Physiological changes during pregnancy Flashcards
What happens to the uterus during pregnancy
Increases in size
Height increases from 7.5 to 35 cm
Weight increases from 50g to 1000g
Lower uterine segment forms
Weight increases during pregnancy
Increase by approx. 12.5kg
due to growth of fetus, enlargement of maternal organs, maternal storage of fat, Increase in maternal blood and interstitial fluid
Breast changes during pregnancy
Increased size and vascularity.
Increased pigmentation of nipple and areola.
Montgomery tubercles appear on the areola (dilated sebaceous glands)
Colostrum like fluid expressed.
Musculoskeletal changes during pregnancy
Increased lumbar lordosis
Relaxation of pelvic joints and ligaments due to progesterone and relaxin.
Haematological changes during pregnancy
Plasma volume increases by 15 % in first trimester and continues to increase until the third trimester when it peaks at approx. 50% more than non-pregnant levels. Remains increased until term.
Often a notable increase in maternal plasma volume of around 1 litre 24hrs post delivery.
When does blood plasma return to normal
Returns to non pregnant levels by 6 days post delivery!
Platelet cahnges
Increase in platelet turnover
No change in platelet count in majority of pregnant women which suggests increase in production to compensate for increased consumption.
Changes to clotting in pregnant women
Increase in factors VII, VIII, IX, XII, fibrinogen and fibrin degradation products
Factors III and XI decrease.
Endogenous anticoagulants such as antithrombin and protein S fall.
What happens to th heart during pregnancy
Anatomically the heart is pushed upwards and rotated forwards with lateral displacement of the left border
Ejection systolic murmur normal due to turbulence secondary to increased blood flow through normal heart valves
Heart sounds louder, first heart sound split
Occasional diastolic murmur
What happens to cardiac output during pregnancy
Heart rate increases by 15% by end of first trimester and 25% by end of second trimester in comparison with non pregnant values. This increase is maintained until term.
Stroke volume increased by 20% at 8 weeks and up to 30% by the end of second trimester until term.
Increased cardiac output secondary to increased heart rate, stroke volume and reduced systemic vascular resistance.
Respiratory changes furing pregnancy
Tidal volume increases by 30% in early pregnancy, 40-50% by term
Fall in functional residual capacity
Thoracic anatomy changes – elevation in diaphragm, change in lung volume
Respiratory rate generally unaffected, but can be slight hyperventilation
pO2 increased, pCO2 decreased – mild respiratory alkalosis
Glucose metabolism changes in pregnancy
Pregnancy is associated with an insulin-resistant condition similar to that of type 2 diabetes.
Increasing oestrogen and progesterone lead to pancreatic beta cell hypertrophy and insulin excretion which alter maternal carbohydrate metabolism.
Secretion of human placental lactogen, prolactin, cortisol, oestrogen and progesterone induce insulin resistance. These hormones are found in significantly greater levels in pregnant women.
What causes iodine deficiency in pregnancy
loss through increaserd GFR and reduced renal tubular absorption. Active transport of iodine to fetoplacental unit and fetal thyroid activity also deplete maternal pool in second trimester.
Pituitary changes during pregnancy
Significant enlargement of pituitary during pregnancy (up to 35%)
This relates to an increase in the number of prolactin secreting cells. Prolactin levels are increased 10-20 fold in comparison with non pregnant values
Gonadotrophin levels (LH and FSH) are suppressed by high concentrations of oestrogen and progesterone
Basal levels of GH and ADH remain unchanged.
Changes to adrenal gland during pregnancy
Free and bound cortisol levels increase during pregnancy. Levels of serum and urinary cortisol increase 3 fold by term.
Hepatic synthesis of cortisol binding globulin is also increased.
Normal diurnal variation in ACTH and cortisol levels.
Levels of angiotensin II increased 2-4 fold.
Plasma renin activity increased 2-3 fold.
Plasma and urinary levels of aldosterone are increased 3 fold in the first trimester and 10 fold by the third trimester.
Changes to the liver during pregnancy
Increased liver metabolism
20-40% fall in serum albumin concentration.
Alkaline phosphatase (ALP) concentration increases 2-4 fold. Largely due to placental production of ALP.Normal levels in third trimester up to 400U/l
No significant change in bilirubin concentration.
ALT upper limit of normal range falls to 32 (40), GGT upper limit falls to around 40 (50), AST upper limit falls to around 30(40)
GI changes during pregnancy
Changes in GI motility during pregnancy including reduced lower oesophageal pressure, reduced gastric peristalsis and delayed gastric emptying.
GI motility inhibited, increased large and small bowel transit times.
Constipation, nausea and vomiting are common in pregnancy.
What is labour
Involuntary contractions of the uterine smooth muscle occur intermittently throughout the third trimester (Braxton hicks)
Diagnosis of labour made when regular painful contractions lead to effacement and dilatation of the cervix.
Cervical ripening
Softening of the cervix prior to labour
Increased vascularity, stromal hypertrophy, glandular hypertrophy and hyperplasia.
Occurs in response to oestrogen, relaxin and prostaglandins breaking down cervical connective tissue.
Prostaglandins are produced by the placenta, the uterine decidua, the myometrium and the membranes.
This leads to an increase in the oestrogen:progesterone ratio
Ripening involves reduction in collagen, increase in glycosaminoglycans, increase in hyaluronic acid, reduced aggreghation of collagen fibres
What is the purpose of progesterone and oestrogen in terms of contractions
Progesterone typically inhibits contractions and oestrogen increases the number of gap junctions between smooth muscle cells, increasing contractility.
Oxytocin effect in contractions
Responsible for initiating uterine contractions.
During pregnancy it has limited action as low number of oxytocin receptors, and it is inhibited by relaxin and progesterone.
At approx. 36 weeks under influence of oestrogen there is increase in number of oxytocin receptors present within myometrium.
Uterus begins to respond to pulsatile release of oxytocin from posterior pituitary.
Oxytocin production increased by afferent impulses from the cervix and vagina.
Contractions result in a feedback loop to the posterior pituitary to release more oxytocin leading to stronger contractions which drives process of labour
Effects of prostaglandins and oxytocin in contractions
Prostaglandins - more intracellular calcium released per action potential, increasing the force of contractions.
Oxytocin – lowers threshold for action potentials, increasing frequency of contractions.
Second stage of labour
Fibres of myometrium do not fully relax following each contraction.
Steady reduction in uterine capacity so that pressure inside becomes stronger as labour progresses and aids expulsion of the fetus.
Labour third stage
Uterine muscle fibres contract to compress blood vessels supplying the placenta which then shears away from uterine wall.
Contractions continue until placenta and membranes have been delivered.
