A baby’s gender is determined by the sperm on day one. If the sperm is carrying an X chromosome, the baby will be a girl. If the sperm is carrying a Y chromosome, the baby will be a boy. With a normal pregnancy, the genital parts of the baby become visible by ultrasound after 14 weeks of pregnancy.

What You Need to Know about Ultrasounds for Baby’s Sex Determination

Facts about Pregnancy Ultrasound scans:

• Boys and girls look the same in 1st trimester.
• Gender determination by ultrasound would be just guessing game before 14 weeks, genital tubercle starts showing up after this stage.
• The “nub theory” predicts genital tubercle can show upwards for boys and downward for girls but it is not visible in most of the cases by 15 weeks.
• The ultrasound scans done between 12-16 weeks have the highest rate of mistake, accuracy rate is 85-90 % due to small size, slight anatomical difference between penis or clitoris and constant movements of the baby.
• The accuracy rate goes higher between 16 to 20 weeks, 95-98%, depending on baby, mother and operator related factors.
• The gender is more accurately determined after 20 weeks of pregnancy, with 99 % accuracy.
• 2D ultrasound is more reliable than 3D before 22 weeks of pregnancy as cord or fingers mimic penis on 3D images

Factors that Affect the Reliability of Results & Quality of the Images:

• Swollen genitals with girls can look like testicles on 3D images. This is frequently seen due to the hormones passing from mother to the baby.
• 3D gender images might not be obtained at any stage due to the position of the baby.
• At any stage, correct determination of gender depends of many factors such as baby’s position and movements, amniotic fluid, location of the cord and placenta, single or multiple babies etc.
• Mother’s size has significant impact on correct gender determination. When the ultrasound waves must travel through more tissues, the image quality gets poor.
• The ultrasound machine’s resolution and operator’s knowledge and experience can also effect gender determination.
• The person who performs the scan is the only person to tell you just how accurate « that » particular diagnosis is, at that particular scan.

UC BABY Gender Reveal Sessions

At UC Baby we accept gender reveal clients only after 16 weeks. If we can’t see the genital organs clearly at any stage, we offer a free repeat scan to visualize the area with better clarity.

Written by: Tina I Ureten MD, RDMS, RDCS