Editing Pregnancy test (section)

=== Human chorionic gonadotropin (hCG) ===
[[File:How hCG Is Used To Indicate a Positive Pregnancy Test.svg|thumb|This image depicts how the hormone hCG, produced by pregnant people's placentas, is detected in urine pregnancy tests to indicate a positive result.]]

Identified in the early 20th century, [[human chorionic gonadotropin]] (hCG) is a [[Glycoprotein hormones, alpha polypeptide|glycoprotein hormone]] that rises quickly in the first few weeks of pregnancy, typically reaching a peak at 8- to 10-weeks [[Gestational age (obstetrics)|gestational age]].<ref name=":122">{{Cite journal|last=Cole|first=Laurence A|date=2010|title=Biological functions of hCG and hCG-related molecules|journal=Reproductive Biology and Endocrinology|language=en|volume=8|issue=1|page=102|doi=10.1186/1477-7827-8-102|issn=1477-7827|pmc=2936313|pmid=20735820 |doi-access=free }}</ref><ref name="ReferenceA">{{Cite journal|last1=Braunstein|first1=G. D.|last2=Rasor|first2=J.|last3=Danzer|first3=H.|last4=Adler|first4=D.|last5=Wade|first5=M. E.|date=15 November 1976|title=Serum human chorionic gonadotropin levels throughout normal pregnancy|journal=American Journal of Obstetrics and Gynecology|volume=126|issue=6|pages=678–681|doi=10.1016/0002-9378(76)90518-4|issn=0002-9378|pmid=984142}}</ref> hCG is produced by what will become the [[placenta]].<ref>{{Cite book|title=Medical physiology: principles for clinical medicine|date=2009|publisher=Lippincott Williams & Wilkins|editor-last1=Rhoades|editor-first1=Rodney|editor-last2=Bell|editor-first2=David R.|isbn=978-0-7817-6852-8|edition=3rd|location=Philadelphia|oclc=144771424}}</ref> hCG testing can be performed with a blood ([[Serum (blood)|serum]]) sample (typically done in a medical facility) or with urine (which can be performed in a medical facility or at home). The assays used to detect the presence of hCG in blood or urine are generally reliable and inexpensive. Secretion of hCG can occur as soon as 6 days following ovulation and on average 8–10 days following ovulation; this is the earliest hCG can be detected in a blood sample.<ref>{{Cite journal|last1=Wilcox|first1=A. J.|last2=Baird|first2=D. D.|last3=Weinberg|first3=C. R.|author3-link=Clarice Weinberg|date=10 June 1999|title=Time of implantation of the conceptus and loss of pregnancy|journal=The New England Journal of Medicine|volume=340|issue=23|pages=1796–1799|doi=10.1056/NEJM199906103402304|issn=0028-4793|pmid=10362823|doi-access=free}}</ref><ref name="ReferenceA"/><ref>{{Cite journal|last1=Lenton|first1=E. A.|last2=Neal|first2=L. M.|last3=Sulaiman|first3=R.|date=June 1982|title=Plasma concentrations of human chorionic gonadotropin from the time of implantation until the second week of pregnancy|journal=Fertility and Sterility|volume=37|issue=6|pages=773–778|doi=10.1016/s0015-0282(16)46337-5|issn=0015-0282|pmid=7115557|doi-access=free}}</ref>  The hCG concentration in blood is higher than in urine. Therefore, a blood test can be positive while the urine test is still negative.<ref>{{Cite journal|last1=O'Connor|first1=R. E.|last2=Bibro|first2=C. M.|last3=Pegg|first3=P. J.|last4=Bouzoukis|first4=J. K.|date=July 1993|title=The comparative sensitivity and specificity of serum and urine HCG determinations in the ED|journal=The American Journal of Emergency Medicine|volume=11|issue=4|pages=434–436|doi=10.1016/0735-6757(93)90186-f|issn=0735-6757|pmid=8216535}}</ref><ref>{{Cite journal|last1=Davies|first1=Suzy|last2=Byrn|first2=Francis|last3=Cole|first3=Laurence A.|date=June 2003|title=Human chorionic gonadotropin testing for early pregnancy viability and complications|journal=Clinics in Laboratory Medicine|volume=23|issue=2|pages=257–264, vii|doi=10.1016/s0272-2712(03)00026-x|issn=0272-2712|pmid=12848444}}</ref>

Qualitative tests (yes/no or positive/negative results) look for the presence of the [[beta subunit of human chorionic gonadotropin]] in blood or urine. For a qualitative test the thresholds for a positive test are generally determined by an hCG cut-off where at least 95% of pregnant people would get a positive result on the day of their first missed period.<ref name=":322">{{Cite book|title=Handbook of clinical laboratory testing during pregnancy|date=2004|publisher=Humana Press|editor-last=Gronowski|editor-first=Ann M.|isbn=1-58829-270-3|location=Totowa, N.J.|oclc=53325293}}</ref> Qualitative urine pregnancy tests vary in sensitivity. High-sensitivity tests are more common and typically detect hCG levels between 20 and 50 milli-international units/mL (mIU/mL). Low-sensitivity tests detect hCG levels between 1500 and 2000&nbsp;mIU/mL and have unique clinical applications, including confirmation of medication abortion success.<ref>{{Cite journal|last1=Raymond|first1=Elizabeth G.|last2=Shochet|first2=Tara|last3=Bracken|first3=Hillary|date=July 2018|title=Low-sensitivity urine pregnancy testing to assess medical abortion outcome: A systematic review|journal=Contraception|volume=98|issue=1|pages=30–35|doi=10.1016/j.contraception.2018.03.013|pmid=29534996|s2cid=206967147|issn=0010-7824}}</ref> Qualitative urine tests available for home use are typically designed as [[lateral flow test]]s.

Quantitative tests measure the exact amount of hCG in the sample. Blood tests can detect hCG levels as low as 1&nbsp;mIU/mL, and typically clinicians will diagnose a positive pregnancy test at 5mIU/mL.<ref name=":322" />
{| class="wikitable"
|+Table 1. Human chorionic gonadotropin (hCG) detection thresholds by test type and sample type
!
!Urine pregnancy test
!Blood pregnancy test
|-
|Detection thresholds
|'''High-sensitivity:'''
Qualitative test: 20 to 50 mIU/mL, depending on test

'''Low-sensitivity:'''

Qualitative test: 1500-2000 mIU/mL, depending on test
|'''Qualitative test:'''
5 to 10 mIU/mL, depending on test

'''Quantitative test:'''

1 to 2 mIU/mL for an ultrasensitive test
|}
There is a multilevel urine pregnancy test (MLPT) that measures hCG levels semiquantitatively. The hCG levels are measured at <25, 25 to 99, 100 to 499, 500 to 1999, 2000 to 9999, and >10,000 mIU/mL. This test has utility for determining the success of medication abortion.<ref>{{Cite journal|last1=Raymond|first1=Elizabeth G.|last2=Shochet|first2=Tara|last3=Blum|first3=Jennifer|last4=Sheldon|first4=Wendy R.|last5=Platais|first5=Ingrida|last6=Bracken|first6=Hillary|last7=Dabash|first7=Rasha|last8=Weaver|first8=Mark A.|last9=Ngoc|first9=Nguyen Thi Nhu|last10=Blumenthal|first10=Paul D.|last11=Winikoff|first11=Beverly|date=May 2017|title=Serial multilevel urine pregnancy testing to assess medical abortion outcome: a meta-analysis|journal=Contraception|volume=95|issue=5|pages=442–448|doi=10.1016/j.contraception.2016.12.004|pmid=28041991|issn=0010-7824}}</ref><ref>{{Cite journal|last1=Lynd|first1=Kelsey|last2=Blum|first2=Jennifer|last3=Ngoc|first3=Nguyen Thi Nhu|last4=Shochet|first4=Tara|last5=Blumenthal|first5=Paul D.|last6=Winikoff|first6=Beverly|date=2013|title=Simplified medical abortion using a semi-quantitative pregnancy test for home-based follow-up|journal=International Journal of Gynecology & Obstetrics|language=en|volume=121|issue=2|pages=144–148|doi=10.1016/j.ijgo.2012.11.022|pmid=23477704|issn=1879-3479|doi-access=free}}</ref>
[[File:Pregnancy ultrasound 110302111147 1123360.jpg|thumb|Single intrauterine pregnancy, first trimester. The gestational sac is pictured (black-appearing on ultrasound) containing a fetal pole and yolk sac (circular structure beneath fetal pole.)]]