LH strips: What they are and how to use them.

What are LH strips or OPK?

LH strips or OPK are helpful in understanding when your body is going to ovulate. This helps you understand when you’re in your peak fertility window and how to time intercourse if you’re trying to conceive.

They are urine test strips, known as ovulation predictor kits. They measure LH, or luteinizing hormone, found in your urine. 

As your estrogen levels rise in your follicular phase, they will eventually rise high enough to trigger your brain to release LH (aka luteinizing hormone). LH triggers ovulation. You can expect ovulation to happen ~24-48 hours after you see the positive on your LH strip/OPK.

How do I use OPKs/LH strips?

In the days leading up to your expected ovulation, you can start using the LH strips, the lines may get darker as we get close to ovulation. Once positive or the darkest line, it indicates that you are about to ovulate. This can happen 24-48 hours later.

LH strips do not confirm that you’ve ovulated. They PREDICT ovulation. You can have a positive OPK and not ovulate. To confirm ovulation, you need to measure blood progesterone or track your basal body temperature. 

If you have an irregular or absent period, this can be tricky. One tip is to pay attention to your cervical mucus. Cervical mucus increases in response to rising estrogen levels, which will eventually trigger your LH to surge. If you start to notice cervical mucus, you can start tracking using the LH strips.

I notice multiple lines, am I doing something wrong?

Some people have longer surges and others have quick surges. If you’re tracking over several days, you want to note the darkest LH line, and note that as your “surge day”. I find the app, Premom very helpful. It allows you to take a photo of your LH strip and its compares the darkness of the lines for you, identifying your most likely peak day.

I’ve tried LH strips and they aren’t working.

Some people may find that using the OPKs are tricky - either never getting a positive and or always getting a positive. This can feel frustrating.

Just as everyone's cycles are unique in cycle length, flow etc, so are people's LH secretion patterns. One study measured and studied the variability in different LH patterns (swipe to see).

You can have (see figure below):

• A single fast peak
• A double peak
• A prolonged peak presents as a plateau.

You can also have a wide range of what is a normal LH release for your body. 

For example: someone may have a lower LH and that is enough to trigger an ovulation for their body, but not quite high enough for the test to register as positive. In this case, if you’re having a regular cycle, and showing signs of cervical mucus, you’re likely ovulating. Something like basal body temperature can be more helpful here, to confirm when specifically you’re ovulating.

Or, you might be missing your “peak” when you test. In this case, you may want to test more often (i.e. 2-3 times in a day to try and catch your peak).

Or someone may have a hormonal imbalance causing their LH to be high for longer period of time. This is something I commonly see in PCOS. It could also mean your LH pattern is a plateau and tends to stay positive a little longer. In this case, we’ll want to measure your blood LH levels and chat about options to regulate this (there are ways to do this!).

If it’s not working for you, it doesn’t necessarily mean that something is wrong. There are other tools you can use to figure out your peak window, and if this is challenging, then it’s time to connect so we can figure it out together.

Figure 1: Different types of LH surges

If you’re having trouble finding your LH strip and having irregular cycles, this may be a sign that you’re not ovulating and need to be evaluated further.

In Health,

Dr. Ashley Damm, BSc. ND

Naturopathic Doctor - Women’s Health and Fertility

Vancouver, BC

References:

• Direito A, Bailly S, Mariani A, Ecochard R. Relationships between the luteinizing hormone surge and other characteristics of the menstrual cycle in normally ovulating women. Fertil Steril. 2013 Jan;99(1):279-285.e3. doi: 10.1016/j.fertnstert.2012.08.047. Epub 2012 Sep 19. PMID: 22999798.