Strengths and limitations
This RCT is to the best of our knowledge the largest study in this
field. Compliance with the intervention was registered by the
physiotherapists to ensure accuracy of the data and this is also
considered a strength. The degree of exertion during exercise sessions
was subjectively measured using The Borg Scale of Percived Exertion
(26). The use of accelerometers would have made it possible to
objectively determine the actual time and intensity (27). It is a
strength that WHO-5 is a simple, validated patient-reported outcome
measure, used as an outcome in the obstetric field (22), although not
validated in a population of pregnant women. The generalisability of the
trial results is limited due to a selected population of women at high
risk for perinatal depression where the participants were highly
educated, had a high level of physical activity before, during and after
pregnancy, had normal BMIs, and understood the Danish language. It might
be seen as a limitation that a large proportion of eligible women
declined to participate. Based on the legislation, The Ethics Committee
of the capital region of Denmark could not to let us describe the
characteristics of those who declined to participate. We cannot rule out
that there is a greater proportion of multi parous among the women who
declined to participate. In this study population approximately 25% was
multi parous, and in the population of pregnant women referred to
Rigshospitalet, the proportion of multi parous is approximately 40%.
One of the inclusion criteria was depression and/or anxiety requiring
treatment by a psychiatrist, general practitioner or a psychologist
within the last ten years before pregnancy. This information was
self-reported, which is considered a strength in the context, since mild
to moderate mental disorders are often diagnosed and treated outside
primary care and thus not registered in the medical records nor in The
Danish Psychiatric Central Research Register
(28). To
strengthen the validity of self-reported diagnoses, the pregnant women
were asked to elaborate on the circumstances related to the diagnosis,
including symptoms and treatment, when contacted by telephone by a
specialised midwife.