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Perinatal outcomes associated with late preterm births: a population based study

Presented at the Neonatal Society 2007 Summer Meeting (programme).

Khashu M1, Narayanan M2, Osiovich H1

1 Childrens’ & Womens’ Health Centre of British Columbia, Vancouver, Canada
2 Academic Clinical Fellow, University of Leicester, Leicester, UK

Background and Aims: Progressive advancement in the care of the extreme preterm infants has been associated with a shift of focus away from the larger preterms. There is growing realisation that these infants, born between 33 to 36 weeks, are at increased risk of mortality and morbidity than infants born at term (1,2). There is, however, a dearth of population based mortality and morbidity statistics for this cohort. The aim of this population based study was to compare the mortality and morbidity of late preterm infants to those born at term.

Methods: Using data from the British Columbia (BC) Perinatal Database Registry we analysed all singleton births between 33 to 40 weeks gestation from April 1999 to March 2002 in the province of British Columbia in Canada. We divided this birth cohort into late preterm (33-36 weeks, n=6381) and term (37-40 weeks, n=88867) groups. We compared mortality data, indicators of neonatal morbidity and maternal factors between the groups. The variable definitions used were based on preset definitions of the database.

Results: All mortality statistics including still birth rate, perinatal, neonatal and infant mortality rates were significantly higher (p<0.001) in the late preterm group. The late preterm group had a significantly higher incidence of respiratory morbidity* (Relative risk (RR) = 4.38, 95% confidence interval (95%CI) = 4.16-4.62) and infection† (RR = 5.2, 95%CI= 4.57-5.91). They had significantly longer duration of inpatient admission (142 hours vs 57 hours, p <0.001), needed resuscitation at birth more frequently (RR=1.52, 95%CI=1.42-1.62) and had 5 minute APGAR score <7 more often (RR=2.27, 95%CI=1.91-2.71) than the term group. Maternal factors that were more common in the late preterm group included chorioamnionitis‡ (p<0.001), hypertension (p<0.001), diabetes (p<0.001), thrombophilia (p<0.001), prelabour rupture of membranes (p<0.001), primigravida (p<0.001) and teenage pregnancy (p=0.002).

Conclusions: Our data supports recent literature(1,2) regarding neonatal mortality and morbidity in larger preterm infants and calls for a review of care for this group at the local, national and global level to optimise the care and outcomes for these infants. Reorganisation of services and increased resource allocation to provide better support to this group may be needed in most hospitals and community settings. These findings may also influence decisions regarding delivery at late preterm gestation as well as parental counselling.

*Respiratory morbidity: Respiratory distress syndrome or other conditions which caused respiratory distress.
†Neonatal infection: Physician defined variable which included culture proven or suspected sepsis.
‡Chorioamnionitis: Physician defined variable which included suspected or proven infection of the amniotic cavity.

1. Wang ML, Dorer DJ, Fleming MP, Catlin EA. Clinical outcomes of near-term infants. Pediatrics. 2004; 114(2):372-6.
2. Raju TN, Higgins RD, Stark AR, Leveno KJ. Optimizing care and outcome for late-preterm (near-term) infants: A summary of the workshop sponsored by the National Institute of Child Health and Human Development. Pediatrics. 2006;118(3):1207-14.

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