REFERENCE RANGES FOR UMBILICAL ARTERY DOPPLER INDICES AMONG PREGNANT WOMEN IN ILE-IFE, NIGERIA

Abstract

Background: The unacceptably high stillbirth rate in Nigeria, majority of which are antepartum stillbirths demands formidable antenatal interventions. Notable among these interventions is the fetal umbilical artery Doppler velocimetry. Optimal utilization of this surveillance technique is however currently hindered by the unavailability of population- specific set of normal reference values for the Doppler indices in Nigerian hospitals.

Objective: This study aims to construct indigenous, gestational age-specific reference ranges for umbilical artery pulsatility index, resistance index and systolic/diastolic ratio of normal, singleton pregnancies in Ile-Ife, Osun state.

Study Site-: Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC) Ile-Ife, Osun State, Nigeria.

Study design-: A descriptive, longitudinal study.

Methods: Three hundred and forty-four booked pregnant women with singleton fetuses between the gestational ages of 28 to 31 weeks were recruited for the study. The umbilical artery Pulsatility Index (PI), Resistance Index (RI) and Systolic to Diastolic ratio (S:D) were measured and repeated four-weekly till delivery. The data was analyzed with SPSS 17.0. The mean ± standard deviation of the umbilical artery PI, RI and S/D ratio was determined between gestational ages of 28 and 40 weeks, and centile tables (95% range between 2.5th and 97.5th centiles) were constructed. Regression equations were generated for the indices, andPearson’s correlation was used to establish relationship with gestational age, birthweight and parity. The charts generated were compared with reference charts from Zurich and Norwegian populations.

Results: The normative umbilical artery doppler centiles constructed in this study demonstrated significant inverse correlation with gestational age, such that the RI reduced by 0.013, while the PI and S:D ratio reduced by 0.027 and 0.71 respectively for each additional week of pregnancy. There was a significant negative correlation between the RI (r =-0.207 , p = 0.001 ), PI (r = -0.17 , p= 0.01), S:D ratio ( r = -0.25 , p<0.001 ) and neonatal birth weight, but not with maternal age and parity. Although similar, the curves of the three indices demonstrated subtle differences from centile curves generated from Norwegian and Zurich populations.

Conclusion: Reference centiles for umbilical artery doppler indices based on serial longitudinal data have been generated. The doppler indices demonstrate variations across gestational ages and populations. The use of indigenous, population and gestational age- specific centiles as constructed in this study should be utilized in antenatal fetal surveillance in order to combat the bothersome perinatal morbidity and mortality in Nigeria.

REFERENCE RANGES FOR UMBILICAL ARTERY DOPPLER INDICES AMONG PREGNANT WOMEN IN ILE-IFE, NIGERIA