Abstract
BackgroundInfants born late preterm (34 + 0 to 36 + 6 weeks GA (gestational age)) are known to have higher neonatal morbidity than term (37 + 0 to 41 + 6 weeks GA) infants. There is emerging evidence that these risks may not be homogenous within the term cohort and may be higher in early term (37 + 0 to 38 + 6 weeks GA). These risks may also be affected by socioeconomic status, a risk factor for preterm birth.MethodsA retrospective population based cohort of infants born at 34 to 41 weeks of GA was assembled; individual and area-level income was used to develop three socioeconomic (SES) groups. Neonatal morbidity was grouped into respiratory distress syndrome (RDS), other respiratory disorders, other complications of prematurity, admission to a Level II/III nursery and receipt of phototherapy. Regression models were constructed to examine the relationship of GA and SES to neonatal morbidity while controlling for other perinatal variables.ResultsThe cohort contained 25 312 infants of whom 6.1% (n = 1524) were born preterm and 32.4% (n = 8203) were of low SES. Using 39/40 weeks GA as the reference group there was a decrease in neonatal morbidity at each week of gestation. The odds ratios remained significantly higher at 37 weeks for RDS or other respiratory disorders, and at 38 weeks for all other outcomes. SES had an independent effect, increasing morbidity with odds ratios ranging from 1.2–1.5 for all outcomes except for the RDS group, where it was not significant.ConclusionsThe risks of morbidity fell throughout late preterm and early term gestation for both respiratory and non-respiratory morbidity. Low SES was associated with an independent increased risk. Recognition that the morbidities associated with prematurity continue into early term gestation and are further compounded by SES is important to develop strategies for improving care of early term infants, avoiding iatrogenic complications and prioritizing public health interventions.
Highlights
Infants born late preterm (34 + 0 to 36 + 6 weeks gestational age (GA)) are known to have higher neonatal morbidity than term (37 + 0 to 41 + 6 weeks GA) infants
Excluded from the cohort of 25 834 newborn records were 24 records that could not be matched with the population registry or maternal health records, 436 infants who moved before their first birthday and 62 which were missing birth weight, GA or income data, resulting in a final cohort of 25 312 infants
2.5% of the total infants, accounted for only a small proportion of morbidity as demonstrated in the unadjusted outcomes (Figure 1). In these graphs it is demonstrated that all outcomes decrease with increasing GA and this pattern continues past 37 weeks (Figure 1)
Summary
Infants born late preterm (34 + 0 to 36 + 6 weeks GA (gestational age)) are known to have higher neonatal morbidity than term (37 + 0 to 41 + 6 weeks GA) infants. There is emerging evidence that these risks may not be homogenous within the term cohort and may be higher in early term (37 + 0 to 38 + 6 weeks GA) These risks may be affected by socioeconomic status, a risk factor for preterm birth. A small number of studies have demonstrated persistent risks in early term gestation (defined as 37 to 38 completed weeks) casting doubt on the practice of considering all infants born at 37 weeks GA as a homogenous term group. Ruth et al BMC Pregnancy and Childbirth 2012, 12:62 http://www.biomedcentral.com/1471-2393/12/62 Investigating this gradient is important since mean gestational age at delivery continues to shift to the left, with higher numbers of late preterm and early term deliveries [1,12,13]. Small decreases in morbidity per infant when many infants are affected have large public health and resource impacts [2,20]
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