Detection of small for gestational age fetuses by the combination of clinical risk factors and ultrasonography

Abstract

Clinical risk factors of fetal growth retardation and targeted ultrasound examinations were combined to detect small for gestational age (SGA) fetuses below the 10th percentile weight for age in 1122 unselected singleton pregnancies, in which the true gestational age was confirmed by ultrasonography at 18 weeks. The prevalence of SGA infants was 6.0% in this population. A risk group of 236 (21%) mothers was referred for an ultrasound examination of fetal growth by the midwives of maternity welfare centers on the basis of low symphysis-fundal height or five other major maternal risk factors (pregnancy associated hypertension, loss of weight gain, a previous SGA infant, pre-pregnancy weight below 50 kg, any smoking during pregnancy). The sensitivity and positive predictive value of the clinical part of the study were 83.6 and 23.7%, respectively. Fetal growth was assessed by measuring both biparietal diameter (BPD) and transverse abdominal diameter. In the clinically selected risk group, 83.9% of the SGA fetuses could be detected by this method using a cutoff level of −1 standard deviation (SD). The two-step screening combining clinical and ultrasonographic methods in the detection of SGA fetuses in general population showed a sensitivity of 70.1%, a specificity of 95.5%, a positive predictive value of 49.5%, and a negative predictive value of 98.1%. After ultrasound examination, the definitive risk group for SGA was 8.5% of the total material of 1122. Although the total number of ultrasound examinations was decreased by about half, the ability of the screening to detect SGA fetuses was in this study even better than that of a routine screening performed twice during pregnancy with the same ultrasound method.