Study design and setting
This was a cross-sectional hospital-based study carried out over a period of 4 months (January to April 2018) at the Yaounde Gynaeco-obstetric and Paediatric Hospital (YGOPH). The YGOPH is one of the tertiary health care facilities in Yaounde, the capital city of Cameroon. Inaugurated in 2002, the YGOPH has a capacity of 240 beds; it offers mainly gynaeco-obstetric and paediatric care to patients. The study was approved by the Institutional Review Board of the Faculty of Heath Sciences of the University of Buea and the Ethical Committee of the YGOPH.
The study involved children between 5 and 10 years, born between 2007 and 2012 at YGOPH, who used to consult in this hospital for pediatric problems, and whose parents/guardians gave their consent. We excluded from the study children suffering from renal and urinary tract malformations, CKD, diabetes, HIV infection, hepatitis B and C infection, and sickle cell disease. Children born between 2007 and 2012 were identified from the maternity registers and recorded in a book. Based on the BW of the maternity register, children were divided into 3 groups: LBW (<2500g), NBW (2500-3999g) and HBW (≥4000g). We used the sample size calculation formula for cross-sectional studies and considered the clinical prevalence of hypertension in children of 3.5% to obtain a minimum sample size of 70 participants [31, 32] ; we selected 1 HBW child for 2 LBW and 4 NBW children. The recruitment of LBW and HBW participants was consecutive on their appearance in the register while NBW children were randomly selected. In case of refusal to participate, the next name on the register was selected and the procedure repeated.
For each eligible participant, the child’s parent/guardian was contacted through a phone call during which the study procedures were fully explained and an appointment fixed based on their availability. During the meeting with the parent/guardian and their child, the study was once again explained to them and an assent form signed. A self-designed and pre-tested questionnaire was used for data collection. Data collected included socio-demographic details (age, sex), clinical characteristics (weight, height, systolic and diastolic blood pressure), maternal history of pregnancy (age, type of pregnancy, maternal illness, smoking and alcohol consumption), birth characterisitics (weight, gestational age, and history of child reanimation and/or hospitalization) and laboratory parameters (proteinuria, and serum and urinary creatinine). We used an appropriate cuff size of 13.5 to 22 cm according to the American Academy of Pediatrics guidelines to measure BP . After 5 minutes of rest with the participant in the sitting position, the back supported and feet uncrossed on the floor, we used an automated sphygmomanometer (OMRON HEM705CP, Omron Matsusaka Co, Matsusaka City, Mie-Ken, Japan) to measure BP on the right arm placed at the level of the heart, stretched out on the table with the palm facing up. The cuff was appropriately placed and then the machine was switched on. Three readings were taken consecutively and their mean calculated and recorded. Using BP table levels for sex, age and height percentiles, the BP percentile was recorded. When the BP was ≥ 90th percentile, it was repeated weekly up to two times; when it remained the same on the third measurement, it was measured using an aneroid sphygmomanometer twice consecutively; the mean of these measures were calculated and recorded as the final value.
Each participant provided 50ml first morning mid-stream urine for an immediate semi-quantitative measurement of dipstick proteinuria using the CombiScreen 7SL PLUS 7 test strips (Analyticon Biotechnologies AG, D-35104 Lichentenfeis, Germany). Participants with at least traces on urine dipstick for proteinuria on the first sample were given an appointment one week later to repeat the urine dipstick. Those with a second urine sample still showing at least traces for proteinuria were seen one week later for another urine dipstick test. When the proteinuria persisted even just as traces after the second repeated urine dipstick, we proceeded to estimate the 24-hours proteinuria from urine protein to creatinine ratio (PCR). We equally collected 3 ml of whole blood from an antecubital vein for serum creatinine and subsequent calculation of the GFR. Urine and blood samples were transported to the laboratory for processing. Serum and urinary creatinine were measured with a kinetic modification of the Jaffé reaction using a Human visual spectrophotometer (Human Gesellschaft, Biochemica und Diagnostica mbH, Wiesbaden, Germany) and Beckman creatinine analyzer (Beckman CX systems instruments, Anaheim, CA, USA) while urinary protein was measured using pyrogallol red-molybdate complex with Teco diagnostics tests (Teco Diagnostics, Anaheim, CA, USA).
Definitions and calculations
Delivery was categorized as preterm (<37 weeks of gestation), normal (37 to 42 weeks) or post-term (>42 weeks). We grouped children in percentiles using the World Health Organisation height and weight for age percentile reference charts release in 2007 . According to weight, underweight (<5th percentile for age), normal weight (5-<95th percentile for age) or overweight (≥95th percentile for age) were distinguished. For height, short stature (< 5th percentile for age), normal height (5-<95th percentile for age) or tall stature (≥95th percentile for age) were considered. BMI was estimated as weight (kg)/square height (m2). It was stratified into underweight (<5th percentile for age and sex), normal weight (5-85th percentile for age and sex), overweight (85-95th percentile for age and sex) and obesity (≥95th percentile for age and sex). BP was either normal [systolic blood pressure (SBP) and diastolic blood pressure (DBP)] <90th percentile for sex, age and height), elevated (SBP and/or DBP ≥90-<95th percentile for sex, age and height) whereas hypertension was defined as SBP and/or DBP ≥ 95th percentile for sex, age and height after three occasions according to the American Academy of Pediatrics guidelines to define BP categories and stages . Dipstick proteinuria was defined by a persistent proteinuria (at least traces) after three measurements. The 24 hours proteinuria was estimated from PCR and proteinuria corresponded to a PCR≥200mg/g. The Schwartz equation was used for estimate glomerular filtration rate (eGFR)  ; it was either increased (≥120 ml/min/1.73 m2), normal (90-<120 ml/min/1.73 m2) or decreased (<90 ml/min/1.73 m2).
Data were entered and coded using EPI info version 7.0 and analysed using Statistical Package for Social Science (SPSS) version 23.0. Considering the non-Gaussian distribution of continuous variables, medians and interquartile ranges (IQR) were computed for continuous variables. Frequencies and proportions were computed for categorical variables. Frequencies were compared using the Fisher exact test or the Chi-square test where appropriate. To compare continuous variables according to BW strata, we used the non-parametric U-test of Mann-Whitney or the H-test of Kruskal-Wallis, where indicated. The Spearman correlation was used to correlate the BW with other continuous variables. A p-value was considered statistically significant at <0.05.