Saturday, October 22, 2011

BMI and Blood Pressure Measurement in Pregnancy

BP Cuff Size Chart
(exact cutoffs may vary by brand)
We've written before about the importance of using a large cuff for blood pressure measurement in women of size.

Yet sometimes using a large BP cuff for women of size is not done routinely, especially in obstetrics.  

Here's yet another study documenting the importance of the correct cuff size in "obese" women in pregnancy.  

Note that Class One obesity is usually BMI 30-35, Class Two is usually BMI 35-40, and Class Three is BMI over 40.

In this study, nearly half of Class One obese women needed a large cuff, and with Class Two and above, 100% needed a large cuff.  

My BMI is about 48 and has been for all four of my pregnancies, which occurred in the mid-90s through the mid 2000s.  Research on the importance of blood pressure cuff size in "obese" people had been around for years before that, yet getting the correct cuff size was a problem in three of my four pregnancies.

And I still hear stories about use of the wrong cuff size from other high-BMI women, inside and outside of pregnancy, even today.

In theory, care providers know about the importance of the correct cuff size, but in practice, many don't follow the guidelines, don't think cuff size really makes that much difference, don't really check what size cuff was used (even when encountering a high BP in a large person), and don't emphasize the importance of cuff size adequately to the nurses and techs who do the actual BP measurements most of the time.

Yes, BP taken at the wrist with a regular cuff can be done for a ballpark figure in high-BMI people, but is not accurate enough for decision-making purposes. It tends to overestimate blood pressure in many cases.

A large or thigh cuff  (depending on arm circumference) used on the arm is the only really accurate method of BP measurement in "obese" people.

You need accurate data on which to base care decisions. Ensuring the correct cuff size is a very simple but extremely important way that care providers can improve care for women of size.

Hypertens Pregnancy. 2011;30(4):396-400. Body Mass Index and Blood Pressure Measurement during Pregnancy. Hogan JL, et al.  PMID: 20726743

Objective. The accurate measurement of blood pressure requires the use of a large cuff in subjects with a high mid-arm circumference (MAC). This prospective study examined the need for a large cuff during pregnancy and its correlation with maternal obesity.

Methods. Maternal body mass index (BMI), fat mass, and MAC were measured.

Results. Of 179 women studied, 15.6% were obese. With a BMI of level 1 obesity, 44% needed a large cuff and with a BMI of level 2 obesity 100% needed a large cuff. 

Conclusion. All women booking for antenatal care should have their MAC measured to avoid the overdiagnosis of pregnancy hypertension.


dee.calarco said...

I've often wondered if doctors and nurses do this partly on purpose, so that they have ammunition in pressuring us to diet. Several doctors have been visibly annoyed when my numbers have all come out in the healthy range. (except BMI, of course)

Unknown said...

I am someone who has had personal experience with this issue. At my family practitioner, I'd been having slightly high blood pressure and having it taken was rather painful, so I was a little worried it when I got pregnant. I go to my OB, where I know for sure they used a large cuff and voila! Suddenly I have great blood pressure and having it taken is completely comfortable (which probably helped my blood pressure even more.) It was wonderful to suddenly know that I was okay!

I don't know for sure that the nurse at my family doctor wasn't using the large cuff, but the numbers are awfully suspicious. I promise you that when I go back, I will be speaking up about it!

Tanz33 said...

Hang on, Kimmi - I thought blood pressure readings were always painful, they always have been for me? I sit there 'panting' while they take it. Hell, in labour with my first set of twins the blood pressure machine they had me on squeezed me so hard my hand and fingers swelled up and I had to get my rings cut off.

Is it actually to do with the size cuff they use (the pain)?

YourPlusSizePregnancy said...

This is SO important. I also wish nurses/aides would learn to be more discrete about this. They try the small cuff on then realize and say "I have to go get the BIGGER cuff." They ought to know by looking at you OR it should be on your chart. It is hard enough to feel good about yourself but to have to encounter this at each visit, makes it very uncomfortable.

Unknown said...

Tanz - That experience sounds terrible!

I remember when I was younger/thinner it being less painful, and it has been again with the nurse I've been seeing at my OB's office. I can't say for SURE that its because of the cuff, it might be due to her technique, but a too-small cuff being more painful makes logical sense to me.

With the machines, I have always found it to be VERY painful. I think to get a good reading, they have to over tighten? I generally refuse them now because often they can't even get a good reading on me.