False positive ovulation tests
Dear Professor Winston,

I am a 34 year old lady who has been trying to conceive (for the second time) for over 18 months. I had no real trouble in conceiving the first time. I was commenced on cerezette after my first child and had no periods with it. Since coming off cerezette 20 months ago my periods have been irregular. Now my cycle is roughly about 39-42 days. I have seen gynaecologists and they suggest an HSE which I am waiting for and progesterone 21 bloods. I have been using digital ovulation tests to predict ovulation successfully and went for progesterone 21 bloods 7 days after ovulation. These have came back low and I was told I didn’t ovulate although I was not given the level by my GP. I’m also showing other signs of ovulation or thought I was. Can you show signs of ovulation and have positive ovulation tests and not actually ovulate? Thank you for your time, G.

Dear G,

If you really had a progesterone test on day 21 which was low and this was during a 39 – 42 day cycle, this is entirely to be expected. The progesterone only rises about 12 – 14 days before the next menstrual period. So it is obvious that the timing of this test was likely to be wrong and I am a bit surprised the doctor didn’t point this out. You may need several blood samples for progesterone to get the timing right and it would be ideal if these were combined with the occasional ultrasound to confirm the development of an ovulatory follicle in one or other ovary.

But with a prolonged menstrual cycle after coming off the pill it is really quite likely you are not ovulating regularly, though this may return to normal in time. Incidentally, the value of these ’digital’ tests for ovulation is pretty dubious and I would be reluctant to use them in this situation – it is all too easy to miss the LH peak. I think you probably need induction of ovulation, probably with a drug like clomiphene taken by mouth and monitored by ultrasound, and you should have around an 80% chance of conception.

Best wishes
Robert Winston

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