Physiological changes in pregnancy

Management of both healthy& diseased pregnancy necessitate knowledge of the physiology of normal pregnancy. In early pregnancy, the developing fetus, corpus luteum & placenta produce a lot off hormones & substances that lead to many maternal local &systemic changes including cardiovascular, respiratory &renal. most of these physiological adaptation are completed during 1st trimester.
Volume homeostasis:
1.maternal blood vol. expand during preg. start at 6-8 weeks of pregnancy. There is increase in ECF(Plasma)>ICF& this account for 8-10kg increase in maternal wt.
2. There is 6.5-8.5 increase in total body water by the end of pregnancy
3.increase in COP& renal blood flow
4. increase in plasma volume lead to haemodilution &physiological anemia(decrease in Hb concentration & hematocrit.
5. decrease in plasma osmolality by 10 mOsmol/kg& there is decrease in thirst threshold
6.decrease in osmotic & oncotic pressure(determined by albumin) by 20% , also there is increase in GFR& probably lead to development of peripheral oedema
Factors lead to fluid retention : a. sodium retention b.dec.thirst threshold c. dec. oncotic pressure.