From the Guidelines
The luteinizing hormone (LH) surge occurs approximately 24-36 hours before ovulation, and in the context of intrauterine insemination (IUI) in natural cycles, IUI should be performed 1 day after LH rise. This timing is crucial for maximizing the chances of conception, as the egg remains viable for only about 24 hours after ovulation 1. The LH surge is triggered when estrogen levels reach a threshold that switches estrogen's effect from negative to positive feedback on the hypothalamus and pituitary gland.
- Key factors influencing the outcome of IUI include the timing of insemination, with various methods available for timing, including LH testing or monitoring follicle growth by ultrasound combined with HCG injection 1.
- In IUI in natural cycles, LH testing is the most applied method for timing, and IUI should be performed 1 day after LH rise, as there is no evidence to recommend for or against a specific method of timing IUI in natural cycles 1.
- The LH surge typically lasts 24-48 hours, with ovulation occurring about one day after the peak, and this timing is important for conception planning.
- Women tracking fertility often monitor this surge using over-the-counter LH test kits, which detect the hormone in urine, allowing them to time intercourse or IUI accordingly.
- The LH surge also triggers the remaining follicular cells to transform into the corpus luteum, which produces progesterone during the second half of the menstrual cycle to prepare the uterine lining for potential implantation.
From the Research
LH Surge Timing
- The luteinizing hormone (LH) surge is a significant event in the menstrual cycle, marking the impending ovulation 2.
- The LH surge typically occurs 24-30 hours before ovulation, with a two to four fold increase above baseline levels 2.
- Ovulation is considered to occur 28-36 hours after the beginning of the LH rise or 8-20 hours after the LH peak 2.
- The timing of the LH surge can vary, with most ovulations occurring between 16 and 28 hours after the positive test is observed 3.
Variability in LH Surge
- Individual LH surges can be extremely variable in configuration, amplitude, and duration 4.
- LH surges marked by several peaks are associated with smaller follicle sizes before rupture and lower LH levels on the day of ovulation 4.
- LH surges lasting more than 3 days after ovulation are associated with lower estrone-3-glucuronide (E3G) before ovulation, a smaller corpus luteum, and lower pregnanediol-3α-glucuronide (PDG) values during the first 4 days after ovulation 4.
Detection of LH Surge
- Urinary LH tests can be used to detect the LH surge, with most commercially available tests being a cheap and easy way to reliably detect LH surges 5.
- However, the LH surge itself marks the impending end of the fertile window, and using LH tests to determine the fertile window may lead to misclassification of women as fertile when the fertile window has already closed 5.
- The start of the LH surge typically occurs between midnight and 0800 hours in the majority of women 6.