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Kenneth C Schoendorf

Publications and source records attributed to Kenneth C Schoendorf.

At least 19 recordsLinked to original sources
PubMed2006

The use of United States vital statistics in perinatal and obstetric research.

Vital statistics data have been used to track maternal and child health in the United States since the early 1900s. The breadth of information collected on birth and death certificates coupled with advances in computer processing have made possible critical perinatal and obstetric research. These enhancements also facilitate potentially problematic uses of the same data. This commentary explores characteristics of the United States Vital Statistics System and presents some thoughts with regard to the appropriate use of these data. The advantages of vital statistics include representativeness and the ability to examine subpopulations. Limitations include possible underreporting of medical conditions and procedures, lack of ability to ascertain clinical intent, and the well-known issues with gestational age reporting. Analyses based on vital statistics are important in informing future clinical research projects. However, respecting the limitations of vital statistics data enhance their appropriate role in obstetric and perinatal research.

Epidemiologic Research Design↗
PubMed2006

Relationships between air pollution and preterm birth in California.

Air pollution from vehicular emissions and other combustion sources is related to cardiovascular and respiratory outcomes. However, few studies have investigated the relationship between air pollution and preterm birth, a primary cause of infant mortality and morbidity. This analysis examined the effect of fine particulate matter (PM(2.5)) and carbon monoxide (CO) on preterm birth in a matched case-control study. PM(2.5) and CO monitoring data from the California Air Resources Board were linked to California birth certificate data for singletons born in 1999-2000. Each birth was mapped to the closest PM monitor within 5 miles of the home address. County-level CO measures were utilised to increase sample size and maintain a representative population. After exclusion of implausible birthweight-gestation combinations, preterm birth was defined as birth occurring between 24 and 36 weeks' gestation. Each of the 10 673 preterm cases was matched to three controls of term (39-44 weeks) gestation with a similar date of last menstrual period. Based on the case's gestational age, CO and PM(2.5) exposures were calculated for total pregnancy, first month of pregnancy, and last 2 weeks of pregnancy. Exposures were divided into quartiles; the lowest quartile was the reference. Because of the matched design, conditional logistic regression was used to adjust for maternal race/ethnicity, age, parity, marital status and education. High total pregnancy PM(2.5) exposure was associated with a small effect on preterm birth, after adjustment for maternal factors (adjusted odds ratio [AOR] = 1.15, [95% CI 1.07, 1.24]). The odds ratio did not change after adjustment for CO. Results were similar for PM(2.5) exposure during the first month of pregnancy (AOR = 1.21, 95% CI [1.12, 1.30]) and the last 2 weeks of pregnancy (AOR = 1.17, 95% CI [1.09, 1.27]). Conversely, CO exposure at any time during pregnancy was not associated with preterm birth (AORs from 0.95 to 1.00). Maternal exposure to PM(2.5), but not CO, is associated with preterm birth. This analysis did not show differences by timing of exposure, although more detailed examination may be needed.

Adolescent↗
PubMed2006

Fine particulate matter (PM2.5) air pollution and selected causes of postneonatal infant mortality in California.

Studies suggest that airborne particulate matter (PM) may be associated with postneonatal infant mortality, particularly with respiratory causes and sudden infant death syndrome (SIDS). To further explore this issue, we examined the relationship between long-term exposure to fine PM air pollution and postneonatal infant mortality in California. We linked monitoring data for PM<or=2.5 microm in aerodynamic diameter (PM2.5) to infants born in California in 1999 and 2000 using maternal addresses for mothers who lived within 5 miles of a PM2.5 monitor. We matched each postneonatal infant death to four infants surviving to 1 year of age, by birth weight category and date of birth (within 2 weeks). For each matched set, we calculated exposure as the average PM2.5 concentration over the period of life for the infant who died. We used conditional logistic regression to estimate the odds of postneonatal all-cause, respiratory-related, SIDS, and external-cause (a control category) mortality by exposure to PM2.5, controlling for the matched sets and maternal demographic factors. We matched 788 postneonatal infant deaths to 3,089 infant survivors, with 51 and 120 postneonatal deaths due to respiratory causes and SIDS, respectively. We found an adjusted odds ratio for a 10-microg/m3 increase in PM2.5 of 1.07 [95% confidence interval (CI), 0.93-1.24] for overall postneonatal mortality, 2.13 (95% CI, 1.12-4.05) for respiratory-related postneonatal mortality, 0.82 (95% CI, 0.55-1.23) for SIDS, and 0.83 (95% CI, 0.50-1.39) for external causes. The California findings add further evidence of a PM air pollution effect on respiratory-related postneonatal infant mortality.

Air Pollutants↗
PubMed2005

Contextual effect of income inequality on birth outcomes.

BACKGROUND: Though associations between income inequality and birth outcome have been suggested, mechanisms underlying this relationship are not known. In this analysis, we examined the relationship between income inequality and preterm birth (PTB) and post-neonatal mortality (PNM) to explore two potential mechanisms-the proposed psychosocial stress and neo-material pathways. METHODS: Data on singleton births from 1998 to 2000 were obtained from the CDC's National Center for Health Statistics' Linked Birth and Infant Death files. The Gini Index was utilized to measure income inequality and was divided into tertiles representing high, medium, and low county-level inequality. To determine the association between the birth outcomes and county income inequality and to account for clustering within counties, we employed generalized estimating equation (GEE) modelling. RESULTS: PTB increased from 8.3% in counties with low income inequality to 10.0% in counties with high inequality. The Gini Index remained modestly associated with PTB after adjusting for individual level variables and mean county-level per capita income within the total population (AOR: 1.06; 95% CI 1.03-1.09) as well as within most of the racial/ethnic groups. PNM increased from 1.15 deaths per 1000 live births in low inequality counties to 1.32 in high-inequality counties. However, after adjustment, income inequality was only associated with PNM within the non-Hispanic black population (AOR: 1.20; 95% CI 1.03-1.39). CONCLUSIONS: These findings may provide some support for the association between income inequality and PTB. Further research is required to elucidate the biological mechanisms of income inequality.

Adult↗
PubMed2005

The influence of maternal age on very preterm birth of twins: differential effects by parity.

For singleton births, parity can modify the effect of maternal age on birth outcomes such as low birthweight and preterm birth; however, it is unknown whether this relationship exists for twin births. As the rate of twin births increases among older women, it is important to understand how parity may influence the relationship between maternal age and adverse birth outcomes. The NCHS Matched Multiple Birth Data Set, which contains all twin births in the USA from 1995 to 1998, was analysed. Parity was grouped into two levels (primiparous--no prior live births, and multiparous--at least one prior live birth), and maternal age was divided into the following groups: 20-24, 25-29, 30-34, 35-39, and 40 years or more. Very preterm birth was defined as births occurring before 33 weeks. Logistic regression was used to obtain odds ratios (OR) to estimate the risk of very preterm birth, and to determine the relationships between parity, maternal age, and very preterm birth. Among primiparae, women 40 years and older had a reduced risk of very preterm birth compared with women of 25-29 years (OR 0.74 [95% CI=0.66, 0.84]). Among multiparae, women 40 years and older had the same risk of very preterm birth compared with women of 25-29 years (OR 1.00 [95% CI=0.90, 1.12]). However, stratification by education revealed that the age gradient was limited to women with >12 years education among primiparae. The effect of maternal age on very preterm birth of twins differs according to parity. To some extent, that effect is further modified by education. Therefore, future analyses of maternal age and twin birth outcomes should account for measures of obstetric history and other factors, which may influence these results.

Adult↗
PubMed2005

Air pollution and birth weight among term infants in California.

OBJECTIVE: To examine associations between birth weight and air pollution among full-term infants in California. METHODS: We matched exposure data collected from air pollution monitors for small particles (PM(2.5)) and carbon monoxide (CO) to California birth records for singleton births delivered at 40 weeks' gestation in 2000 using the locations of the monitors and mother's residence. Pollution measurements collected within 5 miles of the mother's residence, averaged for the time period corresponding to the duration of pregnancy and each trimester, were used as exposure variables. Logistic and linear regression models were used to estimate the associations between the pollution measures and 2 pregnancy outcomes: small for gestational age (SGA) and birth weight. Variations of the models were used to examine the robustness of the findings. RESULTS: The adjusted odds ratio for SGA for exposure in the highest compared with lowest quartile of PM(2.5) was 1.26 (95% confidence interval [CI]: 1.03-1.50). We found no association between CO and birth weight or SGA after controlling for maternal factors and PM(2.5) (mean birth weight difference: 2.6 g; 95% CI: -20.6 to 25.8). The difference in mean birth weight for infants with a 9-month exposure in the highest quartile of PM(2.5) compared with that of infants who were exposed in the lowest quartile was -36.1 g (95% CI: -16.5 g to -55.8 g); this difference was similar after controlling for CO. We did not find PM(2.5) exposure during a particular trimester most important for assessing birth weight; trimester-level associations were similar to those found using the 9-month exposure variable. CONCLUSIONS: We found an increased odds of SGA and a small difference in mean birth weight between infants with the highest and lowest exposures to PM(2.5) but not CO. These findings have important implications for infant health because of the ubiquitous exposure to fine particulate air pollution across the United States.

Air Pollutants↗
PubMed2004

Comparing exposure metrics in the relationship between PM2.5 and birth weight in California.

Although studies suggest that air pollution is linked to perinatal outcomes, the geographic characterization of exposure to pollution differs between the studies. We compared neighborhood- and county-level measures of air pollution exposure, while examining the association between particulate matter less than 2.5 microm in aerodynamic diameter (PM(2.5)) and birth weight among full-term births in California in 2000. To reduce the effects of demographic variability, our analysis was limited to two populations of 8579 non-Hispanic white and 8114 Hispanic mothers who were married, between 20 and 30 years of age, completed at least a high school education, and gave birth for the first time. Measurements from the nearest monitor, and average and distance-weighted average of monitors within a 5-mile radius from each mother's residence (constituting neighborhood metrics) and the mean of monitors within each mother's county of residence were considered. PM(2.5) measurements, provided by the California Air Resources Board, were calculated to correspond to each mother's 9-month gestation period. Although metrics within the 5-mile radii and the county were highly correlated (r(2)=0.78), the county-level metric provided a stronger association between PM(2.5) and birth weight (beta=-4.04, 95% confidence interval =-6.71, -1.37) than the metric for the average of all monitors within 5-miles (beta=-1.38, 95% confidence interval =-3.36, 0.60) among non-Hispanic white mothers; similar results were observed among the Hispanic sample of mothers. Consequently, inferences from studies using different definitions of air pollution exposure may not be comparable.

Adult↗
PubMed2004

Trends in sepsis-related neonatal mortality in the United States, 1985-1998.

BACKGROUND: In the United States, bacterial sepsis affects up to 32,000 live births annually. In the 1990s, intrapartum antibiotic prophylaxis (IAP) was recommended to prevent maternal-infant transmission of group B Streptococcus (GBS), a leading cause of sepsis occurring in the first week of life (early onset sepsis). Since IAP has been used, early onset GBS disease declined 70%; however, increased antibiotic use associated with IAP might lead to more severe or antimicrobial resistant etiologies of sepsis. To understand the influence of IAP on neonatal sepsis, in general, we evaluated neonatal mortality from sepsis before and after IAP recommendations were issued. METHODS: Using the National Center for Health Statistics Linked Birth/Infant Death Datasets, we compared trends in sepsis-related early neonatal mortality (<7 days) and late neonatal mortality (7-27 days) among singleton United States births from 1985 through 1991 to 1995 through 1998 [data beyond 1998 not included because of International Classification of Diseases (ICD)-10/ICD-9 coding differences]. We compared trends in mortality between the 2 time periods by estimating the average annual percent change in mortality using log linear regression and stratified by gestational age. RESULTS: Combined early and late neonatal mortality from sepsis averaged 39.6/100,000 live births from 1985 through 1991 and 31.8/100,000 live births from 1995 through 1998. Early neonatal mortality from sepsis averaged 24.9/100,000 live births from 1985 through 1991 and 15.6 from 1995 through 1998; late neonatal mortality averaged 14.8/100,000 live births from 1985 through 1991 and 16.2 from 1995 through 1998. Early neonatal mortality declined more steeply after IAP recommendations were issued, 5.0% annually from 1995 through 1998 versus 3.0% annually from 1985 through 1991. Late neonatal mortality increased more from 1995 through 1998, 5.0% annually compared with 0.5% from 1985 through 1991. CONCLUSIONS: Lower mortality rates and greater declines in early neonatal mortality from sepsis during 1995-1998 indicate greater survival of infants beyond 7 days of life and suggest an association with GBS disease prevention efforts. Thus these findings provide some evidence for continuing IAP for GBS-colonized women. Our findings of apparent increasing trends in late neonatal mortality from sepsis necessitate follow-up with clinical studies.

Female↗
PubMed2003

US childhood asthma prevalence estimates: the Impact of the 1997 National Health Interview Survey redesign.

The 1997 redesign of the National Health Interview Survey (NHIS) affected US childhood asthma prevalence estimates. The 1997 asthma attack prevalence estimate for children 0-17 years was 5.4%. Pre-redesign NHIS childhood asthma period prevalence estimates peaked in 1995 at 7.5%. It is unclear whether the difference reflects the change in survey methodology or changing asthma prevalence. To examine the impact of the NHIS redesign on childhood asthma prevalence estimates, the authors analyzed the 1988 NHIS that contained two sets of asthma questions: the core survey used until 1996 and the Child Health Supplement (CHS) with questions more similar to those in the redesigned 1997 NHIS. The authors measured the difference between 1988 core and CHS childhood asthma prevalence estimates to calculate an inflation factor for 1997-2000 NHIS estimates. The 1988 CHS questions produced asthma prevalence estimates 19-34% lower than the 1988 core question, depending on the methodology used to assess the difference. Inflating the 1997 asthma attack prevalence estimate by these differences yielded modified 1997 estimates ranging from 6.5% (95% confidence interval: 5.6%, 7.5%) to 7.3% (95% confidence interval: 6.4%, 8.2%). The change in the 1997 NHIS asthma questions likely explains much of the difference in asthma prevalence estimates between 1995 and 1997.

Adolescent↗
PubMed2003

Excessive maternal weight gain patterns in adolescents.

The objective of this study was to examine the correlates of excessive maternal weight gain among adolescent mothers in the United States. Data from the Centers for Disease Control & Prevention 2000 natality file were analyzed to examine weight gain among adolescents (< or=19 years) compared with their older counterparts (> or=20 years). Using the Institute of Medicine guidelines, we defined excessive weight gain as more than 40 pounds. Our study population was restricted to singleton births, delivered after 36 weeks of gestation, who did not live in California. Maternal weight gain distributions were tabulated by maternal age and other maternal characteristics. Demographic characteristics potentially associated with maternal weight gain were compared for adolescents and older mothers. We further evaluated the role of parity and maternal race on the relationship between excessive weight gain and maternal age. Odds ratios and 95% confidence intervals were estimated using logistic regression. Over 27% of adolescent mothers gained excessive weight during pregnancy, although approximately 18% of their older counterparts gained more than 40 pounds. The association between young maternal age and weight gain was stronger for primiparous women than multiparous women and stronger among non-Hispanic white and non-Hispanic black mothers than Hispanic mothers. Adolescents were more likely to gain excessive weight than their older counterparts in nearly all demographic categories, regardless of parity or race. Adolescents are at high risk of gaining an excessive amount of weight during pregnancy and should be monitored during pregnancy by dietetics professionals.

Adolescent↗
PubMed2003

The effect of birth weight discordance on twin neonatal mortality.

OBJECTIVE: To estimate the association between birth weight discordance and neonatal mortality controlling for the effects of fetal growth, and to understand the differences in the incidence of mortality between larger and smaller infants. METHODS: This analysis is based on the National Center for Health Statistics matched multiple birth data set file containing all twin births in the United States from 1995 through 1997. Birth weight discordance was grouped into four levels (15-19%, 20-24%, 25-29%, and 30% or more). Generalized estimating equations were used to obtain adjusted odds ratios and 95% confidence intervals to estimate the mortality risk associated with discordance after adjusting for fetal growth. RESULTS: Mortality was 11 times higher among highly discordant smaller twins (30% or more) compared with nondiscordant smaller twins (43.4 and 3.8 per 1000, respectively). Risk estimates ranged from 1.08 (95% confidence interval 0.85, 1.38) among 15-19% discordant twins to 2.05 (95% confidence interval 1.66, 2.51) among 30% or more discordant twins. Larger twins had similar risk estimates. After accounting for the association between fetal growth and discordance, mortality risk was substantially higher among smaller and larger twins who were highly discordant (30% or more). In addition, there was little difference in the magnitude of risk estimates between highly discordant smaller and larger twins. CONCLUSION: After controlling for fetal growth, smaller and larger twins affected by higher levels of birth weight discordance (25% or more) remain at disproportionate risk for neonatal mortality when compared with other smaller or larger twins. Additionally, smaller twins do not have an elevated risk compared with larger twins after adjusting for their different fetal growth distributions.

Birth Weight↗
PubMed2003

Does postpartum length of stay affect breastfeeding duration? A population-based study.

BACKGROUND: Short postpartum hospital stays may leave inadequate time for women to receive assistance with breastfeeding. Women leaving the hospital early may also have household responsibilities that could interfere with breastfeeding. This study examined the relationship between postpartum length of stay and breastfeeding cessation. METHODS: This study used data from 10,519 respondents to the California Maternal and Infant Health Assessment (MIHA) surveys from 1999 to 2001. MIHA is an annual statewide stratified random sample, population-based study of childbearing women in California. Survival analysis was used to examine the relationship between length of stay and length of time breastfeeding. Women were asked about the number of nights their infant stayed in the hospital at birth, whether they breastfed, and if so, the age of the child when they stopped. Hospital stay was defined in three categories: standard (2 nights for a vaginal delivery, 4 nights for a cesarean section), or shorter or longer than the standard stay. RESULTS: Approximately 88 percent of women initiated breastfeeding. Unadjusted predictors of breastfeeding cessation included short or long postpartum stay; young maternal age; Hispanic, African American, or Asian/Pacific Islander race/ethnicity; being unmarried; low income or education level; primiparity; being born in the 50 United States or the District of Columbia; smoking during pregnancy; and low infant birthweight. After adjustment for potential confounders, women with a short stay remained slightly more likely to terminate breastfeeding than women with a standard stay (relative risk, 1.11, 95% confidence interval 1.01, 1.23). CONCLUSION: Women who leave the hospital earlier than the standard recommended stay are at somewhat increased risk of terminating breastfeeding early.

Adolescent↗
PubMed2003

Disparities in exposure to air pollution during pregnancy.

Previous research shows poorer birth outcomes for racial and ethnic minorities and for persons with low socioeconomic status (SES). We evaluated whether mothers in groups at higher risk for poor birth outcomes live in areas of higher air pollution and whether higher exposure to air pollution contributes to poor birth outcomes. An index representing long-term exposure to criteria air pollutants was matched with birth certificate data at the county level for the United States in 1998-1999. We used linear regression to estimate associations between the air pollution index and maternal race and educational attainment, a marker for SES of the mother, controlling for age, parity, marital status, and region of the country. Then we used logistic regression models both to estimate likelihood of living in counties with the highest levels of air pollution for different racial groups and by educational attainment, adjusting for other maternal risk factors, and to estimate the effect of living in counties with higher levels of air pollution on preterm delivery and births small for gestational age (SGA). Hispanic, African-American, and Asian/Pacific Islander mothers experienced higher mean levels of air pollution and were more than twice as likely to live in the most polluted counties compared with white mothers after controlling for maternal risk factors, region, and educational status [Hispanic mothers: adjusted odds ratio (AOR) = 4.66; 95% confidence interval (95% CI), 1.92-11.32; African-American mothers: AOR = 2.58; 95% CI, 1.00-6.62; Asian/Pacific Islander mothers: AOR = 2.82; 95% CI, 1.07-7.39]. Educational attainment was not associated with living in counties with highest levels of the air pollution index (AOR = 0.95; 95% CI, 0.40-2.26) after adjusting for maternal risk factors, region of the country, and race/ethnicity. There was a small increase in the odds of preterm delivery (AOR = 1.05; 95% CI, 0.99-1.12) but not SGA (AOR = 0.96; 95% CI, 0.86-1.07) in a county with high air pollution. Additional risk of residing in areas with poor air quality may exacerbate health problems of infants and children already at increased risk for poor health.

Air Pollutants↗
PubMed2003

Contribution of excess weight gain during pregnancy and macrosomia to the cesarean delivery rate, 1990-2000.

OBJECTIVE: After declining for many years, cesarean delivery rates recently increased. To explore whether this increase is associated with excess weight gain during pregnancy, resulting in macrosomic infants who require cesarean delivery, we examined trends in excess weight gain, macrosomia, and cesarean delivery. METHODS: Analysis of 1990-2000 US Natality Files of birth certificate data were restricted to first birth, singleton infants of 37 to 42 weeks' gestation to avoid confounding by repeat cesarean delivery, complications of multigestational pregnancy, and preterm and postterm birth. Excess weight gain was defined according to current guidelines (41+ lb) and macrosomia as birth weight >4000 g. RESULTS: From 1990-2000, excess weight gain rose steadily from 18.6% to 24.2%. There was a 19.3% decline in macrosomic infants among women who gained excess weight compared with an 11.9% decline among women who gained 15-40 lb, although the absolute risk remained substantially greater among women who gained excess weight (eg, 14.2% vs 7.2%, in 2000). From 1990-1997, cesarean delivery declined by 20.2% among women who gained excess weight compared with 15.7% among women who gained 15 to 40 lb. After 1997, cesarean delivery increased in all weight gain categories, and absolute risks in 2000 were 25.8% for women who gained excess weight compared with 21.6% for women who gained 15-40 lb. Overall, women who gained excess weight accounted for 24.1% of cesarean deliveries in 1990 and 28.1% in 2000. CONCLUSIONS: Excess weight gain and macrosomia do not seem to be the primary factors that contribute to the recent increase in cesarean delivery because cesarean delivery rates have increased in all weight gain categories and macrosomia rates have decreased steadily from 1990-2000. Nonetheless, women who gain excess weight account for a growing proportion of cesarean deliveries because their relative numbers have grown.

Birth Certificates↗
PubMed2002

The influence of proximity of prenatal services on small-for-gestational-age birth.

Some studies suggest that prenatal services may decrease the risk of poor fetal growth for full-term infants, but have not examined the influence of the availability of community health and social services. The availability of prenatal services may have a stronger effect among women already at high risk of a small-for-gestational-age (SGA) birth. Singleton full-term (> or = 37 weeks gestation) California births for 1997-98 (n = 744,736) were geocoded to maternal Census tract of residence. Women were placed into one of three demographic risk groups utilizing combinations of maternal age, marital status, parity, and education. SGA was defined as birthweight less than the 10th percentile for gestational age. Locations of WIC sites, prenatal care providers, and perinatal outreach programs were geocoded. Multilevel logistic regression was used to model the influence of community health care services on SGA, adjusting for additional maternal and community factors. There was no association between SGA and community services available for either high- or low-risk women, in either unadjusted or adjusted models. The addition of maternal prenatal care utilization to models did not change the results. Maternal residence near prenatal services was not associated with SGA, regardless of demographic risk; other community factors may warrant consideration.

Adult↗
PubMed2002

Changing patterns of low birthweight and preterm birth in the United States, 1981-98.

Low birthweight (LBW) and preterm birth are primary risk factors for infant morbidity and mortality in the US. With increasing multiple births and delayed childbearing, it is important to examine the separate contributions of these characteristics to the increases in LBW and preterm birth rates. US natality records from 1981, 1990 and 1998 were used to calculate LBW (% births <1500, 1500-2499, <2500 g) and preterm (% births <29, 29-32, 33-36, <37 weeks gestation) rates. Data were stratified by maternal race (black or white) and plurality (singleton vs. multiple birth). LBW and preterm rates among singletons were adjusted for maternal age to examine the influence of demographic shifts on LBW trends. From 1981 to 1998, LBW increased 12% among white infants, but remained relatively stable among black infants. During the same time, preterm birth increased 23% among white infants compared with 3% among black infants. For both black and white infants, the increase in LBW and preterm births was greater among multiple births than among singletons. Adjustment for maternal age did not reduce the temporal increase in LBW or preterm birth among singletons. Black infants continue to experience a markedly higher incidence of LBW and preterm birth, but the racial gap in these outcomes has narrowed slightly in recent years as a result of increasing LBW and preterm birth among white births. The differing trends for white and black infants are the consequence of a disparate trend in the incidence and outcome of multiple births coupled with increases in LBW and preterm birth among white singletons. Understanding the differential patterns in birth outcomes among white and black infants is necessary to develop effective interventions designed to decrease racial disparities in pregnancy outcome.

Black or African American↗
PubMed2002

Implications of cleaning gestational age data.

Gestational age is an important birth characteristic examined in epidemiological studies. Though there are well-documented problems with the reporting of gestational age on birth certificates, schemes for addressing this issue have not been systematically evaluated. With singleton births from the 1995-97 US linked birth/infant death files, we compared a handful of perinatal outcome estimates derived from the resulting analytical files using two published methods often used to manage inconsistent gestational age data. The first method (Alexander et al., 1996), provides cut-points for implausible birthweight-gestational age combinations and excludes infants with birthweights outside a plausible range. The second (Zhang and Bowes, 1995), provides different cut-points for implausible birthweight-gestational age combinations and then substitutes the clinical gestational age estimate for the original value, if available, reducing the number of births at the affected gestational age, but excluding fewer births from the resulting analytical files. The Alexander method excluded 0.4 of our study population and the Zhang method reassigned and excluded 1.0 and 0.2, respectively; however, over 20 of birth records with gestational age 28-30 weeks were modified by either method. Using either method, more high-risk than low-risk and more black than white births were excluded. These differential exclusions affected corresponding perinatal outcome estimates and relative risks between maternal risk groups for preterm delivery, gestation-specific infant mortality and birthweight; overall infant mortality rates were not affected. Systematic comparisons between results of different studies will need to consider the data modifications used, the populations affected, and the outcomes assessed when drawing conclusions.

Black or African American↗