Advice on 20 week scan/BMI

[FirstTimeMum199]

So I am here for any advice regarding scans and a high BMI. When I found out I was pregnant my BMI was 42 which I know is medically ‘severely obese.’ For context I’m quite short at 5ft and I’ve always carried weight in my stomach. I do eat relatively healthy and try my best. I was told because of my BMI my pregnancy would be high risk. I had my 12 week scan and everything was fine. I’ve had my bloods and blood pressure done regularly, and I take aspirin and have my urine checked for protein that could indicate pre-eclampsia. So far I have had no complications and things seemed to be going well.

I have just had my 20 week anomaly scan and from the sonogram they couldn’t see everything they needed to. They also couldn’t tell the baby’s gender. I have been booked in for a re-scan, but they did say that the things they could see and checked were all fine. They didn’t really give me a reason why they couldn’t see everything and didn’t go through my measurements with me. I have read through my notes when I got home and the baby’s femur and head are measuring within the growth lines, however the abdomen is measuring bigger and on the top of the expected growth lines. Because they didn’t mention it I am hoping/assuming it’s all okay. But I am also worried between the bigger measuring abdomen and the fact they couldn’t see everything.

I was also told at a previous scan that I had an anterior placenta, however now at my 20 week scan I was told I have a posterior placenta which is low lying. Is it normal for the placenta to move from anterior to posterior? I know I should have asked these questions at my appointment but I was very overwhelmed and quite disheartened, I couldn’t really think straight. I am going to make a list of questions for my midwife and speak to them at my re-scan.

But I was wondering if anyone has had a similar experience and can offer some advice? I am just worried and want to make sure baby stays healthy.

It took three scans for them to see everything they needed when I was pregnant with my first. No one ever mentioned my weight (BMI of 37)as an issue, they just said the baby was not in the right position to image certain things - the heart chambers were the trickiest iirc. Sometimes they book for a couple of weeks later when the baby is bigger and detail is easier to see

The images are much less clear with a raised BMI and especially so if, as you said, you carry your weight on your abdomen. The more tissue there is between the baby and the probe, the less clear the image as the sound waves have to travel further and it causes beam attenuation.
It is most likely because of this they have rebooked you, as no matter how long they keep trying for, it won’t make the images any clearer.
The only solution is to rebook at an advanced gestation (before 22 weeks) so the baby is bigger and hopefully the smaller details are easier to see.
This does happen frequently and does not mean that there are any concerns, just that they simply could not see clearly enough to say.
It may feel disheartening but the sonographer has done the right thing to bring you back, as opposed to accepting poor quality, non diagnostic images and potentially missing something.

The placenta position is much easier to see at 20 weeks and is often documented wrong early, on when it is less clear. The sonographer has picked up that it’s posterior and low, so that is what you stick by for now, until it is checked again (and hopefully high).

It is always awkward to give women a reason as to why they are rebooked when it is because of raised BMI, as quite often they don’t want to hear the true reason and you don’t want to offend/ upset people.

As PP mentioned, a high BMI does make things difficult to see. It's usually noted on your scan notes as something like "poor visibility due to high maternal BMI"

I also have a high BMI and have needed a 20 week rescan in both my pregnancies. But it was due to baby being in an awkward position each time, which was recorded in the scan notes. What parts of baby were unable to be visualised were also on the scan notes. Neither rescan was successful. My first pregnancy I had a third scan which was successful. My second, even though there was loads that couldn't be measured still, no rescan was offered. Both babies were born perfectly healthy.

I wouldn't be too worried about baby's measurements at this point. What centile does your notes say the abdomen is on? The important thing bear in mind is that baby is growing fast, and it's not even growth. It's growth spurts all over. Could just be the abdomen had just finished a spurt, but not everything else had caught up yet. Also, as with the 12 week scan, we're still talking millimetres. With visualisation being difficult, the sonographer could be out slightly, making the measurement out.

I don't know about why the placenta would have changed from anterior from posterior. But I would assume the 20 week one is the correct one, and the first sonographer was mistaken.

Best of luck with your rescan, and the rest of your pregnancy.

The difficultly in seeing everything they need to is not always due to high BMI, but a higher BMI can definitely make it harder. Just to context - I have a high BMI and had to go back for another scan as they could not check the heart completely. My sister is very slim and she also had to go back for the same reason. You hear of it very often with women of all shapes and sizes :-)