FACTORS ASSOCIATED WITH MATERNAL CELL CONTAMINATION IN AMNIOCENTESIS SAMPLES AS EVALUATED BY FLUORESCENT IN-SITU HYBRIDIZATION

Objective: To determine which patient- and procedure-related factors c ontribute to maternal cell contamination in uncultured amniocentesis f luid. Methods: One hundred thirty amniotic fluid (AF) samples were obt ained by three operator groups: maternal-fetal medicine faculty (n = 5 0), general obstetrician gynecologists (n = 50), and obstetrics and gy necology residents supervised by maternal-fetal medicine faculty (n = 30). These groups were designated ''most,'' ''intermediate,'' and ''le ast experience,'' respectively. Study variables were recorded at the t ime of the procedure. Amniotic fluid cells from male fetuses underwent fluorescent in situ hybridization. Maternal cell contamination was ca lculated by analyzing 100 cells and determining the number of XX and X Y cells. A control system was created to validate the methods used for AF processing and cell counting. Results: Median maternal cell contam ination was 2.0%. Maternal cell contamination did not vary with body m ass index (r = -.13, P = .14), gestational age (r = .08, P = .35), or placental location (P = .55). Maternal cell contamination was signific antly elevated with placental penetration (6.0% compared with 1.0%, P < .001), two passes (27.5% compared with 2.0%, P = .002), blood-tinged fluid color (14.0% compared with 2.0%, P < .001), and operator inexpe rience (''intermediate experience'' compared with ''most experience,'' 4.5% compared with 1.0%, P = .026). Maternal cell contamination did n ot differ between the ''most experience'' and ''least experience'' gro ups (1.0% compared with 2.0%, not significant). Concordance between de tected and actual maternal cell contamination in the control system wa s extremely high (concordance coefficient = 0.98, P = .008), confirmin g the validity of the techniques used. Conclusion: Our techniques of c ell counting and maternal cell contamination calculation are accurate. Maternal cell contamination is increased with placental penetration, two passes, and operator inexperience. However, with expert supervisio n, inexperienced physicians can perform amniocentesis without an incre ase in maternal cell contamination. (Obstet Gynecol 1998;92:551-6. (C) 1998 by The American College of Obstetricians and Gynecologists.).