Baby: Week 4

An intricate exchange of blood is going on between you and your mother now.

4 weeks from conception. Human embryo measuring approximately 13 mm crown to rump. The upper limbs, fingers and face are developing and growing rapidly. Photo credit - Ralph Hutchings Getty Images

An intricate exchange of blood is going on between you and your mother now. Your heartbeat (about 150 beats per minute) pushes blood down the umbilical cord into the placenta and close to your mum’s blood vessels along the uterine wall. Your blood carries out carbon dioxide waste, while your mother’s blood passes oxygen and nutrients to you. Your mother must be careful to protect you from injury from X-rays, alcohol, drug usage, certain infections and vitamin deficiencies.[1]

The supply of oxygen and nutrients are powering some real growth! Your kidneys and liver, intestines and appendix are now growing, and the neural tube connecting your brain and spinal cord will close this week. Arm and leg ‘buds’ form this week, as do the folds that become your neck and lower jaw.[2]

Your facial features are now beginning to form, with dark spots marking the eyes, and tiny openings and pits for the nostrils and ears. Muscle and bone tissues are building. And your pituitary gland, which releases hormones, is forming.[3] Your body begins to take on a C-shaped curvature.[4] Growth and change are happening all around, from major shapes to minor details.