Fetal cell detection for chromosome analysis from leaking amniotic fluid in pregnancies with rupture of membranes

Objective: In this study, our goal was to assess the feasibility of using vaginally obtained amniotic fluid samples for prenatal chromosome analysis by fluorescence in situ hybridization (FISH) in pregnancies with ruptured amniotic membranes. Methods: Twenty-four pregnant women with known male fetal gender were retrieved for the study. All had ruptured membranes either artificially (AROM) or spontaneous (SROM) at term or at preterm gestations (PPROM). Samples from leaking amniotic fluid were collected during speculum examinations and slides were prepared for FISH using probes specific for chromosomes X and Y. Fetal cell detection rate was calculated as percentage of XY nuclei. Specimen volume, presence of mucus, presence of blood, gestational age, artificial versus spontaneous rupture of membranes and time elapsed until specimen processing were compared with regard to fetal cell detection rate. Results: There were 12 patients with AROM (50%) and 12 with SROM (50%). Only two of those were preterm (8.3%). Six of the specimens were bloody (25%) and 16 (66.6%) were macroscopically with mucous. The proportion of male fetuses identifiable by FISH was 100% (95% CI: 86%, 100%) after exclusion of technical failures (n=4). Overall, fetal cell detection rate was 6.4%. Samples collected after AROM had borderline higher percentage of fetal cells compared with SROM after adjusting for presence of blood in the sample (p=0.07). In addition, bloody samples had a significantly higher percentage of fetal cells than those that were not bloody (p=0.01). Conclusion: Amniotic fluid collection for prenatal chromosome analysis by interphase FISH is a feasible, non-invasive and reasonable approach on rupture of membranes patients and may be accomplished on preterm premature rupture of membranes with known male fetus pregnancies when indicated. Further studies are needed to assess the value of molecular analysis to differentiate fetal cells with higher specificity for female fetuses.