Nationwide description of live Japanese births by day of the week,hour, and location

To characterize temporal variations of live births in Japan, we analyzed data on the 1,203,147 births of 1998. In hospitals, with 20+ beds, the daily average of live births was significantly lower at weekends and national holidays (mean=1,433, SD = 100) than on weekdays (mean = 1,957, SD = 126). Hourly distributions of live births showed a single sharp peak at 1:00-2:59 pm on weekdays with a small peak at an earlier hour on Saturdays, Sundays and national holidays. The results in clinics, with no bed or less than 20 beds, were similar to those in hospitals except on Saturdays. The difference in the daily average of live births between Saturdays and weekdays was smaller in clinics than that found in hospitals, and hourly distributions on Saturdays resembled those of weekdays but not Sundays or national holidays. Maternity homes showed no differences in the mean number of daily live births over the days of the week including national holidays, and no clear peak of percentage distributions of hourly live births on each day of the week. The present study suggests that the weekly and hourly variations observed in hospitals and clinics are not due to a biological rhythm of labor, but to obstetric intervention in the timing of delivery, either through induction of labor or elective cesarean section.     

The distinctive characteristics of the hourly distribution of live births on specific days in Japan

Objectives

Anomalous variations in live births on February 29/March 1, April 1/April 2 and the days before the New Year holidays/New Year holidays have been reported in Japan. The distribution of live births was investigated on those days and whether or not such dates were selected due to obstetric intervention is discussed.

Methods

Using a method similar to the \(\overline{\text{X}}\)–R control chart, anomalous variations in the hourly number of live births were detected. The number of unusual births was estimated.

Results

The number of live births at 13:00–16:59 hours was significantly higher from December 24 to 28 and significantly lower from December 29–January 3, February 29, and April 1, especially on weekdays. In hospitals, the increases from 9:00–12:59 and 13:00–16:59 hours from December 24 to 27 were approximately 10 and 25 %, respectively, of the expected births for those times in the mid-1980s; thereafter, the rates were 30 and 35 %. After 2000, the child births at 13:00–16:59 hours on February 29 and April 1 decreased by approximately 35 % in hospitals and clinics. The numbers of live births at 0:00–0:59 hours were significantly higher on March 1 and April 2 until 2001.

Conclusion

Anomalous variations at 0:00–0:59 hours may be associated with fictitious reporting on birth certificates. Anomalous variations from 13:00 to 16:59 hours on weekdays suggest that many individuals may avoid obstetric intervention on February 29 and April 1 and that the number of higher-risk deliveries may significantly increase in the daytime on the days before the New Year holidays due to obstetric intervention for institutional reasons.

     

Continuous measurements of outdoor 222Rn concentrations for three years at one location in Colorado

Measurements were made of 222Rn concentrations outdoors in Ft. Collins, Colorado, using a continuously sampling scintillation flask between January 1993 and December 1995. These data were analyzed for hourly, daily, and seasonal variations. The average 222Rn concentration at 1 m above the ground was 18 +/- 10 Bq m(-3) with a geometric mean of 15 Bq m(-3) and a geometric standard deviation of 1.7. Hourly averaged data indicated a diurnal pattern with the outdoor 222Rn concentration reaching a maximum in the early morning between 4:00 a.m. and 6:00 a.m. and a broad minimum between 1:00 p.m. and 4:00 p.m. in the afternoon. An analysis also indicated that the outdoor 222Rn concentrations were consistently lowest during the spring (March and April) and highest during the late summer (July-September).     

Implausible birth weight for gestational age

Various rules have been proposed to identify and exclude live births with implausible values of birth weight for gestational age from large perinatal data sets. The authors carried out a preliminary evaluation of common rules by examining the frequency and nature of rule-based exclusions among live births in Canada (excluding Ontario) between 1992 and 1994. There were 625 (0.09%), 133 (0.02%), 170 (0.02%), and 2,858 (0.40%) live births identified for exclusion by a median birth weight for gestational age +/-4 standard deviations (SD) rule, a +/-5 SD rule, a rule based on expert clinical opinion, and a modification of Tukey's rule, respectively. The birth weight and gestational age distribution of the exclusions depended on the particular rule used; for example, 12.1% and 0.3% of live births of > or =4,500 g were excluded under Tukey's rule and the rule based on expert opinion, respectively. Infant mortality rates among those excluded were 8-13 times higher than among all live births. Current rules for identifying implausible birth weight for gestational age tend to flag live births at high risk for infant death. Such rules may erroneously attenuate temporal trends in important perinatal outcomes.     

Distribution of birth weight for gestational age in Japanese infants delivered by cesarean section

Background

Neonatal anthropometric charts of the distribution of measurements, mainly birth weight, taken at different gestational ages are widely used by obstetricians and pediatricians. However, the relationship between delivery mode and neonatal anthropometric data has not been investigated in Japan or other countries.

Methods

The subjects were selected from the registration database of the Japan Society of Obstetrics and Gynecology (2003–2005). Tenth centile, median, and 90th centile of birth weight by sex, birth order, and delivery mode were observed by gestational age from 22 to 42 weeks among eligible singleton births.

Results

After excluding 248 outliers and 5243 births that did not satisfy the inclusion criteria, 144 980 births were included in the analysis. The distribution of 10th centile curves was skewed toward lower birth weights during the preterm period among both first live births and second and later live births delivered by cesarean section. More than 40% of both male and female live births were delivered by cesarean section at 37 weeks or earlier.

Conclusions

The large proportion of cesarean sections influenced the skewness of the birth weight distribution in the preterm period.Key words: birth weight, distribution, gestational age, cesarean section, preterm     

Decline and loss of birth seasonality in Spain: analysis of 33,421,731 births over 60 years

BACKGROUND AND AIM: Several seasonal variations have been found in birth rates in different countries at different periods. The characteristics of the rhythmic patterns vary according to geographical location and chronological changes. This study presents data on spanish birth seasonality over six decades. METHODS: A time series composed of 33,421,731 births in Spain in the period 1941-2000 was analysed. The series comes from the National Institute of Statistics and was processed according to the following norms: (1) normalisation of the duration of months and years; (2) clinical analysis of temporal series (isolation of seasonal component); (3) Fourier's spectral analysis; and (4) cosinor analysis (adjustment to the cosine curve of two harmonics). RESULTS: Significant seasonal rhythm was found in the set of births, both for a 12-month period and a 6-month period. The rhythm shows bimodal morphology, with a pronounced birth peak in April and a smaller one in September. These peaks correspond to July and December conceptions, respectively. The major birth peak shifted to March-May between the 1940s and the 1980s. Birth rhythm changed after the 1960s, with a decrease in amplitude and later loss of seasonality in the 1990s. CONCLUSIONS: In Spain, seasonal birth rhythm shows a decline from 1970, and, finally, lack of birth seasonality in 1991-2000. This trend is similar to other European countries, although Spain shows a more intense loss of seasonality.     

Birth rates and reproductive risk in adolescents in Chile, 1990-1999]

OBJECTIVE: For Chilean teenage mothers under 15 years old and from 15 to 19 years old, to evaluate the trends in birth rates and reproductive risk for the period of 1990-1999. METHODS: A database was constructed using data from the Demography Yearbook (Anuario de demografía) volumes published by Chile's National Institute of Statistics (Instituto Nacional de Estadísticas) for 1990-1999. From that database we calculated the trends in the number of live births and in the rates of maternal mortality, late fetal mortality, neonatal mortality, and infant mortality among the teenage mothers under 15 and from 15 to 19 years old. We calculated the risk odds ratio (OR) for both of those age groups in comparison with women from 20 to 34 years old. The groups were compared using Fisher's exact test or the chi-square test, and the analysis of trends in the period studied was carried out with Pearson's correlation, with an alpha level of 0.05. RESULTS: In the period studied, for the teenage mothers under age 15, the respective rates for maternal mortality, late fetal mortality, neonatal mortality, and infant mortality were 41.9 per 100 000 live births, 5.1 per 1 000 live births, 15.2 per 1 000 live births, and 27.4 per 1 000 live births. For the adolescents from 15 to 19 years, the corresponding rates were 19.3, 4.1, 8.1, and 16.6; for the women 20-34 years old, they were 26.8, 5.0, 6.7, and 12.1. The adolescents under 15 had higher risks of maternal mortality (OR = 1.56; 95% confidence interval (CI): 0.50 to 4.31; P = 0.372) and of fetal mortality (OR = 1.02; 95% CI: 0.76 to 1.36; P = 0.890), but those differences were not statistically significant. However, the younger adolescents did have significantly higher risks of neonatal mortality (OR = 2.27; 95% CI: 1.92-2.68; P < 0.0001) and of infant mortality (OR = 2.39; 95% CI: 2.04 to 2.62; P < 0.0001). In comparison to the women 20-34 years old, the teenage mothers from 15 to 19 years old had significantly lower risks of maternal mortality (OR = 0.72; 95% CI: 0.56 to 0.92; P < 0.008) and of fetal mortality (OR = 0.81; 95% CI: 0.77 to 0.86; P < 0.0001) but significantly higher risks of neonatal mortality (OR = 1.20; 95% CI: 1.16 to 1.25; P < 0.0001) and of infant mortality (OR = 1.38; 95% CI: 1.35 to 1.42; P < 0.0001). Among both the older teenage mothers and the mothers 20-34 years old there was a significant downward trend in maternal, fetal, neonatal, and infant mortality rates in the period studied; in the younger adolescents only neonatal mortality and infant mortality declined significantly. There was a rising trend in the number of live births among the two groups of teenage mothers, but that trend was statistically significant only for the mothers under 15; among mothers 20-34 years old there was a statistically significant downward trend. CONCLUSIONS: In the period studied, the Chilean teenage mothers faced greater reproductive risk than did the women 20-34 years old. The number of live births among teenage mothers tended to rise during the 1990-1999 period, but the change was significant only for the mothers under age 15. These results point to the need to develop programs that improve both sex education and birth control practices starting in early adolescence.     

An excess of tetralogy of Fallot in Malta

STUDY OBJECTIVE: To estimate birth prevalence of tetralogy of Fallot (TF) in Malta. DESIGN: Retrospective data collection and analysis, and comparison with earlier epidemiological studies dealing with congenital heart disease. SETTING: Regional hospital providing exclusive diagnostic and follow up services for the entire country of Malta. PATIENTS: All Maltese live births diagnosed as having TF. MAIN RESULTS: The birth prevalence of TF in Malta for the period 1980-1994 was 0.64/1000 live births (95% confidence intervals 0.48, 0.85/1000 live births). This was significantly higher than previously reported in the medical literature. CONCLUSIONS: The Maltese gene pool seems to have a genetic predisposition towards live births with TF. Population genetic studies with emphasis on the prevalence of 22q11 microdeletion may yield clues regarding the cause of the high rate of this condition.

 

     

Down's syndrome: occurrence and outcome in the north of England, 1985-99

This study reports changes in the prevalence and outcome of Down's syndrome pregnancies within a 15-year period in a defined geographical population in the north of England. Cases of Down's syndrome in births and terminations of pregnancy occurring between 1985 and 1999, were identified from the Northern Congenital Abnormality Survey. The total prevalence for the 15 years was 15.2 per 10 000 births and terminations of pregnancy [95% CI 14.2, 16.2]. Total prevalence showed an upward trend over time, due largely to increasing maternal age. Sixty-seven per cent of cases resulted in live births, and the overall live birth prevalence was 10.3 per 10 000 live births [95% CI 9.4, 11.1]. The proportion of cases resulting in termination of pregnancy rose from 15% in 1985-89 to 38% in 1995-99; the rate of increase was greater in women aged < 35 years. Forty-five per cent of live born infants had an additional anomaly recorded. Survival at 1 year was 78% for those with an additional anomaly recorded, and 96% for those without. There was a non-significant trend towards improved survival in all infants with Down's syndrome, from 87% in 1985-94 to 92% in 1995-99. Despite increasing termination of Down's syndrome pregnancies resulting from the greater availability of antenatal screening and diagnosis, there has been no significant reduction in live birth prevalence. These infants have high rates of co-existing structural anomalies and are at high risk of death in the first year of life. There is a continuing need to address the reasons for poor survival for Down's syndrome infants, and to plan for their complex health and social care needs. These findings are useful for parents deciding on prenatal screening, as well as for clinicians and health service managers.     

Small-for-gestational-age births in the United States: an age-period-cohort analysis

BACKGROUND: During the last 2 decades, the rate of low birthweight has increased, as has the rate of preterm delivery, among both whites and blacks. Examination of causes for these secular trends has focused largely on changes in the distributions of maternal age and, less commonly, on birth cohort. Little is known as to how age, period, and birth cohort interact on trends in small births at term. METHODS: The U.S. natality files were used to assess trends in term (>/=37 weeks gestation) small-for-gestational age (SGA) births for 7 5-year maternal age groups (15-19 through 45-49 years), 6 delivery periods (1975, 1980, 1985, 1990, 1995, and 2000), and 12 5-year maternal birth cohorts (1926-1930 through 1981-1985). SGA births were defined as sex-specific birthweight below the 10th percentile for gestational age based on 1995 livebirths in the United States. Logistic regression models were fit to determine the independent effects of age, delivery period, and birth cohort on term SGA trends, separately for blacks and whites. RESULTS: Between 1975 and 2000, term SGA births declined by 23% (from 21% to 16%) among blacks and by 27% (from 12% to 9%) among whites. Term SGA births declined with increasing age up to 30-34 years, but increased among older women. Within strata of maternal age, the risk also declined with later maternal birth cohorts, among both blacks and whites. The strongest influence on SGA trends was from maternal age, followed by maternal birth cohort, and lastly by delivery period. In general, for any combination of age, period, and birth cohort, blacks showed 1.5- to 2-fold higher rates of term SGA than whites. CONCLUSIONS: The persistence of strong maternal age effects on risk of term SGA births suggests that the effect of age is at least partly the result of biologic factors. Term SGA trends were generally consistent for blacks and whites, although the magnitude of difference in the risks for combinations of age, period, or mother's birth cohort was higher among blacks than whites.     

Secular trends in sex ratios at birth in North America and Europe over the second half of the 20th century

CONTEXT: A previous study showed that significantly more boys were born in southern latitudes in Europe than in northern latitudes and the converse pattern was observed in North America. OBJECTIVE: This study analyses secular trends in gender ratios for live births over the second half of the 20th century. Design, setting, participants: Analysis was carried out from a World Health Organisation dataset comprising live births over the above period. This included 127034732 North American and 157947117 European live births. MAIN OUTCOME MEASURES: Analysis of trends in gender ratios for countries in both continents. RESULTS: The findings show a highly significant overall decline in male births in both Europe and North America (p<0.0001), particularly in Mexico (p<0.0001). Interestingly, in Europe, male births declined in North European countries (latitude>40 degrees, p<0.0001) while rising in Mediterranean countries (latitude congruent with 35-40 degrees, p<0.0001). These trends produced an overall European male live birth deficit 238693 and a North American deficit of 954714 (total male live birth deficit 1193407). CONCLUSIONS: No reasonable explanation/s for the observed trends have been identified and the causes for these trends may well be multifactorial.     

Rethinking How to Promote Maternity Care-Seeking: Factors Associated With Institutional Delivery in Guinea

This article presents findings from a study on women's delivery care-seeking in two regions of Guinea. We explored exposure to interventions promoting birth preparedness and complication readiness among women with recent live births and stillbirths. Using multivariate regression models, we identified factors associated with women's knowledge and practices related to birth preparedness, as well as their use of health facilities during childbirth. We found that women's knowledge about preparations for any birth (normal or complicated) was positively associated with increased preparation for birth, which itself was associated with institutional delivery. Knowledge about complication readiness, obstetric risks, and danger signs was not associated with birth preparation or with institutional delivery. The study findings highlight the importance of focusing on preparation for all births—and not simply obstetric emergencies—in interventions aimed at increasing women's use of skilled maternity care.     

Trends in low birth weight infants and changes in Baltimore's childbearing population, 1972–77

Linked birth and death records provided the population for a study of trends in low birth weight (LBW) rates in Baltimore between 1972 and 1977 and of the effect of changes in the characteristics of the childbearing population on these trends. The impact of shifts in the birth weight distribution on neonatal mortality rates was also investigated. Trends were analyzed for unstandardized LBW rates as well as for rates standardized on the distributions of maternal age, education, gravidity, prior pregnancy losses, and marital status.Between 1972 and 1977, the 1,500 and 2,000 gm rates rose significantly by approximately 1 infant per 1,000 live births per year among whites and 2 infants per 1,000 live births among nonwhites. Despite declines in rates for most weights, the effect of these increases was a rise in neonatal mortality rates for both races, but especially for nonwhites.The population of women delivering in Baltimore in 1977 became slightly older, slightly more educated, and of higher gravidity than in 1972, but these changes had little impact on yearly fluctuations in LBW rates. In contrast, increases in births to unmarried women and to women with at least one prior pregnancy loss were related to rising LBW rates. For both races, standardization on marital status and prior pregnancy losses diminishes the increase in the LBW rate over the study period, especially when standardization is performed simultaneously for both variables. These findings hold within maternal age, education, and gravidity groups. However, the LBW rates for nonwhite teenage mothers and for nonwhite women with 12 years of less education increased significantly over the study period, regardless of standardization.     

Overview of the National Infant Mortality Surveillance (NIMS) project--design, methods, results

The recent slowdown in the decline of infant mortality in the United States and the continued high risk of death among black infants (twice that of white infants) prompted a consortium of Public Health Service agencies to collaborate with all States in the development of a national data base from linked birth and infant death certificates. This National Infant Mortality Surveillance (NIMS) project for the 1980 U.S. birth cohort provides neonatal, postneonatal, and infant mortality risks for blacks, whites, and all races in 12 categories of birth weights. (Note: Neonatal mortality risk = number of deaths to infants less than 28 days of life per 1,000 live births; postneonatal mortality risk = number of deaths to infants 28 days to less than 1 year of life per 1,000 neonatal survivors; and infant mortality risk = number of deaths to infants less than 1 year of life per 1,000 live births.) Separate tabulations were requested for infants born in single and multiple deliveries. For single-delivery births, tabulations included birth weight, age at death, race of infant, and each of these characteristics: infant's live-birth order, sex, gestation, type of delivery, and cause of death; and mother's age, education, prenatal care history, and number of prior fetal losses at 20 weeks' or more gestation. An estimated 95 percent of eligible deaths were included in the NIMS tabulations. The analyses focus on three components of infant mortality: birth weight distribution of live births, neonatal mortality, and postneonatal mortality. The most important predictor for infant survival was birth weight, with an exponential improvement in survival by increasing birth weight to its optimum level. The nearly twofold higher risk of infant mortality among blacks was related to a higher prevalence of low birth weights and to higher mortality risks in the neonatal period for infants weighing 3,000 grams or more, and in the postneonatal period for all infants, regardless of birth weight. Regardless of other infant or maternal risk factors, the black-white gap persisted for infants weighing 2,500 grams or more.     

Large social disparities in spontaneous preterm birth rates in transitional Russia

OBJECTIVE: This study estimated the effect of maternal sociodemographic, obstetric and lifestyle factors on the risk of spontaneous preterm birth in a Russian town. METHODS: All women with singleton pregnancies registered at prenatal care centres in Severodvinsk in 1999 comprised the cohort for this study (n=1559). Analysis was based on spontaneous live singleton births at the maternity home (n=1103). Multivariable logistic regression was applied to quantify the effect of the studied factors on the risk of preterm birth. Differences in gestation duration were studied using multiple linear regression. RESULTS: In total, 5.6% of all spontaneous births were preterm. Increased risks of preterm delivery were found in women with lower levels of education and in students. Placental complications, stress and a history of fetal death in previous pregnancies were also associated with elevated risks for preterm delivery. Smoking, hypertension and multigravidity were associated with reduced length of pregnancy in metric form. CONCLUSION: In addition to medical risk factors, social factors are important determinants of preterm birth in transitional Russia. Large disparities in preterm birth rates may reflect the level of inequalities in transitional Russia. Social variations in pregnancy outcomes should be monitored.     

The close relation between birth, abortion and employment rates in Sweden from 1980 to 2004

Birth and abortion rates in Sweden have fluctuated since 1980 while the proportion between the rates are the same at the beginning and end of the period. An increase in birth rates in the late 1980s resulted in a peak in 1991 and 1992, with 124,000 live births each year. Thereafter followed a steady decline in the rate until 2000, when the number of live births was about 90,000. At that point, the trend changed to an increase. The aim of this analysis was to investigate any relation between employment rates and the number of live births among women aged 20-34, and at the same time to explore the trend for abortion rates compared to the trend for live births. The relation between employment status and live birth rate is statistically more significant for women than men, and the rates have a higher correlation for the period after 1986. Young adults in this age group are vulnerable to economic cycles that can explain this covariation but the decline in birth rates in economically developed societies has multidimensional aspects and many other possible explanations. Much has been done in recent years in Sweden to decrease household inequality for families with children to avoid the risk of relative poverty, but the fact that there is no explicit health policy to reduce the abortion level that remain unchanged since the early 1980s may appear as a notable lack of strategy in a country with many other health-related goals.     

Perinatal health and mother-child health care in the municipality of S?o Luís, Maranh?o State, Brazil.

The purpose of this article was to evaluate socioeconomic and demographic indicators, reproductive health, use of prenatal, childbirth, and neonatal services, and anthropometric data for mothers and infants. The authors performed a cross-sectional analysis of a systematic sample of 2,831 hospital births in S?o Luís, Maranh?o State, from March 1997 to February 1998 at ten public and private maternity hospitals. The sample was stratified proportionally according to the number of births in each maternity hospital. Mothers answered a standard questionnaire. Of the total, 97.9% were live births and 98% were singletons. Prenatal coverage was 89.5%, and prevalence of cesarean sections was 33.8%. A physician provided prenatal care in 75.7% of cases and performed 73.8% of the deliveries. The Unified Health System covered the costs of 76.4% of the prenatal visits and 89.7% of the deliveries. A pediatrician was present in the delivery room in 50.2% of cases. The low birth weight rate was 9.6% and the preterm birth rate 13.9%. Reasons for concern included a high percentage of adolescent mothers, single mothers (or without partners), the high cesarean rate, and the high percentage of births attended by unqualified personnel.     

Risk factors for neonatal and post-neonatal mortality in the Central-West region of Brazil: linkage between live birth and infant death data banks

This article focused on risk factors for neonatal and post-neonatal mortality by linking live births and infant death records. The study was conducted in the municipality of Goiania, in the Central-West region of Brazil. A total of 20,981 live births and 342 infant deaths constitute the retrospective cohort. Neonatal and post-neonatal mortality risks were estimated in this cohort study of live births by logistic regression. In the neonatal period, the highest ORs were for delivery in public hospitals (OR = 2.28; 95% CI 1.57-3.32), pre-term neonates (OR = 8.94; 95% CI 5.85-13.67), and low birth weight (OR = 8.92; 95% CI 5.77-13.79). Cesarean delivery appeared as a protective factor (OR = 0.58; 95% CI 0.43-0.78). For post-neonatal mortality, the highest ORs were for illiterate mothers (OR = 6.25; 95% CI 1.25-31.27), low birth weight (OR = 3.12; 95% CI 1.67-5.84), and delivery in public hospitals (OR = 2.65; 95% CI 1. 13-6.23). The linkage identified socioeconomic variables that were more important risk factors for post-neonatal than neonatal mortality.     

Reproductive factors and risk of papillary thyroid cancer in women

The authors conducted a population-based case-control study of 410 women residing in three counties in western Washington State who were aged 18-64 years when diagnosed with papillary thyroid cancer in 1988-1994 and 574 controls to assess the effects of pregnancy history and other aspects of reproductive life on risk of this disease. Among women aged 45-64, the authors observed no associations with number of live births, age at first live birth, or age at last live birth. Risk was somewhat increased in women <45 years who had given birth within the previous 5 years; this association was most evident among women who reported that cancer symptoms had led to diagnosis. Among women who had given birth within the last 5 years, risk was greatest among those with two or more births during that time period (relative risk (RR) = 4.2, 95% confidence interval (CI): 2.0, 8.9, relative to parous women whose last birth was >5 years before the reference date). Risk of thyroid cancer was also associated with lactation during the previous 5 years (e.g., RR = 2.9, 95% CI: 1.5, 5.5, among parous women who had breastfed > or =12 months, vs. 0-1 months, during that interval). Our results suggest that thyroid stimulation during both pregnancy and lactation may result in a transient increase in risk of papillary thyroid cancer.     

Time of birth and risk of intrapartum and early neonatal death

BACKGROUND: Previous studies have found that infants born at night and during weekends and holidays have an increased risk of perinatal mortality. However, these associations may be confounded by the distribution of high-risk deliveries according to time of birth. METHODS: We undertook a population-based cohort study of 694,888 singleton births without elective cesarean section in Sweden between 1991 and 1997. We estimated relative risks of intrapartum and early neonatal death according to the hour, day and month of delivery. Estimated risk ratios were adjusted for gestational age, birth weight for gestational age, malformations, induction of labor, breech presentations and year of birth. RESULTS: Infants of high-risk deliveries were more often delivered during daytime (8:00 am to 7:59 pm). Compared with infants born during daytime, infants born at night were at increased risk of early neonatal death (adjusted risk ratio = 1.28; 95% confidence interval = 1.13-1.46), but not intrapartum death (1.05; 0.71-1.54). If this association is causal, 12% of early neonatal deaths can be attributed to the increased risk among nighttime births. There was no association of weekend or holiday births with risks of intrapartum or early neonatal death. CONCLUSIONS: Infants born at night may be at increased risk of early neonatal death.