal clinics, Västra Götaland County, Sweden, 2005-2010. POPULATION: The study included 42 018 women with ultrasound-dated singleton pregnancies who delivered at Sahlgrenska University Hospital. Data (including 282 713 SF height measurements) were extracted from the hospital's computerised obstetric database. METHODS: Linear and binary regression analyses were used to derive prediction models with deviations in birthweight (BW) and SF height by gestational age as dependent and independent variables, respectively. Receiver operating characteristic curves were generated to evaluate the predictive value of the model in detecting SGA. MAIN OUTCOME MEASURES: Birthweight and small-for-gestational-age. RESULTS: Symphysis-fundus height accounted for 3% of individual BW variance at 24 weeks, increasing gradually to 20% at 40 weeks. Maternal factors explained an additional 10 percentage points of BW variance. Receiver operating characteristic curves confirmed that SF height was a stronger SGA predictor in late than in early pregnancy. Using an SGA relative risk cut-off limit of ≥2-fold, the overall sensitivity was 50% and the overall specificity 80%. Only the most recent SF measurement was useful in predicting BW deviation; previous measurements added nothing to the predictive value. CONCLUSIONS: The ability of SF measurements to detect SGA status at birth increases with gestational age. Only the most recent SF measurement has predictive value; a static or falling pattern of SF values did not increase SGA likelihood. TWEETABLE ABSTRACT: New SF curves predict SGA best in late pregnancy; only the most recent SF measurement has predictive value.