Amniocentesis is performed after week 16 of gestation (usually between weeks 16 and 19), when the lab and/or ultrasound findings render further testing necessary, always taking into account the age of the mother and her medical history. A fine needle is inserted transabdominally under continuous ultrasound guidance, and a small quantity of amniotic fluid is aspired and studied in the lab. The rapid analysis results (QF-PCR) for the main chromosomes (T21, T18, T13, sex chromosomes) are available in 2 working days, while the karyotype and molecular karyotype results are available in 10 working days. The accuracy of the results is close to 99.9%. Amniocentesis is performed only if there are indications, as the risk of miscarriage is 0.1% in the general population.