FETAL SIZE AND GROWTH VELOCITY IN THE PREDICTION OF INTRAPARTUM CESAREAN-SECTION FOR FETAL DISTRESS

Objective To evaluate and compare third trimester ultrasound measureme nts of fetal size and growth velocity in the prediction of intrapartum operative delivery for fetal distress and admission to the special ca re baby unit in a low risk antenatal population undergoing labour at t erm. Design Retrospective analysis of prospectively collected ultrasou nd data. Setting Ninewells Hospital, Dundee, Scotland. Population Thre e hundred and ninety-eight women previously enrolled in a longitudinal study of intrauterine volume undergoing: labour at a gestational age of >37 weeks. Method Fetal abdominal area (FAA) standard deviation sco res (Z scores) were calculated for size at 32 and 36 weeks of gestatio n together with the growth velocity Z scores between these two gestati onal ages. Receiver-operator characteristics were calculated for fetal abdominal area Z scores at 32, 36 weeks and velocity Z scores in the prediction of caesarean section for fetal distress and/or admission to the special care baby unit. Main outcome measures Intrapartum caesare an section for fetal distress and admission to the special care baby u nit with a diagnosis of perinatal hypoxia. Results Pregnancies ending in caesarean section for fetal distress or admission to the special ca re baby unit (n=17) had significantly lower fetal abdominal area Z sco res at 36 weeks of gestation (mean Z score -0.71 vs -0.18) and lower f etal abdominal area growth velocity (mean Z score -1.31 vs -0.01). Tak ing a cutoff Z score of -1.2 derived from the receiver-operator charac teristic curve, fetal abdominal area velocity has a sensitivity of 65% and specificity 75% for caesarean section for fetal distress and/or a dmission to the special care baby unit. Conclusion Growth velocity of the fetal abdominal area in the third trimester is superior to a singl e measurement of the fetal abdominal area at either a mean of 32 or 36 weeks of gestation in the prediction of caesarean section for fetal d istress and admission to the special care baby unit in low-risk women labouring at term. These results support the hypothesis that in the th ird trimester at least, growth rate in utero is more relevant to intra partum performance and immediate perinatal outcome than estimates of f etal size alone.