The impact of adjustment for parity and mid-upper-arm circumference on sensitivity of symphysis-fundus height measurements to predict SGA foetuses in Mozambique.

BACKGROUND

With a new symphysis-fundus height (SFH) growth chart, based on Mozambican women with ultrasound-dated singleton pregnancies, the aim was to examine the possibility to enhance sensitivity of predicting small for gestational age (SGA) newborns by attempts to adjust the chart for parity and for mid-upper-arm circumference (MUAC).

METHODS

Two antenatal clinics were chosen in the suburban area of Maputo City. A cohort of 904 consecutively recruited antenatal clients was followed until birth. Gestational age was determined by ultrasound at enrolment. The growth of the SFH was measured every 2-3 weeks. Women with multiple pregnancy or with gestational age >21 weeks at enrolment were excluded. Attempts were made to adjust SFH measurements for parity and MUAC by developing a mathematical model to increase sensitivity of the SFH method to predict a foetus being SGA.

RESULTS

Parous women had on average 0.5-1 cm higher SFH readings than nulliparous women. Women with a body mass index (BMI) <19 and women with BMI >27 had approximately 1 cm lower and 1 cm higher readings, respectively, compared with women of normal BMI. There was a significant correlation between BMI and MUAC (r = 0.621; P < 0.001). The usefulness of SFH measurements to predict SGA newborns was analysed. The sensitivity was 49%, the specificity was 66%, the positive predictive value was 14% and the negative predictive value, 93%. By using the correlation between BMI and MUAC we tried to find a simple and useful method to improve the sensitivity of SFH to detect SGA foetuses. By reducing the SFH measurement by 1 cm for women with MUAC >29 and by 1 cm for multiparous women the sensitivity raised to 65% at the expense of reducing the specificity to 51%. Using a linear function of BMI, MUAC and parity to adjust the SFH measurement for each individual woman, it was possible to get a sensitivity of 70% with a corresponding specificity of 56%.

CONCLUSION

By using BMI, MUAC and parity, it might be possible to improve the sensitivity of the SFH growth chart in predicting newborn being SGA but mostly at the expense of specificity.