Palpation of the Fetal Head.
The fetal head can be palpated directly through the uterine wall and the flaccid membranes. Measurement of the tip of the nose to the forehead can assist in determining the approximate age of the fetus. At 70 days of gestation the distance from the tip of the nose to the top of the forehead is 15 mm, at 80 that distance is 35 mm, at 90 days 55 mm, at 100 days 90 mm, and at 120 days the distance is 105 mm.
Drost M (1982)