Human Growth and Development / Unit 2 HGD 0201 worked example, 60 to 90 seconds
Which Test Finds What
The idea
Each prenatal test answers a different kind of question. Ultrasound images the body, so it finds structural differences: an organ that has not formed normally, or limbs that are short or missing. Maternal serum screening measures proteins in the pregnant person's blood and flags risk for further testing. Amniocentesis and chorionic villus sampling examine fetal cells, so they detect chromosomal disorders such as Down syndrome and some single-gene disorders, at some risk of miscarriage.
In practice
A pregnant patient who took thalidomide early in pregnancy: the question is her baby's limbs, so the test is ultrasound.
Where people slip
Match the test to the kind of problem. A structural question, the shape or presence of a body part, calls for imaging. A question about chromosomes or genes calls for fetal cells. A blood screen narrows risk but does not settle it. On the exam, a drug taken early that affects limb formation points to ultrasound, because the other tests look for chromosomal or biochemical conditions.
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