THE USEFULNESS OF HCG AND UNCONJUGATED ESTRIOL IN PRENATAL-DIAGNOSIS OF TRISOMY-18

Objective To evaluate the usefulness of the two maternal serum markers , human chorionic gonadotrophin (hCG) and unconjugated oestriol (uE(3) ), in the prenatal diagnosis of trisomy 18. Design Retrospective evalu ation of uE(3) and hCG levels at mid-trimester in cases of trisomy 18 pregnancies identified from a series of women screened for Down's synd rome. Setting From a series of 53,893 women screened in the antenatal centre of University Hospital of Caen (France), 22 cases of trisomy 18 were diagnosed either after amniocentesis for maternal age, elevated risk of Down's syndrome, or fetal abnormalities and/or growth retardat ion on ultrasound assessment, or after birth. In addition, 11 cases of trisomy 18 identified prenatally in two other centres were included. Results Individual hCG and uE(3) levels for pregnancies with trisomy 1 8 were significantly lower than in unaffected pregnancies: mean hCG wa s 0.62 multiples of the median (MoM) and median hCG was 0.5 MoM. uE(3) was a much more effective marker than hCG. Mean uE(3) was 0.40 MoM an d median uE(3) was 0.37 MoM. It was observed that screening for trisom y 18 based on selection for amniocentesis with cut-off values of 0.55 for hCG and 0.60 for uE(3) would lead to a detection rate of 48% for 0 .8% false positive rate. Using cut-off values of 0.70 MoM for each one of the two markers would detect 79% of cases of trisomy 18 with a 3% false positive rate. Conclusions Our results confirm that low hCG and uE(3) levels observed in the mid-trimester are predictive of an increa sed risk for trisomy 18. Since most fetuses with trisomy 18 exhibit mo rphological abnormalities which should be detected following a careful ultrasonographic examination, biochemical screening could help in the detection of those anatomical defects in selecting for scanning a gro up of high risk women.