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