Effect of Pregnancy on Maternal Physiology Flashcards
During pregnancy, how are the increased metabolic demands of the mother dealt with ?
Increase in metabolic demands on the mother are met by hormone driven physiological adaptation.
What are the main categories of physiological mechanisms of adaptation to pregnancy ?
Anatomical changes Cardiovascular system Respiratory system Renal system Gastrointestinal system
Identify the anatomical changes that occur in pregnancy (including any clinical manifestations or potential pathological processes).
1) Weight gain
2) Varicose veins: Pressure on the inferior vena cava will impede venous return from lower limbs and may impair function of valves (combined with relaxation of vessels and valves via hormonal effects)
3) Musculoskeletal:
-Changes centre of gravity to develop an accentuated lumbar lordosis (CM backache)
-Relaxin causes softening of ligaments. This results in sacroiliac and pubic symphysis pain (CM Pregnancy related pelvic girdle pain (PGP))
-CM - Diastasis recti (separation of rectus abdominis muscles away from the midline)
-CM - Striae gravidarum (atrophic linear scars, i.e. stretch marks)
4) Skin:
-CM – Linea nigra (the linea alba in pregnancy, which then becomes pigmented)
-CM – Melasma (patchy pigmentation of sun-exposed skin)
-CM – increased oestrogen resulting in palmar erythema
and spider naevi
How much weight gain is typically experienced in pregnancy ? Where is this weight gained ?
Weight gain of 12.5 kg (7-14kg) ----- 6kg: uterus, foetus (3.5 kg) and breast (0.5-1kg) 3kg: fat reserves for lactation 1.5kg: Placenta and amniotic fluid Rest is ECF
Identify the CV adaptations that occur in pregnancy.
Blood volume ↑ Blood composition changes Total peripheral resistance ↓ Cardiac output ↑ BP ↓
Explain the changes in BV and blood composition in pregnancy (including any clinical manifestations or potential pathological processes).
Blood V:
♪ Plasma volume increases 50% in pregnancy
♪ Notable due to decrease in TPR resulting in R/A/A system
Blood composition:
♪ Haematopoiesis is increased (up 30%) (so erythrocyte V also increases) but increase in plasma volume (up 50%) means that red cell count, haematocrit and haemoglobin concentration are all reduced.
CM Physiological anaemia
♪ Small increase in WBC
♪ Increase platelet production, but increased destruction so no overall change in count
♪ Increase in clotting factors with thromboembolism risk.
→ PP - VTE
Explain the changes in TPR in pregnancy (including any clinical manifestations or potential pathological processes).
♦ Uteroplacental circulation is characterised by high volume, low resistance flow as uterine spiral arteries and arterioles lose the capacity to vasoconstrict.
♦ Pregnancy hormones reduce sensitivity to pressor agents such as angiotensin, hence peripheral vasodilatation (CM - heat-intolerance).
♦ Reduced total peripheral resistance (TPR) triggers the renin-angiotensin-aldosterone system increasing blood volume.
CM – Ejection systolic murmur
♦ Additional factors that may favour vasodilation, maintaining normal (low) blood pressure:
- Oestrogen increases vascular endothelial growth factor (VEGF) and nitric oxide (NO) production in endothelial cells.
- Endothelial cells release prostacyclin (prostaglandin I2 or PGI2).
How much does CO increase in pregnancy ? How much do its two components increase ?
Cardiac output (CO) increases by 30-50% between weeks 6-28 (~6L).
- Increase in heart rate (HR) from 70/min to 80-90/min.
- Increase in stroke volume (SV) by ~10%.
Explain the changes in CO in pregnancy.
Cardiac output (CO) increases between weeks 6-28 (~6L).
In late pregnancy, cardiac output (CO) sensitive to posture: can fall because of inferior vena cava obstruction by uterus resulting in hypotension/fainting when lying flat (reduced venous return).
How long after pregnancy does CO return to normal ?
By 6 weeks post-partum, cardiac output (CO) returns to pre-pregnancy condition.
Which parts of the body especially benefit from increased CO in pregnancy ?
Increase in blood flow to uterus, breast and skin.
How is BP measured in a pregnant woman ?
Measured semi-recumbent (not lying flat) using Korotkoff phase 5 for diastolic.
Explain the changes in BP in pregnancy.
- Related to changes in circulating plasma volume and peripheral resistance.
- Although cardiac output (CO) increases, BP normally falls in second trimester.
- Systolic falls ~5-10mmHg.
- Diastolic falls ~10-15mmHg.
Identify the main pathologies associated with pregnancy, and state adaptations in which body system they are caused by.
Pre-eclampsia (CV)
Eclampsia (CV)
Gestational diabetes (GI)
Define pre-eclampsia.
Placental problem involving increased vascular resistance in placenta, causing:
- Decreased blood to placenta (poor placental perfusion can cause foetal growth restriction)
- Hypertension in the mother
- Renal arteriolar endothelial damage causes oedema, glomerular damage and proteinuria (‘acute atherosis’)
May involve failure of the second wave of trophoblast invasion that normally impairs the capacity of material spiral arterioles to constrict (12-16 weeks).
