Despite a controlled parenting intervention, continuing through the neonatal period and after discharge, we were unable to detect any differences on a range of measures of parenting and infant behaviours between the intervention and control. The confidence interval for the primary outcome suggests that the benefit of the intervention is at most 4.7, which is substantially less than the 0.5 standard deviation (approximately 9.6) that we a priori regarded as clinically significant. Thus the lack of statistical significance was not due to low power.
Most successful parenting programmes have been aimed at mothers with specific difficulties such as low socioeconomic status and adolescent pregnancies.12
The parents in our study were not particularly disadvantaged in this respect, with IMD scores indicating rather lower levels of economic and social disadvantage than the average population. There did, however, appear to be an excess of mothers with worryingly high levels of parenting stress above the cut‐off for concern. This suggests that there was a need for support within this group, particularly because other studies of vulnerable children have suggested that levels of parenting stress increase as difficulties and disabilities become more apparent.18
There were other indications of the group's vulnerability. For example, ratings for the HOME responsiveness subscale were indicative of difficulties in the area of communication and emotional reinforcement. The mean scores of 8.8 and 9.1, recorded for the intervention and control groups, respectively, could be considered low and are comparable with the mean of 9.1 found by Armstrong et al
in a group of disadvantaged parents with history of social or psychological difficulties.33
The NCATS caregiver scores were also markedly low suggesting that, as a group, mothers did not effectively engage in the teaching activity with their infants. This was particularly evident at discharge when nearly a quarter scored below the cut‐off level, indicating cause for concern. These results support previous research findings that premature infants receive less stimulation and physical contact from their mothers than full‐term infants34
and that parental interactions are less sensitive and responsive.23
One explanation for the failure of PBIP to improve mother and infant outcomes may be that the “dose” of intervention was too low to influence the mother's attitudes and behaviour compared with other powerful influences on her during the period her baby was in hospital. Armstrong et al
's parenting intervention,33
which did demonstrate an effect on parenting stress and HOME scores, used a more extended programme with weekly visits up to six weeks after birth, fortnightly up to three months and monthly up to six months. The average time given to delivering the intervention was less in our study (about 6 h in total) than in Armstrong's study (12 h).36
As brief interventions have been found to be effective,12
a more important factor may have been the timing of the intervention. We felt that the provision of early support would be important to promote optimal parenting because more effective maternal coping in the period after birth has been linked to more responsive parenting after discharge.37
There is emerging evidence, however, that interventions commenced later have greater impact on parent and child outcomes.12
Indeed in recent studies showing beneficial effects of developmentally focused interventions with mothers of premature infants, the interventions commenced either just before discharge38
or after discharge.39
Another issue in the present study may have been the context in which the intervention was delivered. At the time of the study the units in the study did not have resources for developmental care and were limited in their provision of additional contact between mothers and infants (eg, Kangaroo care), which has been shown in non‐randomised trials to offer advantages for mothers and babies.40
Thus the intervention may have conflicted with the ethos of standard nursing care and so had less impact.
Strengths and weaknesses of the study
The study was appropriately powered to detect differences in the primary and secondary outcomes and the groups were extremely well matched in terms of infant and maternal characteristics. There is a possibility of recruitment bias in a cluster‐randomised design as recruitment happens after randomisation,41
but the high recruitment rates, baseline balance and lack of differences in response rates between the two groups are all evidence against such a bias. Measures were chosen to represent valid and reliable indices of the constructs of interest. Excellent reliability was demonstrated for both the NCATS and the HOME parental emotional and verbal responsiveness scale. Researchers were blind to the study allocation of participants.
It may be too early as yet to detect beneficial effects of the programme. A longitudinal study of a supportive parenting intervention with low birthweight infants found that the benefits of early intervention only became apparent after three years of follow up.42
There was also evidence of a widening advantage for the experimental group in terms of child behaviour and cognitive development by the age of 9 years.