Objective
The objective of the study was to determine the relationship between nighttime delivery and neonatal encephalopathy (NE).
Study Design
The design of the study was a retrospective population-based cohort of 1,864,766 newborns at a gestation of 36 weeks or longer in California, 1999-2002. We determined the risk of NE associated with nighttime delivery (7:00 pm to 6:59 am ).
Results
Two thousand one hundred thirty-one patients had NE (incidence 1.1 per 1000 births). Nighttime delivery was associated with increased NE (odds ratio [OR], 1.13; 95% confidence interval [CI], 1.03–1.20), birth asphyxia (OR, 1.18; 95% CI, 1.08–1.29), and neonatal seizures (OR, 1.17; 95% CI, 1.07–1.28). In adjusted analyses, nighttime delivery was an independent risk factor for NE (OR, 1.10; 95% CI, 1.01–1.21), as were severe intrauterine growth retardation (OR, 3.8; 95% CI, 3.1–4.8); no prenatal care (OR, 2.0; 95% CI, 1.4–2.9); primiparity (OR, 1.5; 95% CI, 1.4–1.7); advanced maternal age (OR, 1.3; 95% CI, 1.16–1.45); and infant male sex (OR, 1.3; 95% CI, 1.2–1.4).
Conclusion
Future studies of time of delivery may generate new strategies to reduce the burden of NE.
Neonatal encephalopathy (NE) is an important contributor to long-term motor and cognitive disability in children and occurs in 2-4 per 1000 term births. Infants with moderate to severe NE have a 50-60% chance of either dying or developing long-term disabilities from cerebral palsy, mental retardation, or epilepsy. Neonatal encephalopathy is often attributed to birth asphyxia, even though the underlying pathogenesis of NE is heterogeneous and poorly understood.
For Editors’ Commentary, see Table of Contents
Perinatal deaths caused by asphyxia have been considered a sensitive indicator of quality of care during labor and delivery. It is thus assumed that some cases of NE could be prevented with improved quality of care. However, the strength of the relationship between quality of care and NE is unknown, especially given that intrapartum complications are absent in the vast majority of infants with NE.
Nighttime deliveries occur in the setting of decreased staffing and increased physician fatigue, both of which may have an impact on quality of care. Previous studies have suggested that nighttime delivery may be associated with an increased risk of neonatal mortality. Nighttime delivery has also been linked to increased neonatal deaths attributed to intrapartum asphyxia. However, in the largest study that distinguished infants by gestational age, only preterm infants born at night experienced increased neonatal mortality.
During the months of July and August, teaching hospitals frequently employ house officers who have just recently completed their medical education and are thus less experienced. Two studies in England have reported higher intrapartum death rates in the summer. This finding has been attributed to an “annual leave effect,” having a potential impact on staffing levels and resulting in decreased supervision of junior medical staff. Weekend births may also result in a relatively higher rate of neonatal deaths. However, population studies in Europe and Sweden have not confirmed the presence of a weekend birth disadvantage.
There are no recent studies of the relationship between weekend delivery and neonatal outcome in the United States. Whether neonatal outcomes differ in teaching and nonteaching hospitals during the summer months has also not been evaluated to our knowledge. The relationship between the time of delivery and the incidence of NE in term infants has not been studied previously. In a recent California population, we examined the association between NE and factors that have potential implications for quality of care, including hour, day, and month of delivery.
Materials and Methods
We examined a population-based retrospective cohort using the California-linked birth infant death file created specifically to study perinatal outcomes. The data set contains information from birth and death certificates linked to state-wide hospital discharge data for mother and infant. We included all infants born in California at a gestation of 36 weeks or longer (term gestation), from Jan. 1, 1999, to Dec. 31, 2002. In this population, we identified infants with NE by searching hospital discharge diagnoses. Infants with extreme birth weights (<1500 g or >5500 g) or maternal ages (<12 or >55 years) were excluded from the study, as were infants with missing data regarding hour of birth.
Neonatal encephalopathy was our primary outcome of interest. Because NE represents a broadly characterized and nonspecific disorder, we attempted to limit heterogeneity by focusing on more severe cases. To be categorized as having NE, a newborn infant had to meet at least 1 of the following birth hospitalization discharge diagnostic criteria:
- 1
Severe birth asphyxia ( International Classification of Diseases, Ninth Revision [ICD-9-CM] code 768.5).
- 2
Neonatal seizure (codes 779.0, 345-345.9, and 780.3).
- 3
Mechanical ventilation (code 96.70, 96.71 or 96.72) associated with any of the following diagnoses suggestive of NE: birth asphyxia (codes 768.5, 768.6, and 768.9); neonatal seizures (codes 779.0, 345-345.9, and 780.3); cerebral irritability or central nervous system depression (codes 779.1 and 779.2); hypotonia or other perinatal conditions (codes 779.8 and 779.9); fetal distress associated with infant morbidity (codes 768.2-768.4); birth trauma or encephalopathy resulting from birth injury (codes 767.8 and 767.9); intrapartum anoxia or brain hemorrhage resulting from birth trauma (code 767.0); congenital encephalopathy or unspecified anomaly of nervous system (code 742.9); or anoxia or encephalopathy (code 348.1 and 348.3).
- 4
Neonatal death (within 28 days of delivery) associated with any of the diagnoses listed in the previous text.
Given the heterogeneity of the term NE, we also studied the relationship between time of delivery and birth asphyxia (codes 768.5, 768.6, or 768.9), as well as the relationship between time of birth and neonatal seizures (codes 779.0, 345-345.9, or 780.3).
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