Symphysis-fundus measurements for detection of small for gestational age pregnancies

BACKGROUND: In Sweden measurements of the symphysis-fundus (SF) distance are used to detect small for gestational age (SGA) pregnancies. The aim of this study was to evaluate the efficiency of Swedish ultrasound-based SF reference curves in detecting SGA pregnancies. METHODS: To assess the sensitivity for detection of SGA pregnancies we performed a case-control study. Through the Swedish Medical Birth Register we identified all singleton SGA infants born in Uppsala in 1993-1997 and randomly recruited non-SGA singleton infants as controls. We included 169 term and 73 preterm SGA cases and 296 controls, all born at term. The reference curves constructed by Steingrimsdottir (S curve) and Kieler (K curve) were evaluated. Gestational age at the first alarm in the preterm SGA group was recorded. RESULTS: In term pregnancies the S curve showed a sensitivity of 32% and specificity of 90% at a cut-off of -2 SDs. The corresponding values for the K curve were 51% and 83%, respectively. In preterm SGA pregnancies the sensitivity of the S curve was 49% and of the K curve 58%. The first alarm below 2 SDs was noted before 32 weeks in 37% with the S curve and 43% with the K curve for preterm SGA pregnancies. CONCLUSIONS: Both tested Swedish SF reference curves had low sensitivities for term SGA pregnancies. Sensitivity was higher for the preterm group and SF measurements seem to be better for detecting the most severe cases of SGA.