When you first started thinking about having a baby, the phrase “LH surge” probably didn’t cross your mind. But if you’ve been trying to get pregnant for a few months, you start paying a lot closer attention to the vagaries of your hormone patterns each month. And luteinizing hormone, or LH, as it’s commonly referred to, is one of the most important ones to pay attention to if you want to conceive quickly.
We put together a guide to everything you ever wanted to know about LH, and how it can help you get pregnant.
What is LH?
LH is a hormone produced by your pituitary gland that triggers ovulation. Most of the time, blood concentration of LH is between 5 – 20 mIU/mL. But 24 – 36 hours before ovulation, LH levels begin to surge to a peak of 25 – 40 mIU/ml. Since normal LH levels vary between women, another way of defining the LH surge is the first day of your cycle when LH concentration is three times the concentration of the six previous days.1
Why is LH important for getting pregnant?
The LH surge is the most reliable indicator of impending ovulation. If you identify an LH surge, it means that ovulation is likely about two days away. These two days, along the day of ovulation itself, represent peak fertility. In fact, over 70 percent of all pregnancies are conceived during this three-day period.
Does having an LH surge mean that I will definitely ovulate that month?
Not necessarily. In a normal cycle, ovulation usually follows the LH surge. But sometimes you can have an LH surge early in your cycle, before the follicle is ready. If this happens, you’ll have another LH surge later on in your cycle, and ovulate after that one.
Another reason why ovulation may not follow the LH surge are certain conditions that cause elevated LH levels such as PCOS.
And finally, a third reason why the LH surge doesn’t always lead to ovulation is a phenomenon known as luteinized unruptured follicle (LUF). Between 6 – 25 percent of women with infertility have LUF2, and it’s one possible cause of unexplained infertility. It can also occasionally happen to women with otherwise normal cycles3.
In LUF, even though hormone levels leading up to ovulation are normal, the follicle doesn’t rupture, so the egg is never released. In normal menstrual cycles, the ruptured follicle becomes a corpus luteum, which releases progesterone and stimulates the lining of the uterus to build up. But with LUF, even though the follicle never ruptures, it still releases progesterone. From the outside, your cycle will look completely normal: you’ll still get a regular period each month, and you’ll still get positive results with the temperature method or ovulation sticks. In fact, the only way to detect LUF is via ultrasound.
Often, there is no apparent cause for LUF. But it is known that long term use of anti-inflammatory drugs can prevent the follicle from bursting, sometimes leading to LUF. If you’re taking anti-inflammatory drugs for chronic conditions like autoimmune diseases, arthritis, or endometriosis you may want to talk to your doctor about possible impacts on your fertility.
When does the LH surge occur?
The LH surge occurs 24 – 36 hours before ovulation. Of course, it’s hard to know exactly when in your cycle this happens, since all women are different and you may ovulate on different days in different cycles. In a 28-day cycle, your LH surge is probably around day 12. But depending on your cycle, it might be on day 10, day 15, day 20, or another day!
Fun fact: in two-thirds of women, the onset of the LH surge occurs between midnight and 8am.
How can you figure out when your LH surge is?
Unlike progesterone, you can’t monitor LH levels by taking your temperature, and unlike estradiol, you can’t monitor LH levels by examining your cervical mucus. The best way to check your LH levels is to use a urine test.