Am currently undergoing blood tests for fertility issues, and need to book the second, '21 day' test. I have long cycles, so it won't actually be on day 21, but my cycles are also a little unpredictable/irregular in length, so working out exactly when my period will be is tricky. I can sometimes do it based on cervical mucus, but haven't had such obvious signs this month...last month I had a really long 47 day cycle, so perhaps this month is the same, but if it's back to my usual 35-39 days, then I should book for Friday.
What do I do if I go for the bloods on Friday, but then don't get my period? Do I book another appointment? I did ask the doctor this in my initial appointment, but he really wasn't very helpful...