Diagnosis of small-for-gestational-age fetuses between 24 and 32 weeks, based on standard sonographic measurements

Objective To create and validate a formula using sonographic biometry measu rements for the optimal diagnosis of small-for-gestational-age (SGA) fetuse s between 24 and 32 weeks of gestation. Methods A logistic model using gestational age, femur diaphysis length, abd ominal and head circumferences to diagnose SGA was set up in a first group of 64 fetuses born between 24 and 32 weeks (group I). A Receiver Operating Characteristic (ROC) curve was drawn. Our model was compared with standard single ultrasound measurements or combined into an estimated fetal weight ( EFW) formula. An external validation was carried out on a second group of 1 83 fetuses (group II) from another maternity unit (ROC curve and comparison s). Results The area under the ROC curve was 0.91 in group I and 0.93 in group II. Using a 0.5 cut off point for our model yielded a sensitivity of 76% an d specificity of 91% for group I. This model is more specific than most oth er measurement methods with a similar sensitivity. Using the same cut off point (0.5) in Group II, our model was more specific (98%) but less sensitive (66%) when compared with single ultrasound measur ements and EFW formulae. By varying the cut off point, we were able to demo nstrate that, for a similar sensitivity, our model had a higher specificity than single ultrasound measurements and had similar specificity to EFW for mulae. Conclusion The logistic model we set up was able to calculate an SGA risk s core between 24 and 32 weeks of gestation in a population at high risk for elective delivery. The cut off point with a view to diagnosis can vary and makes it possible to give greater importance to the sensitivity or specific ity depending on the clinical context.