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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 10th, 25th, median, 75th, and 90th 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 10th, 50th, and 90th 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-21st). 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).
The data presented in this paper were acquired at the Kenya site as part of the Global Network for Women’s and Children’s Health Research ASPIRIN trial. Detailed study methods are described in Hoffman et al. [14, 18]. The Kenyan site (Fig. 1) is situated within the malaria holoendemic Lake region of Western Kenya, specifically the counties of Busia, Kakamega, and Bungoma [19]. The eight geographical clusters within the Kenyan site are served by over 20 health facilities, most operated by the government and staffed by nurse-midwives, clinical officers, and a single medical officer. Three hospitals in the area function as county referral hospitals [20]. There is one tertiary teaching and referral hospital based in Eldoret for the western region with a newly established training program in maternal fetal medicine. Most physicians are generalists, with some trained obstetricians and pediatricians [20]. 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 Eligible subjects were pregnant nulliparous women carrying singleton pregnancies. An early ultrasound was performed between 6 + 0/7 and 13 + 6/7 weeks gestational age for accurate pregnancy dating. From this ultrasound, the estimated day of delivery was determined using the ACOG algorithm [21, 22], which was programed onto a handheld android device. Eligible women were then randomized to a daily regimen of low dose aspirin or placebo and followed to 42 days post pregnancy completion. Randomization was performed by site, with the randomization sequence for each site provided by the data coordinating center (RTI) using a computer algorithm based on a randomly permuted block design with varied block sizes. The primary analysis included data from Kenya and 5 other countries (India, Pakistan, Guatemala, Zambia, and Democratic Republic of Congo) and found that the aspirin intervention reduced delivery < 34 weeks; no impact on birthweight was observed [14]. Within the Kenya population, mean birthweight and gestational age were comparable by treatment arm. The analysis of variance was statistically significant for birthweight (p = 0.0167), but the difference of means was not clinically significant (~ 63 g). The analysis of variance for gestational age was not statistically or clinically significant. Infants born to subjects were weighed on platform scales either at a delivery in a health facility, or if born outside of a facility, at the home of the local village elder [23]. For infants delivered at participating public health facilities, the weighing scales used were those provided by the Government of Kenya; our study team did not have control over the make or model of infant weighing scales utilized. The weights of infants born within the community-setting, and weighed by village elders, were obtained using scales (Perlong Medical Equipment Co., Ltd.RGZ-20 Nanjing, China) provided by our research team. Only infants with a measured birth weight (BW) were included in this analysis. For subjects experiencing either a stillbirth or an infant death before the 42-day follow-up period, the assumed cause of death was determined using a previously published algorithm [24, 25]. Estimated gestational age (EGA) in days at time of delivery or stillbirth was defined as (Date of delivery – Estimated Date of Delivery by ultrasound) + 280. EGA in weeks was defined as EGA Days/7. Completed weeks of gestation was calculated by rounding the EGA weeks to the next larger integer. Statistical analyses were performed using JMP software and SAS version 9.4 (SAS Inc, Cary, NC USA). The 10th, 25th, median, 75th, and 90th BW percentiles for 36 and 43 completed weeks gestation were determined, the resulting percentile points were plotted, and curves determined using a cubic spline technique. Percentile curves for gestational ages less than 36 weeks (n = 57) or greater than 43 weeks (n = 9) were not plotted due to paucity of data for these groups. A signed rank test was used to quantify the comparison of the percentiles generated in this study with those of the INTERGROWTH-21st study. This test was performed twice within each gestational week – once testing the null hypothesis that the Kenya Male median equals the reported median of the INTERGROWTH-21st Male data, and once testing the null hypothesis that the Kenya Female median equals the reported median of the INTERGROWTH-21st Female data. This analysis was non-directional and performed at the alpha = 0.05 significance level.
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