First-trimester Down syndrome screening in renal-transplanted pregnant women: a model for adjusting the false-positives rates.

OBJECTIVE

This study aimed to develop a model to adjust the increased β-hCG levels observed in renal-transplanted women, leading to increased false-positive rates in Down syndrome screening.

METHODS

Detailed data from 11 renal-transplanted and a nested-cohort of 70 pregnant women, matched by age, parity and gestational age were retrieved from our hospital records. Patient's age, multiples of the median (MoM) values for freeβ-hCG, pregnancy-associated plasma protein-A, nuchal translucency, and creatinine concentration and clearance were noted. Freeβ-hCG levels were adjusted according to the deviation of serum creatinine concentration by means of three different methods (median, proportionality and regression). Subsequently, Down syndrome risk was estimated with the three resulting adjusted fβ-hCG values.

RESULTS

After adjustment, the median β-hCG MoM decreased from 2.15 MoM to 1.00 MoM (median method), 1.61 MoM (proportionality method) or 1.16 MoM (regression method). The non-adjusted 27% false-positive rate dropped to 18% (median method) and 10% (proportionality or regression methods) after re-estimation of the Down syndrome risk. In controls, the observed median for β-hCG MoM was 1.12, and the false-positive rate was 5.7%.

CONCLUSIONS

In first-trimester Down syndrome screening, fβ-hCG adjustment by the regression method appears to be the best to match with controls.