Informed consent.
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Clinical Trials as Topic↗
Biomedical subjects
M B Bracken
Publications and source records attributed to M B Bracken.
Musings on the edge of epidemiology.
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Causality↗
Tree-based, two-stage risk factor analysis for spontaneous abortion.
The authors utilize an analytic strategy that combines tree-based analyses with the method of Mantel-Haenszel to evaluate the association of 11 putative risk factors to spontaneous abortion by controlling for 19 potential confounders. Logistic regression is also used for comparison. The data for this study were collected in southern Connecticut, during 1988-1991. The putative risk factors are employment; standing, walking, or sitting more than 2 hours at work; exposure to vibration at work; commuting to work; reaching over the shoulders at work; carrying loads over 9 kg on the job; drinking alcohol or coffee in the first month of pregnancy; and gynecologic problems before pregnancy. The potential confounding factors are maternal age, marriage status, race, years of education mother's height, use of birth control, number of pregnancies, smoking before pregnancy, years of smoking, whether the mother stopped smoking, smoking marijuana, passive exposure to marijuana, chronic problems, infertility cocaine use and history of negative pregnancy outcomes. This analysis indicates that carrying loads over 9 kg on the job at least once a day increases the risk of spontaneous abortion by 70% (relative risk (RR) = 1.71, 95% CI 1.25-2.32). Drinking three or more cups of coffee daily in the first month of pregnancy also elevates the risk of spontaneous abortion (RR = 2.34, 95% CI 1.45-3.77). Reaching over the shoulders at least once daily has a marginally significant impact on spontaneous abortion (RR = 1.35, 95% CI 1.02-1.78). The authors conclude that this analytic strategy offers an efficient approach to the exploration of new risk factors for a disease where many potential confounders already exist.
Abortion, Spontaneous↗
A tree-based method of analysis for prospective studies.
Prospective studies often involve rare events as study outcomes, and a primary concern is to identify risk factors and risk groups associated with the outcomes. We discuss practical solutions to risk factor analyses in prospective studies and address strategies to determine tree structures, to estimate relative risks, and to manage missing data in connection with some important epidemiologic problems. Some of the basic ideas for our strategies follow from work of Breiman, Friedman, Olshen, and Stone, although we propose extensions to their methods to resolve some practical problems that arise in implementation of these methods in epidemiologic studies. To illustrate these ideas, we analyse low birthweight associated risk factors with use of a data set from the Yale Pregnancy Outcome Study.
Bias↗
Maternal caffeine consumption and spontaneous abortion: a prospective cohort study.
We investigated the relation between caffeine beverage consumption and spontaneous abortion in 2,967 pregnant women planning to deliver at Yale-New Haven Hospital in 1988-1992. We evaluated coffee, tea, and soda drinking in the first month of pregnancy in interviews before the end of the sixteenth week of gestation. We obtained information on 98.2% of the pregnancies (including 2,714 singleton livebirths and 135 spontaneous abortions). As compared with abstention from caffeine beverages (coffee, tea, and soda), the adjusted odds ratios for spontaneous abortion associated with consumption of 1-150, 151-300, and > 300 mg caffeine daily were 0.81 [95% confidence interval (CI)) = 0.54-1.20], 0.89 (95% CI = 0.48-1.64), and 1.75 (95% CI = 0.88-3.47), respectively. Drinking > or = 3 cups of tea or coffee was associated with elevated risks of spontaneous abortion (adjusted odds ratio = 2.33, 95% CI = 0.92-5.85; and adjusted odds ratio = 2.63, 95% CI = 1.29-5.34, respectively). These results, if replicated, suggest that some ingredient (or correlate) of tea or coffee may account for some of the observed association of caffeine with spontaneous abortion. In this study, caffeine consumption is more strongly related to spontaneous abortion than alcohol or cigarette use in early pregnancy.
Abortion, Spontaneous↗
Maternal body mass, proportional weight gain, and fetal growth in parous women.
This study is designed to examine the impact of maternal body mass index (BMI), proportional weight gain, and other variables on fetal growth. From a 10% random sample of 5722 Norwegian and Swedish para one and two women (n = 561), three hundred and sixty-nine women for whom prepregnant weight and height were recorded and for whom four fetal ultrasound measurements were taken at 17, 25, 33, and 37 weeks of gestation, were divided into low, average, and high body mass index groups (weight/height2). Fetal growth rate (mm/day) was determined by taking the mean of three measurements of the sagital and transverse diameters of the fetal abdomen (MAD) in each of three study time periods: weeks 17 to 25, first period; weeks 25 to 33, second period; weeks 33 to 37, third period. Proportional weight gain (kilograms gained within a specific time period/prepregnant weight) was measured in those same intervals. Fetal growth rate was significantly slower in the first and second periods, and significantly faster in the third time period for women with a low BMI, compared with those of average BMI. Fetal growth also significantly increased with increases in proportional weight gain in the second and third periods, but not in the first. Fetal growth appears to be independently associated with maternal BMI and proportional maternal weight gain.
Adult↗
Measurement of exposure to environmental tobacco smoke in pregnant women.
The authors compared three methods used to measure exposure to environmental tobacco smoke in pregnant women: personal air monitor, urine cotinine, and questionnaire. Environmental tobacco smoke exposure assessment methods were compared for agreement using Cohen's Kappa and the Spearman rank order correlation coefficient. Women who reported exposure had significantly higher levels of air nicotine concentration compared with women who reported no exposure, but urine cotinine did not differ. Air nicotine was more highly correlated with home exposure (r = 0.34) than work exposure (r = 0.18). Urine cotinine correlated with work exposure (r = 0.14) but neither home nor social exposure. Agreement was "fair" (Kappa = 0.29) when self-reported exposure was compared with air monitor, but agreement was "poor" when urine cotinine was compared with self-report (Kappa = 0.08) and air monitor (Kappa = 0.10). In low environmental tobacco smoke exposure environments, all three methods for measuring exposure may have a role, although modification to monitoring protocols will be needed to improve monitoring sensitivity and exposure classification.
Adult↗
Tree-based risk factor analysis of preterm delivery and small-for-gestational-age birth.
Using data collected at the Yale-New Haven Hospital, New Haven, Connecticut, in 1980-1982, the authors conducted a tree-based statistical analysis using preterm delivery and small for gestational age as outcomes and the following variables as putative risk factors: maternal age, marital status, ethnicity, education, current employment, smoking, alcohol use, caffeine consumption, marijuana use, hormones/diethylstilbestrol used by the mother, gravidity, parity, and passive smoking. The authors' analyses indicate that ethnicity is a leading factor contributing to both outcomes: Black women are more likely to have preterm deliveries as well as to deliver small-for-gestational age infants. The tree-based procedure leads to generally consistent results with more traditional secondary analyses of the same data set, but also provides a more fully integrated picture of the important relation. The full utility of these procedures for hypothesis generation remains to be explored.
Black People↗
American college of epidemiology statement of principles.
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Epidemiology↗
Occupationally related magnetic field exposure and male subfertility.
OBJECTIVE: To determine whether there is an association between occupationally related magnetic field exposure, as estimated in milligauss (mG), and male subfertility. DESIGN: Nested case-control study using three defined case groups and one standard control group. SETTING: Yale New Haven Hospital Infertility Clinic, New Haven, Connecticut. PATIENTS, INTERVENTIONS: Male partners of couples seeking diagnosis and care at the infertility clinic. Men included in the analysis had complete first semen analysis and interview information. Subjects for this investigation consisted of case groups for motility (n = 177), morphology (n = 135), and concentration (n = 172); controls included men normal on all three parameters (n = 304). MAIN OUTCOME MEASURES: Laboratory confirmation in semen analysis of poor morphology, inadequate motility, and low concentration. Comparisons of occupational magnetic field exposure categories are made between case groups and controls. RESULTS: The odds of high job exposure category to magnetic fields (> 3 mG [> 0.3 muT]) for morphology cases were odds ratio (OR) = 0.6, for motility cases OR = 1.1, and concentration cases OR = 1.0 as compared with controls. No significant association was demonstrated for medium exposure (> 2 to 3 mG) among all case groups. Multivariate adjustment for selected risk factors did not substantially change estimates of risk. CONCLUSIONS: A lack of association between occupationally related categories of magnetic field exposure and male subfertility, as evaluated by morphology, motility, and concentration, has been demonstrated. These findings do not substantiate theories of deleterious effects to male reproductive health from magnetic fields.
Adult↗
Exposure to electromagnetic fields during pregnancy with emphasis on electrically heated beds: association with birthweight and intrauterine growth retardation.
Several animal and human studies indicate that fetal growth may be retarded following exposure to electromagnetic fields (EMF). We conducted a prospective study (N = 2,967) to evaluate the relation of birthweight and fetal growth retardation with use of electrically heated beds (electric blankets and heated water beds) during pregnancy. A "nested" study design allowed monitoring of exposure at different stages of pregnancy using both direct and indirect methods. We assessed EMF exposure using personal monitors, home measurement, video display terminal use, and wire code. Exposure to EMF during pregnancy, either at conception, at < or = 16 weeks, or in the third trimester, showed no important relation to risk of low birth-weight or fetal growth retardation. This result was the same whether we used subjective measures of exposure or direct measurement. Use of video display terminals at home or work, exposure to > or = 2.0-milligauss fields as measured by home or personal monitors, and home wire code were unrelated to the reproductive outcomes studied. A time-weighted analysis of electric bed use, which accounted for strength of EMF exposure and hours of use, also showed evidence of no meaningful increase in risk. None of the exposure measures showed a dose response relation to risk. We conclude that risk of low birth-weight and intrauterine growth retardation is not increased after electrically heated bed use during pregnancy.
Adult↗
Human exposure to magnetic fields: a comparative assessment of two dosimeters.
Two types of dosimeters for measuring human exposure to 60 Hz magnetic fields were compared. Fifty adults wore the single-axis, wrist model AMEX (average magnetic field exposure system) and the triple axis, hip-pocket or pouch model AMEX-3D meters for 2 days. Ninety-six percent of the tests were accomplished without apparent dosimeter failure. The average root mean square magnetic flux density measurements with the AMEX-3D (mean = 0.10 microT, S.D. = 0.07, range = 0.03-0.31) were significantly higher than with the AMEX meter (mean = 0.07 microT, S.D. 0.05, range = 0.02-0.27 microT) (t test, P < 0.01). There was substantial correlation between the AMEX and the AMEX-3D measurements (Pearson's correlation coefficient = 0.65, P < 0.01) but poor concordance (Intraclass correlation coefficient = -0.25). These results suggest that there is a wide variation in exposure to extremely low frequency magnetic fields in the population. Magnetic field measurements with the AMEX-3D are nearly always higher than with the AMEX dosimeters. Caution is advised when comparing magnetic field measurements made with different types of dosimeters.
Adult↗
Clinically useful measures of effect in binary analyses of randomized trials.
The results of a randomized clinical trial can be reported using relative and/or absolute estimators of treatment effect. These various measures convey different information, and the choice can influence the physician's appreciation of the size of treatment effect and, subsequently, treatment decisions. We compare the estimators with respect to the clinically relevant information conveyed to physicians, and identify which clinical questions can and cannot be answered directly by each. We also identify opportunities for misinterpretation when one estimator is substituted for another, or when an estimator is mislabeled. Clinically important questions are addressed most directly by reporting both relative and absolute effects using relative risk and its complement, relative risk reduction, and risk difference and its reciprocal, number needed to treat. This is true of estimates of treatment effect derived from a single trial and also from meta-analysis of a group of trials. Because the control group's risk affects the numerical value of the odds ratio, the odds ratio cannot substitute for the risk ratio in conveying clinically important information to physicians. This is especially important when large treatment effects are shown in trials carried out in populations at high baseline risk.
Humans↗
The effect of methylprednisolone, naloxone, and spinal cord trauma on four liver enzymes: observations from NASCIS 2. National Acute Spinal Cord Injury Study.
In order to determine the impact of extremely large doses of methylprednisolone, naloxone, or of spinal cord injury itself, on liver enzymes, we examined the results of SGOT, SGPT, alkaline phosphatase and total bilirubin tests obtained 24 hours, 3 and 10 days after the end of the study drug infusions in spinal cord injured patients entered in the National Acute Spinal Cord Injury Study. The mean values of four liver enzymes, the amount of change between 24 hours and 3 and 10 days post infusion, and the proportion of liver enzyme levels considered to be abnormal did not appear to be affected by either drug protocol. Even when controlling for drug protocol and severity of injury (complete vs incomplete), variation in enzyme levels appeared to be the result of the spinal cord injury, not study drugs. Spinal cord injury is routinely treated with the NASCIS dose of methylprednisolone in many countries. It is reassuring to find no evidence of compromised liver function from this steroid protocol.
Alanine Transaminase↗
The effectiveness of surgery on the treatment of acute spinal cord injury and its relation to pharmacological treatment.
Using data from the Second National Acute Spinal Cord Injury Study (NASCIS II), the authors sought to characterize the role of surgery in the management of traumatic spinal cord injury and to examine the interaction between pharmacological treatment and surgery. Patients who did not undergo surgery had more severe spinal cord injuries initially than those who had surgery. However, no differences in neurological improvement at 1-year follow-up were found between those who underwent surgery and those who did not. The results suggest that either early surgery (< or = 25 hours after injury) or late surgery (> 200 hours) may be associated with increased neurological recovery, particularly motor function, but these results are equivocal. Surgery was not shown to interact with pharmacological treatments, indicating that the effect of drug treatment in NASCIS II, reported elsewhere, is not influenced by surgery. Other independent variables that best predicted improvement in motor score were age of 25 years or younger, incomplete injury, and lower baseline emergency department neurological scores. This study does not provide clinically relevant evidence concerning the efficacy of timing or the value of surgery in treating patients with spinal cord injuries. A randomized study on the timing and efficacy of spinal cord surgery is needed to obtain valid comparisons of the efficacy of surgical treatments.
Adolescent↗
Association of delayed conception with caffeine consumption.
This cross-sectional study investigated the relation between intake of caffeine-containing beverages and time to conception in a population of 1,909 married women in New Haven, Connecticut, between May 12, 1980 and March 12, 1982. Women were interviewed shortly after the first prenatal visit regarding the length of time taken to conceive the index pregnancy, consumption of caffeine during pregnancy, and other exposures occurring prior to and during pregnancy. In logistic regression analyses, intake of caffeine from coffee, tea, and caffeinated soft drinks was associated with an increased risk of a delay of conception of 1 year or more. Compared with no caffeine use, consumption of 1-150 mg/day of caffeine resulted in an odds ratio for delayed conception of 1.39 (95% confidence interval (CI) 0.90-2.13), consumption of 151-300 mg/day of caffeine was associated with an odds ratio of 1.88 (95% CI 1.13-3.11), and that of over 300 mg/day (the equivalent of approximately three cups of coffee) resulted in an odds ratio of 2.24 (95% CI 1.06-4.73), after controlling for last method of birth control used, parity, and number of cigarettes per day. When the risk of conception for each cycle was examined using a discrete analogue of the Cox proportional hazards model, women who reported drinking over 300 mg/day of caffeine had a 27% lower chance of conceiving for each cycle, and those who reported drinking less than 300 mg/day had a 10% reduction in per cycle conception rates compared with women who consumed no caffeine. Risks for coffee, tea, and colas were examined simultaneously in logistic models and were found not to improve the fit of a model that contained a variable for total caffeine intake from all sources.
Beverages↗
Caffeine use during pregnancy: how much is safe?
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Caffeine↗
Offering a celebrity experimental treatment.
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Drugs, Investigational↗