Validity of the " modified triple test " in the first trimester screening for congenital fetal malformations in the high risk group

ABSTRACT

To assess the clinical effectiveness of the combined test using fetal nuchal translucency [NT], maternal serum free beta subunit of human chorionic gonadotrophin [beta -HCG] and pregnancy associated plasma protein -A [PAPP-A] levels during gestational weeks 10 to 14 for screening of congenital fetal malformations. Settings Department of Obstet. and Gyn., Minia University Hospital in co-operation with Feto-Maternal Unit, Am Shams University Hospital. Study Design: One thousand pregnant women [between. 10-14 weeks' gestation] at high risk for fetal malformations were recruited. They were subjected to detailed clinical evaluation, A three-generation family history, nuchal translucency, maternal serum PAPP-A and free beta -HCG. Amniocentesis was done only for 17 cases. Ninty-four malformed fetuses were picked up out of 1000 studied high-risk pregnant women [9.4%]. The most common congenital anomalies diagnosed were the cerebrospinal anomalies [48.7%], gastrointestinal anomalies [35.4%], and cardiac anomalies [15.8%]. Anomalies detected during the first scan were 49 out of 158 [DR 31.01%, Sensitivity 41.38%, specificity 98.63%].Anomalies detected during, the second scan were 125 out of 158 [DR 86.5%, sensitivity 81.6%%, specificity 99.31%]. Amniocentesis has been done for 17 cases [DR 94.1%]. Nuchal translucency had a detection rate [DR] of 80.2% compared with 52%, 43% for free beta - HCG and PAPP-A respectively. NT + free beta -HCGhad a better DR of 86%. The sensitivity of NT in comparison with amniocentesis was 73% whereas the sensitivity of the biochemical markers [PAPP-A and free beta-hCG] was 68%, 64% respectively. When NT and the biochemical markers were combined together, the sensitivity rose up to 89.5% in relation to amniocentesis. Nuchal translucency screening for fetal malformations together with serum screening has been given grade B recommendation by the RCOG working party. As a result of advances in U/S technology; visualization of the first trimester fetus has been markedly improved. By examining fetal anatomy and NT measurement at 10-l4wk, the majority of structural [68%] and chromosomal abnormalities [79%] can be diagnosed in early pregnancy. Adding the serum markers to the age and U/S will improve detection to 90% with a 5% false positive rate