Your baby’s eyes and ears are now clearly identifiable, although the eyelids are fused together to protect the developing eyes. They won’t reopen until about your 30th week. Tissue that will become bone is developing around your baby’s head and within the arms and legs. If you were able to sneak a peek at your baby this week, you might see some tiny ribs. Your baby is now able to move his or her body in a jerky fashion, flexing the arms and kicking the legs.
But you won’t be able to feel these movements until your baby grows a bit larger. Your baby may be able to put a thumb in his or her mouth, but sucking will come later.
When you are 13 weeks pregnant, your uterus is enlarging at a noticeable rate and you will be able to see the first signs of a visible bump. Your nipples have become darker and the blue veins in your breasts are a lot more obvious.
The baby is now 2.9 inches (7,4 cm) long and weighs 0.8 ounce (23 grams). The bone marrow, liver, and spleen have now taken over production of blood cells. The bones are developing and the teeth are in place. The baby may already be practising lip movements to develop the muscles needed for the sucking reflex after the birth.