LH to FSH ratio is the proportion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels measured in the blood. The normal ratio, when measured on day 3 of the menstrual cycle, is about 1:1. This ratio can be disturbed in women with polycystic ovarian syndrome (PCOS), with LH levels rising two to three times to that of the FSH.
FertilitySmarts explains LH to FSH Ratio
Normally, the FSH and LH levels in the blood are almost similar. However, in women with PCOS, the LH to FSH ratio may rise to as high as 2:1 or even 3:1. The LH levels by themselves may remain in the normal range but their levels increase as compared to that of the FSH.
Why do LH levels rise in PCOS? The LH production by the pituitary is under the control of another hormone called gonadotropin-releasing hormone (GnRH). The LH excess in PCOS is perhaps because the pituitary becomes increasingly sensitive to GnRH, which in turn is due to a surplus of ovarian androgens. These androgens further signal hypothalamic GnRH to stimulate the pituitary LH, which again drives ovarian androgen production, thus, sparking a vicious cycle.
A higher LH to FSH ratio can have a detrimental impact on egg quality and implantation potential. It is, however, important to note that not all women with PCOS have a raised LH to FSH ratio.
The day-3 LH/FSH ratio may also help predict IVF outcomes in women with PCOS undergoing ovulation induction with the help of fertility medications. Women with a higher LH/FSH ratio may be able to get pregnant after the use of fertility medications, primarily GnRH analogs. This is because these medicines can reduce the basal LH levels for a long and sustained period of time, which improves the odds of fertility.