Karyotype Analysis of Amniotic Fluid
10mL amniotic fluid was obtained and cultured at 37℃ with amniotic fluid culture medium (Guangzhou Baiyunshan Baidi Biotechnolgy). Before harvesting, 120 μL colchicine (working concentration 50 μg/mL) was added and incubated for 25 min at 37℃. After that, 2 mL pancreatin (Gibco) was added to stop digestion. Unlike peripheral blood, 6 mL of 1% sodium citrate solution was used for hypotonic treatment before 1 mL fixed solution (methanol : glacial acetic acid = 3 : 1) was added for fixation. Total 50 GTG-banded metaphase chromosomes were analyzed. For samples with abnormal chromosomes, a total of 100 metaphases were analyzed.