Anatomical and physiological changes during pregnancy: Every maternal organ adapts to pregnancy ,each at different time and way to accommodate the increasing demand of fetal growth and development . In early pregnancy the developing fetus , the placenta and the corpus luteum produce large quantities of hormones ,growth factors and other substances in to the maternal circulation that triggers the maternal systems to transfer from nonpregnant to pregnant form. This changes report usually by the end of the 6th weeks after the LMP ,this adaptations are to : 1-increase the availability of precursors for hormonal production. 2-improve transport capacity.3-maternal –fetal exchange of oxygen and various nutrient. 4-removal of additional risk factors.
Volume homeostasis
Blood volume expands during pregnancy to allow adequate perfusion to the vital maternal organs , placenta and fetus The increase mainly involve the extracellular fluid volume especially plasma and begun at 6-8wk,plateau at 32-34wks. The total body water increase from 6.5 to 8.5L by the end of pregnancy. Factors contributing to fluid retention: 1-Sodium retention. 2-Decrease thirst threshold. 3-Decrease plasma oncotic pressure. 4-Decrease plasma albumin as a result of hemodilution.Consequence of fluid retention
1-Decrease Hemoglobin concentration and hematocrit 2-Decrease serum albumin level 3-Increase stroke volume . 4-Increase renal blood flowHematology (blood)
Hemoglobin concentration fall from 13.3 to 10.9 g/dL because of the discrepancy between the 1000-1500 ml increase in the plasma volume and the increase in the erythrocyte mass 280ml. Iron demand increases leading to increase iron absorption from GIT. Increase in TIBC (iron transporting mechanism ). Pregnancy without iron supplementation may lead to depletion of the iron stores ( serum ferritin ,bone store ). Plasma folate decrease due to increase GFR but RBC folate do not to decrease to the same extend. Maternal platelet count usually unchanged or it may be reduced due to aggregation , increase platelet count in postpartum period so increase thromboembolic event at this period. WBC count increase in pregnancy this mainly the poly morph nuclear cells from the 3rd weeks of gestation and more pronounced in the postpartum. ESR is increased.Haemostasis and coagulation
Pregnancy is a hyper coagulable state and return to normal after 4 weeks postpartum , at term about 500 ml of blood pass to the placental bed every minutes so without effective hemostatic mechanism woman may rapidly die from blood loss. Almost all clotting factors including and serum fibrinogen are increased. Reduction in plasma fibrinolytic activity.Respiratory system
Anatomical changes The neck , oropharyngeal tissues , breasts and chest wall are affected by weight gain during pregnancy and may lead to difficult intubation during general anesthesia. The vascularity of the respiratory tract mucosa increases leading to nasal congestion and bled easily. As pregnancy progresses the diaphragm is elevated 4cm by the enlarging uterus. The lower ribcage circumference expands by 5 cm. Respiratory muscle function unaffected. Increase pulmonary blood flow.Physiological changes
Increase in the tidal volume from 8 weeks ( in response to progesterone And increase metabolic demand ).Increase minute ventilation by 40% ( amount of air move in and out of lungs in 1minute ) which is the results of tidal volume and respiratory rate .Mild physiological dyspnea common in 5 0%of women.Vital capacity unchanged or slightly increase. Decrease residual volume of the lung as a result of elevation of the diaphragm. All these changes don’t affect the interpretation of the tests of the ventilation ( forced expiratory volume in 1 second and peak expiratory flow rate ).
Blood gas changes
Decrease pco2 . Increase po2. Increase o2 availability to tissues and placenta. Increase production of 2,3 diphosphoglcerate ( 2,3 DPG ) within the maternal RBCs to facilitated oxygen delivery to the fetus .Cardiovascular system
Increase heart rate 10-20% since early gestation and together with the increase stroke volume 10 % lead to an increase in the cardiac output by ( 30-50% ) as the cardiac out put =stroke volume X heart rate . A reduction in the diastolic pressure by about 10-15 mmHg are more than systolic pressure which about 5-10 mmHg leading to increase pulse pressure , later on diastolic pressure increase to pre regnancy level measuring by korotkoff 5 which is the disappearance of sound during blood pressure measurement .Finding on cardiovascular examination:
Palpitation are common ( Premature atrial and ventricular ectopic beats are common) Decrease in mean arterial pressure ( 10% ) as a result of decline in the peripheral vascular resistance. large pulse volume. First heart sound loud and may be spliting . audible third heart sound 80%. Ejection systolic murmur 90%. Continuous systolic murmur 10% due to increase mammary blood flow. Diastolic murmur 20% .ECG Changes
Increased heart rate left axis deviation.Inverted T-wave in lead ІІІ.Q in lead ІІІ & AVF.Non specific ST segment changes.Aortocaval Compression
From mid-pregnancy , the enlarged uterus compresses both the inferior vena cava and the lower aorta when the patient lies supine ; Compression of the aorta may lead to a reduction in uteroplacental and renal blood flow. Compression of the inferior vena cava by the gravid uterus impairs venous return to the heart in supine position . A women will develop significant supine hypotension , and loss of consciouseness is possible. By rolling over on to the left side, cardiac output is return to normal.Gut
Progesterone causing decrease lower esophageal sphincter tone together with elevation of the diaphragm increase the chance of reflux esophagitis. Also progesterone delay stomach and bowel motility leading to constipation , hemorrhoid , and increase the risk of aspiration of the gastric content during general anesthesiaLiver
Increase hepatic blood flow . liver function unchanged. Increase protien production especialy albumin. Serum ALT and AST are slightly reduced. Serum alkaline phosphatase increase due to placental production.
The kidney and urinary tract
Anatomical changes Kidney increase in size with 1-2cm . Increase in the length , there is dilatation of pelvic calycesis systems under the influence of progesterone and return to normal by 6 weeks postpartum. Increase Renal blood flow by 80% in the 2nd trimester.Physiological changes Increase glomerulofilteration rate by 50% after conception. creatinine clearance increased by 25% . plasma renin and angeotensin 2 activity are increased. plasma urea , creatinine , uric acid are decreased due to increase renal excretion . Sodium and potasium metabolism remain unchanged. Renal excretion of calicium ,proteins and folic acid increase. Glycosuria are common and normal in un complicated pregnancy due to increase GFR and exceeding renal threshold for the tubular absorption.