Timing of serum progesterone testing

Posted By confused on March 18, 1999 at 19:53:30:







Is there an optimal time for a serum progesterone test?  My cycles have been 26 days, with ovulation on day 17/18.  I'm 34, have had one pregnancy and lost it, not due to LPD, but a blighted ovum with extremely high HCG (not molar) that required DNC @ 11 weeks because I hadn't spontaneously AB'd yet. I faxed Dr. copies of BBT chart and asked about a progesterone screening.  Nurse called back and said to do test on day 21.  
1. What are normal values for day 21?  
2. Are they based are based on ovulating day 14?
3. If so, would ovulating day 17/18 cause test on day 21 to be abnormally high or low?  
I haven't been able to talk to my Dr. about these questions; nurse says to do it on day 21 then we'll see where to go next.  I found something on Medline from 1989 says optimal time is day 25-26, but I don't know if this is still valid/current.  Also, Dr. counts day 1 as any spotting (usually a day or two prior to red flow); I've read you should count day 1 as first day of red flow.  However you count it, it's still too short between ovulation and spotting.  I'm really confused about when I should have the test and whether it will be valid.  Please help.  Thank you.