Any medics? How crucial are timings of these blood tests?

[SarahAndQuack]

My GP wants to do blood tests on day 5 and day 21 of my menstrual cycle, prior to me doing fertility treatment. I have a form with all the tests on so could give more details (I don't know what all the abbreviations mean but you might!). But they include FSH, LH, and the liver/thyroid functions, so a basic MOT as far as I know.

Question is: how flexible are those days? I forgot to ask the GP when I had the consultation and when I called the practice the receptionist was very nice but basically made it clear that appointments are like hen's teeth and it's really, really hard to fit them in. She's clearly done her best but when I look, she's given me day 6 and day 20. Will that skew the results too much?

I am guessing there must be some flex as everyone's menstrual cycle is different, but I'd love some reassurance!

The hormone tests are most reliable days 2-5 after your period starts. The day 20 blood test is to catch the hormone rise that confirms ovulation has occurred. When to have this depends on the length of your cycle. You should have 7 days before your next expected period Eg day 21 of a 28 day cycle. Out of this the results are unreliable. I often have to ask women to repeat the day 21 test if they have an irregular cycle and don't time it correctly. HTH

Thanks very much, that's really useful. (And I wish my GP had told me! All I was told was day 5 and day 21, and day 21 isn't likely to be the right time).

Oh - and, sorry to trouble you, but when you say the day 21 is to 'confirm' ovulation has occurred, does that mean this test is more accurate than an ovulation test you can buy over the counter? I get perfectly ok positives on those, so if that's all it's doing, I shall be less worried.

@SarahAndQuack

Oh - and, sorry to trouble you, but when you say the day 21 is to 'confirm' ovulation has occurred, does that mean this test is more accurate than an ovulation test you can buy over the counter? I get perfectly ok positives on those, so if that's all it's doing, I shall be less worried.

The otc tests just confirm you get the LH surge and not that your body has ovulated. The blood test does.

Thanks very much, that's really helpful! But, damn, looks as if I should rebook.

Whhhyyyy would you not tell your patient this stuff before sending them off to book an appointment?!