Birth Weight-specific Mortality Research Articles

Crossing Birthweight-Specific Mortality Curves: How a Puzzling Clinical Observation Led to an Important Advance in Epidemiologic Methods.

Clinicians have long noted that although African-American neonates were more likely than white neonates to weigh <2500 grams at birth (low birthweight), among low birthweight infants African-Americans were more likely than whites to survive. However when born at normal weight, African-American infants were substantially less likely to survive. The observation generated much physiological speculation, and several clever mathematical manipulations were devised to "uncross the mortality curves." With the development and dissemination of Directed Acyclic Graphs in the early 2000s, methodologists focused on perinatal epidemiology showed graphically, in an early use of Directed Acyclic Graphs, that birthweight was a "collider", and that controlling for birthweight, whether by regression, stratification or restriction, introduced confounding of the race-mortality association by all unmeasured common causes of birthweight and mortality. These investigations showed that the crossing curves could be explained as an artifact of a conceptually flawed analysis. These results have applicability beyond perinatal epidemiology, including to the "obesity paradox."

Clinical outcome of preterm babies managed for respiratory distress syndrome using nasal continuous positive airway pressure and surfactant: An experience from Ile-Ife, South-Western Nigeria

Background: Respiratory distress syndrome (RDS) is a common cause of morbidity and mortality among preterm babies. It is caused by a deficiency of surfactant; hence, there is reduced lung compliance and increased work of breathing. The use of continuous positive airway pressure (CPAP) ventilation, a noninvasive form of ventilation, as well as the administration of exogenous surfactant, has proven to be very useful in the management of RDS. The use of less invasive techniques in ventilation and administration of surfactant have also been shown to reduce the risk of bronchopulmonary dysplasia and adverse effect of intubation. Objective: The objective is to determine mean oxygen saturation at 1 h, 6 h, and 12 h after commencement of CPAP, the mean values of FiO2 and positive end-expiratory pressure before and after administration of surfactant, and the overall case-fatality rate and birth weight-specific mortality rates. Methods: Study design was a prospective observational study and subjects were inborn babies between 26 and 34 weeks gestation who were managed for RDS with CPAP alone or with additional surfactant. Results: All 104 recruited preterm babies were managed with CPAP. Fifty-six (53.8%) babies also had surfactant administered. The mean weight of the babies was 1.35 (±0.322) kg, and the mean gestational age was 30.95 (±2.24) weeks. Extremely low birth weight (ELBW), very low birth weight (VLBW), and LBW constituted 11.5%, 55.8%, and 32.7% of the study population, respectively. The mean SPO2 before CPAP and 12 h after were 90.93 (±5.39) % and 96.5 (±3.30) %, respectively. The overall case-fatality rate was 18.2%, and birth-weight-specific mortality rates for ELBW, VLBW, and LBW were 58.3%, 15.5%, and 9.7%, respectively. Conclusion: From this study, it is clear that the prompt use of a cost-effective CPAP devices and the administration of surfactant are very effective in reducing morbidity and mortality among VLBW babies. While most local studies focused on the experience with the use of CPAP alone, this study goes further to demonstrate that the use of CPAP and surfactant is more effective in the management of RDS.

Cross-State Differences in the Processes Generating Black-White Disparities in Neonatal Mortality.

The U.S. Black neonatal mortality rate is more than twice the White rate. This dramatic disparity can be decomposed into two components: (1) disparities due to differences in the distribution of birth weights, and (2) disparities due to differences in birth weight-specific mortality. I utilize this distinction to explore how the social context into which infants are born contributes to gaps in mortality between Black and White neonates. I analyze variation in Black-White differences in neonatal mortality across 33 states using 1995-2010 data. For each state, I calculate the contribution of differences in birth weight distribution versus differences in birth weight-specific mortality to the total disparity in mortality between White and Black neonates. Disparities are largely a product of different birth weight distributions between Black and White newborns (mirroring the pattern for the United States as a whole). However, in at least nine states, differences in birth weight-specific mortality make a notable contribution. This pattern is observed even among those from advantaged sociodemographic backgrounds and is driven by differences in mortality among very low birth weight neonates. This calls attention to inequality in medical care at birth as an importantcontributor to racial disparities in neonatal mortality.

A new record linkage for assessing infant mortality rates in Ontario, Canada

ObjectiveInfant mortality statistics for Canada have routinely omitted Ontario—Canada’s most populous province—as a high proportion of Vital Statistics infant death registrations could not be linked with their corresponding Vital Statistics live birth registrations. We assessed the feasibility of linking an alternative source of live birth information with infant death registrations.MethodsAll infant deaths occurring before 365 days of age registered in Ontario’s Vital Statistics in 2010–2011 were linked with birth records in the Canadian Institute for Health Information’s hospitalization database. Crude birthweight-specific and gestational age-specific infant mortality rates were calculated, and rates examined according to maternal and infant characteristics.ResultsOf 1311 infant death registrations, only 47 (3.6%) could not be linked to a hospital birth record. The overall crude infant mortality rate was 4.7 deaths per 1000 live births (95% CI, 4.4 to 4.9), the same as previously reported for the rest of Canada in 2011. Infant mortality was higher in women < 20 years (5.8 per 1000 live births) and ≥ 40 years (5.9 per 1000 live births), and lowest among those aged 25–29 years (3.9 per 1000 live births). Infant mortality was notably higher in the lowest (5.1 per 1000 live births) residential income quintile than the highest (3.4 per 1000 live births).ConclusionUse of birth hospitalization records resulted in near-complete linkage of all Vital Statistics infant death registrations. This approach could enhance the conduct of representative surveillance and research on infant mortality when direct linkage of live birth and infant death registrations is not achievable.

High birth weight and perinatal mortality among siblings: A register based study in Norway, 1967-2011.

BackgroundPerinatal mortality according to birth weight has an inverse J-pattern. Our aim was to estimate the influence of familial factors on this pattern, applying a cohort sibling design. We focused on excess mortality among macrosomic infants (>2 SD above the mean) and hypothesized that the birth weight-mortality association could be explained by confounding shared family factors. We also estimated how the participant’s deviation from mean sibling birth weight influenced the association.Methods and findingsWe included 1 925 929 singletons, born term or post-term to mothers with more than one delivery 1967–2011 registered in the Medical Birth Registry of Norway. We examined z-score birth weight and perinatal mortality in random-effects and sibling fixed-effects logistic regression models including measured confounders (e.g. maternal diabetes) as well as unmeasured shared family confounders (through fixed effects models). Birth weight-specific mortality showed an inverse J-pattern, being lowest (2.0 per 1000) at reference weight (z-score +1 to +2) and increasing for higher weights. Mortality in the highest weight category was 15-fold higher than reference. This pattern changed little in multivariable models. Deviance from mean sibling birth weight modified the mortality pattern across the birth weight spectrum: small and medium-sized infants had increased mortality when being smaller than their siblings, and large-sized infants had an increased risk when outweighing their siblings. Maternal diabetes and birth weight acted in a synergistic fashion with mortality among macrosomic infants in diabetic pregnancies in excess of what would be expected for additive effects.ConclusionsThe inverse J-pattern between birth weight and mortality is not explained by measured confounders or unmeasured shared family factors. Infants are at particularly high mortality risk when their birth weight deviates substantially from their siblings. Sensitivity analysis suggests that characteristics related to maternal diabetes could be important in explaining the increased mortality among macrosomic infants.

Neonatal and Infant Mortality in Korea, Japan, and the U.S.: Effect of Birth Weight Distribution and Birth Weight-Specific Mortality Rates.

Difference in crude neonatal and infant mortality rates (NMR and IMR) among different countries is due to the differences in its two determinants: birth weight distribution (BWD) and birth weight-specific mortality rates (BW-SMRs). We aimed to determine impact of BWD and BW-SMRs on differences in crude NMR and IMR among Korea, Japan, and the U.S. Our study used the live birth data of the period 2009 through 2010. Crude NMR/IMR are the lowest in Japan, 1.1/2.1, compared to 1.8/3.2, in Korea, and 4.1/6.2, in the U.S., respectively. Japanese had the best BW-SMRs of all birth weight groups compared to the Koreans and the U.S. The U.S. BWD was unfavorable with very low birth weight (< 1,500 g) rate of 1.4%, compared to 0.6% in Korea, and 0.8% in Japan. If Koreans and Japanese had the same BWD as in the U.S., their crude NMR/IMR would be 3.9/6.1 for the Koreans and 1.5/2.5 for the Japanese. If both Koreans and Japanese had the same BW-SMRs as in the U.S., the crude NMR/IMR would be 2.0/3.8 for the Koreans and 2.7/5.0 for the Japanese. In conclusion, compared to the U.S., lower crude NMR or IMR in Japan is mainly attributable to its better BW-SMRs. Koreans had lower crude NMR and IMR, primarily from its favorable BWD. Comparing crude NMR or IMR among different countries should include further exploration of its two determinants, BW-SMRs reflecting medical care, and BWD reflecting socio-demographic conditions.

Why do more infants die in the UK than in Sweden? An intercountry comparison of birthweight-specific infant mortality

BackgroundThe UK has one of the highest infant mortality rates in western Europe, whereas Sweden has one of the lowest. A comparison of cohorts with similar characteristics at birth could show the origin of these disparities. This study aimed to compare birthweight-specific and age-at-death-specific mortality rates to assess which groups are most at risk in England and Wales relative to Sweden. MethodsWe used tabulated data on singleton live births and deaths in 2006 for England and Wales and in 2002–06 for Sweden. We examined mortality rates and rate differences per 1000 live births by birthweight (<1000 g, 1000–1499, 1500–2499, 2500–3499, ≥3500) and age-at-death categories (0–6 days, 7–27, 28–365). We calculated the number of excess deaths (deaths that could have been prevented if England and Wales had Sweden's mortality rates in 2006). FindingsThe study included 477 153 births and 1168 deaths in Sweden, and 649 421 births and 2828 deaths in England and Wales. The infant mortality rate in England and Wales was nearly double that in Sweden (4·36 deaths per 1000 live births, 95% CI 4·19–4·52 vs 2·45, 2·31–2·59), resulting in 1238 excess deaths (95% CI 1100–1377). If England and Wales had Sweden's birthweight-specific mortality rates, only 559 excess deaths would have occurred in 2006. The greatest disparities were observed for extremely low-birthweight babies (<1000 g), with 440 (95% CI 360–519) excess deaths (334 within the first week of life [265–404]). Babies with normal birthweights (2500–3499 g) had the second highest number of excess deaths (219, 95% CI 137–302), with 118 occurring in the postneonatal period (61–176). InterpretationThe number of excess deaths in England and Wales relative to Sweden declined substantially after accounting for differences in the birthweight distribution, suggesting that preventive policies in the UK should focus on reducing prenatal risk factors and improving maternal health before and during pregnancy. Differences in registration of live and stillbirths, resuscitation, or obstetric practices could explain some disparities in the early deaths among extremely low-birthweight babies. Excess postneonatal deaths among normal-birthweight babies suggests scope for reducing mortality by improving postnatal support for families. FundingAZ's PhD studentship is supported by awards to establish the Farr Institute of Health Informatics Research, from the Medical Research Council, Arthritis Research UK, British Heart Foundation, Cancer Research UK, Chief Scientist Office, Economic and Social Research Council, Engineering and Physical Sciences Research Council, National Institute for Health Research, National Institute for Social Care and Health Research, and Wellcome Trust (grant MR/K006584/1). The authors' work was independent of their funders.

Very low birth weight and perinatal periods of risk: disparities in St. Louis.

Objective. Very low birth weight (VLBW) is a significant issue in St. Louis, Missouri. Our study evaluated risk factors associated with VLBW in this predominantly urban community. Methods. From 2000 to 2009, birth and fetal death certificates were evaluated (n = 160, 189), and mortality rates were calculated for perinatal periods of risk. The Kitagawa method was used to explore fetoinfant mortality rates (FIMR) in terms of birth weight distribution and birthweight specific mortality. Multivariable logistic regression was used to assess the magnitude of association of selected risk factors with VLBW. Results. VLBW contributes to 50% of the excess FIMR in St. Louis City and County. The highest proportion of VLBW can be attributed to black maternal race (40.6%) in St. Louis City, inadequate prenatal care (19.8%), and gestational hypertension (12.0%) among black women. Medicaid was found to have a protective effect for VLBW among black women (population attributable risk (PAR) = −14.5). Discussion. Interventions targeting the health of women before and during conception may be most successful at reducing the disparities in VLBW in this population. Interventions geared towards smoking cessation and improvements in Medicaid and prenatal care access for black mothers and St. Louis City residents can greatly reduce VLBW rates.

729: Deconstructing trends in perinatal ethnic disparities in Hawaii

ethnic disparities in Hawaii Timothy Dye, Hyeong Jun Ahn, John Chen, Marjorie Mau, Donald Hayes, Dena Towner John A. Burns School of Medicine, University of Hawaii, Obstetrics, Gynecology, and Women’s Health, Honolulu, HI, John A. Burns School of Medicine, University of Hawaii, Biostatistics, Honolulu, HI, John A. Burns School of Medicine, University of Hawaii, Native Hawaiian Health, Honolulu, HI, Hawaii State Department of Health, Family Services Division, Honolulu, HI OBJECTIVE: US OMB Directive 15 (OMB15) outlines requirements for reporting race/ethnicity. Oftentimes a range of distinct ethnicities are aggregated (e.g. “Asians”) in OMB15, perhaps masking important differences. These aggregations are particularly significant in Hawaii, a multiracial/multiethnic state significantly impacted by OMB15. This study’s purpose was to examine perinatal risk trends in Hawaii (HI) and among its ethnicities. STUDY DESIGN: Average Annual Percent Change (AAPC) in neonatal mortality rate (NNMR) and low birthweight (LBW) by state/ethnicity from 1969-2009 was computed using National Center for Health Statistics’ data. Birthweight distribution (BWD) reflecting LBW ( 2500 grams) and VLBW ( 1500 grams), and birthweight-specific mortality rate (BWSM) were generated from HI Department of Health (DOH) published data. RESULTS: HI’s NNMR declined 10 percent faster than did the US NNMR during the 1970s-80s (Table). Similarly, HI’s LBW/VLBW rates declined more rapidly than did US rates. In the 1990s, however, HI’s NNMR declined less rapidly than did the US and HI’s VLBW rate increased faster. These patterns worsened in the 2000s. Three concerning trends emerge. First, the Filipino LBW rate remains highest in Hawaii, 3/4ths higher than the white rate (Figure). Secondly, the Japanese NNMR rapidly increased throughout the 2000s, at a rate almost double that of Hawaiians, for instance (Table). Additionally, the Japanese LBW/VLBW rates increased much faster through the 2000s than they did in other ethnicities. Thirdly, the NNMR among Native Hawaiians remained at 50 percent higher than other ethnicities (Figure). This excess Native Hawaiian mortality is associated with higher BWSM (i.e. higher mortality among LBWs) when compared with other ethnic groups, rather than a skewed BWD. CONCLUSION: OMB15 aggregations mask important perinatal differences among Hawaii’s ethnicities. These patterns suggest that a range of strategies may be required to sufficiently address perinatal-related disparities. (NCRR U54RR026136/ NIMHD U54MD007584). 730 Association of parent smoking during pregnancy with offspring cardio-metabolic risk factors at age 17 Uri Dior, Yechiel Friedlander, Liron Kogan, Shani Shulman, Hagit Hochner Hadassah Medical Center and Hebrew University-Hadassah Medical School, Department of Obstetrics and Gynecology, Jerusalem, Israel, Hebrew University School of Public Health, Epidemiology unit, Jerusalem, Israel OBJECTIVE: Accumulating evidence demonstrates an association of maternal smoking during pregnancy with adverse metabolic neonatal outcomes. However, less is known about the influence of maternal or paternal smoking on cardio-metabolic risk factors in adolescence. Hence, we examined the association of maternal and paternal smoking during pregnancy with offspring weight, height, Body Mass Index (BMI), systolic and diastolic blood pressure (BP) at age 17. STUDY DESIGN: We used a population-based cohort of 11,729 births in Western Jerusalem during 1974-76, with available archival data on maternal, paternal and birth characteristics. Measurements at age 17 were assessed at military induction examinations. Linear regression models were used to evaluate the associations of parental smoking during pregnancy with offspring cardio-metabolic outcomes, after controlling for potential confounders. RESULTS: Maternal smoking during pregnancy, independent of paternal smoking and confounders (including socioeconomic status, maternal prepregnancy BMI and gestational weight gain, and offspring gender and birthweight) was positively associated with offspring’s height, weight and BMI at age 17 (all p-values 0.001, Table). For example, mean weight of offspring of smoking mothers was 1.5kg higher than weight of offspring whose mothers did not smoke. Paternal smoking was independently and positively associated with adolescent weight (p 0.001) and BMI (p 0.002) and negatively associated with systolic BP (p 0.02). An analysis examining whether smoking of at least one parent was associated with offspring outcomes yielded similar results. 3-yr combined low birthweight rate, birthweightspecific mortality rate (<2500 gr), and neonatal mortality rate by ethnicity, Hawaii 2007-2009 (Source: HI DoH) Average annual percent change (AAPC %) for selected perinatal outcomes, 1969-2009, USA, Hawaii, and Hawaii’s largest ethnic groups

Developing a standard approach to examine infant mortality: findings from the State Infant Mortality Collaborative (SIMC).

States can improve pregnancy outcomes by using a standard approach to assess infant mortality. The State Infant Mortality Collaborative (SIMC) developed a series of analyses to describe infant mortality in states, identify contributing factors to infant death, and develop the evidence base for implementing new or modifying existing programs and policies addressing infant mortality. The SIMC was conducted between 2004 and 2006 among five states: Delaware, Hawaii, Louisiana, Missouri, and North Carolina. States used analytic strategies in an iterative process to investigate contributors to infant mortality. Analyses were conducted within three domains: data reporting (quality, reporting, definitional criteria, and timeliness), cause and timing of infant death (classification of cause and fetal, neonatal, and postneonatal timing), and maturity and weight at birth/maturity and birth weight-specific mortality. All states identified the SIMC analyses as useful for examining infant mortality trends. In each of the three domains, SIMC results were used to identify important direct contributors to infant mortality including disparities, design or implement interventions to reduce infant death, and identify foci for additional analyses. While each state has unique structural, political, and programmatic circumstances, the SIMC model provides a systematic approach to investigating increasing or static infant mortality rates that can be easily replicated in all other states and allows for cross-state comparison of results.

Improvements in birth weight-specific neonatal mortality rates in the state of Qatar between 2003 &amp; 2010 and a comparative analysis with the Vermont Oxford Network database report of 2007: A pearl study review

Objective:The study aimed to develop a national reference on birth weight-specific neonatal survival in the State of Qatar to facilitate parental counseling.Study Design:This was a retrospective, analytic, and comparative study.Materials and Methods:The birth weight-specific neonatal mortality data for the years 2003 and 2010, collected from the admission and discharge registers of the neonatal intensive care unit, were stratified using the stratifications given in Vermont Oxford Network (VON) 2007 annual report. Category-wise birth weight-specific mortality and relative risk (RR) of death were compared between Qatar data (2003 and 2010) and VON 2007 report.Results:Qatar's neonatal mortality rate (NMR) dropped from 5 of 1000 in 2003 to 4.4 of 1000 in 2010 (P=0.443) which was significant for birth weight categories 501–750 g and 751–1000 g (P=0.026 and P=0.05, respectively). Qatar's NMR in 2010 was significantly lower than VON's NMR during 2007 (P<0.001) though VON's NMR was significantly lower among birth weight categories 751–1000 g and 1001–1500 g (P=0.001 and P=0.003, respectively). The RR of mortality decreased with increasing birth weight. The decline was very sharp for birth weight categories between 500 and 1500g. The RR was 25 times higher in babies with birth weight less than 750 g as compared to babies with birth weight ≥ 2550 g, both in Qatar and VON data. For birth weight categories 751–1000 g and 1001–1500 g, the RR was twice in Qatar as compared to the VON report (16.8 versus 7.8, and 5.5 versus 2.7, respectively).Conclusions:Qatar's current overall and birth weight-specific NMRs are comparable with the VON report except in birth weight categories 751–1000 g and 1001–1500 g which were higher in Qatar. This needs further in-depth qualitative analysis.

The effects of birth weight and gender on neonatal mortality in north central Nigeria

BackgroundWorldwide 15.5% of neonates are born with low birth weight, 95.6% of them in the developing countries. Prematurity accounts for 10% of neonatal mortality globally. The purpose of this study was to evaluate the effects of birth weight and gender on neonatal outcome.FindingsThe data of 278 neonates managed in the Special Care Baby Unit (SCBU) of Jos University Teaching Hospital (JUTH) over a 2 year period from July 2006 to June 2008 were analyzed.One hundred and fifty nine (57.2%) were males and 119(42.8%) females. There were 87(31.3%) preterm and 191 (68.7%) term babies. Twelve of the babies died. Seven (2.52%) and 5 (1.80%) being males and females respectively. The neonatal mortality rate by gender was not significant (p > 0.05). The neonatal mortality was 25.2 deaths per 1000 live births for boys and 18.0 for girls. The mean birth weights of the preterm and term babies were 1.88 ± 0.47 kg and 3.02 ± 0.50 kg respectively, with a mean gestational age of 30.62 ± 3.65 weeks and 38.29 ± 0.99 weeks respectively.Eighty seven (31.3%) of the babies were of low birth weight, 188(67.6%) were of normal birth weight and 3(1.1%) high birth weight. Of the low birth weight babies, 6(2.2%) were term small for gestational age. Six (2.2%) of the preterm infants had normal birth weight.Eleven of the babies that died were preterm low birth weight. The overall mortality rate was 4.32%. The birth weight specific mortality rate was 126 per 1000 for the preterm low birth weight and 5 per 1000 for the term babies. Birth weight unlike gender is a significant predictor of mortality, mortality being higher in neonates of <2.5 kg (OR = 0.04; 95% Cl 0.005-0.310, p = 0.002) (p = 0.453). Seven (58.3%) and 4(33.3%) of the pre-terms that died were appropriate and large for gestational age respectively. Gestational age is not a significant predictor of neonatal mortality (p = 0.595). Babies delivered at less than 37 weeks of gestation recorded a higher rate of mortality than those of 37 weeks and above (p = 0.000).The subjects showed one or more major clinical indications for admission. The major clinical indications for the preterm and term babies were respectively as follows: neonatal sepsis 63(22.7%) and 124(44.6%); neonatal jaundice 32(11.1%) and 71(24.7%); malaria 9(3.1%) and 13(4.5%); birth asphyxia 3(1.0%) and 7(2.4%). Neonatal sepsis was a common denominator among the babies that died.ConclusionBirth weight unlike gender is a significant predictor of neonatal outcome

Outcome of Low Birth Weight Infants in Diyala Province of Iraq

To measure birth weight-specific mortality rates in the Diyala Province of Iraq and to determine if the causes of neonatal death could identify interventions needed to reduce neonatal mortality rates. We retrospectively compared the outcome of 196 neonates with birth weight 500-2499 g admitted in 2003 with 252 such neonates admitted in 2009. The mortality rate in very low birth weight infant (VLBWI) increased from 12/80 (15%) in 2003 to 51/152 (33.6%) in 2009, (p = 0.003). In LBWI, 10/116 (8.6%) died in 2003 compared to 33/152 (13%) in 2009 (p = 0.29). Sepsis accounted for 35.2% of deaths in VLBWI and 39% in LBWI, Perinatal depression explained 39.2% of deaths in VLBWI and 24.2% in LBWI. The VLBWI mortality in the Diyala province of Iraq doubled in the last 6 years reaching 33.6% in 2009, LBWI mortality increased by 50% reaching 13%. Sepsis and perinatal depression accounted for at least two-third of the deaths.

Thinking outside the curve, part II: modeling fetal-infant mortality.

BackgroundGreater epidemiologic understanding of the relationships among fetal-infant mortality and its prognostic factors, including birthweight, could have vast public health implications. A key step toward that understanding is a realistic and tractable framework for analyzing birthweight distributions and fetal-infant mortality. The present paper is the second of a two-part series that introduces such a framework.MethodsWe propose estimating birthweight-specific mortality within each component of a normal mixture model representing a birthweight distribution, the number of components having been determined from the data rather than fixed a priori.ResultsWe address a number of methodological issues related to our proposal, including the construction of confidence intervals for mortality risk at any given birthweight within a component, for odds ratios comparing mortality within two different components from the same population, and for odds ratios comparing mortality within analogous components from two different populations. As an illustration we find that, for a population of white singleton infants, the odds of mortality at 3000 g are an estimated 4.15 times as large in component 2 of a 4-component normal mixture model as in component 4 (95% confidence interval, 2.04 to 8.43). We also outline an extension of our framework through which covariates could be probabilistically related to mixture components. This extension might allow the assertion of approximate correspondences between mixture components and identifiable subpopulations.ConclusionsThe framework developed in this paper does not require infants from compromised pregnancies to share a common birthweight-specific mortality curve, much less assume the existence of an interval of birthweights over which all infants have the same curve. Hence, the present framework can reveal heterogeneity in mortality that is undetectable via a contaminated normal model or a 2-component normal mixture model.

Excess Hispanic fetal-infant mortality in a midwestern community.

We assessed excess fetal-infant mortality for Hispanic, non-Hispanic white, and non-Hispanic black populations in five contiguous counties of Missouri and Kansas. We conducted a perinatal periods of risk (PPOR) assessment of fetal-infant mortality using electronic linked birth-death record files from 2001 through 2005. We generated an internal reference group in accordance with established PPOR protocol. We used Kitagawa analysis to determine whether excess deaths were due to birthweight distribution (a higher frequency of prematurity or growth retardation) or to higher mortality rates once born at that birthweight (birthweight-specific mortality). We found the excess fetal-infant death rates for Hispanic and non-Hispanic white populations to be similar and considerably lower than that for non-Hispanic black populations. Among Hispanic children, we judged 21.6% of fetal-infant mortality to be excess in relation to the reference population. Within the PPOR matrix, Hispanic excess mortality rates were distributed differently from those of non-Hispanic white and non-Hispanic black populations. Among Hispanic children, 93.6% of the excess mortality could be explained by low birthweight and birthweight-specific mortality, with the greatest contribution attributable to low birthweight. The excess fetal-infant mortality experience of Hispanic people in the five-county region was similar to that of the non-Hispanic white population, but was distributed differently in the PPOR model, which has significance regarding interventions targeting reductions in fetal-infant mortality.

Quantification of collider‐stratification bias and the birthweight paradox

The 'birthweight paradox' describes the phenomenon whereby birthweight-specific mortality curves cross when stratified on other exposures, most notably cigarette smoking. The paradox has been noted widely in the literature and numerous explanations and corrections have been suggested. Recently, causal diagrams have been used to illustrate the possibility for collider-stratification bias in models adjusting for birthweight. When two variables share a common effect, stratification on the variable representing that effect induces a statistical relation between otherwise independent factors. This bias has been proposed to explain the birthweight paradox. Causal diagrams may illustrate sources of bias, but are limited to describing qualitative effects. In this paper, we provide causal diagrams that illustrate the birthweight paradox and use a simulation study to quantify the collider-stratification bias under a range of circumstances. Considered circumstances include exposures with and without direct effects on neonatal mortality, as well as with and without indirect effects acting through birthweight on neonatal mortality. The results of these simulations illustrate that when the birthweight-mortality relation is subject to substantial uncontrolled confounding, the bias on estimates of effect adjusted for birthweight may be sufficient to yield opposite causal conclusions, i.e. a factor that poses increased risk appears protective. Effects on stratum-specific birthweight-mortality curves were considered to illustrate the connection between collider-stratification bias and the crossing of the curves. The simulations demonstrate the conditions necessary to give rise to empirical evidence of the paradox.

Intersecting Birth Weight-specific Mortality Curves: Solving the Riddle

Small babies from a population with higher infant mortality often have better survival than small babies from a lower-risk population. This phenomenon can in principle be explained entirely by the presence of unmeasured confounding factors that increase mortality and decrease birth weight. Using a previously developed model for birth weight-specific mortality, the authors demonstrate specifically how strong unmeasured confounders can cause mortality curves stratified by known risk factors to intersect. In this model, the addition of a simple exposure (one that reduces birth weight and independently increases mortality) will produce the familiar reversal of risk among small babies. Furthermore, the model explicitly shows how the mix of high- and low-risk babies within a given stratum of birth weight produces lower mortality for high-risk babies at low birth weights. If unmeasured confounders are, in fact, responsible for the intersection of weight-specific mortality curves, then they must also (by virtue of being confounders) contribute to the strength of the observed gradient of mortality by birth weight. It follows that the true gradient of mortality with birth weight would be weaker than what is observed, if indeed there is any true gradient at all.

Invited Commentary: Crossing Curves--It's Time to Focus on Gestational Age-specific Mortality

For decades, epidemiologists have observed that, among lower birth weight infants, higher risk infants have lower mortality rates than do lower risk infants. However, among higher birth weight infants, the pattern reverses, leading to a riddle of crossing birth weight-specific mortality curves. The riddle has been considered from different perspectives, including relative z scores, directed acyclic graphs, and, most recently, simulated mathematical models of underlying causal factors that produce the observed curves; similarly paradoxical gestational age-specific mortality curves uncross when calculations include all fetuses-at-risk rather than just infants delivered at a particular gestational age. However, researchers have generally focused on birth weight rather than gestational age, likely because birth weight is accurately measured and, if one assumes that birth weight is an intermediate variable between the underlying causal factors and mortality, is easier to model. Within the framework of existing analytical approaches, adding the complexity of a direct relation between gestational age and mortality, and possibly more complex relations among the casual factors, may be difficult. Nevertheless, duration of pregnancy seems a better proxy for the true construct of interest, whether the baby is mature enough to survive, so shifting attention to understanding the riddle of gestational age-specific mortality is encouraged.

Características biológicas e evitabilidade de óbitos perinatais em uma localidade na cidade do Rio de Janeiro, 1999 a 2003

OBJETIVOS: analisar os óbitos perinatais de uma maternidade pública do município do Rio de Janeiro, Brasil, quanto à características biológicas, critérios de evitabilidade, causas básicas e mortalidade por faixas de peso. MÉTODOS: o estudo de coorte foi realizado de 1999 a 2003, na Maternidade Leila Diniz do Hospital Municipal Raphael de Paula Souza, que é responsável por 50% dos partos de uma área programática 4 (Jacarepaguá e Barra da Tijuca). Foram incluídos óbitos perinatais com peso igual ou superior a 500 g. O instrumento principal de coleta de dados foi a Ficha de Investigação de Óbito Perinatal. Foi aplicada a Classificação de Wigglesworth para avaliar evitabilidade. RESULTADOS: houve 512 óbitos perinatais (377 fetais e 135 neonatais precoces). Os óbitos neonatais se concentraram nos primeiros três dias de vida. Vinte e quatro por cento dos óbitos cursaram com retardo de crescimento intra-uterino. As principais causas foram afecções maternas (hipertensão e sífilis) e complicações de membrana, placenta e cordão. Foram considerados evitáveis cerca de 50% dos óbitos. CONCLUSÕES: o percentual de óbitos evitáveis foi elevado, mais concentrado nos óbitos fetais ocorridos antes do parto, sugerindo inadequação do pré-natal.

Mortality risk of small infants varies with their mother's birthweight and race

We analysed a transgenerational linked birth file to investigate the relationship between maternal birthweight and infant birthweight-specific mortality risk for white and African American infants. Birth records of 267,303 infants born between 1989 and 1991 were linked to records of their mothers, born between 1956 and 1976, and to their own death certificates for those dying in the first year. The means, standard deviations and z-scores were calculated for each race- and generation-specific birthweight distribution. Investigators then analysed the mortality of very small infants (birthweight at least two standard deviations below their mean) for three maternal birthweight categories. Over half of the infant deaths involved births with weights more than two standard deviations below the relevant population mean birthweight (comprising 4.2% of white and 6.9% of African American births respectively). African American infants experienced higher mortality rates at all levels of standardised birthweight, from z-scores of -3 to +3. The relative risk of mortality associated with very small infant size was less for infants delivered to smaller birthweight mothers when compared with those whose mothers were average sized or large at birth. This differential effect was confined to neonatal deaths and was more prominent in the white subpopulation.