A study of early amniocentesis for prenatal cytogenetic diagnosis

First trimester prenatal diagnosis: amniocentesis

Twenty years after midtrimester genetic amniocentesis was first used, first trimester invasive prenatal procedures were introduced. Chorionic villous sampling presents some disadvantages that entitled many centers to look into an alternative for first trimester diagnosis. Early amniocentesis (EA) can be performed effectively, as shown over the years in many observational studies and partially randomized and randomized trials. Recently, a multicenter randomized trial (Canadian Early and Midtrimester Amniocentesis Trial) reported a higher total pregnancy loss, a significant increased incidence of musculoskeletal foot deformities, a significant increased culture failure rate, and an increased postamniocentesis rate of leakage in the EA group compared with midtrimester amniocentesis. These results concerning EA procedures from 11w(+0) to 12w(+6) should be included in any pre-EA counseling. However, further trials have started to evaluate EA procedures between 13w(+0) to 14w(+6).

Early pregnancy prenatal diagnostic testing: risks associated with chorionic villus sampling and early amniocentesis and screening options

Routine amniocentesis is an established test for the prenatal diagnosis of chromosome abnormalities and many single-gene conditions. Chorionic villus sampling and early amniocentesis, which are available in some centers, enable families to receive prenatal test results earlier in the pregnancy. There are concerns regarding the safety of early pregnancy testing because of increased risks for pregnancy loss and possible risks for birth defects. The use of first trimester testing has changed because of these concerns, and alternative methods of screening pregnancies at risk for a chromosome abnormality are being investigated.

Cytogenetic aspects of the Canadian early and mid-trimester amniotic fluid trial (CEMAT)

Cytogenetic results from a large multicentre randomized controlled study of 2108 amniotic fluids obtained at 11+0-12+6 weeks (EA) and 1999 fluids at 15+0-16+6 weeks (MA) were compared. There was no statistically significant difference in the rate of chromosome abnormalities (EA =1.9 per cent; MA=1.7 per cent) or level III mosaicism (EA=0.2 per cent; MA= 0.2 per cent) between the groups. Level I and Level II mosaicism occurred more frequently in MA. Maternal cell contamination was not significantly different between the groups, but maternal cells only were analysed from one bloody EA fluid. The number of repeat amniocenteses because of cytogenetic problems was 2.2 per cent in the EA group compared with only 0.3 per cent in the MA group. On average, culture of EA fluids required one day more than MA fluids. Although both culture success (97.7 per cent) and accuracy (99.8 per cent) were high for patients randomized to the EA group, routine amniocentesis prior to 13 weeks' gestation is not recommended for clinical reasons including an increased risk of fetal loss and talipes equinovarus.