Why Is an Accurate Estimate of Gestational Age Necessary Before

Why is an accurate estimate of gestational age necessary before maternal serum α-fetoprotein (MSAFP) is measured?

A) It is only expressed early in pregnancy
B) It is only expressed in the second trimester of pregnancy
C) One must relate the MSAFP measurement to gestational age because the MSAFP levels change during the pregnancy
D) If it is too late in the pregnancy to do more invasive testing, it's not worth doing MSAFP measurements
E) Because it takes several days to do the MSAFP testing, it can be skipped and invasive testing if the pregnancy is beyond 16 weeks can be done