First trimester combined screening in patients with systemic lupus erythematosus: impact of pre-analytical variables on risk assessment.

BACKGROUND

Prenatal diagnosis of fetal trisomy 21 and other chromosomal abnormalities is based on invasive tests, such as amniocentesis and chorionic villus sampling, which are carried out in women identified through screening as being at high risk for these abnormalities. The most widely used method of screening is the first-trimester combined test which utilizes maternal age, and measurements of fetal nuchal translucency thickness (NT) and maternal serum pregnancy-associated plasma protein-A (PAPP-A) and free β-human chorionic gonadotropin (hCG).

OBJECTIVES

To assess the influence of SLE on the levels of NT, PAPP-A, and β-hCG and whether any alterations in such levels may increase the rate of false positives and the subsequent number of invasive tests.

METHOD

This was a prospective first-trimester screening study for trisomies 21, 18, and 13 by a combination of maternal age, fetal nuchal translucency thickness, and serum PAPP-A and β-hCG at King's College Hospital, London, between March 2006 and February 2011. The study population included 47 cases with maternal SLE and 45,493 without SLE. The results of biomarkers in the SLE and non-SLE groups were compared.

RESULTS

In the SLE group, compared to the non-SLE group, there were no significant differences in median maternal age, fetal NT, or serum PAPP-A MoM, but serum free β-hCG MoM was increased (1.402, IQR 0.872-2.290 vs 0.994, IQR 0.676-1.508).

CONCLUSION

In first trimester screening for trisomies, the measured value of free ß-hCG should be adjusted for maternal SLE to avoid false positive results and overuse of invasive tests.