Fundal height question!

[Brownboots]

Hello

Hoping someone can tell me if my thinking is correct!

I'm 30 weeks pregnant. My fundal height chart has my height and BMI noted on it, which leads me to believe that the lines for the different percentiles are customised to me. I've never asked that direct question, just made the assumption.

I'm 5 ft 5 and at my first contact appointment with my midwife my BMI was calculated at 32. My weight since has gone down by a pound, it didn't drop from sickness and come back up, just hasn't changed all along. I think this is because my appetite has been smaller since getting pregnant, and also before getting pregnant I would drink more than I should, mainly wine and cider. To be a healthy weight I'd have had to have lost 2.5st so it stands to reason to me that by eating more healthily, I would lose fat fairly easily as I had a lot to lose. I've gone through what I eat in a typical day with my midwife and she said I was still getting a good amount, I was just overeating before.

At 28 weeks my fundal height measured quite high, I was a bit surprised as I'd assumed that given the chart was based on BMI I would be smaller as I generally lose weight off my belly first.

At 30 weeks, I measured exactly the same which put me on 10th centile and I've therefore been referred for a growth scan. I've tried not to worry but it's hard!

I'm looking for reassurance that my assumption re weight makes sense and therefore it would make more sense for me to be measuring on the small side. Also, I believe they're pretty unreliable anyway, especially since the measurements were taken by different people so I'm trying to tell myself just not to worry!

Last point is that, first scan where I was.big was in the afternoon after my lunch and I needed a wee, second was at half 9 and i hadn't had my breakfast yet and hadn't long done a wee! I'm assuming that makes a difference too!

Sorry that's far less coherent that I intended.

Fundal height and your BMI are not connected.
The fundal height just gives the midwife an idea of babys growth.
It is measured from the top of the uterus which can be quite hard to find if you have a bigger bmi, and its measured down to the public bone.
The general rule of the thumb is from 28weeks they would expect you to measure approx 28cm, 30weeks 30cm etc. There is room for mistake and for extra growth too which I believe is 3cm. So effectively at 30 weeks they could measure you at 33cm, they may send you for growth scans if they deem it necessary but in reality the fundal height measurement is very subjective.
If youre worried speak to your midwife at your next appointment they will reassure you.

But surely, given the measurement is taken from the outside, body fat impacts it? Like how larger ladies often have a 'B' shaped bump rather than a 'D' shaped, because they still carry fat on their stomachs.

Surely a size 10 woman won't have the same measurements as a size 18?

There's plenty of examples online of growth charts where the centile lines don't match with mine, they're either lower or higher. The difference isn't a lot, but on my chart the difference between 10th and 90th centiles is only 2cm so difference doesn't need to be big.

I think given how small the difference needs to be to cause concern along with the method not being that reliable anyway, I'll just try to push it out of my mind until my growth scan.

But when they measure the measurement isn't of the amount of fat big or little you have but the top of your uterus which grows in pregnancy to accommodate your expanding baby.
They will have to feel right down into your tummy to be able to feel the top of your uterus as - in bigger women it's harder to locate but as I say it goes by the uterus as opposed to how big or little you as a person are

You are right that the projection the give you (the line to follow) is tailored to your height and weight, but it's not your BMI (which sounds odd I know). Fundal height however is not an exact science and getting accurate measurements each time is difficult and will change if baby is back to back or belly to back, if a different tape measure is used or if they can't exactly feel where your uterus ends.

The graph is partly based on bmi from my understanding, however all manner of things can affect the fundal height including a full bladder or baby's position, if you're getting scans anyway I wouldn't worry about it.

I asked this exact question when my fundal height was first measured. I was measuring a week ahead, but then had a growth scan which put my dates as spot on. Like you my booking bmi was 32, sovi asked if this was the reason I measured ahead, they said it shouldn’t really impact on it until your bmi is over (I think but could be wrong) 35. She said that fundal height measurements are only really guides anyway and not to worry. I’m having regular growth scans now anyway because of gestational diabetes so they won’t bother measuring me again.

Scans tomorrow :) baby is moving a lot and I'm not really worried, there were so many different circumstances between the two measurements. Found this page which was really useful if anyone happens across this thread looking for answers themselves! www.perinatal.org.uk/FetalGrowth/B.aspx It says that needing a wee can make the measurement bigger, and that the measurement includes skin and get. Sorry for no paragraphs, it won't let me put any in!