Understanding Your LH Surge
The hormone spike that triggers ovulation—and your key to timing conception.
LH Surge Quick Facts
- What it is: A rapid rise in luteinizing hormone that triggers egg release
- When ovulation happens: 24-48 hours after the surge begins
- How long it lasts: 12-48 hours (varies by person)
- How to detect it: Ovulation predictor kits (OPKs)
What is the LH Surge?
Luteinizing hormone (LH) is produced by your pituitary gland throughout your menstrual cycle. For most of the cycle, LH levels are low—typically 5-25 mIU/mL. But just before ovulation, something dramatic happens.
As your dominant follicle matures and estrogen levels peak, this triggers your brain to release a massive burst of LH—sometimes jumping to 25-100+ mIU/mL within hours. This is the LH surge.
🔬 What the Surge Does
The LH surge triggers a cascade of events:
1. Final egg maturation: The egg completes its development
2. Follicle weakening: Enzymes break down the follicle wall
3. Ovulation: The follicle ruptures, releasing the egg into the fallopian tube
4. Corpus luteum formation: The empty follicle transforms to produce progesterone
Without the LH surge, ovulation doesn't happen. This is why tracking LH is so valuable for TTC—it tells you ovulation is imminent.
LH Surge Timeline
Here's what typically happens once the surge begins:
| Timeline | What's Happening | What You See |
|---|---|---|
| Surge begins (Hour 0) |
LH rapidly rises from baseline | OPK test line starts getting darker |
| Peak surge (12-24 hours) |
LH reaches maximum concentration | OPK shows clearly positive (test ≥ control) |
| Ovulation (24-48 hours after surge start) |
Follicle ruptures, egg released | OPK may still be positive or starting to fade |
| Post-ovulation (48-72 hours) |
LH returns to baseline | OPK returns to negative |
Key Timing Points
- First positive OPK to ovulation: Most commonly 24-36 hours
- Typical surge duration: 12-48 hours
- Best time to have sex: Day of first positive OPK + next 2 days
💡 Why Timing Matters
The egg only survives 12-24 hours after ovulation. Sperm need to be waiting when the egg arrives. Since ovulation occurs 24-48 hours after the surge begins, having sex when you first detect the surge (positive OPK) gives sperm time to reach the fallopian tube before the egg arrives.
Detecting Your LH Surge
Ovulation Predictor Kits (OPKs)
OPKs are the most common way to detect your surge. They test urine for LH levels and show positive when LH crosses a threshold (typically 25-40 mIU/mL).
When to Test
- Time of day: Between 10am and 8pm (LH typically surges in early morning but takes hours to appear in urine)
- Before testing: Reduce fluids for 2 hours so urine isn't diluted
- Start testing: About 4-5 days before expected ovulation
Reading Results
- Positive: Test line as dark or darker than control line
- Negative: Test line lighter than control (even if visible)
Fertility Monitors
Devices like Clearblue Fertility Monitor, Mira, or Inito track hormone levels more precisely and can show you the actual rise and fall of LH (and sometimes estrogen), giving you more data about your unique surge pattern.
Testing Frequency
| Surge Type | Testing Recommendation |
|---|---|
| Normal surge (24-48 hours) | Once daily is usually sufficient |
| Short surge (12 hours or less) | Test twice daily (morning + evening) |
| Approaching expected ovulation | Consider testing twice daily to catch it |
Easy@Home Ovulation Test Strips
Affordable enough to test multiple times daily. Works with the free Premom app to track your T/C ratio over time and see your surge pattern develop.
Mira Fertility Analyzer
Shows actual hormone concentrations, not just positive/negative. Great for understanding your unique LH pattern, especially if you have PCOS or irregular cycles.
LH Surge Patterns
Not everyone's surge looks the same. Here are common patterns:
Standard Surge
- LH rises sharply, peaks, falls sharply
- Duration: 24-48 hours
- Easy to catch with once-daily testing
- Most common pattern
Short/Fast Surge
- LH spikes and drops within 12 hours
- Easy to miss with once-daily testing
- Test twice daily to catch it
- More common than you might think
Plateau Surge
- LH rises, stays elevated for 2-3+ days, then drops
- Multiple positive OPKs in a row
- Ovulation typically occurs at the end of the plateau
- More common with PCOS
Multiple Peaks
- LH rises, drops, rises again
- Body may be attempting ovulation multiple times
- More common with PCOS or stress
- The last surge is usually the one that triggers ovulation
Gradual Rise
- LH slowly builds over several days rather than spiking
- OPKs get progressively darker
- Count the "positive" as when test line matches control
⚠️ Know Your Pattern
Track for a few cycles to learn your unique surge pattern. If you have a short surge and only test once daily, you might miss it every month. Once you know your pattern, you can adjust your testing strategy.
When Things Don't Work
I never get a positive OPK
Possible causes:
- Short surge: You're missing it. Test twice daily.
- Low LH surge: Some women have surges below the test threshold. Try a more sensitive OPK or use a quantitative monitor like Mira.
- Testing at wrong time: Try testing later in the day (afternoon/evening).
- Diluted urine: Reduce fluids for 2 hours before testing.
- Anovulation: You may not be ovulating. If this persists 3+ cycles, see a doctor.
My OPKs are always positive (or always nearly positive)
Possible causes:
- PCOS: Women with PCOS often have chronically elevated LH, making OPKs harder to interpret. Try a quantitative monitor or track other signs (CM, BBT).
- Perimenopause: LH levels rise as you approach menopause.
- Testing too frequently: Some variation is normal. Look for the clear peak/darkest test.
I got a positive OPK but my BBT didn't rise
Possible causes:
- LH surge without ovulation (LUF syndrome): Rare, but your body can surge without releasing an egg.
- BBT reading issues: Poor sleep, illness, or other factors can mask the temp shift.
- Testing error: False positive OPK (rare but possible).
If this happens consistently, mention it to your doctor.
I get multiple LH surges in one cycle
Your body may be "gearing up" to ovulate multiple times before finally succeeding. This is more common with:
- PCOS
- Stress
- Irregular cycles
- Coming off hormonal birth control
Strategy: Keep testing and having sex with each surge. The last surge is most likely to result in ovulation. Confirm with BBT tracking.
What to Do When You Detect Your Surge
The Action Plan
- Day of first positive OPK: Have sex TODAY. This is crucial—sperm take hours to reach the fallopian tubes and need to be in position.
- Day after positive: Have sex again. Ovulation is likely happening today or tomorrow.
- Two days after positive: One more time if you can. This catches late ovulators.
🎯 The Simple Rule
Positive OPK = Have sex in the next 48 hours.
If you only have sex once, make it the day of your positive OPK. If you can have sex twice, do the day of the positive AND the day after. This covers the most likely ovulation window.
After the Surge
- Stop testing. You've got the information you need.
- If tracking BBT: Watch for the temperature rise 1-3 days after your positive OPK. This confirms ovulation occurred.
- Enter the TWW. The two-week wait begins. Test around 12-14 DPO.
The Bottom Line
The LH surge is your body's green light—the signal that ovulation is 24-48 hours away. Detecting it with OPKs gives you the advance notice you need to time sex for maximum chances of conception.
Learn your unique surge pattern, test appropriately (twice daily if you have short surges), and when you see that positive, spring into action. The rest is up to biology. 🧬