Cordiocentesis is done in which period of pregnancy?

Cordocentesis or percutaneous umbilical blood sampling(PUBS) A 22- gauge spinal needle, 13cm in length, is inseed through the maternal abdominal and uterine wall under real time ultrasound guidance using a curvilinear probe.the needle tip is progressed carefully and it punctates the umbilical vein approximately 1-2cm from the placental inseion. The advantages of preferring umbilical vein are1. Vein is larger in size2. Causes less bradycardia3. Less hemorrhage Generally, 0.5-2 ml of fetal blood is collected. It is performed under local anesthetic usually from 18 weeks of gestation. Uses of this procedure-1. Hematological- fetal anemia, bleeding disorder, Rh disease and hemoglobinopathies.2. Fetal infections- toxoplasmosis, viral infection3. Fetal blood gas and acid base status4. Fetal therapy- blood transfusion, drug therapy