Editing Miscarriage (section)

==Risk factors==
{{Further|List of miscarriage risks}}
Miscarriage may occur for many reasons, not all of which can be identified. [[Risk factor (epidemiology)|Risk factor]]s are those things that increase the likelihood of having a miscarriage but do not necessarily cause a miscarriage. Up to 70 conditions,<ref name="John20122" /><ref name="Vai2015"/>{{sfn|Hoffman|page=181–182}}<ref name="auto7">{{cite journal | vauthors = Ali O, Hakimi I, Chanana A, Habib MA, Guelzim K, Kouach J, Rahali DM, Dehayeni M | title = [Term pegnancy on septate uterus: report of a case and review of the literature] | journal = The Pan African Medical Journal | volume = 22 | pages = 219 | date = 2015 | pmid = 26955410 | pmc = 4760728 | doi = 10.11604/pamj.2015.22.219.7790 }}</ref><ref name="TersigniCastellani2014">{{cite journal | vauthors = Tersigni C, Castellani R, de Waure C, Fattorossi A, De Spirito M, Gasbarrini A, Scambia G, Di Simone N | title = Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms | journal = Human Reproduction Update | volume = 20 | issue = 4 | pages = 582–93 | year = 2014 | pmid = 24619876 | doi = 10.1093/humupd/dmu007 | doi-access = free | hdl = 10807/56796 | hdl-access = free }}</ref>{{sfn|Hoffman|page = 172}} infections,<ref name="NHS-Miscarriage-Causes">{{cite web |url=https://www.nhs.uk/conditions/miscarriage/causes/ |title=Miscarriage – Causes |author=<!--No author name given.--> |website=NHS |date=March 9, 2022 |url-status=live |archive-url=https://web.archive.org/web/20230705060654/https://www.nhs.uk/conditions/miscarriage/causes/ |archive-date=July 5, 2023}}</ref><ref name="American College of Obstetricians and 372–9">{{cite journal | title = ACOG Practice Bulletin No.142: Cerclage for the management of cervical insufficiency | journal = Obstetrics and Gynecology | volume = 123 | issue = 2 Pt 1 | pages = 372–9 | date = February 2014 | pmid = 24451674 | doi = 10.1097/01.AOG.0000443276.68274.cc | author1 = American College of Obstetricians Gynecologists | s2cid = 205384229 }}</ref><ref name="LisRowhani-Rahbar2015">{{cite journal | vauthors = Lis R, Rowhani-Rahbar A, Manhart LE | title = Mycoplasma genitalium infection and female reproductive tract disease: a meta-analysis | journal = Clinical Infectious Diseases | volume = 61 | issue = 3 | pages = 418–26 | date = August 2015 | pmid = 25900174 | doi = 10.1093/cid/civ312 | doi-access = free | hdl = 1773/26479 | hdl-access = free }}</ref> medical procedures,<ref name="Tabor-Alfirevic-2010">{{cite journal | vauthors = Tabor A, Alfirevic Z | title = Update on procedure-related risks for prenatal diagnosis techniques | journal = Fetal Diagnosis and Therapy | volume = 27 | issue = 1 | pages = 1–7 | year = 2010 | pmid = 20051662 | doi = 10.1159/000271995 | doi-access = free }}</ref><ref name="Agarwal-Alfirevic-2012">{{cite journal | vauthors = Agarwal K, Alfirevic Z | title = Pregnancy loss after chorionic villus sampling and genetic amniocentesis in twin pregnancies: a systematic review | journal = Ultrasound in Obstetrics & Gynecology | volume = 40 | issue = 2 | pages = 128–34 | date = August 2012 | pmid = 22125091 | doi = 10.1002/uog.10152 | s2cid = 23379631 }}</ref><ref name="Alfirevic">{{cite journal | vauthors = Alfirevic Z, Navaratnam K, Mujezinovic F | title = Amniocentesis and chorionic villus sampling for prenatal diagnosis | journal = The Cochrane Database of Systematic Reviews | volume = 2017 | pages = CD003252 | date = September 2017 | issue = 9 | pmid = 28869276 | pmc = 6483702 | doi = 10.1002/14651858.cd003252.pub2 | publisher = John Wiley & Sons, Ltd | df = mdy-all }}</ref> lifestyle factors,<ref name="NIH2013Epi2" /><ref name="Ol2014"/><ref name="x">{{cite journal | vauthors = Ness RB, Grisso JA, Hirschinger N, Markovic N, Shaw LM, Day NL, Kline J | title = Cocaine and tobacco use and the risk of spontaneous abortion | journal = The New England Journal of Medicine | volume = 340 | issue = 5 | pages = 333–9 | date = February 1999 | pmid = 9929522 | doi = 10.1056/NEJM199902043400501 | doi-access = free }}</ref><ref name="NHS-Miscarriage-Causes"/><ref name="paternal smoking">{{cite journal | vauthors = Venners SA, Wang X, Chen C, Wang L, Chen D, Guang W, Huang A, Ryan L, O'Connor J, Lasley B, Overstreet J, Wilcox A, Xu X | title = Paternal smoking and pregnancy loss: a prospective study using a biomarker of pregnancy | journal = American Journal of Epidemiology | volume = 159 | issue = 10 | pages = 993–1001 | date = May 2004 | pmid = 15128612 | doi = 10.1093/aje/kwh128 | doi-access = free }}</ref> occupational exposures,<ref name="NIH2013Pre"/>{{sfn|Hoffman|page=173}}{{sfn|Hoffman|page=272}} chemical exposure,{{sfn|Hoffman|page=272}} and shift work are associated with increased risk for miscarriage.<ref name=chav>{{cite journal | vauthors = Chavarro JE, Rich-Edwards JW, Gaskins AJ, Farland LV, Terry KL, Zhang C, Missmer SA | title = Contributions of the Nurses' Health Studies to Reproductive Health Research | journal = American Journal of Public Health | volume = 106 | issue = 9 | pages = 1669–76 | date = September 2016 | pmid = 27459445 | pmc = 4981818 | doi = 10.2105/AJPH.2016.303350 }}(review)</ref> Some of these risks include [[endocrine system|endocrine]], [[genetics|genetic]], [[uterus|uterine]], or [[hormone|hormonal abnormalities]], [[reproductive tract infection]]s, and [[tissue rejection]] caused by an [[autoimmune disorder]].<ref>{{cite journal | vauthors = Acién P, Acién M | title = The presentation and management of complex female genital malformations | journal = Human Reproduction Update | volume = 22 | issue = 1 | pages = 48–69 | date = 2016-01-01 | pmid = 26537987 | doi = 10.1093/humupd/dmv048 | doi-access = free }}</ref>

=== Trimesters ===

====First trimester====
{| class="wikitable" style = "float: right; margin-left:15px; text-align:center"
|+ Chromosomal abnormalities found in first trimester miscarriages
! Description
! Proportion of total
|-
| [[XY sex-determination system|Normal]]
| 45–55%
|-
| [[Trisomy|Autosomal trisomy]]
| 22–32%
|-
| [[Turner syndrome|Monosomy X (45, X)]]
| 5–20%
|-
| [[Triploid syndrome|Triploidy]]
| 6–8%
|-
| [[Chromosome abnormality#Structural abnormalities|Structural abnormality]] of<br>the chromosome
| 2%
|-
| Double or triple trisomy
| 0.7–2.0%{{sfn|Hoffman|page=171}}
|-
|[[Chromosomal translocation|Translocation]]
| Unknown<ref>{{cite web |url=https://www.acog.org/-/media/For-Patients/faq100.pdf?dmc=1&ts=20150820T1255284207 |title=Archived copy |access-date=September 14, 2017 |archive-url=https://web.archive.org/web/20170914125252/https://www.acog.org/-/media/For-Patients/faq100.pdf?dmc=1&ts=20150820T1255284207 |archive-date=September 14, 2017 |url-status=dead }}</ref>
|}

Most clinically apparent miscarriages (two-thirds to three-quarters in various studies) occur during the first trimester.<ref name="John20122" /><ref name="NHS-Miscarriage-Causes"/><ref name="webmd">{{cite web | last = Rosenthal | first = M. Sara | title = The Second Trimester | website = The Gynecological Sourcebook | publisher = WebMD | year = 1999 | url = http://www.webmd.com/content/article/4/1680_51802.htm | access-date = December 18, 2006 | url-status = live | archive-url = https://web.archive.org/web/20061201085538/http://www.webmd.com/content/article/4/1680_51802.htm | archive-date = December 1, 2006 | df = mdy-all }}</ref><ref name=Will2013>{{cite book|title=Williams Obstetrics| vauthors = Cunningham F, Leveno KJ, Bloom SL, Spong CY, Dashe JS, Hoffman BL, Casey BM, Sheffield JS|publisher=McGraw-Hill|year=2013|pages=5|chapter=Abortion}}</ref> About 30% to 40% of all fertilised eggs miscarry, often before the pregnancy is known.<ref name="John20122" /> The embryo typically dies before the pregnancy is expelled; bleeding into the [[decidua basalis]] and [[tissue necrosis]] cause uterine contractions to expel the pregnancy.<ref name=Will2013 /> Early miscarriages can be due to a developmental abnormality of the placenta or other embryonic tissues. In some instances, an embryo does not form but other tissues do. This has been called a "[[blighted ovum]]".<ref>{{cite news|url=http://americanpregnancy.org/pregnancy-complications/blighted-ovum/|title=Blighted Ovum: Symptoms, Causes and Prevention|date=2012-04-26|work=American Pregnancy Association|access-date=2017-09-09|language=en|url-status=live|archive-url=https://web.archive.org/web/20170725113127/http://americanpregnancy.org/pregnancy-complications/blighted-ovum/|archive-date=July 25, 2017|df=mdy-all}}</ref><ref>{{cite news|url=http://www.mayoclinic.org/diseases-conditions/pregnancy-loss-miscarriage/expert-answers/blighted-ovum/faq-20057783|title=Blighted ovum: What causes it?|work=Mayo Clinic|access-date=2017-09-09|url-status=live|archive-url=https://web.archive.org/web/20170720141145/http://www.mayoclinic.org/diseases-conditions/pregnancy-loss-miscarriage/expert-answers/blighted-ovum/faq-20057783|archive-date=July 20, 2017|df=mdy-all}}</ref>{{sfn|Hoffman|page=171}}

Successful implantation of the [[zygote]] into the [[uterus]] is most likely eight to ten days after fertilization. If the zygote has not been implanted by day ten, implantation becomes increasingly unlikely in subsequent days.<ref name="pmid10362823">{{cite journal | vauthors = Wilcox AJ, Baird DD, [[Clarice Weinberg|Weinberg CR]] | title = Time of implantation of the conceptus and loss of pregnancy | journal = The New England Journal of Medicine | volume = 340 | issue = 23 | pages = 1796–9 | date = June 1999 | pmid = 10362823 | doi = 10.1056/NEJM199906103402304 | df = mdy-all | doi-access = free }}</ref>

A chemical pregnancy is a pregnancy that was detected by testing but ends in miscarriage before or around the time of the next expected period.<ref>{{cite book|editor1-last=Condous |editor1-first=George |editor2=Tom Bourne |date=2006 |title=Handbook of early pregnancy care |url=https://books.google.com/books?id=_Y3PyNvc6dcC&pg=PA28 |url-status=live |archive-url=https://web.archive.org/web/20170910181311/https://books.google.com/books?id=_Y3PyNvc6dcC&pg=PA29 |archive-date=September 10, 2017 |location=London |publisher=Informa Healthcare |isbn=978-0203016213 |pages=28–29 |df=mdy-all}}</ref>

Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks. Half of embryonic miscarriages (25% of all miscarriages) have an [[aneuploidy]] (abnormal number of chromosomes).<ref>{{cite journal | vauthors = Kajii T, Ferrier A, Niikawa N, Takahara H, Ohama K, Avirachan S | title = Anatomic and chromosomal anomalies in 639 spontaneous abortuses | journal = Human Genetics | volume = 55 | issue = 1 | pages = 87–98 | year = 1980 | pmid = 7450760 | doi = 10.1007/BF00329132 | s2cid = 2133855 }}</ref> Common chromosome abnormalities found in miscarriages include an [[Trisomy|autosomal trisomy]] (22–32%), [[Turner syndrome|monosomy X]] (5–20%), [[Triploid syndrome|triploidy]] (6–8%), [[tetraploidy]] (2–4%), or other structural chromosomal abnormalities (2%).<ref name=Will2013 /> Genetic problems are more likely to occur with older parents; this may account for the higher rates observed in older women.<ref>{{cite web | title = Pregnancy Over Age 30 | website=MUSC Children's Hospital | url = http://www.musckids.com/health_library/hrpregnant/over30.htm | access-date = December 18, 2006 |archive-url = https://web.archive.org/web/20061113233603/http://www.musckids.com/health_library/hrpregnant/over30.htm <!-- Bot retrieved archive --> |archive-date = November 13, 2006}}</ref>

[[Luteal phase]] progesterone deficiency may or may not be a contributing factor to miscarriage.<ref>{{cite journal | vauthors = Bukulmez O, Arici A | title = Luteal phase defect: myth or reality | journal = Obstetrics and Gynecology Clinics of North America | volume = 31 | issue = 4 | pages = 727–44, ix | date = December 2004 | pmid = 15550332 | doi = 10.1016/j.ogc.2004.08.007 }}</ref>

====Second and third trimesters====
Second-trimester losses may be due to maternal factors such as [[uterine malformation]], growths in the uterus ([[Uterine fibroid|fibroid]]s), or [[Cervical incompetence|cervical problems]].<ref name="NHS-Miscarriage-Causes"/> These conditions also may contribute to [[premature birth]].<ref name="webmd" /> Unlike first-trimester miscarriages, second-trimester miscarriages are less likely to be caused by a genetic abnormality; chromosomal aberrations are found in a third of cases.<ref name=Will2013 /> Infection during the third trimester can cause a miscarriage.<ref name="NHS-Miscarriage-Causes"/>

=== Age ===
Miscarriage is least common for mothers in their twenties, for whom around 12% of known pregnancies end in miscarriage.<ref name=Quenby2021/> Risk rises with age: around 14% for women aged 30–34; 18% for those 35–39; 37% for those 40–44; and 65% for those over 45.<ref name=Quenby2021/><!--Supp. Table 2--> Women younger than 20 have slightly increased miscarriage risk, with around 16% of known pregnancies ending in miscarriage.<ref name=Quenby2021/><!--Supp. Table 2-->

Miscarriage risk also [[Paternal age effect|rises with paternal age]], although the effect is less pronounced than for maternal age. The risk is lowest for men under 40 years old. For men aged 40-44, the risk is around 23% higher. For men over 45, the risk is 43% higher.<ref>{{cite journal |vauthors=Muncey W, Scott M, Lathi RB, Eisenberg ML |title=The paternal role in pregnancy loss |journal=Andrology |volume= |issue= |pages= |date=February 2024 |pmid=38334037 |doi=10.1111/andr.13603 |url=}}</ref>

===Obesity, eating disorders and caffeine===
Not only is obesity associated with miscarriage; it can result in sub-fertility and other adverse pregnancy outcomes. Recurrent miscarriage is also related to obesity. Women with [[bulimia nervosa]] and [[anorexia nervosa]] may have a greater risk for miscarriage. Nutrient deficiencies have not been found to impact miscarriage rates but [[hyperemesis gravidarum]] sometimes precedes a miscarriage.{{sfn|Hoffman|page=173}}

[[Caffeine]] consumption also has been correlated to miscarriage rates, at least at higher levels of intake.<ref name="NHS-Miscarriage-Causes"/> However, such higher rates are statistically significant only in certain circumstances.

Vitamin supplementation has generally not shown to be effective in preventing miscarriage.<ref>{{cite journal | vauthors = Balogun OO, da Silva Lopes K, Ota E, Takemoto Y, Rumbold A, Takegata M, Mori R | title = Vitamin supplementation for preventing miscarriage | journal = The Cochrane Database of Systematic Reviews | issue = 5 | pages = CD004073 | date = May 2016 | volume = 2016 | pmid = 27150280 | doi = 10.1002/14651858.cd004073.pub4 | pmc = 7104220 }}</ref> [[Chinese traditional medicine]] has not been found to prevent miscarriage.<ref name=":4" />

===Endocrine disorders===
Disorders of the thyroid may affect pregnancy outcomes. Related to this, iodine deficiency is strongly associated with an increased risk of miscarriage.{{sfn|Hoffman|page=173}} The risk of miscarriage is increased in those with poorly controlled insulin-dependent diabetes mellitus.{{sfn|Hoffman|page=173}} Women with well-controlled diabetes have the same risk of miscarriage as those without diabetes.<ref name=Ferri2017>{{cite book|author=Fred F. Ferri|title=Ferri's Clinical Advisor 2017|url=https://books.google.com/books?id=rRhCDAAAQBAJ&pg=PA1198|year=2017|publisher=Elsevier|isbn=978-0-323-28048-8|page=1198}}</ref><ref name=MehtaGupta2018>{{cite book|author1=Sumita Mehta|author2=Bindiya Gupta|title=Recurrent Pregnancy Loss|url=https://books.google.com/books?id=5KZWDwAAQBAJ&pg=PA185|year=2018|publisher=Springer|isbn=978-981-10-7337-3|page=185}}</ref>

===Food poisoning===
Ingesting food that has been contaminated with [[listeriosis]], [[toxoplasmosis]], and [[salmonella]] is associated with an increased risk of miscarriage.<ref name="NHS-Miscarriage-Causes"/><ref name = gloss/>

===Amniocentesis and chorionic villus sampling===
[[Amniocentesis]] and [[chorionic villus sampling]] (CVS) are procedures conducted to assess the fetus. A sample of amniotic fluid is obtained by the insertion of a needle through the abdomen and into the uterus. Chorionic villus sampling is a similar procedure with a sample of tissue removed rather than fluid. These procedures are not associated with pregnancy loss during the second trimester but they are associated with miscarriages and birth defects in the first trimester.<ref name="Alfirevic"/> Miscarriage caused by invasive prenatal diagnosis (chorionic villus sampling (CVS) and amniocentesis) is rare (about 1%).<ref name="Agarwal-Alfirevic-2012"/>

===Surgery===
The effects of surgery on pregnancy are not well-known including the effects of [[bariatric]] surgery. Abdominal and pelvic surgery are not risk factors for miscarriage. Ovarian tumours and cysts that are removed have not been found to increase the risk of miscarriage. The exception to this is the removal of the [[corpus luteum]] from the ovary. This can cause fluctuations in the hormones necessary to maintain the pregnancy.{{sfn|Hoffman|pages=172–173}}

===Medications===
There is no significant association between [[antidepressant]] medication exposure and miscarriage.<ref name="Ross LE 436–443">{{cite journal | vauthors = Ross LE, Grigoriadis S, Mamisashvili L, Vonderporten EH, Roerecke M, Rehm J, Dennis CL, Koren G, Steiner M, Mousmanis P, Cheung A | title = Selected pregnancy and delivery outcomes after exposure to antidepressant medication: a systematic review and meta-analysis | journal = JAMA Psychiatry | volume = 70 | issue = 4 | pages = 436–43 | date = April 2013 | pmid = 23446732 | doi = 10.1001/jamapsychiatry.2013.684 | doi-access =  | s2cid = 2065578 }}</ref> The risk of miscarriage is not likely decreased by discontinuing [[Selective serotonin reuptake inhibitor|SSRIs]] before pregnancy.<ref name="auto3">{{cite journal | vauthors = Dalke KB, Wenzel A, Kim DR | title = Depression and Anxiety During Pregnancy: Evaluating the Literature in Support of Clinical Risk-Benefit Decision-Making | journal = Current Psychiatry Reports | volume = 18 | issue = 6 | pages = 59 | date = June 2016 | pmid = 27091646 | doi = 10.1007/s11920-016-0698-x | s2cid = 984767 }}</ref> Some available data suggest that there is a small increased risk of miscarriage for women taking any [[antidepressant]],<ref name="auto4">{{cite journal | vauthors = Broy P, Bérard A | title = Gestational exposure to antidepressants and the risk of spontaneous abortion: a review | journal = Current Drug Delivery | volume = 7 | issue = 1 | pages = 76–92 | date = January 2010 | pmid = 19863482 | doi = 10.2174/156720110790396508 }}</ref><ref name="auto5">{{cite journal | vauthors = Nakhai-Pour HR, Broy P, Bérard A | title = Use of antidepressants during pregnancy and the risk of spontaneous abortion | journal = CMAJ | volume = 182 | issue = 10 | pages = 1031–7 | date = July 2010 | pmid = 20513781 | pmc = 2900326 | doi = 10.1503/cmaj.091208 }}</ref> though this risk becomes less [[statistically significant]] when excluding studies of poor quality.<ref name="Ross LE 436–443"/><ref name="auto6">{{cite journal | vauthors = Yonkers KA, Blackwell KA, Glover J, Forray A | title = Antidepressant use in pregnant and postpartum women | journal = Annual Review of Clinical Psychology | volume = 10 | issue = 1 | pages = 369–92 | date = 2014-01-01 | pmid = 24313569 | pmc = 4138492 | doi = 10.1146/annurev-clinpsy-032813-153626 }}</ref>

Medicines that increase the risk of miscarriage include:
* [[retinoids]]
* [[nonsteroidal anti-inflammatory drugs]] (NSAIDs), such as [[ibuprofen]]
* [[misoprostol]]
* [[methotrexate]]<ref name="NHS-Miscarriage-Causes"/>
* [[statin]]s<ref>{{cite journal | vauthors = Grundy SM, Stone NJ, Bailey AL, Beam C, Birtcher KK, Blumenthal RS, Braun LT, de Ferranti S, Faiella-Tommasino J, Forman DE, Goldberg R, Heidenreich PA, Hlatky MA, Jones DW, Lloyd-Jones D, Lopez-Pajares N, Ndumele CE, Orringer CE, Peralta CA, Saseen JJ, Smith SC, Sperling L, Virani SS, Yeboah J | title = 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task&nbsp;Force&nbsp;on&nbsp;Clinical Practice Guidelines | journal = Journal of the American College of Cardiology | volume = 73 | issue = 24 | pages = 3168–3209 | date = June 2019 | pmid = 30423391 | doi = 10.1016/j.jacc.2018.11.002 | doi-access = free }}</ref>

=== Immunisations ===
[[Vaccination|Immunisations]] have not been found to cause miscarriage.{{sfn|Hoffman|page=72}} Live vaccinations, like the MMR vaccine, can theoretically cause damage to the fetus as the live virus can cross the placenta and potentially increase the risk for miscarriage.<ref>{{cite journal | vauthors = Racicot K, Mor G | title = Risks associated with viral infections during pregnancy | journal = The Journal of Clinical Investigation | volume = 127 | issue = 5 | pages = 1591–1599 | date = May 2017 | pmid = 28459427 | pmc = 5409792 | doi = 10.1172/JCI87490 }}</ref><ref name=":6">{{cite journal | vauthors = Bozzo P, Narducci A, Einarson A | title = Vaccination during pregnancy | journal = Canadian Family Physician | volume = 57 | issue = 5 | pages = 555–7 | date = May 2011 | pmid = 21571717 | pmc = 3093587 }}</ref> Therefore, the Center for Disease Control (CDC) recommends against pregnant women receiving live vaccinations.<ref>{{cite web|url=https://www.cdc.gov/vaccines/pregnancy/hcp-toolkit/guidelines.html|title=Pregnancy Guidelines and Recommendations by Vaccine {{!}} CDC|date=2019-04-19|website=www.cdc.gov|access-date=2019-08-01}}</ref> However, there is no clear evidence that has shown live vaccinations increase the risk of miscarriage or fetal abnormalities.<ref name=":6" />

Some live vaccinations include: [[MMR vaccine|MMR]], [[Varicella vaccine|varicella]], certain types of the [[influenza vaccine]], and [[Rotavirus vaccine|rotavirus]].<ref>{{cite web|url=https://www.cdc.gov/vaccines/vpd/vaccines-list.html|title=List of Vaccines {{!}} CDC|date=2019-04-15|website=www.cdc.gov|language=en-us|access-date=2019-08-06}}</ref><ref>{{cite web|url=https://www.vaccines.gov/basics/types|title=Vaccine Types {{!}} Vaccines|website=www.vaccines.gov|access-date=2019-08-06}}</ref>

===Treatments for cancer===
[[Ionizing radiation|Ionising radiation]] levels given to a woman [[Radiation therapy|during cancer treatment]] cause miscarriage. Exposure can also impact fertility. The use of [[chemotherapeutic drugs]] to treat [[childhood cancer]] increases the risk of future miscarriage.{{sfn|Hoffman|page=173}}

===Pre-existing diseases===
Several [[pre-existing diseases in pregnancy]] can potentially increase the risk of miscarriage, including [[Diabetes mellitus|diabetes]], [[endometriosis]], [[polycystic ovary syndrome]] (PCOS), [[hypothyroidism]], certain infectious diseases, and autoimmune diseases. 
Women with endometriosis report a 76%<ref name="ESHRE2015">{{cite web |last1=Saraswat |first1=Lucky |title=ESHRE2015: Endometriosis associated with a greater risk of complications in pregnancy |url=https://endometriosis.org/news/congress-highlights/eshre2015-endometriosis-associated-with-a-greater-risk-of-complications-in-pregnancy/#:~:text=After%20adjustments%20for%20age%20and%20previous%20pregnancy%2C%20results,three%20times%20higher%20for%20ectopic%20pregnancy%20%28OR%202.7%29 |website=endometriosis.org |publisher=European Society of Human Reproduction and Embryology |access-date=14 February 2024 |date=2015}}</ref> to 298%<ref name="PMC9588543">{{cite journal |last1=Schliep |first1=Karen C |last2=Farland |first2=Leslie V |last3=Pollack |first3=Anna Z |last4=Louis |first4=Germaine Buck |last5=Stanford |first5=Joseph B |last6=Allen-Brady |first6=Kristina |last7=Varner |first7=Michael W |last8=Kah |first8=Kebba |last9=Peterson |first9=C Matthew |title=Endometriosis diagnosis, staging and typology and adverse pregnancy outcome history |journal=Paediatric and Perinatal Epidemiology |date=November 2022 |volume=36 |issue=6 |pages=771–781 |doi=10.1111/ppe.12887 |pmid=35570746 |pmc=9588543}}</ref> increase in miscarriages versus their non-afflicted peers, the range affected by the [[Endometriosis#Stages of disease|severity of their disease]]. PCOS may increase the risk of miscarriage.<ref name="NHS-Miscarriage-Causes"/> Two studies suggested treatment with the drug [[metformin]] significantly lowers the rate of miscarriage in women with PCOS,<ref name=metformin>{{cite journal | vauthors = Jakubowicz DJ, Iuorno MJ, Jakubowicz S, Roberts KA, Nestler JE | title = Effects of metformin on early pregnancy loss in the polycystic ovary syndrome | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 87 | issue = 2 | pages = 524–9 | date = February 2002 | pmid = 11836280 | doi = 10.1210/jcem.87.2.8207 | doi-access = free }}</ref><ref name=Khattab>{{cite journal | vauthors = Khattab S, Mohsen IA, Foutouh IA, Ramadan A, Moaz M, Al-Inany H | title = Metformin reduces abortion in pregnant women with polycystic ovary syndrome | journal = Gynecological Endocrinology | volume = 22 | issue = 12 | pages = 680–4 | date = December 2006 | pmid = 17162710 | doi = 10.1080/09513590601010508 | s2cid = 41735428 }}</ref> but the quality of these studies has been questioned.<ref name="RCOG-PCOS">{{cite web|last=Royal College of Obstetricians and Gynaecologists|title=Long-term consequences of polycystic ovarian syndrome|url=http://www.rcog.org.uk/files/rcog-corp/uploaded-files/GT33_LongTermPCOS.pdf|archive-url=https://web.archive.org/web/20090413130238/http://www.rcog.org.uk/files/rcog-corp/uploaded-files/GT33_LongTermPCOS.pdf|url-status=dead|archive-date=2009-04-13|website=Green-top Guideline No. 27|publisher=Royal College of Obstetricians and Gynaecologists|access-date=2 July 2013|date=December 2007}}</ref> Metformin treatment in pregnancy is not safe.<ref name=Acta>{{cite journal | vauthors = Lilja AE, Mathiesen ER | title = Polycystic ovary syndrome and metformin in pregnancy | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 85 | issue = 7 | pages = 861–8 | year = 2006 | pmid = 16817087 | doi = 10.1080/00016340600780441 | s2cid = 42002774 | doi-access = free }}</ref> In 2007, the Royal College of Obstetricians and Gynaecologists also recommended against the use of the drug to prevent miscarriage.<ref name="RCOG-PCOS" /> [[Thrombophilia]]s or defects in coagulation and bleeding were once thought to be a risk of miscarriage but have been subsequently questioned.{{sfn|Hoffman|page=174}} Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. A condition called luteal phase defect (LPD) is a failure of the uterine lining to be fully prepared for pregnancy. This can keep a fertilised egg from implanting or result in miscarriage.<ref>{{cite web|url=https://www.womenshealth.gov/pregnancy/you-get-pregnant/trying-conceive/#4|title=Trying to conceive {{!}} womenshealth.gov|website=womenshealth.gov|access-date=2017-09-11|date=December 13, 2016}}{{PD-notice}}</ref>

''[[Mycoplasma genitalium]]'' infection is associated with an increased risk of [[preterm birth]] and miscarriage.<ref name="LisRowhani-Rahbar2015"/>

Infections can increase the risk of a miscarriage: rubella (German measles), cytomegalovirus, bacterial vaginosis, [[HIV]], chlamydia, gonorrhoea, syphilis, and malaria.<ref name="NHS-Miscarriage-Causes"/>

===Immune status===
Autoimmunity is a possible cause of recurrent or late-term miscarriages. In the case of an autoimmune-induced miscarriage, the woman's body attacks the growing fetus or prevents normal pregnancy progression.<ref name="CarpSelmi2012">{{cite journal | vauthors = Carp HJ, Selmi C, Shoenfeld Y | title = The autoimmune bases of infertility and pregnancy loss | journal = Journal of Autoimmunity | volume = 38 | issue = 2–3 | pages = J266-74 | date = May 2012 | pmid = 22284905 | doi = 10.1016/j.jaut.2011.11.016 | type = Review }}</ref><ref name=":3">{{cite journal|year=2007|title=Female infertility due to abnormal autoimmunity: Frequently overlooked and greatly underappreciated. Part II|journal=Expert Review of Obstetrics & Gynecology|volume=2|issue=4|pages=465–75|doi=10.1586/17474108.2.4.465|vauthors=Gleicher N, Weghofer A, Barad D}}</ref> Autoimmune disease may cause abnormalities in embryos, which in turn may lead to miscarriage. As an example, [[coeliac disease]] increases the risk of miscarriage by an [[odds ratio]] of approximately 1.4.<ref name="TersigniCastellani2014"/>{{sfn|Hoffman|page = 172}} A disruption in normal immune function can lead to the formation of antiphospholipid antibody syndrome. This will affect the ability to continue the pregnancy, and if a woman has repeated miscarriages, she can be tested for it.{{sfn|Hoffman|page=272}} Approximately 15% of recurrent miscarriages are related to immunologic factors.{{sfn|Hoffman|page=182}} The presence of [[Antithyroid autoantibodies|anti-thyroid autoantibodies]] is associated with an increased risk with an [[odds ratio]] of 3.73 and 95% [[confidence interval]] 1.8–7.6.<ref>{{cite journal | vauthors = van den Boogaard E, Vissenberg R, Land JA, van Wely M, van der Post JA, Goddijn M, Bisschop PH | title = Significance of (sub)clinical thyroid dysfunction and thyroid autoimmunity before conception and in early pregnancy: a systematic review | journal = Human Reproduction Update | volume = 17 | issue = 5 | pages = 605–19 | year = 2011 | pmid = 21622978 | doi = 10.1093/humupd/dmr024 | doi-access =  }}</ref> Having lupus also increases the risk of miscarriage.<ref>{{cite web|url=https://www.womenshealth.gov/lupus/pregnancy-and-lupus|title=Pregnancy and lupus|website=womenshealth.gov|access-date=2017-09-11|date=April 20, 2017}}</ref> Immunohistochemical studies on decidual basalis and chorionic villi found that the imbalance of the immunological environment could be associated with recurrent pregnancy loss.<ref>{{cite journal | last1=Kavvadas | first1=Dimitrios | last2=Karachrysafi | first2=Sofia | last3=Anastasiadou | first3=Pinelopi | last4=Kavvada | first4=Asimoula | last5=Fotiadou | first5=Stella | last6=Papachristodoulou | first6=Angeliki | last7=Papamitsou | first7=Theodora | last8=Sioga | first8=Antonia | title=Immunohistochemical Evaluation of CD3, CD4, CD8, and CD20 in Decidual and Trophoblastic Tissue Specimens of Patients with Recurrent Pregnancy Loss | journal=Clinics and Practice | publisher=MDPI AG | volume=12 | issue=2 | date=2022-02-28 | issn=2039-7283 | doi=10.3390/clinpract12020022 | pages=177–193 |pmid=35314592 |pmc=8938768 | doi-access=free }}</ref>

===Anatomical defects and trauma===
Fifteen per cent of women who have experienced three or more recurring miscarriages have some anatomical defect that prevents the pregnancy from being carried for the entire term.{{sfn|Hoffman|page=181}} The structure of the uterus affects the ability to carry a child to term. Anatomical differences are common and can be congenital.<ref>{{Cite journal |last1=Qian |first1=Liang |last2=Ding |first2=Jiashan |last3=Shi |first3=Lan |last4=Yu |first4=Qing |last5=Zhu |first5=Jiawei |last6=Huang |first6=Anfeng |date=2023-12-04 |title=Analysis of hemi-uterus pregnancy outcomes in uterine malformations: a retrospective observational study |journal=BMC Pregnancy and Childbirth |volume=23 |issue=1 |pages=836 |doi=10.1186/s12884-023-06136-w |doi-access=free |pmid=38049742 |pmc=10696795 |issn=1471-2393}}</ref>
{| class="wikitable"
!Type of uterine<br>structure
!Miscarriage rate<br>associated with defect
!References
|-
|[[Bicornate uterus]]
|40–79%
|{{sfn|Hoffman|page=181–182}}<ref name="auto7"/>
|-
|[[Septate uterus|Septate]] or [[Unicornuate uterus|unicornate]]
|34–88%
|{{sfn|Hoffman|page=181–182}}
|-
|[[Arcuate uterus|Arcuate]]
|Unknown
|{{sfn|Hoffman|page=181–182}}
|-
|[[Uterus didelphys|Didelphys]]
|40%
|{{sfn|Hoffman|page=181–182}}
|-
|[[Uterine fibroid|Fibroids]]
|Unknown
|<ref name="NHS-Miscarriage-Causes"/>
|-
|}

In some women, [[cervical incompetence]] or cervical insufficiency occurs with the inability of the cervix to stay closed during the entire pregnancy.<ref name="American College of Obstetricians and 372–9"/><ref name="NHS-Miscarriage-Causes"/> It does not cause first-trimester miscarriages. In the second trimester, it is associated with an increased risk of miscarriage. It is identified after a premature birth has occurred at about 16–18 weeks into the pregnancy.{{sfn|Hoffman|page=181}} During the second trimester, major trauma can result in a miscarriage.{{sfn|Hoffman|page=172}}

===Smoking===
{{See also|Smoking and pregnancy}}
Tobacco (cigarette) smokers have an increased risk of miscarriage.<ref name="x"/><ref name="NHS-Miscarriage-Causes"/> There is an increased risk regardless of which parent smokes, though the risk is higher when the gestational mother smokes.<ref name="paternal smoking"/>

===Morning sickness===
Nausea and vomiting of pregnancy (NVP, or [[morning sickness]]) are associated with a decreased risk. Several possible causes have been suggested for morning sickness but there is still no agreement.<ref name="Kor2014">{{cite journal | vauthors = Koren G | title = Treating morning sickness in the United States--changes in prescribing are needed | journal = American Journal of Obstetrics and Gynecology | volume = 211 | issue = 6 | pages = 602–6 | date = December 2014 | pmid = 25151184 | doi = 10.1016/j.ajog.2014.08.017 | doi-access =  }}</ref> NVP may represent a defence mechanism which discourages the mother's ingestion of foods that are harmful to the fetus; according to this model, a lower frequency of miscarriage would be an expected consequence of the different food choices made by women experiencing NVP.<ref name=Haviland2016>{{cite book|chapter-url=https://books.google.com/books?id=FPgWDAAAQBAJ&q=nausea+vomiting+pregnancy+defense+mechanism+2017&pg=PA310|title=Anthropology: The Human Challenge|last1=Haviland|first1=William A.|last2=Prins|first2=Harald E. L.|last3=Walrath|last4=McBride|first4=Bunny |date=2016|publisher=Cengage Learning|isbn=978-1305863354|pages=31|chapter=12. Human Adaptation to Changing World}}</ref>

===Chemicals and occupational exposure===
Chemical and [[occupational exposure]]s may have some effect on pregnancy outcomes.<ref>{{cite journal | vauthors = Snijder CA, Roeleveld N, Te Velde E, Steegers EA, Raat H, Hofman A, Jaddoe VW, Burdorf A | title = Occupational exposure to chemicals and fetal growth: the Generation R Study | journal = Human Reproduction | volume = 27 | issue = 3 | pages = 910–20 | date = March 2012 | pmid = 22215632 | pmc = 3279127 | doi = 10.1093/humrep/der437 }}</ref> A cause-and-effect relationship can rarely be established. Those chemicals that are implicated in increasing the risk for miscarriage are [[DDT]], [[lead]],<ref>{{cite journal | vauthors = Krieg SA, Shahine LK, Lathi RB | title = Environmental exposure to endocrine-disrupting chemicals and miscarriage | journal = Fertility and Sterility | volume = 106 | issue = 4 | pages = 941–7 | date = September 2016 | pmid = 27473347 | doi = 10.1016/j.fertnstert.2016.06.043 | doi-access = free }}</ref> [[formaldehyde]], [[arsenic]], [[benzene]] and [[ethylene oxide]]. [[Video display terminal]]s and ultrasound have not been found to affect the rates of miscarriage. In dental offices where [[nitrous oxide]] is used with the absence of anaesthetic gas scavenging equipment, there is a greater risk of miscarriage. For women who work with cytotoxic antineoplastic chemotherapeutic agents, there is a small increased risk of miscarriage. No increased risk for [[cosmetologist]]s has been found.{{sfn|Hoffman|page=272}}

===Other===
Alcohol increases the risk of miscarriage.<ref name="NHS-Miscarriage-Causes"/> [[Cocaine intoxication|Cocaine]] use increases the rate of miscarriage.<ref name="x"/> Some infections have been associated with miscarriage. These include [[Ureaplasma urealyticum infection|''Ureaplasma urealyticum'']], [[Mycoplasma hominis infection|''Mycoplasma hominis'']], [[Group B streptococcal infection|group B streptococci]], [[HIV/AIDS|HIV-1]], and [[syphilis]]. [[Chlamydia infection|''Chlamydia trachomatis'']] may increase the risk of miscarriage.<ref name="NHS-Miscarriage-Causes"/> [[Toxoplasmosis]] can cause a miscarriage.<ref name="NHS-Toxoplasmosis">{{cite web |author=<!--No author name given.--> |date=September 10, 2020 |title=Toxoplasmosis |url=https://www.nhs.uk/conditions/toxoplasmosis/ |website=NHS |url-status=live |archive-url=https://web.archive.org/web/20230612022939/https://www.nhs.uk/conditions/toxoplasmosis/ |archive-date=June 12, 2023}}</ref> Subclinical infections of the lining of the womb, commonly known as chronic endometritis, are also associated with poor pregnancy outcomes, compared to women with treated chronic endometritis or no chronic endometritis.<ref>Rimmer MP, Fishwick K, Henderson I, Chinn D, Al Wattar BH and Quenby S. Quantifying CD138+ cells in the endometrium to assess chronic endometritis in women at risk of recurrent pregnancy loss: A prospective cohort study and rapid review. J Obstet Gynaecol Res. 2020.</ref>