Cardiac output in pregnancy is increased by 30 % physiologically . Hence loss of blood at the time of labor is pregnancy is sort of physiological correction .Cardiac patients do get a relief with loss of about 500 ml of blood .
Stress of Labor
Each uterine contraction is a stress to the heart and is akin to infusing 500 ml of saline into maternal circulation .This is further amplified in patients with severe mitral stenosis.
However , the maximum hemodynamic stress for the mother occurs just after delivery when about a 1 to 1.5 litre is auto transfused.One has to watch for deterioration at this point of time.
Why caeserian section is being preferred by many obstetricians in cardiac disease complicating pregnancy ?
Traditional and modern text books clearly mention , natural delivery is best for both fetus and mother in cardiovascular disease .However it is still a debatable issue in real world labor rooms, especially in obstetrical emergencies.These concepts are probably old when surgical risk were considered too high for LSCS .
My current understanding of the issue ( Subjected to correction )
- Normal labor hemodynamics is unpredictable , even so in a women with critical valve obstruction
- It is a “4 cornered obstetrical stress” situation , almost equally distributed between mother , fetus ,spouce and the obstetrician !
- A brief period of controlled stress is better than prolonged uncertainty of labor.
- Since LSCS is done in the presence of an anesthetist in a monitored and controlled setting, even a brief high risk period is acceptable till the baby is taken out.
- Though technically LSCS may add a little risk to fetal life , It has been observed mothers are getting more rapid relief from post partum dyspnea who undergo LSCS.
*There is another reason for the heart to feel comfortable with LSCS in critical mitral stenosis, which threatens to precipitate acute pulmonary edema .The post partum spike in cardiac output could theoretically be less if blood loss in LSCS is accounted .(sort of venesection !)
http://www.ncbi.nlm.nih.gov/pubmed/4025461
Dr.S.Venkatesan MD 
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