Editing Prenatal testing (section)

==By pregnancy stage==

=== Pre-conception ===
Prior to conception, couples may elect to have genetic testing done to determine the odds of conceiving a child with a known genetic anomaly. The most common in the Caucasian population are:{{citation needed|date=February 2022}}
* [[Cystic fibrosis]]
* [[Fragile X syndrome]]
* Blood disorders such as [[sickle cell disease]]
* [[Tay–Sachs disease|Tay-Sachs disease]]
* [[Spinal muscular atrophy]]
Hundreds of additional conditions are known and more discovered on a regular basis. However the economic justification for population-wide testing of all known conditions is not well supported, particularly once the cost of possible false positive results and concomitant follow-up testing are taken into account.<ref>{{cite journal | vauthors = Henneman L, Borry P, Chokoshvili D, Cornel MC, van El CG, Forzano F, Hall A, Howard HC, Janssens S, Kayserili H, Lakeman P, Lucassen A, Metcalfe SA, Vidmar L, de Wert G, Dondorp WJ, Peterlin B | display-authors = 6 | title = Responsible implementation of expanded carrier screening | journal = European Journal of Human Genetics | volume = 24 | issue = 6 | pages = e1–e12 | date = June 2016 | pmid = 26980105 | pmc = 4867464 | doi = 10.1038/ejhg.2015.271}}</ref> There are also ethical concerns related to this or any type of [[genetic testing]].{{citation needed|date=August 2022}}

One or both partners may be aware of other family members with these diseases. Testing prior to conception may alleviate concern, prepare the couple for the potential short- or long-term consequences of having a child with the disease, direct the couple toward adoption or foster parenting, or prompt for [[Preimplantation genetic diagnosis|preimplantation genetic testing]] during [[In vitro fertilisation|''in vitro'' fertilization]]. If a genetic disorder is found, professional [[genetic counseling]] is usually recommended owing to the host of ethical considerations related to subsequent decisions for the partners and potential impact on their extended families. Most, but not all, of these diseases follow [[Mendelian inheritance]] patterns. [[Fragile X syndrome]] is related to expansion of certain repeated DNA segments and may change generation-to-generation.{{citation needed|date=August 2022}}

=== First trimester ===
At early presentation of pregnancy at around 6 weeks, early dating ultrasound scan may be offered to help confirm the [[Gestational age (obstetrics)|gestational age]] of the embryo and check for a single or twin pregnancy, but such a scan is unable to detect common abnormalities. Details of prenatal screening and testing options may be provided.{{citation needed|date=August 2022}}

Around weeks 11–13, [[nuchal scan|nuchal translucency scan]] (NT) may be offered which can be combined with blood tests for PAPP-A and beta-hCG, two serum markers that correlate with chromosomal abnormalities, in what is called the First Trimester Combined Test. The results of the blood test are then combined with the NT ultrasound measurements, maternal age, and gestational age of the fetus to yield a risk score for Down syndrome, trisomy 18, and trisomy 13. First Trimester Combined Test has a sensitivity (i.e. detection rate for abnormalities) of 82–87% and a false-positive rate of around 5%.<ref>{{Cite journal |last1=Carlson |first1=Laura M. |last2=Vora |first2=Neeta L. |date=2017 |title=Prenatal Diagnosis |journal=Obstetrics and Gynecology Clinics of North America |volume=44 |issue=2 |pages=245–256 |doi=10.1016/j.ogc.2017.02.004 |issn=0889-8545 |pmc=5548328 |pmid=28499534}}</ref><ref>{{Cite journal|last1=Malone|first1=Fergal D.|last2=Canick|first2=Jacob A.|last3=Ball|first3=Robert H.|last4=Nyberg|first4=David A.|last5=Comstock|first5=Christine H.|last6=Bukowski|first6=Radek|last7=Berkowitz|first7=Richard L.|last8=Gross|first8=Susan J.|last9=Dugoff|first9=Lorraine|last10=Craigo|first10=Sabrina D.|last11=Timor-Tritsch|first11=Ilan E.|date=November 10, 2005|title=First-trimester or second-trimester screening, or both, for Down's syndrome|journal=The New England Journal of Medicine|volume=353|issue=19|pages=2001–2011|doi=10.1056/NEJMoa043693|issn=1533-4406|pmid=16282175|doi-access=free}}</ref>

[[Cell-free fetal DNA]] is also available during the first trimester of pregnancy.{{cn|date=February 2025}}

=== Second trimester ===
The [[anomaly scan]] is performed between 18 and 22 weeks of [[Gestational age (obstetrics)|gestational age]]. The [[International Society of Ultrasound in Obstetrics and Gynecology]] (ISUOG) recommends that this ultrasound is performed as a matter of routine [[prenatal care]], to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, and to assess for [[congenital malformations]] and [[Multiple birth|multiple pregnancies]] (i.e. twins).<ref>{{cite journal | vauthors = Salomon LJ, Alfirevic Z, Berghella V, Bilardo C, Hernandez-Andrade E, Johnsen SL, Kalache K, Leung KY, Malinger G, Munoz H, Prefumo F, Toi A, Lee W | display-authors = 6 | title = Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan | journal = Ultrasound in Obstetrics & Gynecology | volume = 37 | issue = 1 | pages = 116–26 | date = January 2011 | pmid = 20842655 | doi = 10.1002/uog.8831 | s2cid = 10676445 | doi-access = free}}</ref> The scan can detect [[anencephaly]], open [[spina bifida]], [[cleft lip]], [[diaphragmatic hernia]], [[gastroschisis]], [[omphalocele]], [[congenital heart defect]], [[Renal agenesis|bilateral renal agenesis]], [[osteochondrodysplasia]], [[Edwards syndrome]], and [[Patau syndrome]].<ref>{{Cite web|url=https://www.nhs.uk/Conditions/pregnancy-and-baby/Pages/anomaly-scan-18-19-20-21-weeks-pregnant.aspx|title=Mid-pregnancy anomaly scan – Pregnancy and baby – NHS Choices|last=NHS Choices|website=www.nhs.uk|language=en|access-date=December 4, 2017}}</ref>

A second-trimester [[Triple test#Quadruple test|Quad blood test]] may be taken (the [[Triple test]] is widely considered obsolete but in some states, such as Missouri, where [[Medicaid]] only covers the Triple test, that's what the patient typically gets). With ''integrated screening'', both a First Trimester Combined Test and a Triple/Quad test is performed, and a report is only produced after both tests have been analyzed. However patients may not wish to wait between these two sets of tests. With ''sequential screening'', a first report is produced after the first trimester sample has been submitted, and a final report after the second sample. With ''contingent screening'', patients at very high or very low risks will get reports after the first-trimester sample has been submitted. Only patients with ''moderate risk'' (risk score between 1:50 and 1:2000) will be asked to submit a second-trimester sample, after which they will receive a report combining information from both serum samples and the [[nuchal translucency|NT]] measurement. The First Trimester Combined Test and the Triple/Quad test together have a sensitivity of 88–95% with a 5% false-positive rate for Down syndrome, though they can also be analyzed in such a way as to offer a 90% sensitivity with a 2% false-positive rate. Finally, patients who do not receive an NT ultrasound in the 1st trimester may still receive a Serum Integrated test involving measuring PAPP-A serum levels in the 1st trimester and then doing a Quad test in the 2nd trimester. This offers an 85–88% sensitivity and 5% false-positive rate for Down syndrome. Also, a patient may skip the 1st-trimester screening entirely and receive only a 2nd-trimester Quad test, with an 81% sensitivity for Down syndrome and 5% false-positive rate.<ref>[https://web.archive.org/web/20170212001459/http://www.cdph.ca.gov/programs/pns/Documents/Provider%20Handbook%20%202009%20WEB.pdf The California Prenatal Screening Program]. cdph.ca.gov</ref>

=== Third trimester ===
Third-trimester prenatal testing generally focuses on maternal wellbeing and reducing fetal morbidity/mortality. [[Group B streptococcal infection]] (also called Group B strep) may be offered, which is a major cause of neonatal morbidity and mortality. Group B strep is an infection that may be passed to an infant during birth. Vaginal screening for GBS is performed between 34 and 37 weeks of gestational age, so that mothers that are positive for the bacterium can receive treatment before delivery. During the third trimester, some institutions may require evaluations of hemoglobin/hematocrit, syphilis serology, and HIV screening. Also, before delivery, an assessment of fetal position and estimated fetal weight is documented.<ref>{{Citation|last1=Kitchen|first1=Felisha L.|title=Prenatal Screening|date=2021|url=http://www.ncbi.nlm.nih.gov/books/NBK470559/|work=StatPearls|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=29261924|access-date=June 26, 2021|last2=Jack|first2=Brian W.}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>