Biomedical subjects

Amy H Herring

Publications and source records attributed to Amy H Herring.

At least 19 recordsLinked to original sources

PubMed2006

Patterns of salivary cortisol secretion in pregnancy and implications for assessment protocols.

Cortisol is used in research as a biomarker of psychological stress. Logistical considerations argue for collecting as few samples as possible, balanced against diurnal rhythms and intra-individual variations. 100 pregnant women gave five saliva samples a day for 3 days, at waking, 30 min after waking, and 11:00 a.m., 5:00 p.m., and 9:00 p.m. Timing of collection was confirmed by monitors. Another sample was taken during a clinic visit. Using the 15 measures as the gold standard, correlations and mean area under the curve (AUC) were compared with subsets and the single clinic sample to evaluate alternate collection protocols. Five samples in 1 day, or protocols involving morning and night samples, had the highest correlations with mean AUC (correlation coefficient ranging from 0.82 to 0.88). Standardizing the clinic measurement to a single time of day did not substantially improve correlations with mean AUC. Correlations with measures of reported stress were also not strong.

Adult↗

PubMed2006

Exposure to drinking water disinfection by-products and pregnancy loss.

Previous research has suggested that exposure to elevated levels of drinking water disinfection by-products (DBPs) may cause pregnancy loss. In 2000-2004, the authors conducted a study in three US locations of varying DBP levels and evaluated 2,409 women in early pregnancy to assess their tap water DBP concentrations, water use, other risk factors, and pregnancy outcome. Tap water concentrations were measured in the distribution system weekly or biweekly. The authors considered DBP concentration and ingested amount and, for trihalomethanes only, bathing/showering and integrated exposure that included ingestion. On the basis of 258 pregnancy losses, they did not find an increased risk of pregnancy loss in relation to trihalomethane, haloacetic acid, or total organic halide concentrations; ingested amounts; or total exposure. In contrast to a previous study, pregnancy loss was not associated with high personal trihalomethane exposure (> or =75 micro g/liter and > or =5 glasses of water/day) (odds ratio = 1.1, 95% confidence interval: 0.7, 1.7). Sporadic elevations in risk were found across DBPs, most notably for ingested total organic halide (odds ratio = 1.5, 95% confidence interval: 1.0, 2.2 for the highest exposure quintile). These results provide some assurance that drinking water DBPs in the range commonly encountered in the United States do not affect fetal survival.

Abortion, Spontaneous↗

PubMed2006

The relationship between leisure, walking, and transportation activity with the natural environment.

The purpose of this study was to quantify the agreement between perceived and objective measures of the natural environment and to assess their associations with physical activity. Perception of the natural environment was obtained through survey data. Objective measures of weather and hills were created using Geographic Information Systems (GIS). When objective measures were compared to respondent's perceptions little agreement was found. Objective measures were not associated with any physical activity outcomes; however, several associations were seen between perceived measures and physical activity. These results indicate that researchers should consider perceptions of the natural environment when developing physical activity interventions.

Adult↗

PubMed2006

Predictors of use and consumption of public drinking water among pregnant women.

Disinfection by-products (DBPs) in drinking water may be associated with adverse pregnancy outcomes. However, the results from previous epidemiological studies are not consistent, perhaps in part due to individual variation in water use and consumption. This study was performed to evaluate and describe demographic and behavioral characteristics as predictors of ingested water, showering, bathing, and swimming among pregnant women. Water use and consumption data were collected through telephone interviews with 2297 pregnant women from three geographical sites in the southern United States. The data were analyzed according to demographic, health, and behavioral variables expected to be predictors of water use and thus potential confounding factors relating water use to pregnancy outcome. The candidate predictors were evaluated using backward elimination in regression models. Demographic variables tended to be more strongly predictive of the use and consumption of water than health and behavior-related factors. Non-Hispanic white women drank 0.4 (95% confidence interval (CI) 0.2; 0.7) liters more cold tap water per day than Hispanic women and 0.3 (95% CI 0.1; 0.4) liters more than non-Hispanic black women. Non-Hispanic white women also reported drinking a higher proportion of filtered tap water, whereas Hispanic women replaced more of their tap water with bottled water. Lower socioeconomic groups reported spending a longer time showering and bathing, but were less likely to use swimming pools. The results of this study should help researchers to anticipate and better control for confounding and misclassification in studies of exposure to DBPs and pregnancy outcomes.

Adolescent↗

PubMed2006

Comparison of residential geocoding methods in population-based study of air quality and birth defects.

Our population-based case-control study of air quality and birth defects in Texas relied on the geocoding of maternal residence from vital records for the assignment of air pollution exposures during early pregnancy. We attempted to geocode the maternal addresses for 5,338 birth defect cases and 4,574 frequency-matched controls using an automated procedure with standard matching criteria in ArcGIS 8.2 and 8.3. Initially, we matched 7,266 observations (73%). To increase the proportion of successful matches, we used an interactive procedure for the 2,646 addresses that were initially not geocoded by the software. This yielded an additional 985 matches (37%). Using the same 2,646 initially unmatched addresses, we compared the results of this interactive procedure to those of an automated procedure using lower standards. The automated procedure with lower standards yielded more matches (n=1,559, 59%) but with questionable accuracy. We included the interactively geocoded observations in our final data set. Their inclusion did not affect the estimates of air pollution exposure but increased our statistical power to detect associations between air quality and risk of selected birth defects. The geocoded and not geocoded populations differed in the distribution of Latino ethnicity (51% vs 59%) and ethnicity was independently associated with air pollution exposures (P<0.05). Geocoding status also appeared to modify the association between ethnicity and risk of birth defects; Latina women appeared to have a slightly lower risk of birth defects than non-Latina women in the geocoded population and to have a slightly higher risk in the not geocoded population. Incomplete geocoding may have resulted in a selection bias because of the under-representation of Latinas in our study population.

Air Pollutants↗

PubMed2006

Characteristics that predict locating and interviewing mothers identified by a state birth defects registry and vital records.

BACKGROUND: State vital records are often used to select population-based controls in record-linkage studies of birth defects. However, locating and contacting individuals based on these data sources to collect additional data can be a challenge. METHODS: A large case-control study of air quality and birth defects was conducted in 7 Texas counties in which cases were selected from the Texas Birth Defects Registry and controls from state vital records. In 2004, data from these sources were used to trace mothers of cases and controls who delivered babies in the year 2000 (n=2477) for participation in a computer-assisted telephone interview. A number of factors that predicted whether an individual would be located and interviewed were identified. RESULTS: Between March and August 2004, 38% of the mothers were located, and 38% of the located mothers were interviewed. Case mothers were more likely than control mothers to be located (44 vs. 30%) and, if located, to be interviewed (43 vs. 31%). We compared the characteristics of mothers who were not located (case n=760; control n=777), mothers who were located but not interviewed (case n=344; control n=236), and mothers who were interviewed (case n=256; control n=104). Among both cases and controls, older mothers (>or=30 years) were more likely than younger mothers to be located, and non-Hispanic black mothers were least likely to be located and interviewed. CONCLUSIONS: Despite the utility of vital records as a source of population-based controls in record-linkage analyses, the poor response rate discourages the use of these data sources to contact individuals for a follow-up study 4 years after delivery.

Case-Control Studies↗

PubMed2006

A diet quality index for American preschoolers based on current dietary intake recommendations and an indicator of energy balance.

OBJECTIVE: Based on current dietary intake recommendations and a recommendation to limit sedentary activity in preschoolers, an overall diet quality index for preschoolers (RC-DQI) incorporating a component for energy balance to measure adequacy of nutrition for growth, development, and disease prevention was developed. DESIGN/SUBJECTS: The newly developed index was used in nationally representative samples of 2- to 5-year-olds in the US Department of Agriculture Continuing Survey of Food Intakes by Individuals 1994-96 and 1998 (n=5,437). Index components included added sugar, total fat, polyunsaturated fatty acids, total and whole grains, fruits, vegetables, excess fruit juice, dairy, iron, and an interaction term of total daily energy intake and sedentary behavior (television time). Points were allocated to reflect deficient or excessive intakes. STATISTICAL ANALYSIS PERFORMED: Means and standard errors were used to describe food intakes and RC-DQI scores. Ability to differentiate diets was ascertained using mean intakes of food groups/nutrients followed by a nonparametric test of trends across ordered groups. Correlation coefficients measured dependence among RC-DQI components, nutrients, and overall energy intakes. Component scores of the highest and lowest quartile of RC-DQI were compared. RESULTS: Mean RC-DQI score was 64 points (range=28 to 93). Increasing RC-DQI scores were associated with improved diet quality. Children in the lowest RC-DQI quartile scored lower in all components. CONCLUSIONS: The RC-DQI successfully differentiated diets by level of diet quality. Increasing scores were associated with decreasing consumption of added sugar and juices, and increasing intakes of fiber, essential fatty acids, fruits, and vegetables. The RC-DQI can be used to determine diet quality in groups of preschool-age children.

Child, Preschool↗

PubMed2006

Physical activity and magnetic field exposure in pregnancy.

BACKGROUND: Peak magnetic field exposure was associated with increased risk of miscarriage in 2 recent studies. Reduced physical activity levels in healthy pregnancies may affect measured exposure and thus bias results. METHODS: We recruited 100 pregnant women to wear an Actigraph accelerometer and EMDEX magnetic field monitor for a 7-day period. We evaluated the association between physical activity and magnetic field exposure (peaks and time-weighted average) using generalized estimating equations and linear mixed models. RESULTS: We found a positive association between level of activity and likelihood of incurring elevated exposure in the person-day analysis, most strongly for cutpoints of 16 or 20 mG, for both working and nonworking women among whom odds ratios in the uppermost quartile ranged from 2.1 to 2.6. A positive association was found using person-minutes only among nonworking women. CONCLUSION: Physical activity may affect peak magnetic field exposure. If the early nausea and later cumbersomeness of healthy pregnancies leads to reduced physical activity, this could distort measured magnetic field-health outcome associations.

Adult↗

PubMed2006

Attitudes toward participation in a pregnancy and child cohort study.

While epidemiological studies aim for high participation rates, it is becoming increasingly difficult to recruit and retain participants in lengthy observational studies. We surveyed women who recently participated in the Pregnancy, Infection, and Nutrition Study during their pregnancy to learn more about what initially motivated them to participate in the study, their attitudes about the study protocol, and whether they would allow their child to participate in future studies. Most women were motivated by their interest in science and learning about their pregnancy. In general, women felt quite comfortable with most aspects of the study. Consent forms, telephone interviews and self-administered questionnaires were the most acceptable components of the study, but even specimen collection was well tolerated by this cohort. Women were less comfortable with the possibility of their child participating in future research. This survey confirmed that once women are enrolled, they tend to be willing to complete most components of an intensive study, suggesting that initial efforts for recruitment are most important.

Adult↗

PubMed2006

Methodologic issues in the design and analysis of epidemiologic studies of pregnancy outcome.

Using epidemiology to elucidate the causes of adverse pregnancy outcomes offers unique opportunities and poses distinctive challenges. The context of pregnancy includes contraception and planning, medical interventions altering the natural history, and the tendency for selective participation in demanding research protocols. Several key pervasive issues are considered in detail: 1) the close temporal proximity of determinants and outcomes, which makes separation of causes and effects difficult and introduces the real possibility of reverse causality; 2) non-random allocation of exposure, often done consciously in response to concerns about having a healthy pregnancy or to the health of the pregnancy itself, making confounding a major concern; 3) heterogeneity of pregnancy outcomes, with endpoints such as pregnancy loss and preterm birth arising through diverse pathways that are not easily identified and if grouped, could diminish the magnitude of observed associations; and 4) racial and ethnic disparities, which pose a public health challenge in the USA and offer a potentially important opportunity for identifying preventable causes of adverse pregnancy outcome. Sophisticated biological and statistical methods are needed to advance epidemiologic research in this area.

Epidemiologic Studies↗

PubMed2005

Bayesian model selection and averaging in additive and proportional hazards models.

Although Cox proportional hazards regression is the default analysis for time to event data, there is typically uncertainty about whether the effects of a predictor are more appropriately characterized by a multiplicative or additive model. To accommodate this uncertainty, we place a model selection prior on the coefficients in an additive-multiplicative hazards model. This prior assigns positive probability, not only to the model that has both additive and multiplicative effects for each predictor, but also to sub-models corresponding to no association, to only additive effects, and to only proportional effects. The additive component of the model is constrained to ensure non-negative hazards, a condition often violated by current methods. After augmenting the data with Poisson latent variables, the prior is conditionally conjugate, and posterior computation can proceed via an efficient Gibbs sampling algorithm. Simulation study results are presented, and the methodology is illustrated using data from the Framingham heart study.

Age of Onset↗

PubMed2005

Evaluating change in physical activity with the building of a multi-use trail.

BACKGROUND: Cross-sectional studies suggest a positive association between the presence of trails and physical activity participation. Prospective evaluations of the impact of building a multi-use trail, in terms of change in physical activity levels among nearby residents, are needed. DESIGN: The study was designed as a quasi-experimental noncontrol pre-post design. SETTING/PARTICIPANTS: Participants included 366 adults aged > or =18 years living within 2 miles of the evaluated trail. INTERVENTION: A railway of >23 miles was under development for conversion to a multi-use trail in central North Carolina. A segment of the trail was evaluated by randomly selecting and telephone interviewing adults living within 2 miles of the planned trail before trail construction began and approximately 2 months after completion of construction. MAIN OUTCOME MEASURES: Outcomes were time spent in leisure activity, leisure activity near home, walking, bicycling, moderate activity, vigorous activity, and transportation activity. RESULTS: At follow-up, of the 366 adults living within 2 miles of the trail, 11.0% had not heard of the trail, and 23.1% had heard of the trail and had used it at least once. In multivariable logistic models, leisure activity, leisure activity near home, moderate activity, vigorous activity, and walking for transportation did not significantly change for those who used the trail compared to those not using the trail. CONCLUSIONS: This prospective study of the building of a multi-use trail did not demonstrate an increase in physical activity among adults living near the trail. Other prospective studies are encouraged, to take advantage of rigorously evaluating different types of trails that are to be constructed in rural and urban settings.

Adolescent↗

PubMed2005

Bayesian latent variable models for mixed discrete outcomes.

In studies of complex health conditions, mixtures of discrete outcomes (event time, count, binary, ordered categorical) are commonly collected. For example, studies of skin tumorigenesis record latency time prior to the first tumor, increases in the number of tumors at each week, and the occurrence of internal tumors at the time of death. Motivated by this application, we propose a general underlying Poisson variable framework for mixed discrete outcomes, accommodating dependency through an additive gamma frailty model for the Poisson means. The model has log-linear, complementary log-log, and proportional hazards forms for count, binary and discrete event time outcomes, respectively. Simple closed form expressions can be derived for the marginal expectations, variances, and correlations. Following a Bayesian approach to inference, conditionally-conjugate prior distributions are chosen that facilitate posterior computation via an MCMC algorithm. The methods are illustrated using data from a Tg.AC mouse bioassay study.

Acrylates↗

PubMed2005

Reducing misclassification in assignment of timing of events during pregnancy.

BACKGROUND: Perinatal epidemiology studies often collect only the calendar month in which an event occurs in early pregnancy because it is difficult for women to recall a specific day when queried later in pregnancy or postpartum. Lack of day information may result in incorrect assignment of completed gestational month because calendar months and pregnancy months are not aligned. METHODS: To examine the direction and magnitude of misclassification, we compared 3 methods for assignment of completed gestational month: 1) calendar month difference, 2) conditional month difference, and 3) imputed month midpoint. We used data from the Pregnancy, Infection, and Nutrition Study for simulations. RESULTS: Calendar month difference misclassified 54% of events as 1 month later in pregnancy compared with the actual completed month of gestation. Each of the other 2 methods misclassified approximately 12% of events to 1 month earlier and 12% to 1 month later. CONCLUSIONS: Calendar month difference, a common method, has the greatest misclassification. Conditional month difference and imputed month midpoint, which require little effort to implement, are superior to calendar month difference for reducing misclassification.

Cohort Studies↗

PubMed2005

Should spontaneous and medically indicated preterm births be separated for studying aetiology?

An increasing proportion of preterm births result from medical interventions, and the practice of aggregating all preterm births vs. splitting into spontaneous and medically indicated preterm births is inconsistent. While mechanistic and clinical arguments can be offered for either approach, we empirically evaluated the predictiveness of a range of risk factors for preterm birth in the Pregnancy, Infection, and Nutrition Study. Most influences were shared across the two subsets - African-American ethnicity, advancing age, delivery at a university medical centre, prior preterm birth and smoking. Medically indicated preterm births appeared to be associated with intensity of medical care, higher in the university medical centre and lower for the poorest women. Body mass index was positively associated with medically indicated preterm birth and inversely with spontaneous preterm birth. Given the complexity of the aetiological pathways, both aggregation and disaggregation are well justified and should be included in studies of the causes of preterm birth.

Adult↗

PubMed2005

Probability samples of area births versus clinic populations for reproductive epidemiology studies.

Studies of pregnancy outcome are generally based either on geographically defined populations, often from birth records, or on clinic or hospital populations. We compared women recruited into a clinic-based study, the Pregnancy, Infection, and Nutrition (PIN) Study, with women who resided in the geographical area of the study (Alamance, Orange, and Wake Counties in North Carolina) and gave birth over the corresponding time period (1996-2000). Clinic participants were more likely to be Black, younger, have lower education, be unmarried, have a more frequent history of adverse pregnancy outcome, obtain prenatal care later, and smoke more cigarettes. Despite that profile, the proportion of clinic participants delivering preterm was somewhat lower than among area women overall (10.8% vs. 11.3%). Black/White risk ratios for preterm birth were markedly different for area (1.6) vs. clinic women (1.1), whereas other predictors were similar. Patterns may differ across groups for many reasons, including self-selection of clinics and varying clinical practices.

Adult↗

PubMed2005

Predictors of vaginal bleeding during the first two trimesters of pregnancy.

This study evaluates maternal age, race, cigarette smoking, prior spontaneous abortion, prior induced abortion, and prior preterm birth in relation to vaginal bleeding during the first two trimesters of pregnancy. Information on vaginal bleeding and predictors came from the Pregnancy, Infection, and Nutrition Study, which enrolled 2806 pregnant women at 24-29 weeks' gestation during 1995-2000 in central North Carolina, USA. Generalised estimating equations were applied to take into account repeated episodes of vaginal bleeding during pregnancy. Women with advanced maternal age and passive smoking exposure were more likely to experience more intense vaginal bleeding during pregnancy, as were women with prior preterm birth. More intense bleeding was also more likely to be reported among women with multiple prior spontaneous abortions or multiple prior induced abortions, but not among women with a single prior spontaneous or induced abortion. The combination of prior spontaneous and induced abortion showed a dose-response association with the occurrence of vaginal bleeding during pregnancy.

Abortion, Habitual↗

PubMed2005

A time-series analysis of air pollution and preterm birth in Pennsylvania, 1997-2001.

Preterm delivery can lead to serious infant health outcomes, including death and lifelong disability. Small increases in preterm delivery risk in relation to spatial gradients of air pollution have been reported, but previous studies may have controlled inadequately for individual factors. Using a time-series analysis, which eliminates potential confounding by individual risk factors that do not change over short periods of time, we investigated the effect of ambient outdoor particulate matter with diameter < or = 10 microm (PM10) and sulfur dioxide on risk for preterm delivery. Daily counts of preterm births were obtained from birth records in four Pennsylvania counties from 1997 through 2001. We observed increased risk for preterm delivery with exposure to average PM10 and SO2 in the 6 weeks before birth [respectively, relative risk (RR) = 1.07; 95% confidence interval (CI), 0.98-1.18 per 50 microg/m3 increase; RR = 1.15; 95% CI, 1.00-1. 32 per 15 ppb increase], adjusting for long-term preterm delivery trends, co-pollutants, and offsetting by the number of gestations at risk. We also examined lags up to 7 days before the birth and found an acute effect of exposure to PM10 2 days and 5 days before birth (respectively, RR = 1.10; 95% CI, 1.00-1.21; RR = 1.07; 95% CI, 0.98-1.18) and SO2 3 days before birth (RR = 1.07; 95% CI, 0.99-1.15), adjusting for covariates, including temperature, dew point temperature, and day of the week. The results from this time-series analysis, which provides evidence of an increase in preterm birth risk with exposure to PM10 and SO2, are consistent with prior investigations of spatial contrasts.

Adolescent↗