Maternal physiological changes in pregnancy
Maternal physiological changes in pregnancy are the
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.
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Estrogen, progesterone, and human chorionic gonadotropin (hCG) levels throughout pregnancy.
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Estrogen, progesterone, andtrimesters. Determinations were via radioimmunoassay.[1]
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Levels of sex hormones and SHBG during pregnancy in women.trimesters. Determinations were via radioimmunoassay.[2]
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.[3]
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.[4]
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.[5] 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.[6] The fetal skeleton requires approximately 30 grams of calcium by the end of pregnancy.[5] 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.[5]
Adrenal glands
Total
The adrenal gland also produces more aldosterone, leading to an eight-fold increase in aldosterone.[5] Women do not show signs of hyperaldosterone, such as hypokalemia, hypernatremia, or high blood pressure.
The adrenal gland also produces more
Thyroid
The
Endocrine function tests in pregnancy
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
A woman's breasts grow during pregnancy, typically 1 to 2 cup sizes.[8] A woman who wore a C cup bra prior to her pregnancy may need to buy an F cup or larger bra while nursing.[9] A woman's torso also grows and her bra band size may increase one or two sizes.[10] An average of 80% of women wear the wrong bra size,[11] and mothers who are preparing to nurse can benefit from a professional bra fitting from a lactation consultant.[10] 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.[10] 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.[12]
Many people and even medical professionals mistakenly think that
Breast size does not determine the amount of milk a woman will produce or whether she will be able to successfully breastfeed her baby.
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.[6] 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%).[20] 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.[6] All of these cardiovascular adaptations can lead to common complaints, such as palpitations, decreased exercise tolerance, and dizziness.[6]
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.[21]
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%.[20] These changes occur mostly in the second trimester and prior to 32 weeks gestation.[22] 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.[22] The slight drop in hematocrit or hemoglobin is most pronounced at the end of the second trimester and slowly improves when reaching term.[22]
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.[22] The white blood cell count increases with occasional appearance of myelocytes or metamyelocytes in the blood.[22] During labor, there is a rise in leukocyte count.
Hypercoagulability
A pregnant woman will also become
The increased risk of clots can be attributed to several things. Plasma levels of pro-coagulantion factors increased markedly in pregnancy, including:
Absolute incidence of first VTE per 10,000 person–years during pregnancy and the postpartum period | ||||||||
---|---|---|---|---|---|---|---|---|
Swedish data A | Swedish data B | English data | Danish data | |||||
Time period | N | Rate (95% CI) | N | Rate (95% CI) | N | Rate (95% CI) | N | Rate (95% CI) |
Outside pregnancy | 1105 | 4.2 (4.0–4.4) | 1015 | 3.8 (?) | 1480 | 3.2 (3.0–3.3) | 2895 | 3.6 (3.4–3.7) |
Antepartum | 995 | 20.5 (19.2–21.8) | 690 | 14.2 (13.2–15.3) | 156 | 9.9 (8.5–11.6) | 491 | 10.7 (9.7–11.6) |
Trimester 1 | 207 | 13.6 (11.8–15.5) | 172 | 11.3 (9.7–13.1) | 23 | 4.6 (3.1–7.0) | 61 | 4.1 (3.2–5.2) |
Trimester 2 | 275 | 17.4 (15.4–19.6) | 178 | 11.2 (9.7–13.0) | 30 | 5.8 (4.1–8.3) | 75 | 5.7 (4.6–7.2) |
Trimester 3 | 513 | 29.2 (26.8–31.9) | 340 | 19.4 (17.4–21.6) | 103 | 18.2 (15.0–22.1) | 355 | 19.7 (17.7–21.9) |
Around delivery | 115 | 154.6 (128.8–185.6) | 79 | 106.1 (85.1–132.3) | 34 | 142.8 (102.0–199.8) | –
| |
Postpartum | 649 | 42.3 (39.2–45.7) | 509 | 33.1 (30.4–36.1) | 135 | 27.4 (23.1–32.4) | 218 | 17.5 (15.3–20.0) |
Early postpartum | 584 | 75.4 (69.6–81.8) | 460 | 59.3 (54.1–65.0) | 177 | 46.8 (39.1–56.1) | 199 | 30.4 (26.4–35.0) |
Late postpartum | 65 | 8.5 (7.0–10.9) | 49 | 6.4 (4.9–8.5) | 18 | 7.3 (4.6–11.6) | 319 | 3.2 (1.9–5.0) |
Incidence rate ratios (IRRs) of first VTE during pregnancy and the postpartum period | ||||||||
Swedish data A | Swedish data B | English data | Danish data | |||||
Time period | IRR* (95% CI) | IRR* (95% CI) | IRR (95% CI)† | IRR (95% CI)† | ||||
Outside pregnancy | Reference (i.e., 1.00)
| |||||||
Antepartum | 5.08 (4.66–5.54) | 3.80 (3.44–4.19) | 3.10 (2.63–3.66) | 2.95 (2.68–3.25) | ||||
Trimester 1 | 3.42 (2.95–3.98) | 3.04 (2.58–3.56) | 1.46 (0.96–2.20) | 1.12 (0.86–1.45) | ||||
Trimester 2 | 4.31 (3.78–4.93) | 3.01 (2.56–3.53) | 1.82 (1.27–2.62) | 1.58 (1.24–1.99) | ||||
Trimester 3 | 7.14 (6.43–7.94) | 5.12 (4.53–5.80) | 5.69 (4.66–6.95) | 5.48 (4.89–6.12) | ||||
Around delivery | 37.5 (30.9–44.45) | 27.97 (22.24–35.17) | 44.5 (31.68–62.54) | –
| ||||
Postpartum | 10.21 (9.27–11.25) | 8.72 (7.83–9.70) | 8.54 (7.16–10.19) | 4.85 (4.21–5.57) | ||||
Early postpartum | 19.27 (16.53–20.21) | 15.62 (14.00–17.45) | 14.61 (12.10–17.67) | 8.44 (7.27–9.75) | ||||
Late postpartum | 2.06 (1.60–2.64) | 1.69 (1.26–2.25) | 2.29 (1.44–3.65) | 0.89 (0.53–1.39) | ||||
Notes: Swedish data A = Using any code for VTE regardless of confirmation. Swedish data B = Using only algorithm-confirmed VTE. Early postpartum = First 6 weeks after delivery. Late postpartum = More than 6 weeks after delivery. * = Adjusted for age and calendar year. † = Unadjusted ratio calculated based on the data provided. Source: [29] |
Edema
Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.
Metabolic
During pregnancy, both
An increased requirement for nutrients is given by fetal growth and fat deposition. Changes are caused by steroid hormones, lactogen, and cortisol.
Maternal insulin resistance can lead to gestational diabetes. Increased liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels.[citation needed]
Body weight
Nutrition
Nutritionally, pregnant women require a caloric increase of 350 kcal/day and an increase in protein to 70 or 75 g/day.[
All patients are advised to take
Renal and lower reproductive tract
Progesterone causes many changes to the genitourinary system. A pregnant woman may experience an increase in the size of the kidneys and ureter due to the increase blood volume and vasculature. Later in pregnancy, the woman might develop physiological hydronephrosis and hydroureter, which are normal.
Pregnancy alters the vaginal microbiota with a reduction in species/genus diversity.[32] Physiological hydronephrosis may appear from six weeks.[33]
Gastrointestinal
Changes in the gastrointestinal (GI) system during pregnancy are caused by the enlarging uterus and hormonal changes of pregnancy. Anatomically, the intestine and stomach are pushed up from their original positions by the enlarging uterus. While there aren't any intrinsic changes in the sizes of the GI organs, the portal vein increases in size due to the hyperdynamic state of pregnancy. Elevated levels of
The increased occurrence of gallstones during pregnancy is due to inhibition of gallbladder contraction (as result of increased smooth muscle relaxation mediated by progesterone) and reduced biliary transportation of bile (mediated by estrogen) which results in
Nausea and vomiting of pregnancy, commonly known as morning sickness, is one of the most common GI symptoms of pregnancy. It begins between the 4 and 8 weeks of pregnancy and usually subsides by 14 to 16 weeks. The exact cause of nausea is not fully understood but it correlates with the rise in the levels of human chorionic gonadotropin, progesterone, and the resulting relaxation of smooth muscle of the stomach. Hyperemesis gravidarum, which is a severe form of nausea and vomiting of pregnancy can lead to nutritional deficiencies, weight loss, electrolytes imbalance and is one of the leading causes of hospitalization in the first trimester of pregnancy.[34]
Constipation is another GI symptom that is commonly encountered during pregnancy. It is associated with the narrowing of the colon as it gets pushed by the growing uterus found adjacent it leading to mechanical blockade. Reduced motility in the entire GI system as well as increased absorption of water during pregnancy are thought to be contributing factors.[34]
Dietary cravings and dietary as well as olfactory avoidance of certain types of food are common in pregnancy. Although the exact mechanisms of these symptoms are not fully explained, it is thought that dietary cravings may arise from the thought that certain foods might help relieve nausea. Pica, which is the intense craving for unusual materials such as clay and ice has also been reported in pregnancy.[34]
Hemorrhoids and gingival disease are two common pregnancy associated physical findings involving the gastrointestinal system. Hemorrhoids arise as a result of constipation and venous congestion that are common in pregnancy. Gingival disease is thought to be related to gum softening and edema (swelling from fluid collection) that is mostly observed in pregnancy. The mechanism and reason for the gingival changes are poorly understood.[34]
Immune tolerance
The
Musculoskeletal
Neuromechanical adaptations to pregnancy refers to the change in gait, postural parameters, as well as
.The body's posture changes as the pregnancy progresses. The pelvis tilts and the back arches to help keep balance. Poor posture occurs naturally from the stretching of the woman's abdominal muscles as the fetus grows. These muscles are less able to contract and keep the lower back in proper alignment. The pregnant woman has a different pattern of gait. The step lengthens as the pregnancy progresses, due to weight gain and changes in posture. On average, a woman's foot can grow by a half size or more during pregnancy. In addition, the increased body weight of pregnancy, fluid retention, and weight gain lowers the arches of the foot, further adding to the foot's length and width. The influences of increased hormones such as estrogen and relaxin initiate the remodeling of soft tissues, cartilage and ligaments. Certain skeletal joints such as the pubic symphysis and sacroiliac widen or have increased laxity.[citation needed]
The addition of mass, particularly around the
Lumbar lordosis
To positionally compensate the additional load due to the pregnancy, pregnant mothers often extend their lower backs. As the fetal load increases, women tend to arch their lower backs, specifically in the lumbar region of their vertebral column to maintain postural stability and balance. The arching of the lumbar region is known as lumbar lordosis, which recovers the center of mass into a stable position by reducing hip torque. According to a study conducted by Whitcome, et al., lumbar lordosis can increase from an angle of 32 degrees at 0% fetal mass (i.e. non-pregnant women or very early in pregnancy) to 50 degrees at 100% fetal mass (very late in pregnancy). Postpartum, the angle of the lordosis declines and can reach the angle prior to pregnancy. Unfortunately, while lumbar lordosis reduces hip torque, it also exacerbates spinal shearing load,[37] which may be the cause for the common lower back pain experienced by pregnant women.[38]
Evolutionary implications
Given the demands of fetal loading during pregnancy and the importance of producing offspring to the fitness of human beings, natural selection may have had a role in selecting a unique anatomy for the lumbar region in females. There are sex differences in the lumbar vertebral column of human males and females, which ultimately helps mitigate some of the discomfort due to the fetal load in females. There are 5 vertebrae in the lumbar region for both males and females. However, the 3 lower vertebrae of a female's lumbar region are dorsally wedged while for males, only the lower 2 of the lumbar region are dorsally wedged. When a female arches her lower back, such as during fetal loading, having an extra dorsally wedged vertebra lessens the shearing force. This lumbar sexual dimorphism in humans suggests high natural selection pressures have been acting to improve maternal performance in posture and locomotion during pregnancy.[37]
If natural selection has acted on the lumbar region of
Postural stability
The weight added during the progression of pregnancy also affects the ability to maintain balance.
Perception
Pregnant women have a decreased
Response to perturbations
Under dynamic postural stability, which can be defined as the response to anterior (front) and posterior (back) translation perturbations, the effects of pregnancy are different. Initial sway, total sway, and sway velocity (see figure for description of variables) are significantly less during the third trimester than during the second trimester and when compared to non-pregnant women. These biomechanical characteristics are possible reasons why falls are more prevalent during the second trimester during pregnancy.
Additionally, the time it takes for pregnant women (any stage of pregnancy) to react to a translational disturbance is not significantly different than that of non-pregnant women.[40] This alludes to some sort of stability mechanism that allow pregnant women to compensate for the changes they experience during pregnancy.
Gait
Respiratory
There are many physiologic changes that occur during pregnancy that influence respiratory status and function. Progesterone has noticeable effects on respiratory physiology, increasing minute volume (the amount of air breathed in and out of the lungs in 1 minute) by 40% in the first trimester via an increase in tidal volume alone, as the respiratory rate does not change during pregnancy.[42][43] As a result, carbon dioxide levels in the blood decrease and the pH of the blood becomes more alkaline (i.e. the pH is higher and more basic). This causes the maternal kidneys to excrete bicarbonate to compensate for this change in pH. The combined effect of the decreased serum concentrations of both carbon dioxide and bicarbonate leads to a slight overall increase in blood pH (to 7.44 compared to 7.40 in the non-pregnant state) . If an arterial blood gas (ABG) specimen is drawn on a pregnant woman, it would therefore reveal respiratory alkalosis (from the decrease in serum carbon dioxide mediated by the lungs) with a compensatory metabolic acidosis (from the decrease in serum bicarbonate mediated by the kidneys).
As the uterus and fetus continue to enlarge over time, the diaphragm progressively becomes more upwardly displaced. This causes less space to be available for lung expansion in the chest cavity, and leads to a decrease in expiratory reserve volume and residual volume. This culminates in a 20% decrease in functional residual capacity (FRC) during the course of the pregnancy.
Oxygen consumption increases by 20% to 40% during pregnancy, as the oxygen demand of the growing fetus, placenta, and increased metabolic activity of the maternal organs all increase the pregnant woman's overall oxygen requirements. This increase in oxygen consumption paired with the decrease in FRC can potentially mean that pregnant people with pre-existing and/or comorbid asthma, pneumonia, or other respiratory issues may be more prone to disease exacerbation and respiratory decompensation during pregnancy.[43]
See also
- Parental brain
- Postpartum physiological changes
- Symptoms and discomforts of pregnancy
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