Fetal cells in cervical mucus in the first trimester of pregnancy.

Objectives: The aim of this study was to first evaluate the presence of fetal cells in cervical mucus samples collected in the first trimester of pregnancy and then to compare different laboratory methods for the detection of these cells.

Methods: Mucus samples were collected by using a cytobrush before termination of pregnancy (TOP) from 143 pregnant women between 7 and 12 weeks of gestation. None of the women had undergone an invasive diagnostic procedure prior to cervical mucus sampling. Samples of placental tissue were collected from each patient at TOP. Slides from each sample were first observed under an inverted microscope to detect possible sperm contamination. In the first part of our experiments, 40 mucus samples were treated with a mucolytic solution containing N-acetylcysteine (AC) and were analysed by a polymerase chain reaction (PCR) assay. The second series, consisting of 71 mucus samples, was treated with a mucolytic solution containing dithiothreitol (DTT): all 71 samples were analysed by a PCR-based assay, and an aliquot for fluorescent in situ hybridisation (FISH) analysis was also obtained from 48 out of 71 samples. In the third part of our experiments, performed on 32 mucus samples, mucus trapped on the cytobrush was directly spread on two slides for FISH analysis without any mucolytic treatment. All placental tissue samples obtained at termination were analysed by FISH for fetal sexing.

Results: Overall, the use of PCR-based or FISH analyses on 143 mucus samples resulted in correct sex prediction in 92/143 (64.3%) samples [20/66 (30.3%) cases from known male pregnancies and 72/77 (93.5%) cases from known female pregnancies]. In the AC group, Y-derived sequences were found in 7/23 samples (30.4%) from known male pregnancies and in 1/17 cases from known female pregnancies, with an overall correct sex prediction in 23/40 cases (57.5%). In the DTT group, Y-derived sequences could be amplified in 10/30 samples (33.3%) from known male pregnancies and in 4/41 cases from known female pregnancies, with an overall correct sex prediction in 47/71 cases (66.2%). In the DTT samples analysed by FISH, nuclei bearing XY signals were detected in 5/26 (19.2%) cases from known male pregnancies and in none from female pregnancies, the rate of correct sex prediction being 56.2% (27/48). On untreated mucus samples analysed by FISH, nuclei with XY signals were documented in 3/13 (23%) samples from male conceptuses and in none from known female pregnancies, with an overall correct sex prediction in 22/32 cases (68.7%).

Conclusion: Fetal cells were not detected in a constant and reliable fashion in cervical mucus samples collected in the first trimester of pregnancy. The detection rate was poorly influenced by the use of different laboratory methods. This sampling technique cannot be regarded as a promising tool towards minimally invasive prenatal diagnosis.