Up to 18 weeks
The second trimester starts from the fourteenth week of pregnancy. Your baby is steadily growing, and if you have a scan now, it’ll be possible to tell your baby’s sex. If your doctors think it necessary, they may suggest you have various tests around this time to rule out any abnormalities.The length of your baby’s thighbone will be measured, as well as the diameter of her head. The head measurement will be used to confirm the EDD.
Your Baby’s Progress
She’s looking more human now, with legs longer than her arms and the parts of her legs in proportion. Her skeleton continues to produce more bone, and those parts with sufficient calcium can be seen on X-rays. She now has the same number of nerve cells as an adult. The nerves from her brain begin to be coated in a layer of myelin (protective fat). This is an important step in their maturation because it helps the passage of messages to and from the brain. Connections between nerves and muscles are set up so that your baby’s well-formed limbs can move around their joints when the muscles are stimulated to contract and relax. Now that her arms are long enough, her hands can grasp each other if they touch accidentally, and she can form fists. Her movements aren’t yet under the control of her brain, though. Nor do you notice them yet because she’s not big enough to activate nerve endings on your uterine wall. Second-time mothers tend to feel their baby’s movements sooner.
Your baby’s external genital organs are taking on a more distinctive appearance. A girl’s vaginal plate, the beginnings of her vagina, is clearly developing, and a boy’s testes are well on their way to descending into the scrotum.
Her Support System
The placenta is making the increasing amounts of hormones (chorionic gonadotrophin, estrogen, and progesterone) that are needed throughout pregnancy. It’s also making an assortment of other hormones that keep your uterus healthy and play an essential part in the growth and development of your breasts in preparation for feeding your baby. The placenta forms a barrier against general infection, although not against viruses such as rubella (German measles) and AIDS, and poisons such as alcohol and nicotine. By the end of the sixteenth week, the placenta has grown in thickness to about half an inch (1 cm) and three-and-ahalf inches (7-8 cm) across.
The placenta continues to grow until, at term, it weighs a pound (500 g), and measures an inch and a half (3 cm) thick and 8-10 inches (20-25 cm) across. It’s firmly attached to the uterine wall (usually the upper part).
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