6 Things You (Probably) Didn't Know About The 20-Week Scan

You can find out the sex of your baby, but that's just the tip of the iceberg.
Maskot via Getty Images

There are lots of things we’re told about pregnancy, but when it actually happens to you, you realise there’s so much more to learn. In Unexpected, we’ll chart some of the less spoken about things that happen in the months between finding out you’re pregnant and giving birth.

The 20-week scan – or anomaly scan, as it’s more formally known – is a Pretty Big Deal for parents to be.

It’s the scan where you can hopefully find out the sex of your baby (if you want to know, that is) and whether there are any underlying issues with your baby that need further exploration – hence the ‘anomaly’ part.

If you’ve got yours coming up, you might be wondering what actually happens at the scan. It’s very similar to your 12-week scan, but this one lasts 30 minutes and requires a lot more concentration on your sonographer’s part as they’ve got to look out for a minimum of 11 conditions.

Here are six things you probably didn’t know about the scan.

1. It doesn’t always happen at 20 weeks

Much like the 12-week scan can happen anytime between 10 and 14 weeks, the 20-week scan is usually carried out between 18 and 21 weeks, so don’t feel worried if yours is a little early or late. Sonographers can still find out everything they need to at this stage.

2. You can opt out of the scan if you want

Interestingly, the anomaly scan is optional so if you don’t want it, you don’t have to have it. That said, it’s an important scan for finding out your baby is healthy and developing OK so missing it might be risky.

While at the 12-week scan the baby is measured to determine how many weeks pregnant you are; at the 20-week scan, the sonographer will assess the growth of your baby to make sure they are growing in line with the due date you’ve been given.

“We look at the growth of the baby to make sure things are progressing as we’d expect, and then we basically go through right from the top of the head, all the way down to the feet, and we’re looking at the structures of baby,” says Gill Harrison, professional officer for ultrasound at The Society of Radiographers, who has been scanning babies for 30 years.

3. You might not even find out the sex of your baby

Everyone associates the 20-week scan with finding out the sex of their baby but the reality is you might not even be able to find out that detail. Sonographers aren’t actually obliged to tell you the sex as they’ve got lots to unearth in a relatively short amount of time.

“Some people will want to know the sex of the baby. If that’s part of the policy for the trust then sonographers will look, but it’s not part of the expectation for the NHS screening,” says Harrison.

“If you can’t see it, you wouldn’t be able to spend a lot of extra time looking because that then takes away the time that you should be looking at the really important structures.”

If you do want to find out, it’s best to let your sonographer know at the start of the scan so they can make a mental note to look while they’re doing all of the other checks.

“It’s a real balance between parents desperate to know those bits, but also the real reason for the scan is to make sure that the baby structurally looks normal,” adds Harrison.

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4. The sonographer is taking in loads of information about your baby while you lay there

When your sonographer starts scanning they’ll be checking all of the structures of your tiny baby – making sure their organs are forming well and there aren’t any gaps where there shouldn’t be.

“We go through the brain and make sure the structures are normal,” says Harrison, “we look at the face, the lips, then we go down through the chest and the heart, right down to the abdomen, into the pelvis. So we’re looking at the kidneys, the bladder, the stomach, the diaphragm ... then we look at the limbs and the spine.”

The sonographer will want to check all of these areas look normal and will be keeping an eye out for a minimum of 11 rare conditions. These include:

  • anencephaly (a fatal condition where the skull doesn’t develop)

  • spina bifida (where the spine and spinal cord does not develop properly)

  • cleft lip (a facial birth defect which occurs when a gap forms in the upper lip)

  • diaphragmatic hernia (where there’s a hole in the diaphragm)

  • gastroschisis and exomphalos (where the abdomen does not develop properly)

  • serious cardiac abnormalities

  • bilateral renal agenesis (a serious condition where neither of the kidneys develop)

  • lethal skeletal dysplasia (severe abnormalities of bone growth including rib growth)

  • Edwards’ syndrome and Patau’s syndrome (chromosomal conditions associated with defects in many parts of the body)

They’ll also check how much fluid there is around your baby – if there’s too much or not enough, they then have to consider why this might be.

“Sometimes it’s just one of those things,” says Harrison, “but other times it might be linked to problems with baby’s kidneys or bladder, or a problem with the growth of baby. In the same way, too much fluid might be normal for that pregnancy, but it might also be linked to a swallowing problem or a stomach problem.”

Once that’s all out of the way, the sonographer will check the placenta to see where it’s positioned in relation to the birth canal. “What we don’t want is a placenta that’s completely covering the birth canal and nobody knows about it,” says Harrison. “Because obviously that’s going to stop the baby coming out and if nobody knows about it, that’s a really serious complication.”

Measurements that are taken include: the circumference of the head (HC), abdominal circumference (AC) and femur length (FL). They also measure the cerebellum, which is the brain’s balance centre, and the nuchal fold which is basically a bit of skin at the back of the neck.

“We measure that just to see that it’s not enlarged, as that can be linked to chromosomal problems,” says Harrison.

5. If an anomaly is found, you’ll need more scans

Sometimes issues are flagged up – some of these can be monitored throughout the pregnancy, however in more serious cases, like if the skull or kidneys don’t develop, it will have more serious repercussions for the baby’s survival.

You might be referred to a foetal medicine specialist or to a foetal assessment unit who can then either scan again or investigate further and talk through the implications with you.

6. If your sonographer is quiet, you can ask them to go over the findings with you at the end

Every sonographer is different, so while some might be able to talk you through what they’re doing, others who are less experienced might be really silent for the majority of the scan – and as a parent-to-be, this can be really disconcerting.

“However easy it looks, it’s really quite a complex examination,” says Harrison. “While sonographers want to make it a really good experience, they do have to concentrate hard as well. I talk through the whole scan so parents know what I’m looking at, but somebody who’s less experienced or newly qualified, they might find it hard to do that as it’s so difficult to do.”

If you do have a quiet sonographer, don’t be afraid to ask questions or to ask them to go over the report with you at the end.

Sarah Maxwell for HuffPost