Association of prenatal participation in a public health nutrition program with healthy infant weight gain.

OBJECTIVES: We tested the hypothesis that early enrollment in the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) is associated with a reduced risk of rapid infant weight gain (RIWG). METHODS: We used a longitudinal cohort of mother-infant pairs (n = 157,590) enrolled in WIC in New York State from 2008 to 2009 and estimated the odds of RIWG, defined as a 12-month change in weight-for-age z score of more than .67, comparing infants of mothers enrolled during the first, second, or third trimester of pregnancy with those who delayed enrollment until the postpartum period. RESULTS: After adjusting for potential confounders, the odds of RIWG (odds ratio [OR] = 0.76; 95% confidence interval [CI] = 0.74, 0.79) were significantly lower for infants of women enrolling during the first trimester versus postpartum. Birth weight-for-gestational-age z score (OR = 0.33; 95% CI = 0.32, 0.33) attenuated the estimate of prenatal versus postpartum enrollment (OR = 0.92; 95% CI = 0.88, 0.95; first-trimester enrollees). CONCLUSIONS: The results demonstrate that prenatal WIC participation is associated with reduced risk of RIWG between birth and age 1 year. Improved birth weight for gestational age may be the mechanism through which early prenatal WIC enrollment protects against RIWG.

Given the increasing bias in random digit dial sampling, could respondent-driven sampling be a practical alternative?

PURPOSE: Increasing cellular phone service and nonresponse are causing random digit dial (RDD) users to search for alternative ways of sampling geographically large populations. This study evaluated the feasibility and utility in using a modified version of respondent-driven sampling (RDS) as an alternative method. METHODS: Using RDS, 469 residents of Albany County, New York were enrolled into a telephone-based health survey. Participants answered health and RDS feasibility questions. Results were compared to a previously collected RDD sample and census data. RESULTS: Participation was high (81.4%) and participants referred at least one peer 65.9% of the time. The RDS method produced a more ethnically diverse sample, otherwise respondent demographics were similar to the RDD sample. The most common reason for participating (51.9%) was because a peer told them about the study; 44.9% would not have participated in an RDD study. Persons not willing to participate in a RDD study reported being less healthy and less likely to participate in healthy activities (e.g., have a physical exam in the past 24 months). CONCLUSIONS: Although more research is needed, RDS methods may be developed into a viable alternative for collecting health data from large general populations.

Maternal age and infant mortality: a test of the Wilcox-Russell hypothesis.

It has been argued (e.g., the Wilcox-Russell hypothesis) that (low) birth weight is a correlate of adverse birth outcomes but is not on the "causal" pathway to infant mortality. However, the US national policy for reducing infant mortality is to reduce low birth weight. If these theoretical views are correct, lowering the rate of low birth weight may have little effect on infant mortality. In this paper, the authors use the "covariate density defined mixture of logistic regressions" method to formally test the Wilcox-Russell hypothesis that a covariate which influences birth weight, in this case maternal age, can influence infant mortality directly but not indirectly through birth weight. The authors analyze data from 8 populations in New York State (1985-1988). The results indicate that among the populations examined, 1) maternal age significantly influences the birth weight distribution and 2) maternal age also affects infant mortality directly, but 3) the influence of maternal age on the birth weight distribution has little or no effect on infant mortality, because the birth-weight-specific mortality curve shifts accordingly to compensate for changes in the birth weight distribution. These results tend to support the Wilcox-Russell hypothesis for maternal age.

Modeling the pediatric paradox: birth weight by gestational age.

The "pediatric paradox" of African versus European American infant mortality is often observed with respect to birth weight, but rarely to gestational age, even though the two measures are biologically related. This paper models the pediatric paradox by birth weight and gestational age simultaneously, using Covariate Density Defined mixture of logistic regressions (CDDmlr) fitted to 1985-1988 New York State births. The model controls for unobserved heterogeneity and isolates the pediatric paradox in the "compromised" subpopulation. The paradox is not limited to low birth weights and/or short gestational ages, but surrounds the normal birth range. Nevertheless, the pediatric paradox is only observed in the marginal distribution of birth weight and not the marginal distribution of gestational age. These results are consistent with the hypothesis that higher fetal losses in the "compromised" subpopulation may be responsible for the pediatric paradox and that African versus European American infant mortality differentials are underestimated.

Multiple mortality optima due to heterogeneity in the birth cohort: a continuous model of birth weight by gestational age-specific infant mortality.

Birth weight and gestational age are both important predictors of infant survival. Covariate Density Defined mixture of logistic regressions (CDDmlr), a method that accounts for unobserved heterogeneity, has been applied to birth outcomes using birth weight alone. This paper investigates a CDDmlr model of birth outcomes that includes birth weight and gestational age. Applications to four birth cohorts, composed of all non-Hispanic singleton African/European American female/male live births in New York State from 1985-1988, are presented. Multiple birth weight by gestational age optimal (minimal) mortalities are observed in the birth weight by gestational age-specific mortality surface. Multiple optima have not been mentioned in the published literature, but they do appear in some published plots of birth weight by gestational age mortality. It is possible that misreporting of gestational age contributes to this phenomenon, but it cannot completely explain the locations of the local optima. The global optimum is associated with a "normal" fetal development subpopulation, while the local optima are due to a subpopulation that accounts for most low birth weight, intrauterine growth retarded, pre-term, post-term, and small for gestational age births, as well as, births with misestimated gestational ages. These two subpopulations have significantly different birth weight by gestational age-specific mortality surfaces. Consequently, the presence of multiple optima can be attributed to heterogeneity in the birth cohort. Comparisons of CDDmlr based on birth weight by gestational age and birth weight alone might statistically identify births with "erroneous" gestational age.

Fruit juice intake predicts increased adiposity gain in children from low-income families: weight status-by-environment interaction.

OBJECTIVE: Our goal was to test the hypothesis that increased fruit juice intake and parental restriction of children's eating are associated with increased adiposity gain and whether exposure to nutritional counseling predicted reduced adiposity gain among children. PATIENTS AND METHODS: A sample of parents or guardians of children aged 1 to 4 years who attended 1 of 49 Special Supplemental Nutrition Program for Women, Infants, and Children agencies in New York State were surveyed in 1999 or 2000 (N = 2801). The survey addressed children's dietary intake, parental feeding practices, and parental exposure to nutritional counseling messages to increase fruit, vegetable, and low-fat milk intakes. Each child's height and weight were measured approximately every 6 months for up to 48 months. A prospective cohort design was used in which survey variables were the predictors and the outcome was change in children's adiposity, defined as change in age- and gender-standardized BMI per month (ie, BMI z-score slope). RESULTS: Controlling for gender and ethnicity, the relationship between juice intake and adiposity gain depended on children's initial overweight status. Among children who were initially either at risk for overweight or overweight, increased fruit juice intake was associated with excess adiposity gain, whereas parental offerings of whole fruits were associated with reduced adiposity gain. Each additional daily serving of fruit juice was associated with an excess adiposity gain of 0.009 SD per month. Feeding restriction was greater among parents whose children were initially at risk for overweight or overweight compared with those at a healthy weight. Parental exposure to nutritional messages was not associated with reduced child adiposity gain. CONCLUSION: This study supports the Institute of Medicine recommendations to reduce fruit juice intake as a strategy for overweight prevention in high-risk children.

Spatiotemporal Bayesian analysis of Lyme disease in New York state, 1990-2000.

Mapping ordinarily increases our understanding of nontrivial spatial and temporal heterogeneities in disease rates. However, the large number of parameters required by the corresponding statistical models often complicates detailed analysis. This study investigates the feasibility of a fully Bayesian hierarchical regression approach to the problem and identifies how it outperforms two more popular methods: crude rate estimates (CRE) and empirical Bayes standardization (EBS). In particular, we apply a fully Bayesian approach to the spatiotemporal analysis of Lyme disease incidence in New York state for the period 1990-2000. These results are compared with those obtained by CRE and EBS in Chen et al. (2005). We show that the fully Bayesian regression model not only gives more reliable estimates of disease rates than the other two approaches but also allows for tractable models that can accommodate more numerous sources of variation and unknown parameters.

Rapid infant weight gain predicts childhood overweight.

OBJECTIVE: To determine among a contemporary cohort whether rapid weight gain between birth and 6 months is associated with risk of childhood overweight and if this risk differs by ethnicity and/or breast-feeding history. RESEARCH METHODS AND PROCEDURES: This was a cross-sectional survey in 1999 to 2000 of parents/guardians of children participating in the Special Supplemental Nutrition Program for Women, Infants, and Children in New York State. Measurements were abstracted by chart review, including weight at birth and 6 months, and height and weight at time of survey and every 6 months subsequently. Overweight at 4 years of age was defined as a BMI > or = 95th age- and sex-specific percentiles. RESULTS: The study sample was 32% Hispanic, 19% black, and 49% white; 17% of children were overweight. Rate of infant weight gain (expressed in terms of 100 g/mo) was significantly associated with being overweight at 4 years (odds ratio, 1.4; 95% confidence interval, 1.3 to 1.6 after adjusting for history of breast-feeding, birth weight, and ethnicity). The odds of being overweight at 4 years of age for Hispanic children were twice those of non-Hispanic children (odds ratio, 2.2; 95% confidence interval, 1.5 to 3.3). The population-attributable risk of overweight at 4 years of age was 19% for children in the highest quintile of infant weight gain. DISCUSSION: Among this contemporary, multi-ethnic cohort, rapid infant weight gain was associated with increased risk of being overweight at 4 years of age, independently of potential confounders. Identification of the risk factors contributing to rapid weight gain during infancy might improve early recognition and guide strategies for optimal nutrition to prevent the development of childhood overweight.

Overweight trends among children enrolled in the New York State special supplemental nutrition program for women, infants, and children.

The objective of this study is to describe overweight trends in a large, multiethnic, low-income population of preschool children by race/ethnicity and examine cohort changes in body mass index (BMI) distribution. Cross-sectional data were collected January 1 through March 31, every year, from 1989 to 2003. Subjects were children aged 2 to 4 years participating in the Special Supplemental Nutrition Program for Women, Infants, and Children in New York State. The prevalence of overweight (BMI > or =95th age- and sex-specific percentile of the 2000 Centers for Disease Control and Prevention growth charts) was calculated for each year. Least squares regression compared trends in prevalence by race/ethnicity. Changes in BMI distribution were assessed graphically. Overweight prevalence increased 33% (12% to 16%). Prevalence was highest for Hispanics and lowest for non-Hispanic whites. Rates of increase (0.28 percentage points per year) were the same for Hispanic, non-Hispanic black, and non-Hispanic white children. The BMI distribution shifted toward higher values for all children studied; for 3- and 4-year-old children, the difference increased as BMI increased, indicating that, in 2003, the heaviest children were considerably heavier than the heaviest children were in 1989.

Epidemic and spatial dynamics of Lyme disease in New york State, 1990-2000.

Lyme disease (LD) occurrence in New York State (NYS) has not only increased over time but also spread throughout the state from the original disease focus in southeastern NYS. Few studies have investigated this epidemic and spatial dynamic in great detail. Using data from the NYS Department of Health Lyme Registry Surveillance System, we summarized epidemic and spatial characteristics of LD in NYS for the 11-yr time period from 1990 through 2000. New epidemiological trends associated with age, sex, and residential influences on LD over time were found. An empirical Bayes approach was used to produce maps of smoothed incidence at different time points to give a foundation for future state and local health funding plans and education programs.

Pediatric paradox: heterogeneity in the birth cohort.

Comparisons of birth-weight-specific infant mortality indicate that low-birth-weight African American infants have lower mortality than low-birth-weight European American infants despite higher infant mortality overall-the "pediatric paradox." One explanation is heterogeneity in birth weight. Analyses of African American and European American births suggest that birth cohorts consist of two heterogeneous subpopulations. One appears to account for normal births, whereas the other may consist of compromised births. Estimates of infant mortality indicate that the compromised subpopulation has higher overall mortality but lower birth-weight-specific mortality. We attribute lower birth-weight-specific infant mortality in the compromised subpopulation to higher rates of fetal loss. Compared to European American birth cohorts, African American birth cohorts have (1) higher birth-weight-specific mortality in the normal subpopulation, (2) larger compromised subpopulations, and (3) lower birth-weight-specific mortality in the compromised subpopulation. Consequently, the pediatric paradox is attributable to greater rates of compromised pregnancies and higher fetal losses among African Americans.

A comparative analysis of effects of early versus late prenatal WIC participation on birth weight: NYS, 1995.

OBJECTIVES: This study examined the effects of prenatal participation in the NYS WIC Program on birth weight through enhanced control of selection bias and gestational age bias. Program effects were assessed separately for White, Black, and Hispanic women and subpopulations defined by values of Kotelchuck index of adequacy of prenatal care utilization. METHODS: 1995 New York State Vital Statistics records were linked to WIC certifications, administrative and check redemption files, and to the 1990 federal census of NY county level data. The final data set contained 77,601 records. Birth weight among WIC participants who enrolled early and participated longer were compared to those who enrolled late and participated a shorter time. Selection bias was addressed using classification tree methods as part of a propensity score analysis. Gestational age bias was addressed by analyzing preterm and full-term pregnancies separately. RESULTS: Adjusted estimates showed a significant positive effect of longer prenatal WIC participation on birth outcomes for all groups studied. Infants born to WIC participants who enrolled early were heavier than those who enrolled late by, on average, 70 g for full-term and 129 grams for preterm. Black and Hispanic full-term infants experienced larger WIC effects than Whites (79, 75, 43 g, respectively). Looking at full-term pregnancies using Kotelchuck's index indicated that effects of longer prenatal WIC participation were greatest for the inadequate prenatal care group (83 g). CONCLUSION: Longer prenatal WIC participation was associated with an increase in birth weight overall and for all groups studied. The effect on birth weight of longer participation in WIC was greatest in Black and Hispanic, inadequate and no prenatal care groups.

Barriers to the use of WIC services.

OBJECTIVES: To identify barriers that deter parents/caretakers of infants and children enrolled in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) from taking full advantage of the services provided by the program. SUBJECTS/SETTING: A total of 3,167 parents/caretakers at 51 New York State WIC local agency sites completed a barriers survey. DESIGN: Sixty-eight potential barriers to WIC were identified through a literature review, five focus groups with parents/caretakers of WIC participants, and an expert review panel. The barriers survey was administered person-to-person to parents/caretakers of infants and children on WIC. Statistical analysis Classification tree analysis was used to identify characteristics that best predict WIC check usage behavior. RESULTS: A small set of barriers (n=11) were identified by more than 20% of respondents. Waiting too long was the most frequently cited barrier (48%). Difficulties in bringing the infant/child to recertify and rescheduling appointments were key variables associated with failure to use (ie, pick up or cash) WIC checks. Further analyses indicated that (a) for each additional reported barrier, there was a 2% increase in failure to use WIC checks (P<.0001); (b) waiting for services was related to an increase in the number of people who failed to use checks; and (c) the longer the reported wait, the greater the number of reported barriers (P<.0001). CONCLUSIONS: Conducting this barriers research enabled the New York State WIC to improve services provided to participants and their families. A decrease in waiting times should generally reduce exposure to noisy, crowded facilities and lead to fewer reports of nothing for kids to do.