The validity and reliability of weight and height measurements and body mass index calculations in early pregnancy

Abstract

Obesity is increasing in the UK and this is having an impact on the health of pregnant women and their infants. It is recommended that all pregnant women have their height and weight measured and their body mass index (BMI, kg m(-) ²) calculated and recorded in the midwifery notes. The aim of the present audit was to determine the extent of compliance with this recommendation. An audit was undertaken in a large district general hospital in the South West of England. A convenience sample of the midwifery notes was accessed retrospectively on the post-natal wards. Data collected from the notes included weight, height, BMI and gestational age when first recorded. A total of 486 maternal notes were audited; of these, 9% did not have the BMI recorded. In total, 53.8% of the sample had either height or weight not recorded; however, 90.9% of the sample had a BMI recorded. In addition, 39.7% (n = 126) of heights and 16.0% (n = 63) of weights were recorded in imperial format. There was a high prevalence overweight (26.2%) and obesity (21.3%) amongst the sample. Recommendations for measurement of height, weight and calculation of BMI were not always followed. Where BMI was recorded, many notes had either height or weight missing or had measurements recorded in imperial units. This raises the question of how BMI was calculated and its accuracy. Inaccuracies in BMI could lead to individuals being overlooked as high risk and may not be referred for appropriate care including dietetic care. Accurate anthropometric measurements are important for dietary management and monitoring of weight gain.