Your baby has sufficiently increased in size at this time to have developed a nervous system and muscles capable of allowing him to move. Because he is still so small, he can swim up and down and be in any position at any time.
Your Baby’s Progress
Starting now, form 19 weeks after your LMP, your baby’s rapid growth rate (but not weight gain) starts to slow down, and he matures in other ways. He begins to build up his defence systems. A sheath begins to form around the nerves in his spinal cord to protect them from possible damage. He also has his own primitive immune system, with which he can partially defend himself against some infections.
To produce body heat and maintain his temperature, your baby needs specialized fatty tissue. This is provided by a substance known as brown fat, which started to form during the fourth month. Now, deposits of brown fat begin to build up in areas of his body such as his neck, chest, and crotch. This will continue until term. One of the reasons that premature babies are so vulnerable is that they have insufficient amounts of brow fat and so are unable to keep themselves warm.
His skin will continue to grow, although it will be red and wrinkled because there is so little fat underneath it. From this month on, he becomes increasingly plumper. The baby’s sebaceous glands become increasingly plumper. The baby’s sebaceous glands become active and produce a waxy, greasy substance known as the vernix caseosa, which provides his skin with a protective coating during its long immersion in the amniotic fluid.
Your baby’s body is also covered with fine hair called lanugo. As yet, no one is quite sure of its purpose, but it may help to regulate his body temperature or it may be there to hold the protective vernix caseosa in place.
As his nerve fibers become connected and his muscle development and strength increase, his movements are more purposeful and coordinated. He embarks on his own athletic program- stretching, grasping, turning – which builds up his muscles, improves his motor ability, and strengthens his bones. These movements can make your abdomen sore.
A boy’s scrotum is solid at this stage. A girl’s vagina starts to become hollow, and her ovaries contain about 7 million ova, which will decline to approximately two million by the time she is born. By the time she reaches puberty, 200, 000 to 500, 000 ova will be left, and she will release only 400 to 500 of these during her adult life – approximately one per month.