Physiology of pregnancy Flashcards
Plasma volume changes in pregnancy
Plasma volume increases by 40%
- 2.5–> 3.7 L
8-10kg fluid weight gain (from 11-13 kg weight gain)
Oncotic pressure falls
- Fluid into extracellular space
- Oedema
Mechanism in increased plasma volume
Increase in oestrogen causes stimulation of angiotensinogen pathway.
Progesterone stimulates aldosterone secretion.
Aldosterone increases fluid absorption from the kidneys via Na+ absorption.
- Decreased ANP
- Decreased thirst threshold
- Osmostat resetting [regulates osmolality of EC fluid]
Changes in red blood cells
Red cell mass increases but massive plasma volume increase
- Dilutional anaemia–> decreased concentration of haemoglobin
Increased delivery of blood to uterus
- 3.5 fold
Iron changes in pregnancy
Fall in ferritin
- Body compensated by increasing iron absorption in gut
- Iron essential for increase in red cell mass.
Haemostasis in pregnancy
Hypercoagulable
- Increased plasma fibrogen
- Increased platelets, factor VIII, vWF
During delivery, increase in haemorrhage
- Placental separation
- Myometrial contraction
Changes in WBC during pregnancy
Total WBC increases
Increased neutrophils–> decreased apoptosis
Increases significantly around delivery
Effects of increased blood volume
Increase in cardiac output
- Partially compensates decreased vascular resistance
Decreased
peripheral resistance (35%)
- Progesterone causes increased vasodilatation
Increased BP
Heart changes during pregnancy
Heart enlarges
- Increases venous return
Presence of innocent systolic murmurs
Diastolic murmurs in around 20%
- Must rule out other pathologies
Effects of pregnancy on respiratory system
Increased pulmonary blood flow=
- Increased tidal flow
- Decreased maternal pCO2
- Increased maternal pO2
Increased O2 creates higher concentration gradient for diffusion in placenta.
Effects of pregnancy on renal system
Increase in kidney size (1cm)
Increase in GFR and effective renal plasma flow (50%)
- GFR decreases during third trimester
Tubular reabsorption is not affected
- Glycosuria
Decreased plasma creatinine and urea.
Progesterone–> dilation of renal pelvis and ureter= increased UTI
Effects of pregnancy on GIT
Reflux
- 70%
- Increased abdominal and reduced pyloric pressure
- Backwash of bile
Slowed gut motility (progesterone)
- Constipation
Reflux treatment
Avoid fat and alcohol
Upright posture
Antacids
Glucose metabolism
- First trimester
Increased sensitivity to insulin
- Increased glycogenesis and lipogenesis
Glucose metabolism
- Second trimester
Insulin resistance
Cortisol, progesterone, HPL and oestrogen antagonise insulin–> Increase in FA, glucose levels.
Importance of folate in pregnancy
DNA synthesis, repair and regulation
- Deficiency= neural tube defects
- Supplement given 3 months preconception to prevent NTDs
RBC development
- Deficiency= macrolytic anaemia.
Daily requirement of folate in pregnancy
Increased from 50mg to 400mg
Measuring folate in pregnancy
RBC folate
- Does not change in pregnancy
Thyroid changes during pregnancy
Generally unchanged
Increase iodine absorption–> Increased serum T3 and T4
Oestrogen stimulates increase in TBG
Free T3/4 remain the same or fall slightly
Hypothyroid when–> possible increased TBG, increase thyroid hormones dose.
Hormones secreted by the placenta [6]
hCG
- Human chorionic gonadotrophin
hPL
- Human placental lactogen
CRH
hPG
- Human placental gonadotrophin
Progesterine
Oestrogen
hCG
Peptide hormone secreted by the placenta
- Detectable 8-9 post ovulation
- Peaks 8-10 weeks
- Beta subunit detected in tests
Doubles every 48-72 hours
Produced by trophoblast
- Decreases as progesterone increases
Raise hCG levels causes
Hydatidiform molar pregnancy
Choriocarcinoma
Low hCG levels causes
Ectopic pregnancy
High miscarriage risk
hCG function
Alpha subunit is similar to
- LH (longer half life)
- FSH
- TSH
Maintains corpus luteum secretions (progesterone, oestrogen)
Later pregnancy
- Increases maternal oestrogen secretion
- Modulates maternal immune response
Human placental lactogen [hPL]
Similar to prolactin and GH
- 30 mins half life
Modifies maternal carbs and lipid metabolism
- Meet fetal requirements
- Provides steady glucose state for fetus
Placental growth hormone
Regulates fetal growth
Induces insulin resistance
Placental CRH
Stimulates maternal ACTh and cortisol production
Increased cortisol could:
- Increase maternal glucose
- Possible slower rate of cognitive development [when high in early stage
- Possible accelerated cognitive development when levels are high in later pregnancy
Role of oestrogen
Increased growth of uterus
Changes to cervix
Develops ducts in breast
Stimulates
- Prolactin
- CBG
- SHBG
- TBG
Mostly converted into oestriol
Roles of progesterone during pregnancy
Decreases uterine electrical activity
Immunosupressant
Stimulates lobulo-alveolar development in breasts.
Substrate in cortisol synthesis
