The baby begins sucking their fingers [1]

The baby begins sucking their fingers [1]

At this stage, your baby not only starts to take their fingers to their mouth, but they can also make a fist and grimace. When the uterine walls brush against the baby, they may tremble and make grasping motions. An ultrasound also reveals the first movements of the baby’s chest, which are motions that resemble breathing. And at this time, an ultrasound can allow you to clearly distinguish a single pregnancy from a multiple pregnancy.

Brain development continues rapidly [1] with the differentiation of the cerebral cortex, and the main nuclei developing as part of the central nervous system. The new vestibular system is responsible for motion and spatial orientation. This helps the baby move around in the amniotic fluid. The circulatory system also develops and becomes more specialized. Blood circulation between mother and fetus becomes more effective, and the baby receives all needed nutrients for rapid, healthy growth.

During this stage of pregnancy, the baby develops a cartilage template for bones. It is also possible to detect early signs of milk teeth in the gums. Tiny vocal cords appear in the larynx and fluffy hair forms on the skin, to later become ​​eyelashes and eyebrows.

At this point, sexual differentiation occurs under the influence of genetics and hormones. Testosterone develops external male genitalia, the penis, and the scrotum [2]. Because it is still early in the physical development of the baby, these organs are too small to be accurately determined through an ultrasound, so it is best to wait to determine the baby’s sex until later on.

The corpus luteum has been supplying needed levels of progesterone up until this point, but levels in the placenta are now high enough that it is no longer needed. Placental thickness by the end of this week is around 0.6 inches.

What we can see on an ultrasound

The baby will lie on their back, with their head and buttocks against the uterine wall. You should see the contour of the head and the profile. The head appears somewhat large, but soon it will become more proportionate to the rest of the body. The muscles of the mouth are already working, so you may see the baby open and close it.

The baby’s arms should be visible; a favorite position in the womb is to cross their arms over their chest. Bent legs are visible. The dark, hazy area is the amniotic fluid, which is constantly in flux.

1. amniotic fluid

2. head

3. hand

The following shot shows the baby's head and face.

1. fetal head