Limitations
Our findings were limited by differences in the inclusion criteria of the studies, variation in the
components of the intervention such as duration, intensity and frequency, non-standardised care in the control group and non-uniform definitions of GDM. Furthermore, women in the
intervention group had more than one intervention, such as diet and probiotics, making it difficult
to delineate the beneficial effect of an individual intervention. It is possible that a different
criterion for the diagnosis of gestational diabetes may have yielded changed estimates of effect.
[46] Women in the control group may have accessed these interventions resulting in Hawthorne
effect for the following reasons: interventions were easily accessible, including over the
counter nutritional supplement; and absence of blinding of the women or health care provider,
in any of the included studies. None of the studies evaluated GDM as a primary outcome.
Hence it is possible that the different arms could have been treated differently, such as additional
screening for GDM, and close follow-up in the intervention group, thereby influencing
the outcome. Studies were limited in their reporting on proportion of women who complied
with the intervention, which could have a major influence on the effect size observed.