Fetal development at 18 weeks of pregnancy As the baby grows, the pregnant woman enters the second trimester. At this time, the fetal body system begins to become more complete and the organs gradually take shape. How is your baby\’s development going at 18 weeks of pregnancy? Body Shape and Size The fetus at this time has a distinct shape, and the fingers and toes have also grown into small and regular details. The baby is approximately 14.2 cm long and weighs approximately 190 grams. The baby\’s skin is transparent at this time, so the purple veins will be very obvious. The baby is gaining weight, and the proportions of his head and body are gradually approaching that of a normal adult.