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
+Effect of pregnancy on endocrine function tests. Hormone Test Result FSH, LH GnRH stimulation Unresponsive from third gestation until several weeks postpartum Growth Hormone Insulin tolerance test Response increases during first half of pregnancy and then normalizes until several weeks postpartum TSH TRH stimulation Response unchanged Pancreatic Insulin Glucose tolerance test Peak glucose increases, and glucose concentration remains elevated for longer Adrenal Cortisol ACTH infusion Exaggerated cortisol and aldosterone responses Metyrapone Diminished response Mineralocorticoids ACTH infusion No deoxycorticosterone response Dexamethasone No deoxycorticosterone response
Breast changes
A woman's breasts change during pregnancy to prepare them for breastfeeding a baby. Normal changes include: Tenderness of the nipple or breast An increase in breast size over the course of the pregnancy Changes in the color or size of the nipples and areola More pronounced appearance of Montgomery's tubercles (bumps on the areola)
From about the 16th week of pregnancy the breasts are able to begin to produce milk. It's not unusual for small amounts of straw-coloured fluid called colostrum to leak from the nipples. Breast lumps also sometimes develop during pregnancy but these are generally benign cysts or fibroadenoma which are not cause for concern. If the nipples begin to leak any blood tinged fluid a woman should consult her doctor.
Breast development throughout pregnancy may result in significant Areola and Areolar gland enlargement, erectile nipples, and/or nipple sensitivity.
A woman's breasts grow during pregnancy, typically 1 to 2 cup sizes. A woman who wore a C cup bra prior to her pregnancy may need to buy an F cup or larger bra while nursing. A woman's torso also grows and her bra band size may increase one or two sizes. An average of 80% of women wear the wrong bra size, and mothers who are preparing to nurse can benefit from a professional bra fitting from a lactation consultant. Once the baby is born, after the initial stage of breastfeeding with colostrum, the mother will experience her breasts filling with milk (sometimes referred to as "the milk coming in"). This can happen up to about 50–73 hours after birth. Once full lactation begins, the woman's breasts swell significantly and can feel achy, lumpy and heavy (which is referred to as engorgement). Her breasts may increase in size again by an additional 1 or 2 cup sizes, but individual breast size may vary depending on how much the infant nurses from each breast. Changes in breast size during pregnancy may be related to the sex of the infant, as mothers of female infants have greater changes in breast size than mothers of male infants.
Many people and even medical professionals mistakenly think that breastfeeding causes the breasts to sag (referred to as ptosis). As a result, some new parents are reluctant to nurse their infants. In February 2009, Cheryl Cole told British Vogue that she hesitated to breastfeed because of the effect it might have on her breasts. "I want to breastfeed," she said, "but I've seen what it can do, so I may have to reconsider." In actuality, breastfeeding is not considered to be a major contributor to ptosis of the breasts. In fact, the biggest factors affecting ptosis are cigarette smoking, a woman's body mass index (BMI), her number of pregnancies, her breast cup size before pregnancy, and age.
Breast size does not determine the amount of milk a woman will produce or whether she will be able to successfully breastfeed her baby. Larger breast size pre pregnancy is a sign there are more fatty cells within the breast, which do not affect milk production. A more important indicator is breast changes during the course of pregnancy. If a woman does not experience any nipple or breast changes during pregnancy this is an indication she may have a rare condition such as breast hypoplasia which could lead to more difficulty breastfeeding. Women whose breasts are simply smaller but who have experienced some breast changes are likely to have a successful breastfeeding experience.
Cardiovascular The heart adapts to the increased cardiac demand that occurs during pregnancy in many ways.
Cardiac output (Lit./Min.): 6.26 Stroke Volume (Ml.): 75 Heart Rate (Per min.): 85 Blood Pressure: Unaffected
Cardiac output increases throughout early pregnancy, and peaks in the third trimester, usually to 30-50% above baseline. Estrogen mediates this rise in cardiac output by increasing the pre-load and stroke volume, mainly via a higher overall blood volume (which increases by 40–50%). The heart rate increases, but generally not above 100 beats/ minute. Total systematic vascular resistance decreases by 20% secondary to the vasodilatory effect of progesterone. Overall, the systolic and diastolic blood pressure drops 10–15 mm Hg in the first trimester and then returns to baseline in the second half of pregnancy. All of these cardiovascular adaptations can lead to common complaints, such as palpitations, decreased exercise tolerance, and dizziness.
Uterine enlargement beyond 20 weeks' size can compress the inferior vena cava, which can markedly decrease the return of blood into the heart or preload. As a result, healthy pregnancy patients in a supine position or prolonged standing can experience symptoms of hypotension.
Hematology
Blood volume and hemoglobin concentration
During pregnancy the plasma volume increases by 40-50% and the red blood cell volume increases only by 20–30%. These changes occur mostly in the second trimester and prior to 32 weeks gestation. Due to dilution, the net result is a decrease in hematocrit or hemoglobin, which are measures of red blood cell concentration. Erythropoietin, which stimulates red blood cell production, increases throughout pregnancy and reaches approximately 150 percent of their pregnancy levels at term. The slight drop in hematocrit or hemoglobin is most pronounced at the end of the second trimester and slowly improves when reaching term.
Platelet and white cell count The effect of pregnancy on platelet count is unclear, with some studies demonstrating a mild decline in platelet count and other studies that show no effect. The white blood cell count increases with occasional appearance of myelocytes or metamyelocytes in the blood. During labor, there is a rise in leukocyte count.
Hypercoagulability A pregnant woman will also become hypercoagulable, leading to increased risk for developing blood clots and embolisms, such as deep vein thrombosis and pulmonary embolism. Women are 4-5 times more likely to develop a clot during pregnancy and in the postpartum period than when they are not pregnant. Hypercoagulability in pregnancy likely evolved to protect women from hemorrhage at the time of miscarriage or childbirth. In developing countries, the leading cause of maternal death is still hemorrhage. In the United States 2011-2013, hemorrhage made up of 11.4% and pulmonary embolisms made up of 9.2% of all pregnancy-related deaths.
The increased risk of clots can be attributed to several things. Plasma levels of pro-coagulantion factors increased markedly in pregnancy, including: von Willebrand Factor, fibrinogen, factor VII, factor VIII, and factor X. Both the production of prostacyclin (an inhibitor of platelet aggregation) and thromboxane (an inducer of platelet aggregation and a vasoconstrictor) are increased, but overall there is an increase in platelet reactivity which can lead to a predisposition to clots. There is also increased blood stasis due to the compression of the vena cava by the enlargening uterus. Many factors have been shown to increase the risk of clots in pregnancy, including baseline thrombophilia, cesarean section, preeclampsia, etc. Clots usually develop in the left leg or the left iliac/ femoral venous system. Recently, there have been several case reports of May-Thurner Syndrome in pregnancy, where the right common iliac artery compresses the below left common iliac vein.
Edema