The Late Preterm Infant
-Outcomes
Simon Rowley
August 2011
Who is the late preterm?
• 34 weeks 0 days through 36 weeks 6 days
after last menstrual period
• The lower limit used because it is a
frequent cut-off point for obstetric decision
making and as a criteria for admission to a
level 2 or level 3 NICU
Overview of talk
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The rise in Preterm rates
Physiological changes in the last weeks of pregnancy
Morbidities in the late preterm infant
Short term outcomes -respiratory
Long-term developmental and behavioural outcomes in
the preterm infant
Long term cardiovascular and diabetes risk
Costs to society
Implications for obstetric practice
Parents perceptions of illness severity in their baby
Complications of the Late Preterm Infant –
Darcy J Perinat Nursing Vol 23 No 1 PP 78-86. 2009
• The incidence of prematurity continues to rise
• Late preterm infants (34-36 wks) comprise the
fastest growing population and account for more
than 70% of all preterm births and 8.5% of all
births in the USA(2005)
• Generally less studied as a group
• Morbidity and mortality higher than expected
• The newborn risk in late preterm population is
under appreciated
Survival AT NWH 1959-2003
Late preterm admissions
ACH NICU 2004-2008
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4169 total admissions
1185 infants admitted 34-36weeks
this is 28.5% of total admissions
RDS the main diagnosis other than
prematurity
National Institute of Child Health and Human
Development Workshop July 2005 –Tonse,
Raju et al. Pediatrics 2006;118;1207-1214
• Preterm births in US ↑ 9.1% in 1981 to 12.3% in
2003
• Most of the increase is in proportion of late
preterm births (Davidoff et al Semin Perinatol
2006)
• Underscored the need to educate healthcare
providers and parents about the vulnerability of
late preterm infants
• ‘These infants need diligent evaluation,
monitoring, referral, and early return
appointments not only for post-natal evaluation
but also for continued long term follow-up’
Increase in Late Preterm births
• Increased reproductive technology and multi-fetal
pregnancies
• Advance in obstetric practice with increased surveillance
and medical interventions in pregnancy
• electronic fetal monitoring increased between 19892003 from 68-85% and labour inductions and LSCS
increased correspondingly
• Changing maternal profile –teenage mothers, increasing
maternal age, obesity, gestational diabetes
• Possible approach of clinicians to the late preterm infant
as being similar to the term infant post-natally
What happens to the late preterm
infant after birth?
• Resuscitation
• Transition
• Separation from
parents
• Admission to NICU
• Invasive procedures
• Respiratory support
• Phototherapy
Developmental and Physiological Immaturity
of Late Preterm Infants 1
• From 34.0-36.9 weeks gestation
• Terminal respiratory units-alveolar saccules
become lined with cuboidal type 2 and flat type 1
epithelial cells become mature alveoli lined with
extremely thin type 1 alveolar cells
• Pulmonary capillaries bulge into each terminal
sac
• Adult pool sizes of surfactant attained
Developmental and Physiological Immaturity
of Late Preterm Infants 2
• Apnoea incidence 4-7% (less than 1% at term)
• Mechanism –central -the brain is
developmentally less mature with fewer sulci
and gyri and less myelin. The brain at 34 weeks
is approximately 2/3 size at term
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-other - ↓ susceptibility to hypoxic
resp. depression, ↓chemo-sensitivity to CO2, 
↑resp.inhibition sensitivity to laryngeal
stimulation, ↓ upper airway dilator muscle tone
(all these are SUDI risks)
Developmental and Physiological Immaturity
of Late Preterm Infants 3
• Cardiovascular structural and functional immaturity
restricts reserve during stress.
• Delayed ductal closure and persistent pulmonary
hypertension(or delayed transition) more likely
• Brown fat accumulation, maturation and accumulation of
hormones resposible for brown fat metabolism (
prolactin, leptin, NA, T3, cortisol) peak at term
• Less white adipose tissue, cannot generate heat as
effectively from brown adipose tissue as effectively as
term infants
• Larger SA/body weight ratio increases heat loss
Developmental and Physiological Immaturity
of Late Preterm Infants 4
• Hypoglycaemia inversely proportional to
gestational age
• Glycogen stores double at 36w gestation, in
preparation for birth, and are rapidly depleted
within the first 24 hours of life
• Immature hepatic glycogenolysis, adipose tissue
lipolysis, hormonal dys-regulation, deficient
hepatic gluco-neogenesis and keto-genesis
• Therefore blood glucose drops to nadir at 1-2
hours until alternative pathways activated or
exogenous glucose supplied
Developmental and Physiological Immaturity
of Late Preterm Infants 5
• Jaundice more common. Late preterms 2 times
more likely to have significantly elevated SBR
and persisting 5-7 days
• Lower concentrations of UDPG glucuronosyltransferase
• Enterohepatic circulation secondary to delayed
gut motility and feeding
• Risk of kernicterus increased at lower gestations
• Hyperbilirubinaemia the most common reason
for re-admission
Do Late Preterm
Infants Breast Feed?
Australian longitudinal study: Donath et al. Arch Dis Child Fetal
Neonatal Ed 2008.93.448-450
• 35-36 weeks 88.2% breast feeding initiation rate
• 41% still breast feeding at 6 months age
• 37-39 weeks 92.0% initiation rate
• 54.5% still breast feeding at 6months
• Term infants 93.9% initiation rate
• - 60.5% still breast feeding at 6 months
Kernicterus in Late Preterm Infants
Cared for as Term Healthy Infants. Bhutani,
Semin Perinatol 2006; 30:89-97
Kernicterus Registry
Incidence & Patient Profile
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125 cases in US, 1979 – 2002
“healthy at discharge”
Sources – parents, MDs RNs, literature, med-legal
69% male
Nearly all breastfed [follow up scheduled for 2 weeks]
97% discharge <72 h (58% < 48 h)
25% Late Preterm infants
LGA with kernicterus
 35% Late Preterm infants were LGA*
 25% Term infants were LGA*
The contribution of Mild and moderate
Preterm birth to Infant mortality Kramer et al
JAMA vol 284 no 7 Aug 16 2000
• Landmark study
• Looked at quantitative contribution of mild (34-36)
preterm birth to infant mortality
• Large cohort of US and Canadian births for years 1985
and 1995 (US) and 1985-7 and 1992-4 (Canada)
• RR for deaths from all causes at 34-36 wks gestation
was 2.9 (CI 2.8-3.0) in US and 4.5 ( CI 4.0-5.0) in
Canada
• Early neonatal, late neonatal and post neonatal deaths
contributed 9/1000 livebirths
• Postnatal causes included infection,SIDS and external
causes( NAI and accidental deaths)
Perinatal Outcomes Associated with Preterm Birth at 33 to
36 Weeks’ Gestation: A Population-Based Cohort Study :
Khasu et al Pediatrics 2009; 123
Respiratory Morbidity and Lung Function in
Preterm Infants of 32 to 36 Weeks’ gestational Age
Colin et al Pediatrics 2010;115-128
• Comprehensive search for studies reporting
epidemiologic data and respiratory morbidity in infants
34-36 weeks
• 24 studies identified
• Consistent finding that babies born at 34-36 weeks
experience substantial respiratory morbidity compared
with term infants.
• Levels of morbidity at times equalled that of very preterm
infants
• Longitudinal studies indicate that this reduced level of
pulmonary function early on persists into early adulthood
Decreased expiratory flow in
infants who were healthy late
preterms
Colin et al Pediatrics 2010; 126: 115-128
Respiratory Morbidity and Lung Function in
Preterm Infants of 32 to 36 Weeks’ gestational Age
Colin et al Pediatrics 2010;115-128
Short Term Outcomes of Infants Born at 35 and 36 Weeks Gestation:
We Need to Ask More Questions. Escobar et al. Semin Perinatol 30:2833 2006
NWH Data
RDS incidence related to gestation
in late preterm infants
• 33-34 weeks
• 35-36 weeks
• Term
12%
2%
0.11%
Risk of respiratory morbidity in term infants
delivered by elective LSCS: cohort study
Hansen et al. BMJ Online March 2008
• 2687 infants out of total 34458 delivered by elective
LSCS in years 1998-2006
• Main outcome respiratory morbidity (TTN, RDS,
PPHTNB, serious resp. morbidity (oxygen more than 2
days, CPAP or IPPV) in LSCS compared to vaginal
delivery
• At 37 wks ↑ resp morbidity OR 3.9(2.4-6.5)
• At 38 wks  resp morbidity OR 3.0( 2.1-4.3)
• At 37 wks serious morbidity ↑ 5 fold OR 5.0(1.6-16)
• Results unchanged after exclusion of pregnancies
complicated by diabetes, pre-eclampsia IUGR, or breech
Incidence of Early Neonatal Mortality and
Morbidity After Late Preterm and Term
Cesarian Delivery De Luca et al Pediatrics vol 123
no. 6 2009
• GA specific risk estimates are lowest between
38-40 weeks and should be included in the
consent process
• Elective cesarian delivery is consistently
associated with increased intrapartum and
neonatal mortality, risk of admission, and
respiratory morbidity compare to planned
vaginal delivery
• No advantage of PVD over emergency cesarian
delivery
Incidence of Early Neonatal Mortality and
Morbidity After Late Preterm and Term
Caesarian Delivery De Luca et al Pediatrics vol 123
no. 6 2009
Special Care admissions
Incidence of Early Neonatal Mortality and
Morbidity After Late Preterm and Term
Caesarian Delivery De Luca et al Pediatrics vol 123
no. 6 2009
Respiratory morbidity
Incidence of Early Neonatal Mortality and
Morbidity After Late Preterm and Term
Caesarian Delivery De Luca et al Pediatrics vol 123
no. 6 2009
Elective Cesarian vs Planned Vaginal Delivery
Getting evidence into obstetric practice;
appropriate timing of caesarian section
Nicholl and Cattell Australian Health review 2010,34,90-92
• Aim: to reduce rate of term elective CS with no medical
indication before 39 completed weeks, from 30% to 10%
of all term elective CS (both private and public) over a 6
month period in 2007
• Method: multidisciplinary project formed to investigate
the extent of the problem and work out the intervention
which was essentially pre-emptive education of all
midwifery and obstetric staff and provision of evidence
folders in key clinical areas
Perinatal Outcomes Associated with Preterm Birth at 33 to
36 Weeks’ Gestation: A Population-Based Cohort Study :
Khasu et al Pediatrics 2009; 123