Editing Pregnancy test (section)

=== False negative ===
[[Type I and type II errors|False negative]] readings can occur when testing is done too early. hCG levels rise rapidly in early pregnancy and the chances of false negative test results diminish with time (increasing [[Gestational age (obstetrics)|gestational age]]).<ref name="wilcox2">{{cite journal|vauthors=Wilcox AJ, Baird DD, [[Clarice Weinberg|Weinberg CR]]|year=1999|title=Time of implantation of the conceptus and loss of pregnancy|journal=New England Journal of Medicine|volume=340|issue=23|pages=1796–1799|doi=10.1056/NEJM199906103402304|pmid=10362823|doi-access=free}}</ref> Less sensitive urine tests and qualitative blood tests may not detect pregnancy until three or four days after implantation.<ref>{{cite journal|vauthors=Wilcox AJ, Baird DD, Weinberg CR|date=June 1999|title=Time of implantation of the conceptus and loss of pregnancy|journal=New England Journal of Medicine|volume=340|issue=23|pages=1796–9|doi=10.1056/NEJM199906103402304|pmid=10362823|doi-access=free}}</ref> [[Menstruation]] occurs on average 14 days after ovulation, so the likelihood of a false negative is low once a menstrual period is late. Ovulation may not occur at a predictable time in the [[menstrual cycle]]. A number of factors may cause an unexpectedly early or late ovulation, even for people with a history of regular menstrual cycles.<ref>{{Cite journal|last=Chard|first=T.|date=May 1992|title=Pregnancy tests: a review|journal=Human Reproduction (Oxford, England)|volume=7|issue=5|pages=701–710|doi=10.1093/oxfordjournals.humrep.a137722|issn=0268-1161|pmid=1639991}}</ref> Medical providers often struggle to 'rule out' pregnancy for medical testing or treatment that cannot be conducted during pregnancy before they can do an accurate urine pregnancy test.<ref>{{cite journal |last1=Brown |first1=Eliza |date=2020 |title=Projected diagnosis, anticipatory medicine, and uncertainty: How medical providers 'rule out' potential pregnancy in contraceptive counseling |journal=Social Science & Medicine |volume=258 |pages=113–118 |doi=10.1016/j.socscimed.2020.113118 |doi-access=free |pmid=32569949 }}</ref> 

More rare, false negative results can also occur due to a "[[hook effect]]", where a sample with a very high level of hCG is tested without dilution, causing an invalid result.<ref>{{Cite journal|last1=Griffey|first1=Richard T.|last2=Trent|first2=Caleb J.|last3=Bavolek|first3=Rebecca A.|last4=Keeperman|first4=Jacob B.|last5=Sampson|first5=Christopher|last6=Poirier|first6=Robert F.|date=January 2013|title="Hook-like effect" causes false-negative point-of-care urine pregnancy testing in emergency patients|journal=The Journal of Emergency Medicine|volume=44|issue=1|pages=155–160|doi=10.1016/j.jemermed.2011.05.032|issn=0736-4679|pmid=21835572|doi-access=free}}</ref>