Evaluation of amniotic fluid cell filtration: an experimental approach to early amniocentesis

Early amniocentesis with the filtration technique: neonatal outcome in 123 singleton pregnancies

OBJECTIVE

To evaluate results of a prospective study of pregnancies in which early amniocentesis with the filtration technique was performed at 10-13 weeks' gestation (mean 12.3 weeks' gestation).

METHODS

123 singleton pregnancies in which early amniocentesis with the modified filtration technique was performed at 10-13 weeks' gestation (mean 12.3 weeks' gestation). The amniotic fluid was aspirated into the syringe and reinjected through the filter.

RESULTS

All the procedures were performed successfully by a single needle insertion. Neither dry taps nor filtration failures occurred. The mean time of amniocentesis was 4.02 min (95% confidence interval, 3 min and 36 s to 4 min and 18 s). The karyotyping success rate was 99.2%. Temporary amniotic fluid leakage occurred in three women (2.4%). There were 110 (89.4%) live births. Two cases of stillbirth occurred at week 38 and week 40. Two unintended losses occurred within three weeks after sampling (1.62%). Another additional unintended fetal death was notified at the 20-week screening ultrasonography. The total fetal-loss rate was 10.6%. In one case, talipes equinovarus was detected at the 20-week screening ultrasound study.

CONCLUSIONS

Further studies are needed to determine the risk of amniotic leakage and its relation to duration of the procedure in patients undergoing early amnifiltration.

First trimester amnifiltration: technical, cytogenetic and pregnancy outcome of 104 consecutive procedures

OBJECTIVE

To investigate the technical, cytogenetic and pregnancy complications of first trimester amnifiltration for the diagnosis of fetal karyotype.

DESIGN

Observational study.

SETTING

The fetal medicine unit, UMDS St Thomas' Campus, London.

SUBJECTS

One hundred and four women seeking prenatal diagnosis of fetal karyotype.

MAIN OUTCOME MEASURES

Sampling success, culture rate, harvest time and karyotype, pregnancy outcome and complications.

RESULTS

Sampling was successful in all 104 cases, but equipment failure forced the procedure to be changed to early amniocentesis in eight (7%) cases. The karyotype was normal in 101 (97%) cases, abnormal in three. The mean harvest time was 14 days (range 9-26 days; SD = 3.4), and three cultures failed (2.8%). Pregnancies resulted in 99 (95%) live births, with a mean gestation of 277 days (range 182-300 days; SD = 16). There was one termination for trisomy 21 and four spontaneous miscarriages (3.8%). Amniotic fluid leakage occurred in six cases (5%), all resulted in live births, five at term and one at 35 weeks.

CONCLUSIONS

This study demonstrates that amnifiltration is technically possible in the first trimester of pregnancy, and that samples can be successfully karyotyped. The harvest time for culture is similar to early amniocentesis and chorion villus sampling. The rate of fetal loss, adjusted by the estimated natural loss, is 1.7%, which compares favourably with both chorionic villus sampling and early amniocentesis.

Experience with early amniocentesis

Literature concerning early genetic amniocentesis, obtained before 14-15 weeks of gestation, has been examined and compared. Key figures of post-procedural spontaneous fetal losses have been compared as well as cytogenetic data from the published series. Cytogenetically more samples fail to grow in the early weeks, but the diagnostic accuracy seems to be comparable with that of amniocentesis obtained in the later weeks. A sampling method, improving the cell yield by means of filtration, has been developed in order to lower the risk of culture failure and reduce the reporting time in the gestational weeks 11 to 13. The filter technique is under evaluation in a randomized trial. Detection of neural tube defects with early amniotic fluid sampling is possible, but whether the detection rate is comparable to that of standard amniocentesis remains to be seen. Although the safety of early amniocentesis has not yet been evaluated in a randomised study, data from almost 5,000 cases suggest that the procedure related loss rate is approximately 1%, and thus the same as for standard amniocentesis and chorionic villus sampling.