Flashcards in 13.0 Maternal Adaptations to Pregnancy Deck (32)
In humans, what changes occur to the sex hormones in late gestation?
Oestrogen to progesterone ratio ↑
Progesterone stays stable (different to animals where progesterone decreases)
What does the change in oestrogen:progesterone ratio in late gestation induce?
Lactation and parturition
What hormones (other than sex hormones) increase during pregnancy?
2) Placental lactogen/placental variant GH
4) Cortisol and aldosterone (adrenal cortex)
- These do not actually increase. Just more are recorded in blood because of an increase in globulins (stimulated by oestrogen)
What happens to prolactin levels during pregnancy?
Increases (pituitary gland enlarges 30-50%)
What does increase in prolactin cause?
Mammary gland changes
What are the complications that can occur with enlargement of pituitary during pregnancy?
1) Blindness can occur if there is pre-existing acromegaly
2) Post-partum haemorrhage can cause Sheehan syndrome (Simmond disease)
What is Sheehan syndrome (Simmond disease)?
Ischaemia of the anterior pituitary due to compromised blood supply from the venous plexus.
Sufferers do not lactate and do not resume menstrual cycle
What is the average weight gain in pregnancy?
12.5kg (Due to foetus + placenta + fat)
What are the CVS changes in pregnancy?
1) ↑ Blood volume
2) Changes in blood composition
- ↑ RBC (but greater ↑ in plasma → overall haemodilution)
- ↑ clotting
3) ↑ CO
4) No change to BP
Features of pre-eclampsia:
1) HTN ( >140/90mmHg)
2) Non-dependent oedema (usually hands and face)
What are the renal changes in pregnancy?
1) ↑ GFR
2) ↑ Na⁺ reabsorption
3) ↑ erythropoietin
What are the respiratory changes in pregnancy?
1) ↓ compliance and FRC
2) ↑ tidal volume
What are the metabolic changes in pregnancy?
1) Maternal insulin resistance
2) ↓ gastric emptying and ↑ GIT transit time
3) ↑ liver metabolism
What are the behavioural changes in pregnancy?
↑ food acquisition (cravings etc but also nausea/vomiting)
What is the definition of a small infant?
What are the maternal factors that influence foetal size?
How does placental size correlate to foetal size?
↑ placental size → ↑ foetal size
What are the foetal factors that influence foetal size?
What is the mechanism that explains why foetal Hb has a higher affinity for oxygen than adult Hb?
Human foetal Hb has a ↓ affinity for 2,3 DPG therefore has an ↑ affinity for O₂ binding
What are the differences between foetal circulation and adult circulation?
• Differs from adult circulation in the following ways:
1. Supplies the placenta
- 55% of combined cardiac output goes to the placenta
- Placenta has low resistance
- Total peripheral resistance and blood pressure are lower in fetuses
2. Bypasses the lungs
- Only 7-13% of cardiac output goes to lungs
- Pulmonary vascular resistance is high in utero
3. Has two shunts
i. Foramen ovale (FO)
ii. Ductus arteriosus (DA)
- Achieves pulmonary bypass
- R + L heart beat in parallel in fetus
4. Total CO (both ventricles) =4x higher than in adults
What hormone is responsible for maturation of foetal tissue before birth?
↑ glucocorticoids (cortisol)
What induces parturition?
↓ progesterone:oestrogen ratio → ↑ prostaglandin synthesis
(in humans progesterone stays the same but oestrogen increases)
What fetal hormones are released to begin parturition induction?
1) Cortisol → fetal tissue maturation
2) DHAS → rapid ↑ in maternal oestrogen
What maternal hormones are released to begin parturition?
1) Oestrogen → cervical ripening and uterine contractions
2) CRH → ↑ fetal adrenal DHAS secretion, ↑ PG availability in uterus + ↓ myometrial contractions (↑cAMP)
Mechanism of myometrial contractions:
1) ↑ oestrogen (↓P:O) → ↑ actin + myosin expression and CAP proteins
2) ATP + myosin light chain kinase (MLCK) needed
3) Ca²⁺ → + CAM → + MLCK
4) ↑Ca²⁺ influx → contractions
Substances that stimulate uterine contractions
How are uterine contractions coordinated?
Via gap junctions
What contractions precede labour?
What are the three stages of labour?
Stage 1 = uterine activity + cervical dilation
- 10-12hrs (primagravida) / 6-8hrs (multigravida)
- Blood + mucus
- Cervix → 10cm
- +ve feedback contractions
Stage 2 = expulsion of fetus
- 45-120mins (primagravida) / 15-45mins (multigravida)
- Voluntary effort needed
- Most dangerous stage for baby
- Mother's BP ↑ (30/25mmHg)
Stage 1 = placental expulsion
- Uterus continues to contract until placenta is removed
- Retained placenta = risk of haemorrhage