Physiological changes during pregnancy

Question 1

What happens to the uterus during pregnancy

Answer 1

Increases in size
Height increases from 7.5 to 35 cm
Weight increases from 50g to 1000g
Lower uterine segment forms

Question 2

Weight increases during pregnancy

Answer 2

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​

Question 3

Breast changes during pregnancy

Answer 3

Increased size and vascularity.​

Increased pigmentation of nipple and areola.​

Montgomery tubercles appear on the areola (dilated sebaceous glands)​

Colostrum like fluid expressed.

Question 4

Musculoskeletal changes during pregnancy

Answer 4

Increased lumbar lordosis​

Relaxation of pelvic joints and ligaments due to progesterone and relaxin.​

Question 5

Haematological changes during pregnancy

Answer 5

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.​

Question 6

When does blood plasma return to normal

Answer 6

Returns to non pregnant levels by 6 days post delivery!​

Question 7

Platelet cahnges

Answer 7

Increase in platelet turnover​

No change in platelet count in majority of pregnant women which suggests increase in production to compensate for increased consumption.​

Question 8

Changes to clotting in pregnant women

Answer 8

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.​

Question 9

What happens to th heart during pregnancy

Answer 9

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

Question 10

What happens to cardiac output during pregnancy

Answer 10

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.​

Question 11

Respiratory changes furing pregnancy

Answer 11

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​

Question 12

Glucose metabolism changes in pregnancy

Answer 12

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.​

Question 13

What causes iodine deficiency in pregnancy

Answer 13

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.​

Question 14

Pituitary changes during pregnancy

Answer 14

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.​

Question 15

Changes to adrenal gland during pregnancy

Answer 15

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.​

Question 16

Changes to the liver during pregnancy

Answer 16

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)​

Question 17

GI changes during pregnancy

Answer 17

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.​

Question 18

What is labour

Answer 18

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.​

Question 19

Cervical ripening

Answer 19

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

Question 20

What is the purpose of progesterone and oestrogen in terms of contractions

Answer 20

Progesterone typically inhibits contractions and oestrogen increases the number of gap junctions between smooth muscle cells, increasing contractility.​

Question 21

Oxytocin effect in contractions

Answer 21

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​

Question 22

Effects of prostaglandins and oxytocin in contractions

Answer 22

Prostaglandins - more intracellular calcium released per action potential, increasing the force of contractions.​

Oxytocin – lowers threshold for action potentials, increasing frequency of contractions.​

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Question 23

Second stage of labour

Answer 23

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.​

Question 24

Labour third stage

Answer 24

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.​

Question 25

How is bleeding controlled

Answer 25

Contraction of the uterus constricts blood vessels in the myometrium​

Pressure exerted on placental site once delivered by the walls of the contracted uterus.​

Normal blood clotting mechanism​