BACKGROUND: Non-invasive methods to assess the foetal genome during pregnancy 
will provide new opportunities to offer pregnant women a more comprehensive 
genetic diagnosis of their established foetus. The aim of this study was to 
determine the presence and frequency of foetal cells in transcervical cell (TCC) 
mucus samples from pregnant women and determine their suitability for early 
prenatal diagnosis.
METHODS: Syncytiotrophoblasts in aspirated TCC mucus samples were identified by 
immunostaining with the foetal-specific antibody NDOG1. Genetic analysis of 
foetal cells was performed by laser capture microdissection and quantitative 
fluorescent PCR (QF-PCR).
RESULTS: In 116 of 207 (56%) TCC samples, abundant syncytiotrophoblasts were 
retrieved. However, when TCC samples were stratified for the presence of 
chorionic villous fragments, syncytiotrophoblasts were identified in 85 of 109 
(78%) samples. Significant numbers of syncytiotrophoblasts were found in TCC 
samples collected between 6 and 9weeks of gestation (mean 741, range 25-2884). 
QF-PCR analysis of NDOG1 positive syncytiotrophoblasts and matching maternal DNA 
confirmed their foetal origin and correct foetal cell sexing was achieved in 97% 
of TCC samples. The one discordant sex diagnosis was associated with a dizygotic 
dichorionic twin pregnancy resulting from the implantation of a female T21 
embryo and a normal male embryo, where the female T21 foetus had succumbed at 
6weeks of gestation and was vanishing.
CONCLUSIONS: Syncytiotrophoblasts can be successfully isolated from TCC samples 
and represent a suitable source of cells for genetic analysis of the established 
foetus in early pregnancy. The study highlights a vanishing twin as a potential 
cause for discordant non-invasive prenatal test results.