12 Weeks- Development

Your Baby This Coming Week

Your baby is about the size of a peach and is growing rapidly. Crown to rump, your baby measures 2.6 to 3.1 inches (6.5 to 7.8cm) and weighs 0.5 to 0.7 ounces (14 to 20g).

Your baby's legs are longer than her arms and her skin is red and transparent. Her eyelids are fused together and won't open for about four more months. Her arms are long enough to reach her mouth and she may begin to place her thumb in her mouth. Her sucking reflex, however, is not yet developed.

The tissue that will become your baby's bones is being laid out, especially around her head and her arms and legs. Some ribs may be distinguished at this time. The nose and chin are more prominent now.

Your Body This Coming Week

You are beginning your second trimester of pregnancy.

Your uterus is growing rapidly and is filling the pelvis and moving up into the abdomen. If you are still having morning sickness, it may stop around this point.

Some women will get stretch marks on the breasts, hips and buttocks that may show up this early. They will later fade but will probably not disappear altogether. Some women experience itching around this time but it is more common later in pregnancy.

You probably have noticed changes in your breasts. They are becoming larger and heavier and the areola is probably darkening. They are preparing to secrete milk for your baby!

Your placenta is now well developed and is responsible for hormone production which was previously manufactured by your ovaries. Estrogen and progesterone are the primary hormones which are now being produced. These hormones are necessary for maintaining your pregnancy and inducing the changes necessary for it to progress.

Your baby will begin to practice breathing in the next few weeks as her chest rises and falls in mock breathing motions. She will also swallow small amounts of amniotic fluid which will be passed as urine.

Your placenta is providing all of your baby's needs for nutrition, oxygen and waste disposal, though the amniotic fluid will become more important later on.

All major components of the body are formed and now must grow and mature. From now on, your baby's development will consist primarily of organ maturity and growth and body refinement.