Our definition for adherence included achievement of at least four
dietary aims and/or the physical activity aim and the weight gain
recommendation. Our analyses on adherence suggest that
achievement of the aims of all these three components of the
intervention (rather than only part of them) is associated with a
lower risk for LGA and may be associated with lower risk of
GDM.
Another possible reason for negative result concerning GDM
prevention may be the risk group status of the women recruited to
the trial. Since we included women with at least one GDM risk
factor, most women had quite low risk for developing GDM. If we
had included women with high risk of GDM, e.g., obese women or
women with previous insulin-treated GDM, the results might have
been different.
Our study did not show an increase in the incidence of adverse
events or preterm birth in the intervention group. Thus, lifestyle
counseling implemented by the nurses may be considered safe.
Our counseling procedure has been shown to be feasible [15,16],
and it may be more applicable in maternity health care than
interventions delivered by research nurses or other staff. In a
study with individual randomization, not only statistical power,
but also risk for contamination between trial arms would have
been higher than in our cluster-randomized trial. The generalizability
of our findings is higher than efficacy trials due to
implementation in real-world instead of laboratory settings,
although limited to women with no abnormal findings in OGTT
during 8–12 wk gestation.
Limitations of our study also include the absence of late
pregnancy measurement of maternal glucose intolerance, and
owing to this, we were not able to assess maternal endpoints close
to delivery, and thus high birthweight was used as a marker of
longstanding glucose intolerance during pregnancy. Inaccuracy in
birthweight, crown-heel length, and head circumference measurements
in hospital is likely to be nondifferential, since the possibility
of such errors was equal in both groups. Secondly, the differences
between groups might have been even larger if this inaccuracy had
not existed. An inevitable limitation is also that the women and the
nurses in the usual care group could not be blinded for the purpose
of the study, which may have resulted in changes in their health
behavior or counseling practices.