Abstract:
Background: An accurate estimation of foetal birth weight is an integral part of the assessment of pregnant women in modern
obstetric practice. Globally, there is a rise in the prevalence of maternal obesity, a condition that is associated with negative
pregnancy outcomes. The estimation of foetal birth weight in obese pregnant women is an important consideration in improving
delivery outcomes. The clinical method of foetal birthweight estimation is especially important in our environment where imaging
techniques are not readily available at most health facilities where women deliver.
Methods: The study was a hospital based prospective observational study of term pregnant women who booked for antenatal care
and delivered at Our Lady of Apostles Hospital, Jos. The body mass index at delivery was used to assess obesity in 79 participants
who met the study criteria. The foetal birth weight was estimated clinically by multiplying the symphysio-fundal height by the
abdominal circumference at the level of the umbilicus and this was compared with the actual foetal birth weight measured by
weighing the babies within 30 minutes of birth. The mean of the clinically estimated foetal birth weight was compared with the mean
of the actual foetal birth weight. The absolute error, the absolute percent error and the proportion of estimated foetal birth weight
within ±10% of the actual birth weight were also used to assess accuracy of the clinical method of foetal birth weight estimation.
Results: The prevalence of maternal obesity in the study was 22.2%. The mean of the clinically estimated foetal birth weight
(4396.14g) was significantly higher than the mean of the actual foetal birth weight (3664.68g) (p <0.0005). The absolute error and the
absolute percent error increased significantly with increasing BMI group, p=0.038 and 0.044 respectively. The proportion of the
clinically estimated foetal birth weight within ±10% of actual birth weight significantly decreased with increasing BMI group (p =
0.042).
Conclusion: Maternal obesity significantly reduces the accuracy of the clinical method of foetal birth weight estimation. A reliance
on this method to estimate foetal birth weight in obese pregnant women may result in unnecessary and costly obstetric interventions.
It is recommended that as much as possible imaging techniques should be used to estimate foetal birth weight in obese pregnant
women.
