Can you always trust your ultrasound scan results when it comes to the sex of your baby? The simple answer is no. That's right, girl/boy predictions done by expert sonographers are not correct 100% of the time. (Although they are right most of the time!)


Can a gender scan for a girl or boy be wrong?

Yes. Reading info from a scan is all about interpretation. Sonographers are highly skilled in identifying a lot of detail from a fairly blurry image, which can be made a lot harder if your baby isn't playing ball and is in a tricky position. And getting it wrong does happen.

Jan Steward of Ultrasound Direct says the way you can be most certain of your baby's sex is when sonographers look at the ‘potty shot’ like the one below.


“When we scan we always give the parents an example picture of what we call the potty shot and then we look together and I point out why we think it's a boy or girl.

"We give a professional opinion but there are a few cases when there is a surprise. There is no such thing as 100%”

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"My friend is a midwife and she said this happens quite often," reveals nikkiandnell on our forum, "which is why they often won't tell you 100% what the sex is.

"In my scan the sonographer actually saw the girl parts (rather than just not seeing boy parts) and pointed them out to us, but even then she said she couldn't tell us for certain.

"I painted my nursery in beige and creams and haven't told anyone apart from our parents - just in case. It will certainly be very strange if they have made a mistake." Nikki went on to have a girl, by the way.

When MFM editor Susie went for her 20-week scan for her first child, the sonographer couldn't answer her question. "I was keen to know in advance what sex our baby was, but the sonographer said she couldn't tell," recalls Susie, whose baby turned out to be a girl.

How many weeks' pregnant do I have to be to find out the sex of my baby?

"You are usually able to find out the sex of your baby during the anomaly scan, which happens around 20 weeks," says Nigel Thompson, Professional Officer for ultrasound at the Society and College of Radiographers.

“The sex of your baby is reasonably accurately determined by ultrasound from 12 weeks but most NHS departments will not offer an opinion until at least 16 weeks and more commonly not until the anomaly scan.

"Private providers may of course offer it, however.”


It’s also important to remember that while your sonographer probably will share their opinion with you, this is not 100% certain.

There are also theories about how to predict your baby's sex from your 12-week dating scan:

Alternatively, you can book a private gender scan before your 20-week scan. These are available from around 14-15 weeks.

"The ideal time is from the 14th or 15th weeks of pregnancy," explains Dr Geetha Venkat, Director of the Harley Street Fertility Clinic. "This is when the baby’s sexual organs have grown to a point at which they can be correctly identified.”

Can a boy ultrasound be mistaken for a girl?

“The most accurate way to be sure if it is a boy is if you get a positive identification on the penis and scrotum,” says Nigel. “It would still not be 100 percent certain but definitely in the upper 90%.”

Forum mum LouiseMurray managed to get some pretty strong proof of her little boy's sex on her scan pictures, saying: “I got a whole scan pic of my little one's willy at my 20 week scan so I'm positive it's a boy. That'll be one to embarrass him with when he's older!”

For girls looking for the ‘3 lines’ can be helpful, like in the potty shots above. “This is basically identifying the labia. The 3 lines just describes the upper part and the lower part and is a good way of determining a female.”

And sometimes how confident - or otherwise - your sonographer sounds can be a key to how sure they are about your baby's sex.

lilylou asked upfront. “At my 20 week scan I was told I was having a boy and I asked how sure the sonographer was. She said she was 100% sure. I was worried about buying loads of stuff for one sex so I think I will trust 100%. If she said 'think' i would have maybe been a bit more cautious and bought neutral for the big items.” And lilylou had... a boy.

Bride Carly Barley adds, “I was told I was having a boy at my scan so I was most surprised when a beautiful little girl popped out! But they were never that sure. The sonographer said she 'thought' it was a boy, so I took it with a pinch of salt and bought mostly neutral things. But saying that I don’t know anyone else who has been told the wrong sex.”

Should you get a private scan for a 2nd opinion?

For some who felt the NHS prediction was not definitive enough, there's the choice of paying for another look with a private scan.

"At my 20 week scan we asked to know the sex, and the sonographer said our baby had legs tightly closed," explains Happy2Hook. “She said she couldn’t see any obvious boy bits, and apologised at not being much help on the matter!

"I booked a private scan that night for the week after. The whole experience was amazing. The lady checked 3 times and showed us the 3 little lines of the girly bits A hamburger she called it!

"At the start of the scan we had to sign a disclaimer to say we wouldn’t sue if they got it incorrect and that they could only be 95% (or something like that!) accurate.”