Maternal Cell Contamination:
The presence of maternal cells in uncultured amniotic fluid may result in an error in the interpretation of prenatal tests such as direct DNA analysis and rapid aneuploidy detection by fluorescence in situ hybridisation (FISH). The presence of maternal cells was correlated with the amount of blood present in the amniotic fluid as defined by visual examination of the cell pellet after centrifugation.
The overall rate of maternal cell in uncultured amniotic fluid as identified using X and Y‐specific probes was 21·4 per cent, compared with 0·2 per cent in the cultured fluid. Microarray-based comparative genomic hybridization results may be occasionally achieved without maternal cell studies.
Impact on Maternal Cell:
The array and software design allowed detection of larger copy-number variations at higher levels of the maternal cell than smaller copy-number variations. The smallest duplications and deletions were obscured at 22–31% and 55–58% maternal cell contamination, respectively.
As knowledge of the maternal cell level aids in interpretation of array results, we recommend concurrent, independent maternal cell contamination studies for all fetal samples for accurate and timely results.
When MCC is encountered in traditional cytogenetic analysis, it is usually at low levels and seldom interferes with accurate determination of the fetal karyotype. Thus, MCC testing has rarely been performed on samples undergoing standard cytogenetic analysis.