Weight and height measurement: potential impact in obstetric care

To assess the accuracy of reported weight and height in a pregnant population.

Participants were recruited when attending their nuchal translucency scan if they attended with an 'antenatal screening for Down syndrome and other conditions' laboratory form (used for the maternal serum screening in the first trimester (MSS1) blood test) that had weight and/or height recorded. Participants' weight and height were measured by trained recruitment centre staff and body mass index (BMI) was calculated. Differences in reported (MSS1) and measured weight, height and BMI were analysed using Bland-Altman plots.

248 women participated. Only 23% (n=56) of participants had a weight recorded on the MSS1 laboratory form that was within plus or minus 0.5 kg of measured weight: 62% (n=155) had an under-reported weight, and 15% (n=37) an over-reported weight. 30% (n=74) of participants had a correctly reported height: 26% (n=63) an under-reported height, and 44% (n=107) an over-reported height. 6% (n=14) of participants had a correctly reported BMI: 69% (n=166) had an under-reported BMI, and 25% (n=60) an over-reported BMI. 17% of participants (n=40) were incorrectly classified by BMI category based on MSS1 data.

Our study suggests that there are considerable inaccuracies in the recording of weight and height during pregnancy in New Zealand. This results in a false reduction in BMI in many women which can affect clinical care.