Why Did Pregnancy Amniocentesis Become Much Less Common?

One panelist says the number of invasive pregnancy procedures, including amniocentesis and chorionic villus sampling, has decreased. A primary driver is better screening for chromosomal disorders such as Down syndrome with cell-free DNA.

A tube of maternal blood contains fragments of placental DNA, and the sample screens the pregnancy for chromosomal conditions. The test is best for trisomies 21, 18, and 13, and for fetal sex. It is less good for other findings. Clinicians can run it as early as nine or ten weeks, and it is recommended to be offered to all pregnant patients.

Before cell-free DNA, a serum screen looked at three or four protein markers in maternal blood. When the protein levels for gestational age fit an increased risk of a chromosomal disorder, an amniocentesis was recommended. The positive predictive value of a positive test was five percent. For everyone who screened positive for a baby with Down syndrome, or trisomy 21, only five percent were actually carrying a baby with Down syndrome. A co-host asked whether the newer screen takes away much of the incentive for amniocentesis, and one panelist agreed.