Editing Prenatal testing (section)

=== 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}}