T2 L18: Physiology of Pregnancy Flashcards
what happens to the plasma volume in pregnancy
increases by 40%
from 2.5-3.7L
11-13kg weight gain
what does the decrease in osmotic pressure cause
Causes a shift of fluid into extra cellular space
Increased hydration of connective tissue
Oedema (lower limbs, hands and face)
what is the mechanism of increased plasma volume
Slight decrease atrial natriuretic peptide (ANP)
Decreased thirst threshold (increased fluid intake)
Re-setting osmostat
INCREASED PLASMA VOLUME
what happens to the red blood cell oxygen availability
red cell mass increased by 25% (1.3L to 1.7L)
plasma volume increased by 40%
13.3 to 10.9 g/dL at 36 weeks
dilutional anaemia
what occurs to iron levels
fall in ferritin levels
increased iron absorption from gut
what is a hypercoagulable state and what is its purpose during pregnancy
Increase plasma fibrinogen (increased ESR), platelets, factor VIII & von willebrand factor
Marked effect at delivery
500 ml/min blood loss at placental separation
myometrial contraction - 10% of all fibrinogen used up
what occurs to white blood cells during pregnancy
Concentration does not fall during pregnancy
Total WBC increases in pregnancy
Increase in neutrophils (reduced apoptosis)
Marked increased around delivery
what does increased blood volume have implications on in the cardiovascular system
cardiac output
peripheral resistance
blood pressure
what is cardiac output and what does SV require to increase
SV x HR
Increased SV requires increased heart volume
how does the heart change during pregnancy
Heart enlarges by 12% (increased venous return)
Innocent systolic murmurs are common (~90%)
Diastolic murmurs (~20%) – require investigation to rule out other pathologies,
- may be innocent – reflecting increased flow across atrioventricular valves
- will require further investigation to rule out cardiopathies – but be aware…
- change in cardiac axis/position result in changes on ECG and xray
what happens to peripheral resistance
Peripheral vasodilatation (effect of progesterone)
Peripheral resistance decreases by 35%
what happens to your blood pressure
decrease resistance partly compensated by increase in cardiac output results in a small change in BP
what happens to the respiratory system
Increased pulmonary blood flow matched by -
—Increase tidal flow
Decrease maternal pCO2 & increase maternal pO2
Increased availability of O2 to tissues and aids passive diffusion at the placenta i.e. higher concentration gradient
what are the effects of cardiovascular and respiratory changes
High blood flow maximises pO2 on maternal side of the placenta
Foetal haemoglobin (HbF) has a higher affinity for O2 compared with maternal adult Hb (HbA)
Increased cardiac output may increase flow in skin aiding heat loss (high metabolic state)
what happens to renal system
Kidney increases 1cm in size during normal pregnancy
GFR and effective renal plasma flow increase 50+%
BUT tubular reabsorption capacity is unchanged
leads to a decrease in glucose reabsorption thus glycosuria is common
what occurs at the molecular levels in the renal system
Plasma levels of creatinine and urea decrease in pregnancy
All the increments are present by the second trimester
Reduction in GFR of 15 % during the third trimester
Dilatation of renal pelvis and ureters (progesterone) - increased urinary tract infections in pregnancy
what happens to the GI system
Gastro-oesophageal reflux up to 70 %:
- due to increase abdominal pressure, reduced pyloric sphincter with back wash of bile secondary to hormonal changes
- simple measures: avoidance of fat and alcohol
- upright posture and antacids
Slowing of gut motility and constipation (progesterone effect)
what happens to glucose metabolism
First trimester: increased sensitivity to insulin thus mothers increase glycogen synthesis and fat deposition
Second trimester: insulin resistance
- cortisol, progesterone, HPL, & oestrogen are all insulin antagonists
- thus glucose levels may rise and there is an increase in fatty acids (another source of energy for the fetus)
what happens to the folate during pregnancy
DNA synthesis, repair and regulation
- Important in rapid cell division (embryos)
- Deficiency in pregnancy associated with neural tube defects (NTDs)
RBC development
-Macrocytic anaemia
Daily requirement increased from 50mg to 400mg (normal diet)
Plasma folate represents current nutritional status, but
Significant tissue stores (e.g. liver) – RBC folate is a good biomarker (no change in pregnancy)
Dietary deficiency can take months to become significant
No need for folate supplementation but prevents neural tube defects thus routinely given preconception to 3 months
what happens to your thyroid function
Increased iodine absorption
Increased serum T3 and T4 levels
Increase in thyroid binding globulin (oestrogen)
As only unbound T3 and T4 is active, levels of free T3 and T4 remain the same or fall slightly
In general thyroid function remains unchanged
If hypothyroid may need to increase dose due to increased TBG levels
what hormones does the placenta produce
Protein hormones:
hCG (human chorionic gonadotrophin)
hPL (human placental lactogen)
hPG (human placental gonadotrophin
CRH (corticotropin releasing hormone)
Steroids:
Progesterone
Oestrogen (oestriol)
what happens to the HCG hormone
First detectable 8-9 days after ovulation & peaks at 8-10 weeks
Beta subunit used as the pregnancy test
Doubles every 48-72 hours
Produced by the trophoblast
Produced in large quantities by hydatidiform molar pregnancy & choriocarcinoma
Usually significantly lower in ectopic pregnancy & risk of miscarriages
Alpha subunit very similar to LH, FSH,TSH
Has LH type properties but longer half life (24 h)
Maintains corpus luteum secretion of progesterone & oestrogen
Decreases as the placental production of progesterone increases
Later in pregnancy may have a role in maternal oestrogen secretion and modulation of the maternal immune response
what happens to the human Placental Lactogen
Similar structure to prolactin and growth hormone
The bigger the placenta, the more hPL
Half life ~ 30 min
Not functioning as a stimulator of lactogenesis
Alters maternal carbohydrate and lipid metabolism to provide for foetal requirements
- Mobilizing maternal free fatty acids
- Inhibits maternal peripheral uptake of glucose
- Increases insulin release from pancreas
Aim is a steady state of glucose for the fetus
what happens to the placental growth hormone
Placental Growth Hormone secreted by the placenta responsible for regulating fetal growth
Induces maternal insulin resistance
No evidence of that maternal GH or fetal GH required for fetal growth
what happens to the Placental corticotrophin-releasing hormone (CRH)
Stimulates production of maternal:
adrenocorticotropin hormone (ACTH)
cortisol
? Increased cortisol believed to be detrimental to the foetus ?
High levels early linked to slower rate of cognitive development post-partum
High levels late linked to accelerated cognitive development post-partum
Increased cortisol can result in increased maternal glucose
what happens to progesterone
Maintains uterine quiescence by decreasing uterine electrical activity
Immune suppressor ( HLA )
Lobulo-alveolar development in breasts
Substrate for fetal adrenal corticoid synthesis eg cortisol
what happens to oestrogen
Growth of the uterus, cervical changes
Development of ductal system of breasts
Stimulation of prolactin synthesis
Stimulation of corticol binding globulin (CBG), sex hormone binding globulin (SHBG), thyroxin binding globulin (TBG)
Both maternal & foetal dehydroepiandrosterone (DHEA-S) is converted to oestriol (aromatase)
90% as oestriol (to modulating uteroplacental blood flow)
