The gender of a baby can be reliably determined typically from around the 14th to 16th week of pregnancy through ultrasound, with the highest accuracy between 18 and 22 weeks during the anatomy scan. However, earlier determination is possible with advanced testing methods: Non-Invasive Prenatal Testing (NIPT), a blood test, can detect the baby's gender as early as 10 weeks with over 99% accuracy. Additionally, some prenatal gender DNA tests claim to determine gender as early as 6 weeks using a blood sample from the mother, also with high accuracy. Ultrasound gender prediction can start around 11 to 13 weeks using methods like the "nub theory," but accuracy improves significantly after 14 weeks. The absolute certainty of a baby's gender only comes at birth. Genetic diagnostic tests like amniocentesis or chorionic villus sampling can confirm gender earlier but are typically used for medical reasons due to associated risks.

Summary of Gender Determination Timing and Methods

Method| Earliest Timing| Accuracy/Notes
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Blood Test (Prenatal Gender Test)| As early as 6 weeks| Up to 99.9% accuracy
NIPT (Non-Invasive Prenatal Test)| Around 10 weeks| >99% accuracy, screens for fetal DNA
Ultrasound (Nub Theory)| 11-13 weeks| ~70-98% accuracy depending on timing
Ultrasound (Anatomy scan)| 14-22 weeks| 95-98% accuracy, highest confidence at 18-22 weeks
Amniocentesis / CVS| 10-12 weeks (diagnostic)| Nearly 100% but invasive with some risk

Thus, if you want to find out the gender as early as possible with high accuracy, a blood test like NIPT around 10 weeks or a specialized prenatal gender test from 6 weeks is your best option. Otherwise, an ultrasound scan around 18-22 weeks is the standard reliable approach.