High BBT, no period, BFN

Hi,

I've got a question from a client that has flummoxed me, thought I would ask you wise women.

She's been TTC for several months and has been charting. Her LMP was 46 days ago, her BBT has remained high for 20 days. She took a HPT and got a BFN.

She says she's had some breast tenderness and feels a bit tired, but otherwise is fine, no other symptoms.

I don't know enough about the biology side of things, the books say 18-20 days of high BBT confirms pregnancy. I'm wondering, if her period is just late, would the BBT stay high for all those days? How many days before the bleed does the temp go down? In a long period, say 40-60 days, would the BBT be high or low? If high, for how long?

Anyway I suggested she see a doc for a blood test, but she is not much into doctors. I thought I would ask y'all, because now I am curious about the hormones and the high BBT. I guess my question is: we know the BBT stays high for 20 days or longer if a woman is pregnant. What if she is just having a very late period - could she still have 20 days or so of high BBT?

TIA.

1) well the temperature will drop below the coverline (average temp) the day of the period coming or the day before the period comes (usually).

2) she may be having a very long cylce (ovulated later than the average day 14) and this is why it has been a long time since her LMP.

3) she may have taken her temp incorrectly at some point and so the day she thinks she ovulated may not be right which means it may be too early to get a BFP.

4) it could be an annovulatory cycle where she hasnt ovulated at all yet (but probably not if her BBT has been high)

sorry cant offer much help, but i would recommend waiting another few days and do another HPT or really a Blood test would be the best choice though.