Baby Development: Weeks 13-16
Your baby's hands have 27 bones connected by ligaments, which are structurally complete. The feet, with separated toes and developed heels, are also nearly formed. Fetal development parallels the developmental stages of infancy. Because your baby will use his hands before he walks on his feet, hands develop earlier in utero than feet do. Your baby can suck her thumb, strengthening and filling out the cheek and jaw muscles.
Your baby's eyes have moved forward and ears have moved upward on the head. The neck is straighter and strong, and the head is able to turn. Now your baby can move around in her amniotic bath, although you cannot yet feel these movements.
This month your baby will double in length to six inches in a sitting position and quadruple its weight from 1-4 oz. The curled fetus now begins to straighten out, as the back grows stronger and the head becomes proportionally smaller than the rapidly lengthening body.
In the second trimester, your baby's fetal brain develops folds on its surface, signaling the advancement of its many regions, especially in the forebrain that controls the intellect, motor control and memory. Brain development continues years after birth. The fingertips already have ridged patterns unique to each baby. Even identical twins have different patterns.