Editing Prenatal testing (section)

==== First/Second/Third trimester Screen ====
The first, second, combined, and third trimester screens typically consist of an ultrasound (abdominal and/or transvaginal) and maternal blood/serum testing. The ultrasound is used to visually assess the growth, development, and activity of the fetus through imaging observations and measurements. The ultrasound portion of the first trimester screen can include a nuchal translucency screen and a fetal nasal bone determination screen. The available blood tests from the first trimester screen can test for plasma protein A and human chorionic gonadotropin. The second trimester screen looks at specific blood markers, to include the estriol, inhibin and human chorionic gonadotropin hormones and often consists of Alpha-fetoprotein (AFP) screening. Any abnormal results from these screening tests can indicate the possibility of abnormal conditions such as Trisomy 18, Trisomy 21 (Down syndrome), and spina bifida.<ref name="www.acog.org-3" />