OBJECTIVE: The objective of the study was to evaluate the performance of first trimester combined screening in cases of placental/fetal, mosaic or non-mosaic, autosomal trisomy other than trisomy 21, 18, or 13, and in cases of aneuploidy for a marker chromosome with focus on biochemical markers.

METHOD: We identified 66 cases in three large databases including 357 675 pregnancies from October 2003 to January 2014.

RESULTS: Seventy-seven percent of the 66 cases were screened positive at the combined first trimester screening (cFTS) for trisomy 21 or trisomy 18 or 13. The multiple of median (MoM) of Pregnancy Associated plasma protein A (PAPP-A) of the different aneuploidy groups ranged from 0.2 to 0.5 MoM, whereas the MoM of maternal serum free - β - human chorionic gonadotropin (FβhCG) was approximately 1.0 MoM. The exceptions being 0.2 MoM for cases involving chromosome 8 (n = 7) and 0.5 MoM for cases involving chromosome 9 (n = 3). The nuchal translucency MoM was approximately 1.0 MoM in all aneuploidy groups.

CONCLUSION: The cFTS program for trisomy 21, 18, and 13 is also sensitive to a broad range of rare chromosomal trisomies and chromosomal mosaicisms, primarily because of a strong detection capacity of PAPP-A MoM.