Study design and period
A facility-based unmatched case-control study was conducted at public hospitals in Northeast Amhara, Ethiopia from March 15th to April 25th, 2019.
Study Area
The study was conducted in Northeast part of Amhara region, Ethiopia. The study was employed in six randomly selected governmental hospitals (Debre Birhan Referral hospital, Tarmaber Primary Hospital, Kemisie General Hospital, Dessie Referral Hospital, Borumeda Hospital, and Woldia general Hospital).
Source Population
All newborns who were born in public hospitals of Northeast Amhara, Ethiopia.
Study Population
All newborns who were born in selected public hospitals of Northeast Amhara, during data collection time.
Inclusion And Exclusion Criteria
Inclusion criteria
Cases
All alive singleton preterm newborns (< 37 completed weeks of gestation) who was born in study hospitals of northeast Amhara.
Controls
All alive singleton term newborns (37 completed weeks to 42 weeks) at the same hospitals.
Exclusion Criteria
Sample Size Determination
Sample size was determined by using EPI info version 7.2.2.6 by a double-population proportion difference formula. Different variables that have a high contribution for PTB was used and the variable that yields the highest sample size was selected. The sample size was calculated considering the following assumptions: r = 3 (ratio of controls to cases), 80% power and 95% confidence level. ANC < 4 with P Control = 42%, P Case = 60.7% was selected. Based on this, the sample size was 323. By considering a 10% non-response rate, the final sample size was 356 with 89 cases and 267 controls.
Sampling Technique
The total sample size was allocated proportionately according to their caseloads for selected hospitals. Cases were preterm newborns (gestational age < 37 completed weeks) and controls were term newborns (gestational age of ≥ 37 weeks to 42 weeks). Systematic sampling technique was employed to select controls and cases every fifth intervals and every two intervals respectively. The first participant was selected by lottery method.
Study Variables
Dependent variable
Preterm birth (Yes/No)
Independent Variables
Socioeconomic factors (including paternal age & education), obstetric history related factors, history of adverse birth outcomes, Obstetric complications, maternal medical conditions, behavioral factors, maternal anthropometrics, and infant characteristics.
Operational Definition
Preterm birth
Newborns born before 37 completed weeks of gestation
underweight
Mothers with MUAC less than 23 cm (17, 18)
Alcohol drinking
(19, 20)
A unit of alcohol
It is equivalent to 17.7 ml or 14 g of pure strength alcohol
Binge drinkers
mothers who drink ≥ 3 drinks at a time/per seat
Drinkers: mothers who use at least one unit of any alcohol during their pregnancy categorized into three levels:
Passive smoking
living with someone who smoked during the mother's pregnancy
Data Collection Tools And Procedures
Data was collected using interviewer-administered, structured pretested questionnaires and record review. The questionnaires include data on socio-demographic characteristics, obstetrics characteristics, infant characteristics, maternal anthropometrics, medical disorders, maternal infections, and behavioral factors. The questionnaires were prepared for this study by reviewing different kinds of literature from related studies and EDHS 2016, (14, 15, 21–23). Additional file
Confirmation of Gestational age was taken from documentation and for non-recorded data, information was taken from mother’s report of LNMP. The data was collected by six trained midwifery graduates and supervised by MSc nurses.
MUAC was measured by using flexible non- stretched tape taken at mid-point of left upper arm at relaxed position, without any clothing and with optimal tape tension between acromion process on shoulder blade and tip of olecranon process of ulna. Height was also measured using height Stadiometer with sliding head bar without shoes, standing erect, with shoulder blades, buttocks and heels touching the measuring board, looking straight ahead, shoulders relaxed, arms at sides, legs straight and knees together, feet flat and with heels together. Two height measurements were taken and average was used if readings are within 1 cm each other and record to the nearest 1 cm.
Data Quality Control
Data collectors and supervisor were trained for half a day on objective and methods of the study, study tools, how to approach the patient, and take anthropometric measures. In order to assess the validity and reliability of the tool and clarity of the variable, pre-test was done on 5% of the sample size newborns who were delivered out of the study hospitals two weeks ahead of data collection. During the data collection process, regular monitoring and supervision of the overall activity was done by the supervisors and principal investigator to check for completeness and ensure the quality of data. Besides, data cleaning and coding was carried out before analysis. The measurement tool was prepared in English and translated into local language (Amharic).
Data Processing And Analysis
The collected data were checked for completeness and entered into EPI info version 7.2.2.6 and exported to SPSS version 23 for analysis. Data were summarized using text, tables, and graphs. Model goodness of fit test was checked by Hosmer-Lemeshow test (P-value = 0.224) and fitted. Multicollinearity between independent variables was assessed by using VIF (1.1–1.27) and no problem detected. Binary logistic regression model was used to measure the association between preterm birth and risk factors. Variables that had P-value ≤ 0.2 on bi-variable regression analysis and had association with preterm birth in previous studies were fitted into the multivariable logistic regression model to assess their association with the outcome variable. Adjusted Odds ratio (AOR) with 95% confidence interval (CI) was calculated and P value ≤ 0.05 declared statistically significant.