Thanks Carol, but if the mmol value you gave was for 17-OHP (every molecule has a different value for the number of mg in a mmol) it would have a molecular weight of 180 not the 298 I had calculated it to be.  I couldn't believe I was that far off so I did some checking and found a chemistry site that gave the molecular weight for progesterone as 314.46. From that I came up with a value of about 330 for 17-OH progesterone.  Not quite as bad an error but still significantly off from my original calculation.

This is giving me a headache and I can imagine the effect it must be having on everyone else so I'll leave it at that.

Joan