PRENATAL DETECTION OF HEART-DEFECTS AT THE ROUTINE FETAL EXAMINATION AT 18 WEEKS IN A NONSELECTED POPULATION

Few studies have addressed the prenatal detection rate of congenital h eart defects in a non-selected population at 18 weeks of gestation. Ou r objective was to assess the change in the prenatal detection rate of congenital heart defects in such a population that resulted from inco rporating the four-chamber view at the second-trimester routine ultras ound examination. The prenatal detection rate of heart defects was pro spectively compared between 4435 fetuses in Phase I who were scanned w ithout special attention to the heart, and 7459 fetuses in Phase II wh o were scanned incorporating the four-chamber view. Of the 49 heart de fects in Phase 1, 17 (35%) were critical and three (18%) of these were detected prenatally. Of the 90 heart defects in Phase II, 23 (26%) we re critical, six (26%) of these were detected prenatally at the 18 wee ks' routine scan, and three were detected in the third trimester, prov iding a total prenatal detection rate of 39%. A defect was classified as critical when a surgical repair was likely to be required because o f gross structural complexity having a functional significance, e.g. t ransposition of the great arteries, hypoplastic left heart syndrome, a trioventricular septal defect, coarctation of the aorta, and large ven tricular septal defect. No non-critical heart defects were detected pr enatally in either of the phases. The incidences in the total populati on were II and 12/1000 in Phases I and II, respectively. Thirty-two pe r cent of the critical and 16%; of the non-critical defects had associ ated abnormalities and/or abnormal karyotype. Implementation of the fo ur-chamber view increased the prenatal detection rate of critical hear t defects. To improve the results significantly, education and an exte nded fetal heart examination are necessary.