Quality of the evidence
Using the GRADE approach, we considered the quality of the evidence
relating to excessive GWG as high quality. Although moderate
heterogeneity was present, we upgraded our assessment of
evidence quality from moderate-to-high quality as findings were
precise and robust to sensitivity analysis. We graded the evidence
with regard to the risk of low GWG as high quality as these estimates
were consistent and precise across included studies. We
downgraded the evidence with regard to preterm birth (no statistically
significant difference) to moderate due to risk of bias concerns
from attrition and under-reporting. We graded the quality
of the evidence for pre-eclampsia, caesarean delivery and macrosomia
as high quality and most other outcomes, as moderate quality.
We downgraded some evidence due to heterogeneity. Many factors
might have contributed to this heterogeneity including obvious
and subtle differences in the types of interventions, types of
participants (e.g. BMIs, parity, age), delivery of the intervention
(e.g. whether the intervention was incorporated into antenatal visits
or delivered separately by a dietician), timing of the measurements
(e.g. weight gain assessed at 34 versus 38 weeks), timing
of commencement of the intervention (e.g. first, second or third
trimester), sample sizes, etc. An in-depth evaluation of individual
interventions was beyond the scope of this review; however, our
impression was that the more intensely monitored/supervised the
intervention, the better the study results.