Physiology of Pregnancy

Question 1

What is the functions of the hormone relaxin that is released during pregnancy?

Answer 1

Works alongside oestrogen and progesterone to increase the pliability and extensibility of connective tissue - allows for birth of the baby

Particularly affects:

• Symphysis pubis
• Sacroiliac joints

Question 2

What is the effect of pregnancy on the curvatures of the spine?

Answer 2

During pregnancy the increase in weight and change in weight distribution causes a need for the woman to lean backwards as the centre of gravity is no longer over the feet

This causes a change in the curves of the spine along its whole length

Question 3

How is the mothers metabolism affected during pregnancy?

Answer 3

• Basal metabolic rate increases, nutrition for fetus
• Human placental lactogen acts against maternal insulin (relative insulin insensitivity during pregnancy - can lead to gestational diabetes)
• Increased lipid storage in maternal tissues, FA’s are essential for fetal organogenesis

Question 4

When can fatigue due to pregnancy be quite overwhelming for the mother?

Answer 4

During the first trimester

Likely due to hormonal changes and gets better during the second trimester

May return near the end of pregnancy due to workload of advanced pregnancy and discomfort / difficulty sleeping

Question 5

How does pregnancy affect the mothers chances of experiencing heartburn? Why?

Answer 5

Increases it

Hormonal changes cause more frequent relaxation of the lower oesophageal sphincter. There is also delayed gastric emptying and a longer transit time of food into the stomach.

Pressure from the expanding uterus only makes this worse

Question 6

Is the development of oedema a worrying sign during pregnancy?

Answer 6

Not usually, 80% of pregnant women develop oedema due to:

• Compression of the IVC & increased blood volume
• Sodium and water retention during pregnancy, and a decreased ability to excrete sodium and water

While common, oedema can also be an important sign indicating pre eclampsia

Question 7

What changes can be seen in the breasts of a pregnant mother?

Answer 7

• Increase in size, vascularity and tenderness
• Increased pigmentation of the areola and appearance of a secondary areola
• Montgomery tubercles appear on the areola
• Colostrum (first milk) like fluid can be expressed from the end of the third month in some cases

Question 8

How does pregnancy affect maternal iodine demands? Why? What may occur as a result of this?

Answer 8

Iodine requirements increased because:

• Iodine is actively transported to fetoplacental unit
• urinary iodine excretion is doubled due to increased GFR & decreased tubular reabsorption

Thyroid gland may hypertrophy to ensure it traps adequate iodine

Question 9

How are free and protein bound T3 & T4 levels affected during pregnancy?

Answer 9

The liver increases thyroid binding globulin (TBG) production, the thyroid also increases T3 & T4 production

So level of free T3 & T4 does not change, but there is higher protein bound thyroid hormones

Question 10

How can hyperemesis gravidarum lead to biochemical hyperthyroidism? Treatment?

Answer 10

Because BHCG (a pregnancy hormone) has subunits that are very similar to TSH and can result in overstimulation of the thyroid gland

Treated with beta blockers - symptomatic treatment as condition will resolve with time

Question 11

What can be a serious complication of Graves Disease in pregnancy?

Answer 11

The TSH receptor antibodies can cross the placenta and result in fetal / neonatal hyperthyroidism

Question 12

How does pregnancy affect immune function?

Answer 12

Pregnancy results in a general state of immunosuppression to allow for foetal tolerance

Can increase susceptibility to infection but also improve conditions such as Crohn’s and RA

Question 13

How are blood volume and red blood cell mass affected by pregnancy? What does this result in?

Answer 13

The circulating blood volume increases by 50-70%
Red blood cell mass increases by about 40%

This unequal increase causes the physiological anaemia of pregnancy

Question 14

Why are cardiac diseases the leading indirect cause of maternal death in the UK?

Answer 14

Because there is increased blood volume, increased weight and increased oxygen requirements in pregnancy

The heart needs to work harder not only during pregnancy but until the maternal body has returned to pre-pregnancy levels

Previously unknown cardiac issues often become much more serious during pregnancy

Question 15

How is systemic vascular resistance affected by pregnancy? Why?

Answer 15

It is reduced, and is at its lowest between 20-32 weeks

The resistance drops because of circulating vasodilators and diversion of blood flow into the low pressure uteroplacental unit

Question 16

What are some examples of tissues with increased blood flow during pregnancy?

Answer 16

Kidneys - 60-80% more blood flow during pregnancy

Hands & feet (peripheries)

Nasal mucosa - increased risk of nose bleeds & feeling of congestion / stuffiness

Question 17

How is cardiac output affected during pregnancy? Why is this?

Answer 17

CO is increased by 30-50% due to increased in

• Stroke volume
• Heart rate: HR of a pregnant woman tends to be 10-20 beats higher

Question 18

Why should you never lie a pregnant woman flat?

Answer 18

Because vena cava compression due to the pregnant uterus will cause a reduction of CO by about 25% - the patient will end up fainting

Question 19

What is intrapartum autotransfusion of contractions?

Answer 19

It is the autotransfusion of blood into the maternal circulation during childbirth

Contractions force 300-500mL of blood from the uteroplacental capacitance vessels into the maternal circulation

Question 20

How can cardiac output change during labour?

Answer 20

Pain - increased circulating catecholamines due to pain cause increased HR, BP and CO (CO by about 10%)

Immediately after delivery CO can rise another 80% due to:

• Lack of uteroplacental unit to be supplied
• Immediate relief of caval compression

Question 21

How long does it take the cardiovascular system to return to pre-pregnancy levels after delivery?

Answer 21

Most changes normal by 3 months

• 3 days post delivery blood volume down 10%
• BP returns to normal by about 6 weeks
• Systemic vascular resistance and heart rate return to normal over about 2 weeks

Question 22

How are respiratory rate and tidal volume affected by pregnancy? What occurs as a result of this?

Answer 22

Tidal volume and respiratory rate both increase during pregnancy

Because of this relative hyperventilation PCO2 levels are lower during pregnancy, and pregnant women tend to be in a state of compensated respiratory alkalosis

Question 23

How does the enlarged uterus affect functional residual volume?

Answer 23

Functional residual capacity reduces by 20-30%

This is further reduced by lying in the supine position - another reason not to lie a pregnant woman flat

Question 24

Why can some woman experience an improvement in their asthma during pregnancy?

Answer 24

Because of the bronchodilator effect of progesterone

Question 25

How does Hg concentration change during pregnancy? What is an acceptable value compared to the normal value?

Answer 25

It decreases due to disproportionate increase in plasma volume and red cell mass

Pregnant: 105 g/L
Normal: 120-160 g/L

Question 26

What is the most common haematological deficiency in pregnancy?

Answer 26

Iron deficiency anaemia

Due to the 2-3 fold increase in iron requirements mainly for use by the foetus, more common in twin pregnancies

Question 27

What developmental issue can Fe deficiency in pregnancy cause?

Answer 27

Intrauterine growth restriction

The baby will be smaller than it should due to iron deficiency

Question 28

How are white cell count and neutrophil count affected during pregnancy?

Answer 28

They are increased

A WCC of up to 16x109 g/L is normal in pregnancy

Question 29

How is the maternal coagulation system affected by pregnancy?

Answer 29

Pregnancy is a hypercoaguable state

Clotting factors VII, IX and X increase along with fibrinogen

Fibrinolytic activity decreases

Changes happen very early in pregnancy and can persist for 6 weeks after delivery

Question 30

Why is the risk of DVT, pulmonary embolism and thromboembolism increased during pregnancy?

Answer 30

Due to the hypercoaguable state of pregnancy

Also because of venodilation and reduced venous return causing increased venous stasis in the lower limbs

Question 31

Why can a physiological hydronephrosis usually be seen during pregnancy? (more pronounced on the right)

Answer 31

• Because the urinary collecting system becomes dilated due to the relaxation of smooth muscle of the ureter caused by progesterone
• Mechanical compression of the urinary collecting system by the uterus

Question 32

How are urea and creatinine levels affected by pregnancy?

Answer 32

GFR and creatinine clearance increase by about 50% during pregnancy (increased blood flow)

Urea & creatinine are much lower during pregnancy

The kidneys also excrete more protein during pregnancy

Question 33

How are secretion of vitamin D, erythropoietin and renin affected by pregnancy? Excretion of water and sodium?

Answer 33

Secretion of vitamin D, erythropoietin and renin all increased

Excretion of sodium and water decreased

Question 34

What are some usually worrying renal signs that may be seen during pregnancy?

Answer 34

Glycosuria

Microscopic haematuria (due to bleeding from small vessels in dilated renal function)