Maternal cell contamination of amniotic fluid samples obtained by open needle versus trocar technique of amniocentesis.

Objective: To determine the incidence of maternal cell contamination (MCC) in the open-needle amniocentesis sampling technique compared with the trocar-in-place technique.
Methods: A retrospective analysis was conducted on 2,498 mid-trimester amniocenteses performed in two tertiary care centres in Canada. The University of Alberta centre used the open-needle (without the trocar) technique and the University of British Columbia centre used the standard (with the trocar in place) technique. Data were gathered regarding the nature of the amniotic fluid, number of needle passes, amniocentesis results, and the occurrence of maternal cell contamination. The statistical analysis used logistic regression, and controlled for the potential confounders of bloody fluid taps and requirement for more than one needle insertion.
Results: The incidence of maternal cell contamination was 1.16% with the open-needle technique and 0.78% with the standard trocar-in-place technique (p < 0.315), with a power of 42%.
Conclusion: The data suggested there is no significant increase in maternal cell contamination with the open-needle versus trocar-in-place techniques of amniocentesis. However, the small sample size, combined with the low prevalence of the outcome of interest (MCC), provides insufficient power to draw firm conclusions about the difference in MCC between the two techniques.