Results
We identified 57 eligible Cochrane systematic reviews and 1 IPD
meta-analysis focussing on primary or secondary PTB prevention in
pregnant women containing 373 potentially eligible RCTs (Figure 1).
These Cochrane reviews were published between 2006 and 2019 (median year
2017). From the 373 eligible RCTs, we were able to include 350 RCTs for
data extraction (Figure 1) coming from 56 reviews (See Table S1 for
overview of SRs and RCTs included). These 350 RCTs were published
between 1967 and 2019, with a gradual increase in publications over time
untill 2015, followed by lower numbers of studies in the years 2016-2019
due to an expected delay in the uptake of RCTs in systematic reviews
(Figure S1). The 350 RCTs randomised a total of 400,903 participants in
all continents, with a higher cumulative number of trials performed in
North America (n=92 trials, n=82,241 randomised women) and Europe (n=93
trials, n=56,653 women) and an increase of trials coming from Asia (n=71
trials, n=114,573 women) with a steep rise after the millennium (Figure
S1).
There were 108 RCTs published before 2000 (including 122,742 randomised
women), 104 RCTs between 2000-2009 (including 118,928 randomised women)
and 138 RCTs between 2010-2019 (including 159,233 randomised women)
showing no significant difference in randomised women per published
study between the three time frames. General characteristics of the
total RCTs sample and stratified for publications between the three time
frames are shown in Table 1. Some potential increase over time was seen
in the number of multicenter trials (93/212 [43.9%] before 2010 and
74/138 [53.6%] ≧2010; RR 1.22, 95%CI 0.98-1.52, with a stable
median of 5 to 6 participating centers). A substantial increase was
observed in the reporting of primary outcomes (139/212 [65.6%]
before 2010 and 120/138 [87%] ≧2010; RR 1.33, 95%CI 1.18-1.49),
power calculations (141/212 [66.5%] before 2010 and 109/138
[79.0%] ≧2010; RR 1.19, 95%CI 1.04-1.35) and use of a Data Safety
Monitoring Board (43/212 [20.3%] before 2010 and 42/138
[30.4%] ≧2010; RR 1.50, 95%CI 1.04-2.17) (Table 1). Stratification
by low/high impact factor and by publication year before 2010 and ≧2010
among high impact factor publications are shown in supplementary
material (Table S2).
The median sample size in the 350 trials was 224 (IQR 106 to 803; Table
1). Median inclusion time was 2.3 years (range 1 month to 10.8 years).
From the total of 400,903 randomised women, data was analysed for
363,417 (90.6%) women.