Measurement in plasma: Fetal Fib₄₂₀ level is higher than adult. Two representative plasma samples prepared from each source, adult blood (lanes 1 and 2) and umbilical cord blood (lanes 3 and 4), were subjected to SDS-PAGE under reducing conditions, transferred to nitrocellulose, and probed with either anti-VI (left panel) or anti-β (right panel) as described in Materials and Methods. The plasma samples in the right panel were diluted so that they contained approximately 25 ng total fibrinogen per lane. Lanes in the left panel contained 100 times more plasma than the corresponding lanes in the right panel.