A 19-week fetus has changed dramatically from the time of your positive pregnancy test, when he was much smaller than a pencil eraser. By the 19th week of gestation, the fetus is definitely recognizable as a human being. The first fetal ultrasound, often scheduled between weeks 18 and 20, might amaze you by revealing the detailed development that has taken place in the last 5 months.
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Size and Structure
A fetus at 19 weeks gestation is about 6 inches measured from head to bottom -- what doctors call the crown to rump measurement -- or 10 inches from head to heel. Since the muscle tissues and body skeleton have now developed and the baby has straightened out, doctors often start measuring from head to heel at this point. A 19-week-old fetus measures about 8 1/2 oz. At 19 weeks gestation, a baby's arms and legs have grown to be in proportion to the rest of his body and are complete, right down to the fingernails. Most women will fetal fetal movement by this point.
Your baby's face is well developed by week 19. His eyes are fused shut and will remain so until around week 25, but the eyes are structurally intact. His ears have moved up from their original low-set position; he has begun to hear. He can suck and swallow. If you could see under his gums, you'd see his tooth buds forming. He has little subcutaneous fat in his face, giving his face a somewhat skeletal appearance. The head is still large in comparison to the body and will remain so even after birth.
Skin and Hair
The baby's skin at 19 weeks is covered in vernix caseosa, a waxy substance resembling cheese, which protects the skin from the amniotic fluid. The skin has begun to plump out a bit instead of being red and wrinkled, since fat has started to accumulate under the skin surface. Blood vessels are still visible through the skin. A 19-week-old fetus has started sprouting hair on her head for the first time, which may or may not be lost before or shortly after birth. She also has another type of hair, a fine soft layer of hair called lanugo, that covers her entire body.
The internal and external genitals have fully formed and can be spotted on an ultrasound taken at 19 weeks, as long as the baby is in a position where the technician can see between the fetus' legs.
All the major organs are in place and functioning. The spinal cord nerve development has begun and the brain is experiencing rapid growth. You can hear your baby's beating heart through Doppler ultrasound and visualize it on the ultrasound screen. The kidneys begin to produce urine and the gastrointestinal tract produce the first stool, called meconium. The alveoli, where gases re exchanged in the lungs, have not yet developed enough to support life if the baby were to be born this early.