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We analyzed data from over 11,500 ovulation tests to figure out when people were most likely to detect a surge in luteinizing hormone (LH) — the hormone that helps predict ovulation.
Based on our research, we recommend testing your LH in the afternoon (between 12pm-6pm) for the best chances of catching your LH surge. If you’re trying to conceive, we also recommend testing twice a day when you’re in your fertile window to maximize your chances of catching your surge. (And try to stay consistent about the time of day that you test.)
Why are afternoons the best time to test LH? In this post, we’ll walk you through the research and data that forms the basis for our recommendation.
We analyzed data from over 11,500 strips from people who consented to research that’s been approved by an external institutional review board. Here’s what we found:
- Strips logged after 12PM were 57% more likely to show LH surges relative to strips before 12PM.
- People who tested multiple times a day were 71% more likely to detect an LH surge, compared to people who tested once.
Refresher: Why LH surges matter
Hormones are intricately involved in all aspects of the menstrual cycle, and certain ones are more or less important at different phases of the cycle. Ovulation is when an egg is released from an ovarian follicle, at which point it’s possible for it to meet up with sperm in a process called fertilization. If sperm isn’t there when an egg gets to the fallopian tubes, fertilization and conception aren’t possible, making pinpointing the timing of ovulation *crucial* to either promote or avoid conception.
But how does the egg know it’s ready to venture out of the follicle? About 24-48 hours before ovulation, your body experiences a big jump in luteinizing hormone (LH), and it’s this surge that coaxes the egg out of its follicle (small caveat: LH surges can look different across people). The highest chances of conception are on the day of your LH surge and the day after, meaning that catching this surge can help you determine whether you’re in your fertile window.
An ovulation test measures the amount of LH in urine. While some tests use pre-set thresholds for what is considered a surge — usually 25 mIU/mL — and tells you whether a sample is above or below that value, our test and app allow you to pinpoint the numerical amount of LH in your urine. This allows you to better keep track of what your unique LH pattern may look like, and is also helpful for the 1 in 10 people who have surge levels below 25 mIU/mL.
There’s no clear clinical guidance on when to test LH
Two things are clear: (1) It’s best to stay consistent about the time of day that you test (when testing once a day), and (2) because LH surges can be short, it’s best to test twice a day when you’re nearing your anticipated fertile window.
There was less clear guidance on the best time of day to test. ACOG and ASRM do not have recommendations on when during the day to test, which may be part of the reason why different manufacturers of LH tests have such different recommendations.
We initially recommended testing in the morning, because this is when urine is most concentrated, and because it’s easier to remember to test first thing in the morning rather than at a specific time later on in the day. But, one year later, we have enough data to make a stronger, science-backed recommendation.
What over 11,500 Ovulation Test strips taught us about testing LH
Our clinical research team analyzed 11,500 ovulation test strips to determine the best time to catch an LH surge. A few disclaimers about our work:
- We only used data from people using Modern Fertility Ovulation Test strips who explicitly consented to participating in research in the app. Modern Fertility research projects (including this one) are approved by an external ethics committee known as an institutional review board (IRB).
- If people scanned a strip more than once within the same hour, we counted these as “duplicates,” and took the median value of all the scans in that hour.
- For this analysis, we took a threshold-based approach of defining a surge, and counted any strip value of 25 mIU/mL or greater as a surge.
We did a few different analyses, and came to the same conclusion each time. When it comes to our updated recommendation regarding time of day to test, we’ll talk about the results from our analysis of over 9,500 strips from people who scanned their LH once a day. Our results comparing how often surges are detected based on how many times a day people test are also based on the 9,500 strips from people who tested their LH once a day, as well as on the 2,000 strips from people who tested their LH twice a day or more.
The chances of detecting an LH surge after 12pm are 57% higher than your chances of detecting an LH surge before 12pm.
People were more likely to detect a surge if they tested in the afternoon as compared to the morning. Among users who scanned once a day, 4.9% of strips from 6am-12pm clocked in at surge levels, while 7.7% of strips from 12pm-6pm had surge levels — a 57% increase!
Methodology note: These percentages may seem low, but we wouldn’t expect the total percentage of strips with surge levels to be high for a few reasons: (1) We recommend people start measuring their LH at the beginning of their estimated fertile window, which means we expect people to have a few non-surge strips before detecting a surge. (2) People may choose to track LH throughout their full cycle, or when they know they aren’t consistently ovulating. (3) Some users are not testing and scanning frequently enough to catch a surge in the app.
People who test multiple times a day are 71% more likely to detect a surge than people who test once a day.
5.7% of the 9,500 strips from “once-a-day” testers had surge levels, compared to 9.7% of the 2,200 strips from “multiple-times-a-day” testers. This means that people who test more than once a day are 71% more likely to detect a surge.
What this means for you if you’re trying to catch your LH surge
We found that overall, testing in the afternoon and testing more than once a day are two ways to boost your chances of detecting an LH surge and pinpointing your fertile window.
That being said, this recommendation might not work for everyone. Maybe the morning is the only time when you can consistently test your LH — in that case, keep testing in the morning, and try to test more than once a day when you’re in your fertile window (once in the morning, and once in the afternoon).
There also may be people who are more likely to detect their surges in the morning than in the afternoon or evening. For example, we know that if your urine is diluted (by drinking water beforehand, for example) it can affect your LH levels. If you’re someone that’s mega hydrating throughout the day and are likely to have very diluted urine, it may make surges harder to detect. For those people, testing urine first thing in the morning (when it’s most concentrated) might be a better option.
It’s important to figure out what makes sense for you, which can involve a few cycles where you try out different things.
The research doesn’t stop here
Modern Fertility’s clinical and research team will continue to evaluate these numbers to make sure you’re getting the most up-to-date, science-backed recommendations to help you track your cycle and keep tabs on your hormones, regardless of what your reproductive goals may be.
We are *so* grateful to everyone who uses our fertility essentials and consents to research. The more people who consent to research, the faster we’re able to push fertility science forward.