Baby Gender Prediction at 40 Weeks
At 40 weeks, your baby's gender is definitively identifiable on any good quality ultrasound. You're in the third trimester and the external genitalia are fully formed — direct observation gives the highest possible accuracy.
Your Baby at 40 Weeks
- ✦Baby measures approximately 390mm — about the size of a small pumpkin
- ✦All major organs are developed and functioning at 40 weeks
- ✦Baby is gaining weight and building fat deposits steadily
Gender Prediction Methods at 40 Weeks
Nub Theory
Nub theory is no longer relevant at 40 weeks — the genitalia are directly observable and provide near-definitive results from a good quality scan.
Skull Theory
Skull theory can still be applied at 40 weeks as a supplementary method with around 80-85% accuracy.
Chinese Gender Calendar
The Chinese Gender Calendar is always available for a quick cultural check — though at this stage your ultrasound result is almost certainly confirmed.
AI Ultrasound Analysis
AI analysis at 40 weeks achieves ~95-99% accuracy. The fully-formed external genitalia provide clear, unambiguous markers for our model.
Get Your AI Gender Prediction
Upload your 40-week scan — our AI will confirm your baby's gender with near-complete accuracy at this stage.
Upload Your 40-Week Scan →Frequently Asked Questions
Can you tell the gender of a baby at 40 weeks?
Absolutely — at 40 weeks, gender determination is near-certain from a clear ultrasound. Both your sonographer and our AI can give you a highly reliable answer.
How accurate is gender prediction at 40 weeks?
Around 95-99% accuracy from direct observation and AI analysis at 40 weeks. This is as definitive as it gets without a genetic test.
What does a boy/girl look like on an ultrasound at 40 weeks?
At 40 weeks, male and female genitalia are fully formed and clearly visible. Boys show a clearly defined penis and scrotum; girls show the labia with the characteristic three-line appearance.