Protocol and registration
The review protocol was published on PROSPERO and can be accessed through www.crd.york.ac.uk/prospero/display_record.dhp? ID=CRD42019147146. The Cochrane RevMan software was used to write this report and to do the necessary analysis.
Search methods for identification of studies
Our search strategy aimed to find both published and unpublished studies. We followed a three-step search strategy. An initial limited search of MEDLINE/PubMed, EMBASE, CINAHL, Web of science, Cochrane library and JBI library was undertaken followed by an analysis of the text words contained in the title and abstract, and of the index terms used to describe articles. A second search using all the identified keywords and index terms was then undertaken across all included databases and grey literature sources. Thirdly, the reference lists of all identified studies retrieved for critical appraisal were searched for additional studies. The search for unpublished studies included: Google, MedNar, Google scholar, African Journals online, and conference proceedings. Studies published in the English language, and conducted in Sub-Sahara African countries, were included. Initial keywords used were: short birth interval or short birth spacing; preterm or premature birth; pregnant women.
Comprehensive literature search was done three times at least 2 months apart. The last search was done on January 31/2020. The search was mainly done using the following terms or phrases: The following search strategies, used for PubMed, were modified for the various databases using the two important Boolean operators (OR, AND) (table 1).
Table 1: Search strategies used for PubMed and other various databases for the current systematic review and meta-analysis, January 31/2020.
|
Population
|
|
Intervention or Exposure
|
|
Outcome
|
|
Pregnant women
|
|
Short birth interval
|
|
Preterm birth
|
Search terms: Indexed or key words
|
"pregnant women"[MeSH Terms]
OR
"pregnant women"[Title/Abstract]
OR
"pregnant woman"[Title/Abstract]
|
AND
|
"birth interval"[MeSH Terms]
OR
"inter pregnancy interval"[Title/Abstract]
OR
"pregnancy spacing"[Title/Abstract]
OR
"pregnancy interval"[Title/Abstract]
OR
"birth spacing"[Title/Abstract]
OR
"short birth interval"[Title/Abstract]
OR
"short birth spacing"[Title/Abstract]
OR
"short inter pregnancy interval"[Title/Abstract]
OR
"short pregnancy interval"[Title/Abstract]
|
AND
|
"premature birth"[MeSH Terms]
OR
"premature birth"[Title/Abstract]
OR
"preterm birth"[Title/Abstract]
OR
"preterm infant"[Title/Abstract]
OR
"premature infant"[Title/Abstract]
OR
"preterm delivery"[Title/Abstract]
|
Types of study included
Our review considered prospective and retrospective cohort studies, case control studies and analytical cross-sectional studies examining the association between short birth intervals and preterm births.
Condition or domain being studied
Preterm birth, defined as being born alive before 37 completed weeks of gestational age.
Participants/population
Multiparous women for whom there is information on the length of the birth interval between two consecutive births in sub-Saharan African countries.
Intervention(s), exposure(s)
Short birth intervals as a predictor for the risk of preterm birth in pregnant women.
Birth interval: defined as the time elapsed between the date of birth of the preceding infant and the date of birth of the current consecutive infant/sibling. Short birth interval: defined as less than 24 months (< 24 months) between two consecutive births.
Comparator(s)/control
Optimal birth interval (the time elapsed between two consecutive births is two or more years).
Context
Our review considered only studies conducted in sub-Saharan African countries (15).
Main outcome(s): Preterm birth.
Timing and effect measures
We extracted information on raw data for shorter birth intervals and preterm birth from included studies.
Study selection, quality assessment and data extraction
We used EndNote version X8 reference management software to combine database search results and to remove duplicate articles. The studies retrieved from the searches were screened for relevance based on title and abstract, and those identified as being potentially eligible were fully assessed against the inclusion/exclusion criteria. The papers selected for retrieval were assessed by two independent reviewers for risk of bias or methodological validity prior to their inclusion in the review using standardized Joanna Briggs Institute (JBI) quality assessment tools for analytical cross-sectional, case control and cohort studies and there was 90% observed agreement between assessors. Disagreements between assessor were resolved through discussion. Reasons for exclusion of the studies was explained and recorded. PRISMA flow diagram was used to show the process of selection and inclusion of the studies (16). Data were extracted from the papers selected for inclusion in the review using data extraction tool which was prepared using Microsoft excel sheet. The data extraction tool included: data on birth interval (shorter and optimal), primary author name, publication year, study design, study setting, sample size and outcome measures (preterm birth and term birth).
Strategy for data synthesis
Data from the included studies were summarized in a table. All analyses were conducted using RevMan 5.3 software. A random-effects meta-analysis was performed to compute pooled estimates of short birth interval effects on preterm birth with a 95% confidence interval. The magnitude of heterogeneity was estimated using the I² statistic, and heterogeneity was considered significant at a P-value of less than 0.1. Heterogeneity was further investigated using subgroup analyses, and, in addition, sensitivity analyses was carried out to determine the impact of study quality on the results.
Publication bias was assessed by visual inspection of funnel plot of proportion against its standard error, for plot symmetry.
Analysis of subgroups or subsets
To investigate heterogeneity, subgroup analyses was carried out for study setting (Ethiopia, Kenya, Tanzania and Ghana) and study design type (cohort, case-control and cross-sectional). In addition, sensitivity analyses were carried out to investigate the influence of single studies on the overall estimate obtained.