Maternal Changes During Pregnancy
Haematological System
Physiological Changes: - 30-50% increase in blood volume, with approximately 50% of the increase accounted by plasma volume and 18% of the increase accounted by and increase in red blood cell mass. - >50% increase in blood volume in women with multiple pregnancies. - Haematocrit remains relatively unchanged. - Platelets count reduces, with no change in function. - Coagulation factors and fibrinogen increase. - Relative anemia (second and third trimester) due to hypervolaemia and haemodilution (reduced Hb). - Total white blood cell increases, mainly due to a sharp increase in neutrophils and leukocytes with a slight rise in eosinophil count. Basophil, monocyte and lymphocyte numbers remain unchanged. - Blood viscosity decreases during pregnancy due to a proportional an increase in plasma volume. This aids placental perfusion. Clinical Significance: - Blood loss may be difficult to detect in pregnant patients due to increased circulating volume. - Approximately 500ml of blood per pregnancy is lost during childbirth with no compensation. - Postnatal blood volume is reduces to normal facilitated by diuresis causing a reduction in plasma volume and the death of larger RBC as part of their normal lifespan. - Increased clotting factors and fibrinogen create a hypocoagulable state which reduces the risk of haemorrhage during or post delivery. - No change in lymphocytes (B and T cells) may be essential to survival of the foetus.
Respiratory System
Physiological Changes: - Elevated diaphragm and relaxation of the thorax muscles and cartilage cause a change in shape of the chest. - Changes to the chest as we as an increased in O2 demand (16%) result in increased minute ventilation (40%) and tidal volume (500ml to 700mL). However, pO2 increase is only slight with no real change in oxygen-haemogloben dissociation. - Progresterone stimulates the the respiratory centre while catalysing carbonic anhydrase leading to a decrease in pCO2. - The changes to respiration result in a tendency to overbreath (following the mechanisms explained) results in partially compensated respiratory alkalosis. This facilitates gas exchange across the placenta. - Diminished functional residual capacity (200mL). - Upper respiratory tract secretions increase due to increased osetrogens causing stuffiness. Clinical Significance: - Normal pCo2 reduces from 35-45mmHg to 30 to 40mmHg. - Higher chest tubes are required for chest drain. - Intubation is more difficult. - Respiration becomes more diaphragmatic rather than abdominal. - Dyspnoea is common due to increases in minute ventilation, tidal volume and oxygen consumption,
Metabolic
Physiological Changes: - Foetal nutrition comes from the mother resulting in an increased appetite. - Nutrient requirements increase by 10-30% and the average cost of pregnancy is estimate to be around 70,000 kcal. - Basal metabolic rate increases by 20%. - During the first two trimesters fat storage increases due to increased insulin and progesterone. - As pregnancy progresses there is less peripheral use of glucose by the mother due to increased insulin antagonism allowing glucose to become more available to the foetus. - Maternal weigh increases significantly and includes the products of conception, increased water and excess uterine and breast tissue. - The CNS can only use glucose as an energy source but other organs move towards lypolysis for energy production. Clinical Significance: - Calorie intake increases on average by 200kcal/day. On average women require an additional 6g or protein per day but carbohydrate and fat requirements are the same as non-pregnant women. - A healthy diet should provide all the nutrient requirements for pregnant women as a relative increase in food intake will compensate for foetal nutrient requirements. However, iron and folic acid (folate) supplementation may be required as iron is required for RBC expansion (maternal haematological change) and folate is required for foetal development (DNA and RNA synthesis and cell division, thereby faciliting new cell production). Folate deficiency has been linked to neural tube defects. - Increased metabolism results in increased heat production. - Weight gain and loss of 30kg is reported during pregnancy.
Musculoskeletal System
Physiological Changes: - Increased ligamentous laxity. - Lower center of gravity creating lordosis. - Greater back strain. - Parathyroid hormone (PTH), calcitonin and vitamin D levels increase during pregnancy resulting in increased osteoclast activity (bone resorption) to provide adequate levels of Ca2+ and phosphorus for foetal skeletal mineralisation. - hPL may cause an increase in maternal Ca2+ storage in preparation for lactation but dietary Ca2+ does not increase bone density to due the decreased reabsorptive effects of oestrogen on the kidneys. - Ca2+ may be actively transported to the foetus by the placenta to facilate bone mineralisation. - Calcitonin and PTH hormone cannot cross the placenta so the foetus must manufacture its own. - Oestrogen encourages uterine smooth muscle hyperplasia and hypertrophy, mainly during the second half of pregnancy. Interestingly, this is reversible. By 12 weeks the uterus has risen out of the pelvis to become an abdominal organ. - The lower uterine segment differentiates (softens and elongates) during the first 10 weeks of pregnancy increasing from 7cm to 25cm. - During pregnancy the uterus endometrium becomes thicker and blood supply increases in the upper part of the uterus (fondus) creating poles in the uterus (upper compared to lower). - Cervical elasticity increases due to increased mass, water content and vacularity. This allows dilation. - Unlike skeletal muscle uterine smooth muscle contain gap junctions and do not have neuromuscular junctions (and therefore motor units). - Later pregnancy sees an increase the number of gap junctions following changes in oestrogen, progesterone and prostaglandins. This facilitate electrical impulse transfer creating coordinated muscle contractions during labour. - As the foetus grows there is a shift in the centre of gravity causing lumbar lordosis (swayback). Clinical Significance: - Serum Ca2+ begins to fall following fertilisation and reach their lowest levels at 39 weeks. Serum phosphorus and magnesium fall slightly until week 30 before returning to normal levels at full term. - Increased susceptibility to orthopedic injury. - 50% of women will have back aches
Mammary
Physiological Changes: - Mammary glands increase in size and development complete by 6 months. - Secretory activity increases. Clinical Significance: - Breast tenderness and enlargement. - Discharge generally occurs in the prenatal period when mammary glands are developed. The majority of discharge will be colustrum due to inhibition of milk production by progesterone. - Milk production increases when progesterone levels drop following placental discharge.
Gastrointestinal System
Physiological Changes: - Oetrogen causes gums to become swollen and spongy, which may result in bleeding. - Increased uterine volume displaces abdominal contents. - Relatively insensitive abdominal wall. - Progesterone decreases muscle tone and therefore GIT motility. - Delayed gut motility results in increased water absorption (50-200mL of fluid is expelled in faeces from the daily intake of 2L). - Food absorption remains unchanged. - Diminished gastroesophageal sphincter tone. - The liver is displaced superiorly, posteriorly and anteriorly and relative blood flow (based on increased cardiac output) may reduce by up to 30%. Plasma protein production resulting in reduced liver function. - Progesterone reduces muscle tone of the gall bladder causing a volumetric increase and decreased emptying. - Increased Ca2+ absorption by the small intestine. Clinical Significance: - Viable foetus roughly correlates with fundus at the umbilicus. - Increased risk of gingivitis and periodontal disease. - Delayed gastric emptying and increased risk of constipation - Low sensitivity of abdominal physical examination. - Gastric reflux is common. - Reduced liver function makes testing difficult. - Reduced gall bladder tone causes bile salt retention predisposing pregnant women to gall stones or pruritis. - Non-polar lipd soluble drugs are more redily absorbed during pregnancy and readily cross the placenta and the foetals. - Drugs excretion by the foetus is slow and drugs taken in early pregnancy may be teratogenic.
Renal System
Physiological Changes: - The maternal kidney must act as the primary excretory organ for maternal and foetal waste and compensate for increased circulatory volume. - Blood flow to the kidney increases to 500mL/min (a 30-65% increase). - Kidney size increases by 1.5cm. - Glomerular size increases with no change in cell numbers. - Ureters may hold and up to 25 times more unrine (300mL) than non-pregnant patients. - Dilation of renal calyces, pelvis and ureters are accompanied by an increase in glomerular filtration rate (GFR). - GFR increased by 40-50%. reabsorption of electrolytes occurs at greater rates but glucose and amino acid reasbsoprtion does not change leading to increased excretion. - Bladder capacity doubles coupled with a decrease in bladder tone. Clinical Significance: - Increased risk of urinary tract infections during pregnancy. - Urinary incontinence is common. - Pregnant women excrete polar non-lipid drugs more readily.
Endocrine System
Physiological Changes: - The placenta is a new endocrine organ that secretes human chorionic gonadotropin (hCG), progesterone, estrogen, and human placental lactogen (hPL). These hormones facilitate physiological changes. - Progesterone increases insulin secretions and decreases peripheral insulin usage. - Oestrogen increases plasma cortisol by causing increased release of ACTH, an insulin antagonist that results in insulin resistance (decreased cell receptor sensitivity). Pancreatic beta cell hyperplasia and hypertrophy results to increase in insulin secretion as a compensatory mechanism. - Elevated cortisol converts liver glycogen to glucose (glycogenolysis) and increases hepatic glucose production (glucogenesis). - hPL is similar to growth hormone and stimulates foetal development and an increase in the placenta. It also antagonises insulin, thereby facilitating pancreatic beta cell hyperplasia and hypertrophy as per elevated cortisol. - Fotealplacental hormones greatly influence the pituitary gland inhibiting the secretion of follicular stimulating hormone (FSH) and leuteinising hormone (LH). - During puerperium (6 weeks postnatal term) prolactin is produced by the anterior pituitary gland to accommodate lactation. This causes pituitary hypertrophy. - Elevated oestrogen cause and increase in renin. This causes incressed Na+ and Cl- excretion but it is offset by increased aldosterone production (causing Na+ retention). Clinical Significance: - Maternal women have increased blood sugar levels and depleting hepatic glycogen stores. - Cushingoid appearance during pregnancy may be due to elevated cortisol.
Cardiovascular System
Physiological Changes: - The uteroplacental circulation allows for gas, nutrient and waste exchange between the mother and the foetus. - Uterine blood rises to 500mL/min, renal blood flow rises to around 400mL/minute and blood flow to the skin also increases. - Heart chamber volume increases from 70mL to 80mL (12%), thereby facilitating an increase in stroke volume as per the Starling principle, but there is no hypertrophy. - Blood volume increases. - Cardiac output increase. Increased stroke volume, increased contractility and a small increased in heart rate (approximately 15bpm) accounts for this increase. - Peripheral vascular resistance decreases. This results in a slight reduction in arterial systolic blood pressure and a large reduction in arterial diastolic blood pressure. - Pulmonary artery pressure does not change. This causes a decrease in pulmonary vascular resistance, thereby increasing in blood flow to the lungs. - Uterus expansion (which accomodates foetal growith) pushed the heart upwards and laterally moving the apex to 4th rather than the 5th intercostal space and also puts increased pressure on the abdominopelvic veins. Clinical Significance: - Sweating is common due to an increase in blood flow to the skin coupled with an increased metabolic rate. - Relatively higher blood losses may be difficult to detect due to increased blood volume. - Maternal patients have a wider pulse pressure pulse pressure due to the decrease in diastolic blood pressure. - Supine hypotensive syndrome is common due to compression of the inferior vena cava. Transport in left lateral decubitus position. - Reduced blood flow to the peripheries and increased pressure on the pelvic veins can cause varicosities in legs and vulva or anal haemorrhoids. - Heart murmurs due to increased heart volumes may be present but are not abnormal.
