Prenatal Development Although it is less than an inch long, the beginnings of arms, legs, and fingers can already be distinguished in the 7-week-old embryo (top left). The amniotic sac can be clearly seen in this photograph. The fetus at 4 months (top right) measures 6 to 10 inches long, and the mother may be able to feel the fetus’s movements. Notice the well-formed umbilical cord. Near full term (bottom), the 8-month-old fetus gains body fat to help the newborn survive outside the mother’s uterus.

(b) and (c) Petit Format/Nestle/Science Source