Soon after ovulation there are already some changes in a woman’s body. Early changes are due to the metabolic demands brought on by the fetus, uterus and to the increasing levels of hormones, particularly those of progesterone and estrogen. These hormones prepare the lining of the uterus to receive the fertilized ovum. Following ovulation the basal body temperature normally rises about 0.5°F (0.3°C). When a woman is pregnant, the higher temperature persists beyond the 14th day after ovulation.
The most obvious physical changes are weight gain and altered body shape. Weight gain is due not only to the uterus and its contents but also to increase breast tissue, blood and water volume. The average weight gain during pregnancy is 12.5kg.
Other Physiological changes that are brought by pregnancy:
- The breast become larger as the progesterone stimulates tissue growth, and the increased estrogen stimulates the growth of milk ducts.
- The blood volume increases during pregnancy. Blood Volume increases progressively from 6-8 weeks pregnancy and reaches a maximum at approximately 32-34 weeks with little change thereafter. The increase in plasma volume (40-50%) is relatively greater than that of red cell mass (20-30%) resulting in hemodilution and a decrease in hemoglobin concentration. Intake of supplemental iron and folic acid is necessary to restore hemoglobin levels to normal (12 g/dl). In general, the greater the volume of the mother’s plasma, the greater the birth weight of her infant. Other change in the blood during pregnancy is a marked rise in fibrinogen, a blood-clotting factor, probably as a defense mechanism to reduce bleeding in pregnancy.
- The output of the heart increases (volume of blood being pumped by the heart) by 40% during pregnancy, beginning as early as the first trimester. After the 32nd week, the output falls, and it apparently does so whether it is measured with the woman lying on her back or her left side. The latter position is generally thought to be physiologically better for a woman in the last trimester.
- Many women experience shortness of breath especially in the late pregnancy. This phenomenon is the result of the changes in the mechanics of breathing caused by the fact that the heart rotates to the left and the chest diameter increases, while the diaphragm is forced upward by the uterus.
- A woman’s oxygen consumption while resting increases by about 15% to 20% by the time her baby is due. Most of this increased oxygen is used by the baby, but some of the additional oxygen is used by the mother for the increased work of the heart and lungs.
- During pregnancy, each kidney increases in length by 1-1.5cm and the kidney’s filtration of waste materials from the blood increases by 50%. This probably benefits the baby by speeding the passage of the baby’s wastes across the placenta and into the mother’s bloodstream.
Why do women gain so much weight during pregnancy? It is reasonable for pregnant women to gain 25 to 35 lbs. on average even though the average weight of the baby is just less than 10lbs this is because of the following factors:
- 7.5 pounds: average baby’s weight
- 7 pounds: extra stored protein, fat, and other nutrients
- 4 pounds: extra blood
- 4 pounds: other extra body fluids
- 2 pounds: breast enlargement
- 2 pounds: enlargement of your uterus
- 2 pounds: amniotic fluid surrounding your baby
- 1.5 pounds: the placenta