Pure fetal blood samples obtained by cordocentesis: technical aspects of 322 cases.

Three hundred and twenty-two percutaneous umbilical blood samplings were performed over 4 years in our prenatal diagnostic centre. A 3.5 MHz sector ultrasound transducer was used to guide a 22.5-gauge needle under local anaesthesia. Sampling was performed for rapid fetal karyotyping (within 72 h) in 120 cases, for diagnosis of fetal toxoplasmosis in 133 cases, for determination of the severity of Rh immunization in 15 cases, and for diagnosis of congenital rubella in 4 cases. Pure fetal blood was obtained in 98.7 per cent of the cases after two attempts. The approach to the cord was either transamniotic or transplacental. Puncturing was preferentially done at the placental insertion of the cord (72.2 per cent of the cases) and the mean blood sample volume was 3.5 ml. The rate of fetal death in utero was 1.9 per cent, including two cases of amnionitis, one trisomy 18, and one severe bradycardia. The failures were due to sampling at an early stage of pregnancy (before gestation week 18), to maternal obesity, oligohydramnios, and the inexperience of the operator.