In this paper we find that, among a sample of preterm infants matched on a host of sociodemographic and neonatal morbidity characteristics, those who receive any early intervention therapy appear to demonstrate better cognitive function trajectories than those who do not. In addition, at each time point, for preterm infants whose mothers report more supports, receipt of early intervention therapy seems to be particularly beneficial for cognitive function.
Our finding of a positive effect of early intervention therapy of cognitive function of preterm infants is consistent with a large, meta-analysis4
of the effect of early intervention on preterm infants' cognitive function. The authors identified 16 randomized controlled or quasi-experimental studies investigating the effects of developmental interventions (including therapy services) delivered between the ages of birth through 2 years on subsequent cognitive function. The authors conclude that although receipt of early developmental interventions is associated with a clinically significant improvement in cognitive function, heterogeneity in intervention type and frequency precluded making recommendations regarding optimal service delivery for preterm infants. To this end, our results suggest that receipt of any
early intervention services may be associated with improved cognitive function trajectories during years 1 and 2 of age among preterm infants. To our knowledge, ours is the first study to explore the effectiveness of present day (ie, post-1986 authorization of the Individuals with Disabilities Education Act) policy-governed early developmental interventions. However, we were unable to examine specific aspects of early intervention therapy including onset, frequency, and duration. Future research should investigate specific aspects of program effectiveness.
Our findings also highlight the potential for maternal supports to augment early intervention therapy services. Caring for a medically fragile preterm infant is associated with parental psychosocial distress, which interferes with attachment and infant neurodevelopment,37,38
but is mitigated with maternal support interventions during the newborn period.39
The longer term role of maternal supports among families of preterm infants is less wellunderstood. Indeed, the amount of perceived maternal supports among preterm infants is dynamic throughout the first 3 years of life and covaries with maternal wellbeing and infant cognitive function.49
To this end, early intervention programs are mandated to be familycentered.40
In practice, in addition to providing therapy, early intervention therapists also assist families with obtaining child care or public assistance, provide information on developmental milestones or medical specialists, and may be a source of emotional support during family transitions or receipt of difficult news (eg, a new diagnosis).
Lee et al41
underscore the positive influence of maternal supports on infant neurodevelopment. Our findings can contribute to the current literature by suggesting that the positive intervention effects might be greatest in the context of more maternal supports, particularly at 24 months posterm. This may suggest the importance of the early intervention clinician's dual role, that is, to provide direct therapy services and to assess or coordinate family supports. Indeed, the synergistic effect of the two appears to be most influential, especially at 24 months postterm, in promoting optimal cognitive function for infants born preterm.
We acknowledge several limitations of this study. First, propensity score matching it is not a panacea for selection bias. However, these analyses achieved a 78% matching rate, which is consistent with simulation studies32
in which authors used the macro in larger samples, which increases our confidence in the results. However, it is possible that the propensity score matching did not sufficiently reduce selection bias. Although the results were robust to a variety of specifications, we cannot rule out the possibility of residual selection bias, but are confident that the groups are comparable.
The measurement of early intervention therapy was collected by parent report at the 36-month visit. Thus, it is possible that the results were biased by differential recall. We have no means to control for the extent to which this occurred, but the bias would likely be in the direction of underestimating an intervention effect. Similarly, the validity of parent-reported EI services, to our knowledge, has not been previously reported. However, previous authors42–46
suggest that parent-report is a valid proxy for utilization of health and developmental services and health status. Although this literature did not specially examine EI, it suggests that parents can validly report their children's health developmental service utilization. Moreover, the wording of the early intervention question specifically mentioned “physical, occupational, or speech therapy,” “early intervention,” and from “birth to three,” which increases the validity and reliability of parental reports. Moreover, of the children whose parents reported receipt of early intervention or special education, 100% were classified as expected according to their age (ie, all children receiving parent-reported special education were older than 36 months, and all children receiving parent-reported early intervention were younger than 36 months of age).
A related issue is that measurement of “early intervention therapy” can be problematic in a context with varying quality, intensity, and frequency of service delivery, which may limit the generalizability of our results. Moreover, families experiencing the most social disadvantage were more likely to be lost to attrition across the three years of study. This is of particular relevance given that socially disadvantaged families are more likely to experience lower child cognitive function and may experience fewer maternal supports.
Finally, our measure of perceived social support only asked about the presence rather than the quality of social support. Understanding what type of support is most helpful to mothers of preterm infants will assist in developing individualized, developmentally supportive interventions.
However, the strengths of this study underscore its public health policy and health services significance. Our findings contribute to a relatively small literature examining the effect of policy-relevant therapy services on infants born preterm. Moreover, our results, which suggest the importance of maternal supports, have important policy and programmatic implications for service delivery.
Trends in survival of preterm infants have not been matched by improvements in morbidity.47
The effects of preterm birth are persistent and costly.48
Understanding how effectiveness of early intervention may be bolstered has particular relevance to policy-makers, program directors, and practitioners.