(1010) Adequacy of chorionic villus samples in one- vs. two-pass procedures

Objective: At our center, when chorionic villus sampling (CVS) is performed, the initial pass sample adequacy is assessed immediately by an on-site cytogenetic lab. If the initial sample is inadequate, a second pass is done. Thus, a two-pass CVS procedure is a surrogate for specimen adequacy. CVS adequacy may be affected by body mass index (BMI), gestational age (GA), procedure route (transvaginal vs transabdominal), and provider experience. This study assesses risk factors for inadequate samples by comparing one-pass and two-pass CVS procedures.

Study Design: Retrospective cohort study of patients who underwent CVS at a single tertiary center in 2019-2023. Data was obtained via medical record review. Cases with an unknown number of placental entries were excluded. Comparisons were made between two groups: adequate villi (one-pass) and initially inadequate villi (two-pass). Factors compared were BMI, GA, genetic abnormality presence, placental location, route, needle size, and provider experience. Chi-square, Fisher’s test for categorical data, and Wilcoxon rank sum for continuous data were used for analysis.

Results: Of the 408 CVS procedures that met inclusion criteria, 84% were successful after one pass. Maternal BMI was significantly higher in the two-pass than in the one-pass group (27.9 and 25.4, respectively, P=0.02). There was no difference in GA, placental location, presence of genetic abnormalities, and number of fetuses (Table 1). Fellow years of experience was lower in the two-pass group (median 2.0 years, IQR 1.0-2.0) than the one-pass one (IQR 2.0-3.0). There was no difference across CVS route, needle size, or attending years of experience (Table 2).

Conclusion: Higher maternal BMI and fewer years of fellow experience were associated with a two-pass procedure, indicating sample inadequacy. Route of procedure, placental location, and genetic abnormalities were not associated with requiring a second pass. Rate of complications was low in both groups. This suggests that when on-site cytogenetics is unavailable, two-pass procedures should be considered for high maternal BMI and inexperienced operators.