Diagnóstico da restrição de crescimento fetal pela relação diâmetro transverso do cerebelo/circunferência abdominal

Abstract

Objectives: to evaluate the validity of transverse cerebellar diameter (TCD)/abdominal circumference (AC) ratio as an ultrasonographic diagnosis method of fetal growth restriction (FGR). To calculate by receiver operator characteristic (ROC) curve the best cut-off value of TCD/AC ratio. To verify whether TCD/AC has its accuracy modified according to the dependence of type of FGR (symmetric and asymmetric) or according to the time between ultrasonography and deliverance. To compare TCD/AC ratio at its cut-off with the femur length (FL)/ abdominal circumference (AC) ratio. Method: a prospective cross-sectional study, carried out in 250 pregnant women with singleton pregnancies between 20 and 42 weeks of gestation, known accurate gestational age with ultrasound confirmation, living fetuses. Obstetrics sonographic examinations were accomplished until gestation resolution, but only the last one, within 14 days of the deliverance, was used for analysis. Neonates with TCD/AC ratio greater than the cut-off, established by ROC curve were diagnosed as FGR. The same was considered for FL/AC ratio. We classified as gold standard for FGR in new-born infants, who presented birth weight bellow 10th percentile of gestational age according to the growth curves of Lubchenco et al. (1963), corrected according to their sex. Neonates showing FGR and Rohrer ponderal index between 2,2 and 3,0 were labeled as symmetric FGR. Those showing FGR and ponderal index below 2,2 were labeled as asymmetric FGR. Results: prevalence of FGR among the study group was 12,4%. The best cut-off value calculated by ROC curve for TCD/AC ratio was 16,15. The sensitivity, specificity, accuracy, positive predictive values and negative predictive values, likelihood ratio for positive and negative tests were 77,4%, 82,6%, 38,7%, 96,3%, 82%, 4,5 and 3,7, respectively. In the symmetric FGR, sensitivity and specificity were 80,8% and 81,7%, respectively. In the asymmetric FGR, sensitivity and specificity were 60% and 75%, respectively. Results lower than in the symmetric FGR, but not statistically significant (p > 0,05). In the interval zero to seven days between sonographic examination and deliverance, sensitivity and specificity were 81,5% and 82,1%, respectively. In the interval of eight to 14 days, sensitivity and specificity were 50% and 84,3%, respectively, with no statistically significant difference (p > 0,05). The best cut-off value calculated by ROC curve for FL/AC ratio was 22,65, showing sensitivity, specificity, accuracy, positive predictive values and negative predictive values, likelihood ratio for positive and negative tests of 67,7%, 81,7%, 34,4%, 94,7%, 80%, 3,7 and 2,5, respectively. Conclusions: TCD/AC ratio at cut-off 16,15 proved to be an effective method in antenatal diagnosis of FGR, both symmetric as asymmetric, with no influence of interval between ultrasonography examination and deliverance. As a gestational age-independent method, it is useful enough in the occurrence of cases where these data are unknown. FL/AC ratio proved is not so effective as TCD/AC ratio in diagnosis of FGR.