Follicle Stimulating Hormone is a naturally occurring hormone that is produced by the pituitary gland in the brain. It travels through the bloodstream with the purpose of stimulating the growth of ovarian follicles within the ovary in women and sperm production in men.
You may have come across FSH in conjunction with LH (Luteinizing Hormone). Both of these hormones are referred to as ‘gonadotropins’ as they stimulate the gonads (ovaries in women, testes in men), and are hormones that work together in a woman’s cycle to trigger ovulation. But how exactly does FSH in particular affect fertility?
For Women
At the start of a woman’s cycle, oestrogen and progesterone levels are low. This creates a signal to the pituitary gland to release FSH to stimulate follicular growth in the ovary. As ovarian follicles (fluid filled sacs in the ovary containing eggs) start to grow, less FSH is released into the bloodstream. However, as the follicles mature they produce more and more oestrogen which stimulates a surge in Luteinizing Hormone, stimulating the release of an egg from a mature follicle and resulting in ovulation.
Too much or too little of this important hormone can inhibit ovarian function or ovulation. FSH levels naturally start to increase as a woman reaches the menopausal period, but due to outside influences such as stress and weight etc., it is not uncommon for these levels to rise prematurely. Too little of this hormone can indicate an imbalance in the pituitary gland or hypothalamus.
For Men
Levels of FSH in men tend to remain relatively constant throughout the month, but as FSH levels control sperm production it is essential for fertility that levels are within the ‘normal’ range. High levels can indicate that the testes are not functioning as they should be, perhaps due to damage or a genetic condition. If levels are too low this usually indicates that sperm is not being successfully produced.
So how much of this hormone does your body actually need?
For women, somewhere in the range of 2-8.9 IU/L is considered ‘normal’, and enough to successfully support the growth of one follicle. For men, levels need to be between 5-15 IU/L. However, if test results do indicate an imbalance in FSH levels, it is important to note that this does not necessary mean that FSH is the direct cause of any fertility issues you may be experiencing.
FSH Tests
If you are having difficulty conceiving tests can help to find an underlying cause. As FSH levels rise and fall during a woman’s menstrual cycle, levels are typically measured within the first few days of menstruation (days 2-5), and are tested through a simple blood sample, usually in tandem with measuring other hormone levels such as LH. Here at NNFP we are able to do our own independent blood tests if needed.
If you are considering IVF, current NHS IVF regulations look for FSH levels to be under 9 to be eligible for NHS funding. There are of course other criteria to meet, but your GP should be able to offer advice on your eligibility if this is a path you are interested in taking.