LH Surge Meaning: How to Detect Ovulation & Time Conception (2026)

What is the LH Surge?

LH is produced by the pituitary gland and remains relatively low throughout most of your cycle. About 24-36 hours before ovulation, LH levels suddenly spike—this is the 'LH surge.' The surge signals the dominant follicle to release its mature egg, making the next 12-24 hours your most fertile window.

How to Detect Your LH Surge

Ovulation predictor kits (OPKs) detect LH in your urine. Here's how to use them effectively:

• Start testing early: Begin 2-3 days before expected ovulation (around day 10 in a 28-day cycle)
• Test in afternoon: LH is synthesized in the morning and appears in urine later
• Don't use first morning urine: It may not reflect current LH levels
• Reduce fluids 2 hours before: Concentrated urine gives more accurate results
• Test daily at same time: Consistency improves accuracy

Reading OPK Results

Standard OPKs show two lines—a control line and a test line:

• Negative: Test line is lighter than control line—surge hasn't happened yet
• Positive: Test line is as dark or darker than control—surge detected!
• Digital OPKs: Show a smiley face or 'peak fertility' when surge detected
• Semi-quantitative tests: Show rising LH over several days (Clearblue Advanced)

When the LH Surge is Confusing

Sometimes LH testing isn't straightforward:

• PCOS: May have chronically elevated LH, making surges hard to detect
• Short surge: Some women surge for only 12 hours—test twice daily if missing it
• No surge detected: You may be testing too early/late, or may not be ovulating
• Multiple peaks: Can happen; the final peak before temperature rise is the true surge
• Perimenopause: Higher baseline LH can affect test accuracy

LH Levels in Blood Tests

If your doctor orders blood LH testing:

• Day 3 LH: Baseline testing; should be 2-15 mIU/mL
• LH:FSH ratio: Should be close to 1:1; elevated ratio suggests PCOS
• Mid-cycle LH: Surge levels reach 20-100+ mIU/mL
• Low LH: May indicate hypothalamic issues affecting ovulation

Timing Intercourse with LH Surge

For optimal conception timing:

• Before surge: Have intercourse every other day starting 5 days before expected ovulation
• Day of positive OPK: Have intercourse that day
• Day after positive: Have intercourse again to maximize chances
• Don't wait for ovulation confirmation: By then, the fertile window may have passed

Key takeaways

• The LH surge occurs 24-36 hours before ovulation
• Test in afternoon/evening, not first morning urine
• Positive OPK means surge detected—have intercourse that day and the next
• Some conditions like PCOS can make LH surge detection challenging
• LH:FSH ratio over 2:1 may indicate PCOS

Frequently asked questions