26. Physiological changes in pregnancy.
|a.||blood volume increases by about 10% in pregnancy.||False|
|b.||red cell mass and plasma volume increase by similar amounts.||False|
|c.||cardiac output increases from ~4.5 to ~6 litres per minute.||True|
|d.||blood pressure is a function of cardiac output and peripheral resistance, so peripheral resistance must fall in pregnancy.||True|
|e.||the pulse rate rises in normal pregnancy.||True|
|f.||the glomerular filtration rate increases in pregnancy.||True|
|g.||the white cell count rises in normal pregnancy.||True|
See also MCQ1, question 43 "Iron & Pregnancy".
Total blood volume increases by about 30% in normal pregnancy.
The increase is mainly in plasma volume ~ 50%.
The red cell mass rises, but only by about 20%.
This leads to the well-known haemodilution of pregnancy.
A bit like the publican watering the beer.
It also leads to differing views of what constitutes anaemia in pregnancy.
Nelson-Piercy in the Handbook of Obstetric Medicine says that levels < 10.5 gm. / dl. should be regarded as abnormal.
Multiple pregnancy exaggerates these changes.
Blood pressure does not rise significantly.
Indeed, it tends to fall in the second trimester.
So there must be a substantial fall in peripheral resistance to accommodate the increased cardiac output.
Uterine blood flow increases hugely.
And the uterine vasculature is low-resistance if trophoblastic invasion of the spiral arteries has occurred properly.
See MCQ2, question 3 "Pre-eclampsia" and MCQ10, question 1 "Trophoblasic invasion of the spiral arteries".
There is also the 50% increase in renal blood flow to reduce peripheral resistance.
The pulse rate rises by about ten beats per minute.
Renal blood flow increases by up to 50% and is reflected in lower urea and creatinine levels in pregnancy.
The white cell count rises during pregnancy and further in the puerperium.
Nelson-Piercy(page 311) gives figures of:
4 – 11 for the non-pregnant,
and 6 – 16 in pregnancy.
James(page 1680) gives figures of:
4 – 9 for the non-pregnant,
9 for pregnancy,
and 16 for the puerperium.
The relevant units are 109 /litre.
|Return to MCQ1, answer 43. "Iron & Pregnancy"|
|Return to MCQ5, answer 10. "Thrombocytopenia"|
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