Ultrasound is a reliable method for determining a baby's sex, but accuracy increases with gestational age. The visualization of external genitalia is key.
Determining Gender: Timing and Techniques
- Early Ultrasound (12 weeks): At approximately 12 weeks, the genital tubercle can be assessed. This is sometimes referred to as the "nub theory." According to this, a nub angled greater than 30 degrees against the spine suggests a male fetus, while an angle less than 10 degrees or parallel to the spine indicates female. The accuracy at this stage is lower. [Source: Multiple sources including information on the nub theory and its accuracy at 12 weeks.]
- Second Trimester (18-20 weeks): During the second trimester (ideally between 18 and 20 weeks), the external genitalia are usually clearly visible. An ultrasound at this stage can definitively identify the presence of a penis or vulva. [Source: Parents.com, WhatToExpect.com, WebMD, and others describing the increased accuracy in the second trimester.]
- Later Trimesters: The accuracy continues to improve in later trimesters, making the determination even more reliable. [Source: Parents.com]
Visual Indicators:
- Female: A downward-angled genital tubercle or three lines on the ultrasound image are potential indicators of a female fetus. [Source: WhatToExpect.com]
- Male: A visibly discernible penis is the primary indicator of a male fetus.
Accuracy Considerations
The accuracy of gender determination via ultrasound varies depending on several factors, including the skill of the technician, the quality of the equipment, and the position of the fetus. While accuracy is high in the second and third trimesters, it's important to remember that no method is 100% foolproof. Early predictions, like those based on the nub theory, carry a higher margin of error. [Source: WebMD indicating varying accuracy depending on gestational age and other factors.]
