Physiological changes during pregnancy

Question 1

Metabolic changes during pregnancy in the mother

Answer 1

• The basal metabolic rate increases in pregnancy - metabolism changes to ensure adequate nutrition for fetal growth
• A weight gain of 10-14 kg throughout pregnancy would be considered normal
• Pregnancy is a time of relative insulin insensitivity.
  
  • Human placental lactogen produced by the placenta acts against maternal insulin. (*gestational diabetes)
  • There is increased storage of lipids in maternal tissues. Fatty acids are vital for fetal organogenesis.

Question 2

Heartburn / reflux in pregnancy

Answer 2

• During pregnancy food moves more slowly into the stomach and there is delayed emptying.
• Hormones also cause relaxation of the lower oesophageal sphincter meaning contents are more likely to reflux from the stomach back into the oesophagus.
• The mechanical pressure from an enlarging uterus makes this worse as does delayed gastric emptying.

This is one of the reasons why general anaesthetic is much higher risk in pregnancy – these changes mean the risk of aspiration is much higher and increases with advancing pregnancy.

The introduction of regional anaesthesia (spinals and epidurals) made a huge difference to morbidity and mortality of operative procedures in maternity patients.

Question 3

Oedema

Answer 3

80% of pregnant people will develop some oedema particularly towards term. Whilst common, oedema can be an important sign of pre eclampsia

• There is a physiological sodium and water retention and a decreased ability to excrete a sodium and water load.
• The ↑ blood volume of pregnancy and ↓ venous return due to compression of the IVC from the gravid uterus also contributes to peripheral oedema.

Question 4

Thyroid changes in pregnancy

Answer 4

• Liver produces more thyroid binding globulin (TBG) but the total level of thyroxine (T4) and tri iodothyronine (T3) also ↑ so FREE T3 and FREE T4 (active) levels remain the same.
• Pregnancy is associated with a relative iodine deficiency:
  
  • Maternal iodine requirements ↑ because iodine is actively transported to the fetoplacental unit and urinary iodine excretion is doubled because of an ↑ glomerular filtration rate and ↓ renal tubular reabsorption.
  • The thyroid gland therefore works harder to ↑ its iodine uptake and may hyperthrophy to ensure adequate levels of iodine trapped.
• Thyrotoxicosis (overactive throid) occurs in approximately 1 in 500 pregnancies. It is most often due to Graves disease. The antibodies that cause Graves disease (TSH receptor antibodies) can cross the placenta and cause fetal and/or neonatal hyperthyroidism.
• Hypothyroidism affects approximately 1% of pregnancies.
  
  • The fetus is dependent on maternal thyroid function until fetal thyroid function begins at around 12 weeks gestation. It is important to ensure good thyroid replacement prior to pregnancy.

Question 5

Immunosuppression

Answer 5

• In pregnancy there is a general state of immunosuppression to allow for fetal tolerance.
• It unfortunately increases the maternal susceptibility to infection.
• This explains why some autoimmune conditions such as Crohns disease, rheumatoid arthritis, can improve during pregnancy.

Question 6

Cardiovascular system:

The heart has to work much harder during pregnancy due to:

• growing fetus
• the weight gain associated with pregnancy
• ↑ O2 requirements of the uterus and breasts
• Also has to pump blood through the utero placental circulation.

Answer 6

• The circulating blood volume ↑ by 50 —70% of the non-pregnant:
  
  • the L ventricular EDV is increased and can be seen as early as 10 weeks on an echocardiogram (ECHO)
  • The ↑ blood volume can cause problems for people with dilated cardiomyopathy or lesions such as mitral stenosis or pulmonary hypertension.
• ↑CO due to ↑SV. ↑HR too
• Red cell mass also increases but only by about 40% causing a relative haemodilution – this causes the physiological anaemia of pregnancy.
• ↓TPR - due to ↑ circulating vasodilators and the diversion of blood into the low pressure uteroplacental unit - lowest between 20-32 weeks.

Question 7

Post partum CV changes

Answer 7

• Most changes return to normal by 3mth post delivery
  
  • 3 days post delivery the blood volume will have decreased by 10%
• The blood pressure (BP) initially falls then increases again by 3-7 days after birth. It returns to prepregnancy levels by 6 weeks
• TPR begins to increase again over the first two weeks and the heart rate falls to prepregnancy levels over a similar time frame.

Question 8

Respiratory changes in pregnancy

Answer 8

• ↑ oxygen requirements of pregnancy
• Physiological adaptations during pregnancy increase the volume of air and gas exchange of each breath increasing oxygen availability and carbon dioxide removal in the mother and fetus.
• ↑Tidal volume
• ↑ Respiratory rate - can be perceived as SOB. Because of this relative hyperventilation, PCO2 levels are lower in pregnancy and the pregnant healthy person is in a state of compensated respiratory alkalosis.
• ↓Functional residual capacity - air left over in lungs after expiration decreases due to the compression of the diaphragm by the uterus.
• In some but not all pregnancies, asthma improves because of the bronchodilator effect of progesterone.

Question 9

Physiological anaemia of pregnancy

Answer 9

• ↑ circulating blood volume + RBC’s causing a physiological anaemia of pregnancy (so hameoglobin reduces)
• This means that at 28 weeks a haemoglobin (Hg) of 105 g/L or above is considered normal (non pregnant reference range 120-160g/L)

Question 10

1st and 2nd most common cause of pregnancy anaemia

Answer 10

1. Iron deficiency
2. Folate deficiency

Question 11

What happens to the overal WCC and neutrophil count in pregnancy?

Answer 11

It increases in normal pregnancy

Question 12

Pregnancy is a hypercoagulable state.

Name which clotting factors increase and which decrease.

Answer 12

Increase - clotting factors VII, IX and X and Fibrinogen

Decrease - Protein S and C and anti-thrombin 3 levels

Question 13

Changes in Renal system during pregnancy

Answer 13

• There is significant dilatation of the urinary collecting system - due to relaxation of the smooth muscle of the ureter caused by progesterone as well as the mechanical compression by the growing uterus.
• A physiological hydronephrosis (swelling) can be seen and is usually more pronounced on the right.
• With the increase in circulating blood volume and ↓TPR there is an ↑ in renal plasma flow by up to 60-80% in the second trimester settling to a 50% increase through the third trimester.
• Glomerular filtration rate and creatinine clearance ↑ by about 50% meaning that normal levels of urea and creatinine are much lower during pregnancy.
• The kidneys excrete more protein but retain more sodium ( and water).
• Secretion of vitamin D, renin and erythropoietin is increased.
• Microscopic haematuria is more common and if there is no proteinuria, no infection and renal ultrasound and function is normal, is most likely due to bleeding from the small vessels in the dilated renal function.
• Glycosuria is also common.
• UTI’s are more common - antibiotics asap as this can increase risk of pre-term delivery
• Any underlying kidney disease is likely to worsen during pregnancy because of the additional work being done by the renal system.

Question 14

Look

Answer 14

In the event of a maternal collapse/cardiac arrest a pregnant patient MUST be resuscitated on a left lateral tilt or with the uterus manually displaced.

YOU WILL NOT BE ABLE TO RESUSCITATE ANY PERSON WITH A GRAVID UTERUS WHO IS LYING FLAT BECAUSE OF THE REDUCTION IN CARDIAC OUTPUT THIS CAUSES.

Question 15

Why is the risk of DVT increased in pregnancy?

Answer 15

The risk of DVT in pregnancy is increased due to increased venodilation which in turn causes increasing venous stasis in the lower limbs and reduced venous return.