Prepare for your Follicle-Stimulating Hormone (FSH) Blood Test by following these instructions. Take this test two to five days after the start of your period, ideally on day three. It can be taken any time if you do not have periods. Hormonal contraception can affect this test, taking a break from this and using barrier contraception will give more accurate results. Do not take biotin supplements for two days before this test, discuss this with your doctor if it is prescribed.