The LH Surge

When couples decide the time is right to begin a family, figuring out the optimal time for intercourse may help speed up nature’s timeline for achieving pregnancy. Luckily, science provides us with an alerting event that heralds the onset of ovulation.

The LH Surge: Timing is Everything

The physiological event that precedes the release of a woman’s egg is the release of a burst of hormone made in the pituitary. This hormone is called luteinizing hormone and in the fertility field, its release is referred to as the “LH surge”.

What is the LH surge?

The LH surge is a signal from the brain to the ovary that an egg is mature. The brain senses the elevated estrogen levels produced by the maturing egg and releases a burst of luteinizing hormone (LH). When the ovary is bombarded with this burst of LH, the sac-like covering (called the follicle) surrounding the egg thins, allowing the egg to escape.

When does the LH surge occur?

For most women with regular cycles, the LH surge occurs between cycle day 12 and cycle day 16. Use of an ovulation predictor kit around the noon hour during this time period should yield a positive result. For women with irregular cycles, the kits don’t yield positive results consistently and a consultation with a physician is needed.

Detecting the LH surge

Detecting the LH surge is important because it allows accurate prediction of ovulation, thus improving the timing of fertility attempts.

The LH surge can be detected in the urine with a commercially available urine test kit. Most women will surge by 8 am, and it takes about 4 hours for the surge to be detectable in the urine. Therefore, women should plan to use the ovulation predictor kit between 11am and 3pm for the most accurate results.

Unfortunately, about 10% of women who use ovulation kits will not see a positive LH test result and will need their physician’s help to improve fertility timing.

Why is the LH Surge so Important?

On the day the kit returns a positive result, the couple can anticipate ovulation within 12-24 hours. Timing intercourse the day of the LH surge and the day after will ensure sperm exposure during this “window of opportunity” when egg fertilization is most likely.

Scientifically speaking…

The role of the LH surge at the ovarian cellular level is to prompt resumption of meiosis. Meiosis is the cell division process that reduces the chromosome number of a cell by 50%. It is the cell division that occurs only in eggs and sperm. Completion of meiosis allows eggs and sperm to unite and still have the proper number of chromosomes.

In a woman’s ovary the process of meiosis is arrested partway through the reduction process. When a mature egg is exposed to the LH surge, the meiotic process reinitiates. Interestingly, the meiotic process of the egg is not completed until after fertilization, just moments before the sperm’s nucleus merges with the egg’s nucleus.