This test is done 7 days after ovalation, so lets say you have a regular 30 day cycle, u would normallly ovalate on day 15 or
16, so u count 7 days from day
16, which makes it 23 days, which is a week before ur period, so this would be the best day to test. They test this by taking a blood test and the test costs about £50.
Another good test to have is a test to check for blood clotting.