[Value and limits of transabdominal cytogenetic amniocenteses during the first trimester of pregnancy]

To assess the feasibility of amniotic fluid collection during the first trimester of pregnancy for caryotyping.

Echo-guided amniocenteses were performed prior to therapeutic abortions. Withdrawal of at least 5 ml of amniotic fluid for caryotyping was attempted.

55 amniocenteses were attempted in pregnancies between 8 to 12 weeks of gestation. Mean fluid sample was 8 +/- 4.7 ml, range 1-17. Less than 3 ml of amniotic fluid was obtained for cephalo-caudal lengths < 23 mm. At least 5 ml of amniotic fluid were collected in 68% of the pregnancies with a cephalo-caudal length of 23 to 35 mm and in 100% of those with a cephalo-caudal length > 35 mm. There was a correlation between cephalo-caudal length and volume of amniotic fluid sampled (r = 0.72, 95% CI: 0.56-0.83; p < 0.0001). Fourteen of the 45 samples cultured led to satisfactory carytotypes. No caryotypes could be obtained for embryos with a cephalo-caudal length < 27 mm, while the rate of success was 100% in those > 45 mm. Cephalo-caudal lengths were different in cases with successful and unsuccessful caryotypes (p < 0.001).

This preliminary study indicates that it is difficult to obtain adequate amniotic fluid sample when the cephalo-caudal length is < or = 35 mm. A caryotype could be obtained in only 31% of these cases. Success rate was proportional to gestational age. Based on these findings and a review of the literature, it appears difficult to obtain a fetal caryotype by amniocentesis or choriocentesis before 10 weeks gestation.