Pregnancy 10 Weeks

Fetal Development

The average size is approximately 1.25 to 1.68 inches crown to rump, and the baby now weighs a little less than 0.2 ounces.

At the end of this week the fetal period begins, the embryo is now called a fetus, Latin for "Young one" or "Offspring". The external genitalia are showing distinguishing characteristics, although it's still too soon to tel if you are having a girl or boy by ultrasound. If you're having a boy, his testes will begin to produce the male hormone testosterone this week.

The baby's organs and systems are all formed, and now just continue to develop and grow.

Your baby's heart has now separated in 4 chambers, and blood begins to flow through a rudimentary circulatory system. The heart is beating irregularly, ranging from 140-150 beats per minute, about twice as many as yours! Within the aorta the valves and pulmonary blood vessels have completed development. These direct the blood flow to and from the body and lungs. The yolk sac has disappeared and blood production is now taken over by the liver. Once the bones fully mature, the bone marrow will produce the blood. The baby's lungs are growing as the "bronchi" are branching out.

Your baby is now developing elbows, knees, wrists and ankles. Muscle tissue is now forming between the skin and bones. Your baby's neck is more developed, allowing them to slightly lift and turn their head!

The eyelids have grown, but will remain fused shut until about week 25-27 of pregnancy. External ears are completely formed and take their final shape, as well as the upper lip. Tooth buds form inside the mouth. The webbing between the fingers and toes has disappeared, creating seperate digits.

The umbilical cord is formed. During this week the placenta begins to produce progesterone, but the baby doesn't rely on the placenta for nourishment yet.

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