Physiological changes in pregnancy are the adaptations that take place during pregnancy that enable the accommodation of the developing embryo and fetus. These are normal physiological adaptations that cause changes in behavior, the functioning of the heart, blood vessels, and blood, metabolism including increases in blood sugar levels, kidney function, posture, and breathing. During pregnancy numerous hormones and proteins are secreted that also have a broad range of effects.
Hormonal Pregnant women experience numerous adjustments in their endocrine system that help support the developing fetus. The fetal-placental unit secretes steroid hormones and proteins that alter the function of various maternal endocrine glands. Sometimes, the changes in certain hormone levels and their effects on their target organs can lead to gestational diabetes and gestational hypertension.
Fetal-placental unit Levels of progesterone and estrogen rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle. The progesterone is first produced by the corpus luteum and then by the placenta in the second trimester. Women also experience increased human chorionic gonadotropin (β-hCG), which is produced by the placenta.
Pancreatic insulin The placenta also produces human placental lactogen (hPL), which stimulates maternal lipolysis and fatty acid metabolism. As a result, this conserves blood glucose for use by the fetus. It can also decrease maternal tissue sensitivity to insulin, resulting in gestational diabetes.
Pituitary gland The pituitary gland grows by about one-third as a result of hyperplasia of the lactrotrophs in response to the high plasma estrogen. Prolactin, which is produced by the lactrotrophs increases progressively throughout pregnancy. Prolactin mediates a change in the structure of the breast mammary glands from ductal to lobular-alveolar and stimulates milk production.
Parathyroid Fetal skeletal formation and then later lactation challenges the maternal body to maintain their calcium levels. The World Health Organization recommends that women consume 1200 mg of calcium daily during pregnancy. The fetal skeleton requires approximately 30 grams of calcium by the end of pregnancy. The mother's body adapts by increasing parathyroid hormone, leading to an increase in calcium uptake within the gut as well as increased calcium reabsorption by the kidneys. Maternal total serum calcium decreases due to maternal hypoalbuminemia, but the ionized calcium levels are maintained. If there is insufficient calcium intake, the mineral may be taken from the pregnant woman's bones, particularly in the later stages of pregnancy.
Adrenal glands Total cortisol increases to three times of non-pregnant levels by the third trimester. The increased estrogen in pregnancy leads to increase corticosteroid-binding globulin production and in response the adrenal gland produces more cortisol. The net effect is an increase of free cortisol. This contributes to insulin resistance of pregnancy and possibly striae. The adrenal gland also produces more aldosterone, leading to an eight-fold increase in aldosterone. The adrenal gland also produces more androgens, such as testosterone, but this is buffered by estrogen's increase in sex-hormone binding globulin (SHBG). SHBG binds avidly to testosterone and to a lesser degree DHEA.
Thyroid The thyroid enlarges and may be more easily felt during the first trimester. The increase in kidney clearance during pregnancy causes more iodide to be excreted and causes relative iodine deficiency and as a result an increase in thyroid size. Estrogen-stimulated increase in thyroid-binding globulin (TBG) leads to an increase in total thyroxine (T4), but free thyroxine (T4) and triiodothyronine (T3) remain normal.
Endocrine function tests in pregnancy
Breast changes
A woman's breasts change during pregnancy to prepare them for breastfeeding a baby. Normal changes include:
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