18 Weeks of Pregnancy

Up to 18 Weeks of Pregnancy

18 Weeks of PregnancyThe second trimester starts at the 14th week of pregnancy.  Your baby is steadily growing, and if you have a scan at this time it is possible to discern the baby’s sex.  If it is felt necessary, around this time you will be offered various tests to rule out abnormalities.  The length of the femur will be measured, as well as the diameter of the head; this latter measurement will be used to confirm the EDD.  



Your Baby’s Progress  



She is looking more human, with legs longer than arms and the parts of her legs in proportion.  The skeleton continues to produce bone and those parts with sufficient calcium can be seen on X-ray. 


The fetus now contains the same number of nerve cells as an adult.  The nerves from the brain begin to be coated in a layer of protective fat (myelin).  This is an important step in their maturation because it facilitates the passage of messages to and from the brain.  Connections between nerves and muscles are established so that your baby’s well-formed limbs can move at the joints when 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. 



However, movements are not yet under the control of the brain.  Nor do they register with you at first because the fetus is not big enough to activate nerve endings on the uterine wall.   Second-time mother tend to feel fetal activity sooner. The fetus’s external genital organs acquire a more distinctive appearance.  A girl’s vaginal plate, the precursor to her vagina, is clearly developing, and a boy’s testes are at the deep inguinal ring and well on their way to descending into the scrotum. 



Her Support System 


The placenta is producing the increasing amount of chorionic gonadotropin, estrogen, and progesterone that are needed throughout pregnancy.  It also produces an assortment of other hormones that maintain the health of the uterus and play an essential part in the growth and development of the mother’s breasts in preparation for lactation. 


The placenta forms a barier against infection, although not against viruses such as rubella (German measles) and AIDS or poisons such as alcohol and nicotine.  By the end of the 16th week, the placenta has grown to about half an inch (1cm) in thickness and three and a half inches (7-8 cm) across. 


Growth will continue until at term it reaches a weight of 11 pounds (500gm), a thickness of an inch and a half (3cm), and a diameter of 8 to 10 inches (20-25cm).  It is firmly attached to the uterine wall (usually the upper part).

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