Screening for fetal anomalies during the first trimester of pregnancy: transvaginal versus transabdominal sonography

Ultrasound is a sensitive tool for the diagnosis of fetal anomalies during the prenatal period. Most knowledge about the ultrasound images of such anomalies is based on abdominal scanning during the second trimester of pregnancy. The value of transvaginal sonography for evaluating fetal anomalies and a comparison with transabdominal sonography in the first trimester has, to our knowledge, so far not been studied. During a 12‐month period, 800 pregnant women between 9 and 13 weeks of gestation, underwent first a transabdominal scan followed by a transvaginal examination, in order to compare the value of the two techniques. Eight cases of fetal abnormality, including anencephaly, exencephaly, cervical myelomeningocele, cystic hygroma, omphalocele, posterior fossa cyst and syndactyly, were diagnosed by using the transvaginal sonographic approach. The standard abdominal technique failed to detect four of these anomalies, while in the other four only vague and non‐specific fetal abnormalities could be demonstrated. All women with normal abdominal and vaginal sonograms in the first trimester were rescreened transabdominally at mid‐gestation. Five patients with a variety of fetal anomalies, including hydrocephalus, agenesis of corpus callosum, bilateral ureteropelvic junction obstruction, right heart hypoplasia and tetralogy of Fallot, were identified in the rescreening procedure. One case of ventricular septal defect and coarctation of the aorta was not detected at either of the first or second screening procedures. Our findings show that transvaginal sonography is more sensitive than transabdominal sonography in the detection of first‐trimester anomalies. However, since not all fetal anomalies are manifest so early in pregnancy, standard abdominal sonography in the second trimester is still recommended.