Early genetic amniocentesis--4 years' experience

Four hundred and thirty early amniocenteses (EAC) from 10 to 14 weeks' gestation were compared with 300 routine amniocenteses (RAC) from 15 weeks' gestation (control A) and 733 routine amniocenteses from 16 to 18 weeks' gestation (control B) with regard to success rates, various growth parameters, and cytogenetic results. Using both in situ and trypsinization techniques, the success rate was 99.8 per cent for EAC versus 100 per cent for RAC. The average turn-around time for establishing a diagnosis was 8.4 days in EAC versus 8.3 days in 15 weeks' specimens (n.s.) and 7.7 days in 16 to 18 weeks' specimens (p < 0.0001) for the last 200 samples. The banding quality of early specimens compared favourably with that of controls (both 500-550 bphs) and was much better than that in long-term cultured chorionic villus sampling (CVS) (350-400 bphs). For level I and level II mosaicism, no statistically significant differences were noted between EAC and control group A. Comparing EAC with control group B, a significant increase in the number of numerical and structural single cell aberrations was observed (p < 0.025 and p << 0.001, respectively), whereas for multiple cell aberrations only the increase in numerical aberrations was statistically significant (p << 0.001) (chi 2-test). Clinical problems arising from the detection of mosaicism were solved in all cases by investigating parallel cultures. It is concluded that early amniocentesis is a reliable procedure which permits prenatal diagnosis of numerical and structural chromosome aberrations to a high standard.