To evaluate the presence of chromosomal abnormalities when CVS results are ambiguous. To detect the presence of infectious disease such as toxoplasmosis , rubella , or cytomegalovirus in the foetus, so that it can be treated. To perform a blood count and check for anaemia or low platelet levels in the foetus. If this procedure is carried out in the third trimester an overnight fast may be required in case an emergency caesarean delivery is required. Guided by an ultrasound image, the doctor introduces a long, thin needle through the abdomen and uterus into the umbilical cord.
Foetal heartbeat is monitored during the procedure.
The blood is then analysed for the same conditions as in CVs and may be checked for the presence of antibodies. The Yale University School of Medicine Patient's Guide to Medical Tests, Barry L. Zaret M.D., Senior Editor, published by Houghton Mifflin.