How Does The LH Surge Affect Ovulation?

Short Answer: The LH surge actually triggers ovulation.

Luteinising Hormone (LH) is one of the many hormones produced in the pituitary gland, a small organ at the base of the brain. For most of the menstrual cycle, LH levels remain low. However, when a mature egg reaches a certain size there will be a surge in LH. This is generally considered the trigger for ovulation.


Ovulation is the process during which an ovary releases a mature egg. The egg then travels along the fallopian tube, where it awaits fertilisation. LH is important because it starts the whole process off. The interval around the LH surge is often referred to as a woman’s “fertile window”. If a couple is attempting to get pregnant then this is the best time to have sex.

This also means that being able to detect the surge in LH can be extremely useful. Doing so allows us to identify the best time to try to conceive. LH can be detected in blood tests but, more practically, it’s also possible to test for it at home using an ovulation test kit. These kits check your urine for levels of LH. If levels are high the test will be positive, meaning ovulation is about to occur or is occurring currently. This can be a useful way to keep track of your fertility.


So, it can be really helpful to keep track of LH levels in the body. Either by using an ovulation test kit or by having a blood test we can identify the “fertile window”. It’s recommended that if you’re keeping track of your fertility and are still unable to get pregnant after 6 months or so of trying then it’s best to see a fertility specialist. Your doctor should be able to help you find one.