Timing of birth and infant and early neonatal mortality in Sweden 1973-95: longitudinal birth register study

doi:10.1136/bmj.323.7325.1327

BMJ 2001;323:1327 ( 8 December )

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Timing of birth and infant and early neonatal mortality in Sweden 1973-95: longitudinal birth register study

Z C Luo, research associate, J Karlberg, professor.

Clinical Trials Centre, University of Hong Kong, Hong Kong SAR, People's Republic of China

Correspondence to: J Karlberg jpekarl{at}hkucc.hku.hk

Objective: To assess the impact of time of birth on infantmortality and early neonatal mortality in full term and pretermbirths.
Design: Analysis of data from the Swedish birth register,1973-95.
Participants: 2 102 324 spontaneous live births of infantswithout congenitalmalformation.
Outcome measurements: Absolute and relative risk of infant mortality,early neonatal mortality, and early neonatal mortality relatedtoasphyxia.
Results: Infant mortality, early neonatal mortality,and early neonatal mortality related to asphyxia were higher ininfants who were born during the night (9 pm to 9 am) comparedwith those born during the day for 1973-9, 1980-9, and 1990-5.The difference was more dramatic for preterm infants. The largestdifference was observed during 1990-5, when there was a 30% increasein early neonatal mortality (relative risk 1.31, 95% confidenceinterval 1.10 to 1.57) and a 70% increase in early neonatal mortalityrelated to asphyxia (1.70, 1.22 to 2.38) in preterm infants bornduring the night compared with rates for preterm infants bornduring the day. A detailed analysis over 24 hours revealed two"high risk" periods: between 5 pm and 1 am and around 9am.
Conclusions: Infants born during the night have a greaterrisk of infant and early neonatal mortality and early neonatalmortality related to asphyxia than those born during the day.There has been no improvement over the past two decades. The problemis more serious for preterm births and was even worse in the 1990s.Shift changes and the hours immediately after such changes arehigh risk periods for neonatalcare.

What is already known on this topic
Infants born at night have a greater risk of early neonatal mortality and early neonatal mortality related to asphyxia than those born during the day

The causes are unclear but may be related to insufficient or less experienced staff or excess workload during the night

What this study adds
In Sweden the relative risks of infant and early neonatal mortality and mortality related to asphyxia for infants born during the night compared with during the day did not diminish during 1973-95, are greater for preterm infants, and were greater in the 1990s

There are two "high risk" periods for early neonatal mortality: 5 pm to 1 am and around 9 am

The exact reasons are unclear but better vigilance and an improvement in shift changes may be required to improve neonatal health care further

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