What time frame is relevant for assessing the effects of maternal serum alpha-fetoprotein in pregnancy?

The assessment of maternal serum alpha-fetoprotein (MSAFP) is typically recommended during the time frame of weeks 15 to 20 of pregnancy, with the most accurate results generally obtained between the 15th and 18th weeks. This screening test is primarily used to evaluate the risk of certain fetal abnormalities, including neural tube defects and Down syndrome.

Choosing the correct time frame for assessing MSAFP is important because conducting the test too early or too late can yield inaccurate results. In the earlier weeks of pregnancy, particularly before week 15, the levels of alpha-fetoprotein may not yet be indicative of potential fetal abnormalities. Conversely, testing too late in the pregnancy may miss the optimal window for meaningful interpretation and appropriate clinical action.

Therefore, the period between weeks 13 and 16 is indeed a critical window, but the accuracy and best practice firmly support the choice of weeks 15 to 18 as the ideal timing for assessment. This understanding emphasizes the importance of timing in obtaining reliable screening results and making informed decisions about further diagnostic testing or interventions, if necessary.