Birth weight and gestational age distributions in a rural Kenyan population

Abstract

Background: With the increased availability of access to prenatal ultrasound in low/middle-income countries, there is opportunity to better characterize the association between fetal growth and birth weight across global settings. This is important, as fetal growth curves and birthweight charts are often used as proxy health indicators. As part of a randomized control trial, in which ultrasonography was utilized to establish accurate gestational age of pregnancies, we explored the association between gestational age and birthweight among a cohort in Western Kenya, then compared our results to data reported by the INTERGROWTH-21st study.

Methods: This study was conducted in 8 geographical clusters across 3 counties in Western Kenya. Eligible subjects were nulliparous women carrying singleton pregnancies. An early ultrasound was performed between 6 + 0/7 and 13 + 6/7 weeks gestational age. At birth, infants were weighed on platform scales provided either by the study team (community births), or the Government of Kenya (public health facilities). The 10^th, 25^th, median, 75^th, and 90^th BW percentiles for 36 to 42 weeks gestation were determined; resulting percentile points were plotted, and curves determined using a cubic spline technique. A signed rank test was used to quantify the comparison of the percentiles generated in the rural Kenyan sample with those of the INTERGROWTH-21st study.

Results: A total of 1291 infants (of 1408 pregnant women randomized) were included. Ninety-three infants did not have a measured birth weight. The majority of these were due to miscarriage (n = 49) or stillbirth (n = 27). No significant differences were found between subjects who were lost to follow-up. Signed rank comparisons of the observed median of the Western Kenya data at 10^th, 50^th, and 90^th birthweight percentiles, as compared to medians reported in the INTERGROWTH-21st distributions, revealed close alignment between the two datasets, with significant differences at 36 and 37 weeks. Limitations of the current study include small sample size, and detection of potential digit preference bias.

Conclusions: A comparison of birthweight percentiles by gestational age estimation, among a sample of infants from rural Kenya, revealed slight differences as compared to those from the global population (INTERGROWTH-21^st).

Trial registration: This is a single site sub-study of data collected in conjunction with the Aspirin Supplementation for Pregnancy Indicated Risk Reduction In Nulliparas (ASPIRIN) Trial, which is listed at ClinicalTrials.gov , NCT02409680 (07/04/2015).

Keywords: Birthweight; Fetal growth; Gestational age; Kenya; Obstetrical ultrasound; Sub-Saharan Africa.

Fig. 1

Map of the study region, located in Busia, Bungoma, and Kakamega counties of western Kenya. Study clusters are outlined in gray. County locations within Kenya are depicted in the inset map

Fig. 2

Consort diagram

Fig. 3

Histogram of measured birth weights. A fitted normal distribution curve is projected onto the actual data

Fig. 4

Scatterplot of Measured Birth Weight (y axis) and gestational age (x axis). A cubic spline was fitted and plotted onto the data. Red points indicate either a fetal or neonatal death

Fig. 5

Birth weight percentile curves are plotted against actual data (n=1189). Only percentiles for 36—42 weeks are plotted due to paucity of data in the other completed weeks of gestation, as well as facillitating comparison with INTERGROWTH 21 data