At what stage of gestation is maternal serum alpha-fetoprotein testing typically performed?

Maternal serum alpha-fetoprotein (MSAFP) testing is typically performed during the second trimester of pregnancy, specifically between 15 and 18 weeks of gestation. This timeframe is critical as it allows for effective screening for potential fetal abnormalities such as neural tube defects and certain chromosomal conditions.

The reason this timing is important is that alpha-fetoprotein is a protein produced by the fetal liver, and its levels can provide valuable information when interpreted alongside other markers and the results of ultrasound findings. Testing too early, such as before 12 weeks, may not yield accurate results since the levels of alpha-fetoprotein might not be sufficiently developed. Performing the test too late, like during the third trimester (24-28 weeks or after 36 weeks), would miss the optimal window for high sensitivity and specificity in detecting certain conditions. Therefore, the period between 15 and 18 weeks allows for the best assessment relative to gestational development.