[[Amniocentesis]] is another invasive procedure which can be used to collect foetal DNA samples.{{medical citation needed|reason=WP:healthlinedotcom|date=July 2023}} This procedure is usually done between the 15th week to 20th week of [[pregnancy]].<ref name=":3">{{Cite web|url=https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=92&contentid=p07762|title=Amniocentesis - Health Encyclopedia - University of Rochester Medical Center|website=www.urmc.rochester.edu|access-date=2019-04-08}}</ref> The purpose of AMC is to extract a small amount of [[amniotic fluid]] as foetal cells may be shed from the foetus and are suspended in the amniotic fluid.<ref name=":3" /> The foetal genome can be found in these cells. Therefore, extracting amniotic fluid can the required foetal genetic material for the genotyping of the RhD gene.<ref>{{cite journal | vauthors = Cotorruelo C, Biondi C, García Borrás S, Di Mónaco R, Martino W, Racca A | title = [Rh system genotyping in amniotic fluid] | journal = Medicina | volume = 61 | issue = 1 | pages = 76–8 | date = 2001 | pmid = 11265629 }}</ref> Before amniocentesis commences, the doctor will inject local anaesthetics to the mother's abdomen.<ref name=":3" /> The doctor will then apply ultrasound to locate the foetus in the uterus.<ref name=":3" /> Under the guidance of the [[ultrasound imaging]], a long, thin, hollow needle will insert through the skin of the abdomen to the uterus of the mother.<ref name=":3" /> The needle is used to withdraw a trace amount of amniotic fluid.<ref name=":3" /> It will then be removed from the maternal body and the amniotic fluid extracted will be sent to the laboratory for further testing.
