What is LH?
LH stands for luteinizing hormone, one of many hormones vital to the female reproductive cycle. LH is present in low levels throughout the woman's cycle, except for about a day and a half before ovulation. The hormone "surges" about 36 hours before ovulation and is detectable using ovulation predictor kits, which use urine. Ovulation occurs about 10 to 12 hours after the peak of the LH surge, and LH levels return to their normally low levels.
Effects on Estrogen
Estrogen builds up in the beginning of a woman's cycle, before ovulation occurs. One form of estrogen, called estradiol, surges right before the LH surge. When LH surges, it causes estrogen production to level off and remain fairly constant throughout the rest of the cycle. This stimulates the thickening of the uterine lining in preparation for implantation.
Effects on Progsterone
The LH surge stimulates ovulation, which occurs 10 to 12 hours after LH peaks. During ovulation, the egg ruptures from the follicle, and after this occurs, progesterone increases greatly as it is produced by this ruptured follicle. The increase in progesterone also helps prepare the uterus for implantation. The woman's body temperature rises slightly during this phase of the cycle.