Nub Theory: 11 Weeks vs 12 Weeks — When Should You Check?
Wondering whether to try nub theory at your 11-week scan or wait until 12 weeks? The difference in accuracy is significant.
Table of Contents
- Accuracy at 11 vs 12 Weeks
- Developmental Differences
- Image Quality Differences
- The Verdict
- Frequently Asked Questions
Accuracy at 11 vs 12 Weeks
| Week | Accuracy | Error Rate | |------|----------|------------| | 11+0 | ~65% | ~35% | | 11+3 | ~70% | ~30% | | 12+0 | ~80% | ~20% | | 12+3 | ~85% | ~15% | | 12+6 | ~88% | ~12% |The jump from 11 to 12 weeks is dramatic — accuracy improves by 10-15 percentage points. This is because the genital tubercle develops significantly during this week.
Developmental Differences
At 11 weeks, the genital tubercle is still in early development. Both boy and girl nubs may look similar — slightly raised but not clearly differentiated. By 12 weeks, the developmental paths have diverged clearly: - Boy nubs have angled upward to 30+ degrees - Girl nubs have flattened to parallel with the spineImage Quality Differences
At 12 weeks, the baby is larger and easier to image clearly. The genital area is more visible, and the nub is more prominent. At 11 weeks, the baby is smaller and the nub is harder to distinguish from surrounding tissue.The Verdict
**Wait until at least 12+ weeks.** The accuracy improvement from 11 to 12 weeks is too significant to ignore. If your NHS scan is at 11 weeks, consider booking a private scan at 12+ weeks specifically for nub theory.Frequently Asked Questions
### Is 11 weeks 6 days accurate enough for nub theory?At 11+6, accuracy is approximately 72%. It's better than 11+0 (65%) but still significantly less accurate than 12+0 (80%). If you can wait just a few more days, your prediction will be much more reliable.
My NHS scan is at 11 weeks — should I book a private scan at 12 weeks?
If nub theory is important to you, yes. A private scan at 12+ weeks will give you a much better image and significantly higher accuracy. Expect to pay £60-£200 for a private early pregnancy scan.
This article is for informational purposes only and does not constitute medical advice.
Last reviewed: June 2026
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