Rh factor testing: Difference between revisions

Revision as of 06:35, 20 October 2020

Revision as of 17:21, 14 January 2021

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=== Invasive extraction ===

Non-invasive [[prenatal testing]] can be used if the mother is RhD-.<ref>{{cite journal | vauthors = Saramago P, Yang H, Llewellyn A, Walker R, Harden M, Palmer S, Griffin S, Simmonds M | title = High-throughput non-invasive prenatal testing for fetal rhesus D status in RhD-negative women not known to be sensitised to the RhD antigen: a systematic review and economic evaluation | journal = Health Technology Assessment | volume = 22 | issue = 13 | pages = 1–172 | date = March 2018 | pmid = 29580376 | pmc = 5890172 | doi = 10.3310/hta22130 }}</ref> However, in the case of maternal RhD status being negative, invasive prenatal testing may be used to determine the foetal RhD status instead. The two most common invasive methods of extracting foetal DNA are [[chorionic villus sampling]] (CVS) and [[amniocentesis]] (AMC).<ref>{{cite journal | vauthors = Carlson LM, Vora NL | title = Prenatal Diagnosis: Screening and Diagnostic Tools | journal = Obstetrics and Gynecology Clinics of North America | volume = 44 | issue = 2 | pages = 245–256 | date = June 2017 | pmid = 28499534 | pmc = 5548328 | doi = 10.1016/j.ogc.2017.02.004 }}</ref> These invasive procedures can be conducted on both RhD+ and RhD- mothers. After the invasive procedure, medications that prevent the Rh [[Immunization|immunisation]] are usually prescribed to RhD- mothers.<ref>{{Cite journal|last=Crowther|first=Caroline A.|last2=Middleton|first2=Philippa|last3=McBain|first3=Rosemary D.|editor1-first=Caroline A|editor1-last=Crowther|date=2013-02-28|title=Anti-D administration in pregnancy for preventing Rhesus alloimmunisation|journal=The Cochrane Database of Systematic Reviews|issue=2|pages=CD000020|doi=10.1002/14651858.CD000020.pub2|issn=1469-493X|pmid=23450526}}</ref>. This is done to avoid the production of maternal anti-D [[Antibody|antibodies]] which may attack the foetal blood cells should the foetus be Rh incompatible with the mother.<ref name="Mechanisms of anti-D action in the">{{cite journal | vauthors = Brinc D, Lazarus AH | title = Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn | journal = Hematology. American Society of Hematology. Education Program | volume = 2009 | pages = 185–91 | date = 2009 | pmid = 20008198 | doi = 10.1182/asheducation-2009.1.185 | url = https://semanticscholar.org/paper/d43570abd49c16a6e563c9a379074ff4b5024ec6 | doi-access = free }}</ref>

==== Chorionic villus sampling ====

[[Chorionic villus sampling]] is usually done between the 10th and 13th week of pregnancy, it samples [[chorionic villi]], which are tiny projections of [[Placenta|placental tissue]].<ref>{{Cite journal|last=Alfirevic|first=Zarko|last2=Navaratnam|first2=Kate|last3=Mujezinovic|first3=Faris|date=4 September 2017|title=Amniocentesis and chorionic villus sampling for prenatal diagnosis|journal=The Cochrane Database of Systematic Reviews|volume=9|pages=CD003252|doi=10.1002/14651858.CD003252.pub2|issn=1469-493X|pmc=6483702|pmid=28869276}}</ref>. As the placental tissues are derived from [[embryonic cell]]s, hence, it contains foetal genetic information that can be used to determine the child's RhD status.<ref>{{cite journal | vauthors = Kickler TS, Blakemore K, Shirey RS, Nicol S, Callan N, Ness PM, Escallon C, Dover G | title = Chorionic villus sampling for fetal Rh typing: clinical implications | journal = American Journal of Obstetrics and Gynecology | volume = 166 | issue = 5 | pages = 1407–11 | date = May 1992 | pmid = 1375812 | doi = 10.1016/0002-9378(92)91612-E }}</ref> There are two types of chorionic villus sampling. Trans-cervical sampling involves inserting a [[catheter]] through the [[cervix]] into the [[placenta]] to obtain villi, [[ultrasound]] is used to guide the catheter to the site of sampling.<ref name=":4" /> Trans-abdominal sampling requires the insertion of a needle through the [[abdomen]] and [[uterus]] to obtain placental tissue.<ref name=":4" /> [[Local anesthesia|Local anaesthesia]] can be applied to reduce pain from [[Minimally invasive procedure|invasive procedures]].<ref name=":4">{{Cite web|url=https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/chorionic-villus-sampling-cvs|title=Chorionic Villus Sampling (CVS)|website=Johns Hopkins Medicine Health Library|language=en|access-date=2019-04-08}}</ref>

==== Amniocentesis ====