Discussion
As a result of early interventions for mothers of preterm infants, positive and clinically meaningful effects were seen for anxiety, depressive symptoms, and self-efficacy. To our knowledge, this review was the first to categorize components of early interventions and link them to maternal outcomes. These components were parent psychosocial support, parenting education, and therapeutic developmental support for the infant. Some form of parenting education was used in all interventions. Interventions that included psychosocial support resulted in better outcomes for mothers of preterm infants.
There were overall positive effects of four interventions on maternal anxiety with improved child outcomes. Anxiety is an important construct to measure in mothers of preterm infants [
21]. The results suggest that it may be more consistently linked to child outcomes than is stress. Parenting education may be a key intervention component associated with decreasing anxiety although all 18 interventions provided some form of education with varying effects on other parent constructs. Only one of the studies that had an effect on anxiety included a parent support component so this component may be a less important aspect of intervention when addressing anxiety.
Three interventions, two with a parent support component, had positive effects on maternal depressive symptoms. The Victoria Infant Brain Studies [
50] and Creating Opportunities for Parent Empowerment [
38,
39] were effective for depressive symptoms as well as anxiety. The Mother Infant Transaction Program [
23,
48,
49,
64] also had an impact on stress. Given that depression is a common and costly problem for mothers of preterm infants [
21,
24], it should be measured consistently as an outcome measure of the effectiveness of interventions. Depressive symptoms for mothers of preterm infants stem from multiple factors (e.g., high perceived stress and low social support) [
77] and therefore multiple intervention approaches that reduce stress and increase social support are required to reduce the development of depressive symptoms.
Only two studies measured self-efficacy and both found positive effects. One study [
55] had a very small sample, and the other [
61] included only African American mothers, limiting the quality and generalizability of the evidence. The positive effects of the interventions on self-efficacy were associated with improved infant outcomes only over the short-term. Intuitively this makes sense because the two interventions used information combined with observation of the infant or active involvement with the infant. Information may be relevant at the time it is delivered, but infants change qualitatively over time and additional information sessions may be important to achieve sustained effects on self-efficacy. Alternatively, interventions for self-efficacy may have limited effects on long term outcomes for preterm infants.
The second most commonly measured construct for parent outcomes was sensitivity/responsiveness and the overall effect was not significant. This construct is difficult to capture as it depends on the child’s skills as well as the parents. Intervention can target only the parent side of interactions. For the three studies that found an increase in sensitivity/responsiveness, two of the interventions included parent support as well as parenting education. All three of the studies that showed little or no change had no parent support but several types of parenting education. Despite Pridham and colleagues’ [
36] integrative review of nursing interventions that encouraged parenting education and discussion of child behaviour, it would appear that more than just education is needed. In addition, Newnham et al. [
49] suggested that aspects of parent-child interactions with preterm infants may be more challenging at different ages, thus time at outcome measurement may be critical in measuring sensitivity/responsiveness. Location for interventions (NICU and home) may influence outcomes that target parent-child interaction resulting in inconsistent outcomes [
56].
Stress was the most commonly measured construct of all maternal psychosocial outcomes. This is not a surprise given that the literature has reported increased stress for families caring for preterm infants [
21‐
23]. However, the meta-analysis suggests that the interventions reviewed have little effect on stress overall. It was not clear why there were limited effects on stress overall when the seven studies were considered together. The two interventions with an effect on stress [
23,
49] used a parent support component combined with an active involvement type of education and also found positive child outcomes. Parenting education alone did not reduce stress. The five studies with little or no effect did not have a parent support component, which may be important for addressing stress. The Parenting Stress Index [
70] was often used allowing comparison across studies but it may be too generic a measure of stress for mothers of preterm infants. Various subscale and total scores of the short and long forms of the measure were used making it difficult to untangle which aspects of parenting stress are of concern for mothers of preterm infants. Alternatively, it may be difficult for interventions to reduce stress by the time of outcome measurements. Kaaresen et al. [
23] measured stress three months after the completion of the intervention and reported reduced stress levels and improved long-term child outcomes. In most studies, stress was measured at completion of the intervention [
38,
39,
49,
61] or within 6 weeks of the intervention [
52]. Studies that used the Parental Stressor Scale- NICU also failed to show positive effects on stress at NICU discharge, a point in time when parent stress levels are reportedly very high [
21,
78]. The time point at which the stress outcome was assessed may influence the apparent effectiveness of interventions. Alternatively, interventions may have different effects on parental stress depending on severity of infant illness. Timing of measurement and subgroup analyses should be considered in future research.
It is clear that no one intervention component is consistently associated with improved parent outcomes. The interventions provided were complex with multiple and varying components. Indeed, parent education was the only component used in all of the interventions and the delivery, type and dose of parenting education varied. Of the interventions that provided direct support to parents, only half measured outcomes for parents. It is encouraging that the studies that provided support found positive effects on parent outcomes that were often associated with improved child outcomes. Parent support may be an important component of interventions for preterm infants.
This review is limited by several factors, such as inclusion of studies published in English only. Inclusion of studies published in other languages may alter the results of meta-analyses. Lack of socio-demographically homogeneous samples (except Teti et al. [
61]) may have influenced the ability to demonstrate effects of the interventions on mothers and preterm infants. One study [
50] had challenges recruiting sufficient sample and was underpowered. Positive effects may not have been identified. The measures used in the studies included in the meta-analyses varied and the results may reflect differences in the construct being measured. It was also not possible to consider the effects of dose, location of the intervention, or study quality when conducting the meta-analyses. Finally, the I
2 statistic suggested significant heterogeneity among the studies in the synthesis. Even using a random effects model, heterogeneity is a limitation in this review.
A problem with many studies in this review was that they reported “caregiver” (e.g., Meijssen et al, [
56]) or “parent” and included data for mothers, only. Other studies (e.g., Spittle [
50]) reported 98% female caregivers without indicating the relationship of the remaining 2% of caregivers to the child. If those caregivers were fathers, then they should be analyzed separately or excluded from analyses because mother-infant and father-infant interactions are different [
79]. Given the small number of fathers who participated in interventions, it is unlikely that this would have had a substantial effect on the overall results. A further limitation of this review is that the key components of the interventions can only be interpreted based upon what the authors of the trials have published. It is possible that our interpretations of the interventions may not reflect what has occurred due to lack of detail regarding intervention content in the reviewed studies.
Our most important recommendation for future research is to measure the effects of intervention components addressing parents to determine whether parent outcomes change, thus altering the child’s proximal environment. One third of the studies in this review did not directly and systematically measure parent outcomes. Consistent measures of parent outcomes would enhance the ability to build the knowledge base. Another suggestion relates to fathers. Spittle et al. [
33] and Orton et al. [
32] noted the lack of evidence-based approaches to evaluate the effectiveness of interventions for fathers. There is a critical need to conduct more rigorous intervention research in the area of interventions for fathers generally, and fathers of preterm infants specifically. Other directions for future research include the content of parenting education. Given the state of science in early brain development, promoting the development of executive functioning, a developmental problem for many preterm infants [
80], is important. In addition, the most efficient and effective manner of delivering parenting education is still unclear. Five studies [
49,
52,
60,
61,
64] used all three types of parenting education with varying effects on parent outcomes. Others [
38,
39,
51] used relatively minimal forms of parenting education (information only) and found effects on parent outcomes. Unmeasured co-morbidities that would affect outcomes for preterm infants should also be captured. For example, Olafsen et al. [
81] address regulatory competence which represents early aspects of communication and joint attention. Thus, regulatory competence may be important to measure as a useful precursor to language development. Finally, the use of other statistical techniques that can model moderators and mediators of the intervention effects on outcomes (e.g., structural equation modeling) may be useful.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
KB, JM, and KAH were responsible for the study conception and design. KAH designed the database search strategies. KB and KAH reviewed articles for relevance and performed critical appraisal. MB critically appraised relevant articles. KB wrote the first draft of the manuscript. KB, JM, KAH, and MB made critical revisions to the manuscript to improve intellectual content. KB and JM obtained the funding. All authors read and approved the final version.