Pregnancy Physiology Flashcards
How are progesterone levels affected during pregnancy?
Increase
Why do progesterone levels increase during pregnancy?
It acts to maintain the pregnancy, prevent contractions and suppress the mother’s immune reaction to fetal antigens
What produces progesterone until ten weeks gestation?
Corpus luteum
What produces progesterone after ten weeks gestation?
Placenta
How are oestrogen levels affected by pregnancy?
Increase
What produces oestrogen throughout pregnancy?
Corpus luteum
How are free thyroid hormone levels affected by pregnancy?
Unchanged
How are total thyroid hormone levels affected by pregnancy?
Increase
Explain the changes to thyroid hormone levels during pregnancy
Due to the fact that oestrogen levels increase during pregnancy, there is an increase in hepatic production of thyroid-binding globulin (TBG)
Resultingly, more free T3 and T4 bind to the TBG, causing more thyroid stimulating hormone (TSH) to be released from the anterior pituitary gland
Therefore, the free T3 and T4 levels remain unchanged, however the total T3 and T4 levels rise
Why is it important that the total thyroid hormone levels increase during pregnancy?
Thyroxin is essential for the foetus’ neural development
However, the foetal thyroid gland is not functional until the second trimester of gestation
Therefore, increasing T3 and T4 levels in the mother ensure that there is a constant supply of thyroxin to the fetus early in pregnancy
Why is iodine deficiency common during pregnancy?
Iodine is actively transported to the fetoplacental unit
Urinary iodine excretion is doubled because of an increased glomerular filtration rate and decreased renal tubular reabsorption
What does hyperemesis gravidarum mean?
Nausea and vomiting during pregnancy
What is hyperemesis gravidarum associated with? Why?
Hyperthyroidism
This is due to the fact that BHCG, a pregnancy hormone, is structurally very similar to TSH
How do we treat hyeperemesis gravidarum?
Betablockers, such as propranolol
This controls the symptoms of tachycardia caused by the high levels of T4
This hyperthyroidism will resolve with the hyperemesis
What is the most common cause of hyperthyroidism?
Grave’s disease
How does hyperthyroidism, caused by Grave’s disease, affect pregnancy?
During pregnancy, the TSH receptor antibodies that cause Grave’s disease can cross the placenta and cause fetal hyperthyroidism
How do we adjust the treatment of pregnant patients with hypothyroidism? Why?
We increase their hypothyroidism medication
This is due to the fact that the fetus is dependent on maternal thyroid function and therefore greater thyroid hormone levels are required
This can then be readjusted back to normal at around back to normal at around 12 weeks gestation, as the fetus thyroid function becomes established
How are anti-insulin hormone (human placental lactogen, prolactin and cortisol) levels affected by pregnancy?
Increased
Why do anti-insulin hormone levels increase during pregnancy?
They increase insulin resistance in the mother and reduce peripheral uptake of glucose
This ensures that there is a continuous supply of glucose for the fetus
How is blood volume affected by pregnancy? By what percentage?
Increases
30-50%
Why does blood volume increase during pregnancy?
This is due to pregnancy activating the renin-angiotensin-aldosterone system (RAAS), leading to an increase in sodium levels and water retention
What effect does an increased blood volume have on patients?
Left ventricular dilatation
Increased diastolic volume
This can be seen as early as ten weeks on an ECHO
How is plasma volume affected by pregnancy?
Increases
How is systemic vascular resistance affected by pregnancy?
Decreases
Why does systemic vascular resistance decrease during pregnancy?
Increased circulating vasodilators
The diversion of blood into the low pressure uteroplacental unit
What effect does a decreased systemic vascular resistance have?
This leads to a decrease in diastolic blood pressure
During which trimester does diastolic blood pressure decrease?
First and second trimester of pregnancy
When is blood pressure lowest during pregnancy?
20-32 weeks
During which trimester does blood pressure return to normal?
Third trimester
How is cardiac output affected by pregnancy? By what percentage?
Increases
30-50%
Why does CO increase during pregnancy?
There is increased SV
How many beats per minute does HR increase by during pregnancy?
10-20 beats higher than their non-pregnant value
What position do we not lie a pregnant patient in? Why?
Flat
This is due to the fact that the pregnant uterus will compress the vena cava, resulting in the patient losing 25% of their cardiac output.
They will therefore faint, which is known as maternal collapse
How do we manage maternal collapse?
The patient must be resuscitated on a left lateral tilt or with the uterus manually displaced
How is tidal volume affected by pregnancy? By how much?
Increases
40% (500 - 700ml)
Why does tidal volume increase during pregnancy?
This is due to the fact that pregnancy results in an increased metabolic rate, which leads to an increased demand for oxygen
How is the respiratory rate affected by pregnancy?
Unaffected
How is residual capacity affected during pregnancy?
Decreases
Why does residual capacity decrease during pregnancy?
This is due to the fact that fetus growth causes upward displacement of the diaphragm
Does a decreased residual capacity during pregnancy affect the total lung capacity? Why?
No
There is also an increase in the transverse and anterior posterior diameters of the thorax
How is intra-gastric pressure affected during pregnancy?
Increases
Why does intra-gastric pressure increase during pregnancy?
This is due to the fact that as the uterus grows there is upward displacement of the stomach
What effect does an increased intra-gastric pressure have?
It predisposes the mother to gastrointestinal reflux, with symptoms such as nausea and vomiting
How is smooth muscle affected by pregnancy?
Relaxes
Why does smooth muscle relaxes during pregnancy?
This is due to an increased production of progesterone and a decreased production of motilin
What effect does smooth muscle relaxation have?
It decreases gut motility, which can lead to pregnant patients suffering from constipation
How is the gallbladder affected by pregnancy?
Relaxes
Why does the gallbladder relax during pregnancy?
This is due to an increased production of progesterone
What effect does gallbladder relaxation have?
It can result in biliary tract status, which predisposes the mother to gallstones
How is renal plasma flow affected by pregnancy? By what percentage?
Increases
25-50%
What does renal plasma flow increase during pregnancy?
This is due to an increased cardiac output and a decreased systemic vascular resistance
Why is microscopic haematuria common during pregnancy?
There is bleeding from the dilated small renal vessels
How do we manage microscopic haematuria during pregnancy?
In order to confirm that there is no underlying pathological cause, we test for proteinuria, conduct an ultrasound scan to look at renal function and test for a UTI
If these are all negative, we should refer the patient to urology urgently
How is the glomerular filtration rate affected by pregnancy? By what percentage?
Increases
30-60%
Why does glomerular filtration rate increase during pregnancy?
This is due to an increased renal plasma flow
How is renal excretion affected by pregnancy?
Increases
Why does renal excretion increase during pregnancy?
This is due to the expanding uterus reducing the capacity of the bladder
Increased GFR
How is urea and creatinine affected during pregnancy?
Decreases
Why does urea and creatine decrease during pregnancy?
This is due to the fact that there is an increased renal excretion and increased renal perfusion
How is aldosterone affected by pregnancy?
Increase
Why does aldosterone increase during pregnancy?
This is due to pregnancy activating the renin-angiotensin-aldosterone system (RAAS)
What effect does aldosterone have on pregnancy?
It increases sodium reabsorption and water retention
How is protein excretion affected by pregnancy?
Increases
What effect does increased protein excretion have?
Decreased blood protein levels
How is ureter and collecting system diameter affected by pregnancy?
Dilated
Why does the ureter and collecting system dilate during pregnancy?
This is due to progesterone relaxing the smooth muscle within the urinary system
What effect does ureter dilatation have? When does this effect usually occur?
It results in physiological right-sided hydronephrosis
These changes cause urinary stasis which predisposes a woman to UTIs, commonly pyelonephritis
Third trimester
How long do haematology changes persist for?
They can persist for up to six weeks after delivery
How are haemoglobin levels affected by pregnancy? What specific level?
Decrease
105g/L
Why is anaemia physiological during pregnancy?
There is an increased red blood cell production
Due to the fact that the plasma volume increases more than red blood cell volume, the concentration of red blood cells actually decreases
How are clotting factor levels affected by pregnancy?
Increase
What four clotting factors increase during pregnancy?
Fibrinogen
Factor VII
Factor VIII
Factor X
When do clotting factors increase?
20 weeks gestation
What effect does increased clotting factor levels have?
This makes pregnant patients hypercoagulable, increasing their risk of deep vein thrombosis and pulmonary embolism
How do we treat hypercoagulable pregnant patients? Why?
Low Molecular Weight Heparin (LMWH)
This is due to the fact that warfarin cannot be given to women as it can cross the placenta and cause teratogenic effects
How is platelet count affected by pregnancy?
Decreases
Why does platelet count decrease during pregnancy?
This is because the increase in plasma volume causes a relative decrease in platelet count
How is WCC count affected by pregnancy? What specific level?
Increases
16 x109g/L
How urate levels affected by pregnancy?
Decreases
Why do urate levels decrease during pregnancy?
This is due to the uricosuric effects from oestrogen and from the increase in renal blood flow
How are albumin levels affected by pregnancy?
Decrease
Why do albumin levels decrease during pregnancy?
This is due to the increased excretion of proteins in the kidney
How are ALP levels affected during pregnancy?
Increase
Why do ALP levels increase during pregnancy?
This is due to the increased secretion of ALP by the placenta.
How are bile acid levels affected by pregnancy?
Increase
Why do bile acid levels increase during pregnancy?
This is due to the increased smooth relaxation in gut, which increases gut motility and nutrient absorption as a result
How are ESR, CRP and D-dimer levels affected by pregnancy?
Increase
