Week Twenty One: Nourishment evolves
You are 21 weeks pregnant. (fetal age 19 weeks)
Your baby's bone marrow has started making blood cells, a job done by the liver and spleen until this point. The placenta has provided nearly all of your baby's nourishment, now your baby will begin to absorb small amounts of sugar from swallowed amniotic fluid.
Based on the size of baby's head, which is about 2 inches (5cm), the date of birth can be determined to within one week. The fetus is steadily gaining fat and has grown a whitish coat of a slick, fatty substance to protect skin in amniotic fluid and to ease delivery.
In girls, the vagina is formed and the ovaries already contain over six million eggs which will be reduced to about 400 by the time of puberty. For boys, the testes begin to descend from the abdomen this week. (Boys don't produce sperm until puberty).
The baby can hear and recognize the mother's voice, and may respond to some types of music.
Your baby now weighs about three-quarters of a pound and is approximately 10 1/2 inches long — the length of a carrot. You may soon feel like she's practicing martial arts as her initial fluttering movements turn into full-fledged kicks and nudges. You may also discover a pattern to her activity as you get to know her better. In other developments, your baby's eyebrows and lids are present now, and if you're having a girl, her vagina has begun to form as well.
Your baby now has fully developed eyelids and eyebrows, and her fingernails have grown to the ends of her fingers. Her skin still looks pink and wrinkly, but is no longer translucent, because fat is being laid down underneath. Your baby now opens and closes her mouth regularly, drinking the amniotic fluid. The waste products are passed back through the umbilical cord and into your bloodstream for your kidneys to dispose of.
Her heartbeat is getting stronger every day, now beating at around 120 to 140 beats per minute. Her lungs are still developing and are too immature for her to survive outside the womb, but she's practicing breathing movements already. When she inhales, her lungs fill with amniotic fluid, which helps her to develop the air sacs she'll need to breathe after birth.
Baby's now the size of a banana!
Baby's digestive system is busy creating meconium (a tarry black substance made of swallowed amniotic fluid, digestive secretion, and dead cells), which will fill the first diaper after birth. And, if baby is a girl, her womb is now stocked up with her lifetime supply of six million eggs (the number will drop to around one million by birth).
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