Physiology of Pregnancy Flashcards
What is the functions of the hormone relaxin that is released during pregnancy?
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
What is the effect of pregnancy on the curvatures of the spine?
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
How is the mothers metabolism affected during pregnancy?
- 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
When can fatigue due to pregnancy be quite overwhelming for the mother?
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
How does pregnancy affect the mothers chances of experiencing heartburn? Why?
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
Is the development of oedema a worrying sign during pregnancy?
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
What changes can be seen in the breasts of a pregnant mother?
- 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
How does pregnancy affect maternal iodine demands? Why? What may occur as a result of this?
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
How are free and protein bound T3 & T4 levels affected during pregnancy?
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
How can hyperemesis gravidarum lead to biochemical hyperthyroidism? Treatment?
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
What can be a serious complication of Graves Disease in pregnancy?
The TSH receptor antibodies can cross the placenta and result in fetal / neonatal hyperthyroidism
How does pregnancy affect immune function?
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
How are blood volume and red blood cell mass affected by pregnancy? What does this result in?
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
Why are cardiac diseases the leading indirect cause of maternal death in the UK?
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
How is systemic vascular resistance affected by pregnancy? Why?
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
What are some examples of tissues with increased blood flow during pregnancy?
Kidneys - 60-80% more blood flow during pregnancy
Hands & feet (peripheries)
Nasal mucosa - increased risk of nose bleeds & feeling of congestion / stuffiness
How is cardiac output affected during pregnancy? Why is this?
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
Why should you never lie a pregnant woman flat?
Because vena cava compression due to the pregnant uterus will cause a reduction of CO by about 25% - the patient will end up fainting
What is intrapartum autotransfusion of contractions?
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
How can cardiac output change during labour?
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
How long does it take the cardiovascular system to return to pre-pregnancy levels after delivery?
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
How are respiratory rate and tidal volume affected by pregnancy? What occurs as a result of this?
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
How does the enlarged uterus affect functional residual volume?
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
Why can some woman experience an improvement in their asthma during pregnancy?
Because of the bronchodilator effect of progesterone
How does Hg concentration change during pregnancy? What is an acceptable value compared to the normal value?
It decreases due to disproportionate increase in plasma volume and red cell mass
Pregnant: 105 g/L
Normal: 120-160 g/L
What is the most common haematological deficiency in pregnancy?
Iron deficiency anaemia
Due to the 2-3 fold increase in iron requirements mainly for use by the foetus, more common in twin pregnancies
What developmental issue can Fe deficiency in pregnancy cause?
Intrauterine growth restriction
The baby will be smaller than it should due to iron deficiency
How are white cell count and neutrophil count affected during pregnancy?
They are increased
A WCC of up to 16x109 g/L is normal in pregnancy
How is the maternal coagulation system affected by pregnancy?
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
Why is the risk of DVT, pulmonary embolism and thromboembolism increased during pregnancy?
Due to the hypercoaguable state of pregnancy
Also because of venodilation and reduced venous return causing increased venous stasis in the lower limbs
Why can a physiological hydronephrosis usually be seen during pregnancy? (more pronounced on the right)
- 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
How are urea and creatinine levels affected by pregnancy?
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
How are secretion of vitamin D, erythropoietin and renin affected by pregnancy? Excretion of water and sodium?
Secretion of vitamin D, erythropoietin and renin all increased
Excretion of sodium and water decreased
What are some usually worrying renal signs that may be seen during pregnancy?
Glycosuria
Microscopic haematuria (due to bleeding from small vessels in dilated renal function)
