Correlation of ultrasound findings and biochemical markers in the second trimester of pregnancy in fetuses with trisomy 21

OBJECTIVE: The aim of the present study was to assess possible correlations between ultrasound findings and maternal serum biochemical ('triple test') markers among fetuses with trisomy 21 in the second trimester of pregnancy. METHODS: The study was a retrospective cohort study of 72 pregnancies affected by trisomy 21 who had a second trimester ultrasound and biochemical screen performed at a single center between 1990 and 1999. The biochemical screen consisted of alpha-fetoprotein (AFP), total beta human chorionic gonadotrophin (hCG) and estriol (uE(3)). Marker levels were expressed in multiples of the median (MoM). The ultrasound findings assessed were major structural anomalies, short humerus length, short femur length, increased nuchal fold thickness (NF), hyperechoic bowel, echogenic intracardiac focus (EIF), ventriculomegaly, choroid plexus cysts and renal pyelectasis. RESULTS: Second trimester maternal serum biochemical markers and ultrasound findings appeared to be largely independent of each other. However, some significant correlations were observed. Estriol was significantly lower when a fetal cystic hygroma was detected on ultrasound compared to those with no cystic hygroma (0.40 vs. 0.70 MoM, p<0.05). The median hCG level was significantly lower in those pregnancies with a normal second trimester fetal ultrasound compared to those with positive ultrasound findings (2.07 vs. 2.87 MoM, p<0.05). Median hCG levels were also significantly higher in those cases with NF> or =5 mm as compared to those with NF<5 mm (2.99 vs. 2.49 MoM, p<0.05). This difference persisted after exclusion of the five cases with cystic hygromas (2.99 vs. 2.49 MoM, p<0.05). A significant positive correlation was observed between log(10) hCG and log(10) NF MoM (Spearman's rho=0.252, p<0.05). NF was significantly greater among fetuses with an identifiable cardiac defect compared with those without a detectable cardiac defect (median of 7.0 mm vs. 3.8 mm, p<0.01). This difference persisted when expressed as multiples of the median (2.8 vs. 1.3 MoM, p<0.01). CONCLUSION: Second trimester ultrasound and biochemical markers are largely independent in fetuses with trisomy 21, however significant correlations between the two were observed in the present series. These may be important in screening protocols that combine second trimester ultrasound and biochemical markers.