Original article
Neurodevelopmental outcome at 12 and 18 months in late preterm infants

https://doi.org/10.1016/j.ejpn.2010.02.002Get rights and content

Abstract

Background

Late-preterms represent the 70% of the whole preterm population and are reported to be at higher risk for mortality and morbidity than term infants.

Aims

To assess neurodevelopmental outcome in low-risk late-preterm infants at 12 and 18 months corrected age, to compare results of corrected and uncorrected age to those of term-born infants, to analyse the possible influence of gender on outcome.

Methods

Sixty-one healthy infants born between 33 and 36 weeks gestational age without major brain lesions were assessed at 12 and 18 months corrected age using the Bayley II scale. A control group of 60 low-risk term born infants underwent the same assessment.

Results

At 12 and 18 months corrected age late preterms showed a mean mental developmental index (MDI) similar to term infants. Comparing the results of the uncorrected age with term infants, the scores were significantly lower at both 12 and 18 months. No gender differences were observed in term-born infants, while male late-preterm infants showed lower MDI than peer females at both ages.

Conclusions

When correcting age for prematurity late-preterms have similar MDI scores to those obtained in term-born infants at 12 and 18 months. In contrast, when using chronological age there is a number of infants with low MDI. As cognitive abnormalities are reported at school age in late preterm infants, our findings raise the question on whether the results obtained using scores uncorrected for age may early identify the infants who will show cognitive difficulties at school age.

Introduction

Late preterm infants (born between 33 and 36 weeks' gestation) are usually considered by parents, caregivers, and health care professionals as developmentally mature and at low risk of morbidity.1 However this population is reported to be at higher risk for mortality and morbidity than term infants.1, 2, 3, 4 The definition of “late preterm” in spite of “near term” confirm the fact that these infants could show some characteristics similar to preterms, related to clinical condition or neurological outcome; besides this expression induce physicians to recoil the inherent risk of these infants.1 In the last two decades, this population has increased progressively and it actually represents the 70% of the whole preterm population1, 2, 3; the reason is not well understood. Some authors relate it to an increased use of reproductive technologies and, as a result, an increase in multi-foetal pregnancies; others to advances in obstetric practice with a consequent increasing in surveillance and medical interventions during pregnancy; it could lead to an earlier identification of foetuses considered to be at risk of stillbirth which results in more deliveries between 34 and 36 weeks' gestation.1, 2, 3 Despite the growing prevalence of these infants, only recently more attention has been paid on their development including them in a follow-up more similar to that of preterm infants.1, 2, 3, 4, 5, 6 Only few authors used a structured assessment to describe the neurodevelopmental profile in childhood,7, 8 reporting that healthy late preterm infants are at greater risk for developmental delay compared with healthy peer term.

We have previously observed using a structured neurological examination,9 that healthy late preterm infants in early infancy could show lower scoring for tone and reflexes than term infants at the same age. No study reported the data of cognitive function of late preterm during the first two years of age, while several studies described the profile of the early development of very preterm infants at low-risk. It is still an unresolved issue whether the developmental assessment of preterm infants should be corrected for preterm birth and up to what age.10 Correction may obscure developmental delay and thereby result in a belated diagnosis of neurological sequelae, while no correction could lead to the over diagnosis of such delay.11 It is possible that the observation of the development of late preterms may help to understand the role of correction for prematurity.

It is also reported in studies on very preterm infants that male gender further affect the development of these infants.12, 13 It would be interesting to see whether this is true in a cohort of late preterms too.

Because of an early identification of neurodevelopmental delay imply an early intervention with beneficial effects on development,14, 15, 16 the aim of the present study was to assess the neurodevelopmental performance in a population of low-risk late preterms, at 12 and 18 months corrected age (CA), comparing results of corrected and uncorrected age to those of term born infants. The possible influence of gender was also be analysed.

Section snippets

Patients and methods

The infants described in this study were part of a large cohort admitted to the Neonatal Unit of the University of Catania between January of 2005 and December of 2006 and consecutively enrolled in a follow-up research program, considering all infants born at a gestational age (GA) <37 weeks. Our follow-up included one assessment for cranial ultrasound (US) during the first week, one after 14 days and one at term age. The last two US scans were done after discharge from the hospital. The

Results

During the study period 60 low risk term born infants and 61 late preterm infants fulfilled the inclusion criteria. In Table 1 are reported the principal clinical characteristics of the population. A prevalence of male sex was reported in both cohorts. Twenty-four (11 females, 13 males) of the sixty-one late preterms showed slightly abnormal US scan, 7 with IVH and 17 with transient flairs.

Discussion

The main objective of the present longitudinal study was to describe cognitive profile of late preterm infants at 12 and 18 months. These infants represent the main portion of infants born prematurely but, because of the relatively lower risk of developing neurological abnormalities compared to infants born at lower gestational age, there are much less information on their follow-up.4, 5, 6, 7, 8, 9 In the present study, we used the BSID II, which has already been used in very preterm6, 20, 21,

Conflict of interest

None of the authors has any conflicts of interest to declare.

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