Search PubMed⌕ Search

Biomedical subjects

C V Ananth

Publications and source records attributed to C V Ananth.

At least 73 records · Page 4Linked to original sources
PubMed1997

Preeclampsia and preterm birth subtypes in Nova Scotia, 1986 to 1992.

The goal of this study was to evaluate the influence of preeclampsia on preterm delivery, examining whether the association varied among preterm birth subtypes defined by gestational age and precipitating events. A population-based, longitudinal study of the association between mild and severe preeclampsia and preterm birth subtypes was conducted among 59,851 women (resulting in a total of 78,086 pregnancies) delivering singleton live births in the province of Nova Scotia, Canada between 1986 and 1992, utilizing the Nova Scotia Atlee perinatal database. Very preterm (< 33 weeks' gestation) and moderately preterm (33-36 weeks' gestation) births were further classified as occurring due to (1) membrane rupture, (2) medical intervention, and (3) spontaneous onset of labor (before membrane rupture). Mild and severe preeclampsia occurred in 8.7 and 1.7% of pregnancies, respectively, after exclusions of multiple births. After adjustment for confounders by multivariable logistic regression based on the generalized estimating equations, severe preeclampsia was strongly associated with the risk of very preterm birth (RR = 80.8, 95% CI: 54.2-120.6), and moderately preterm birth (RR = 41.8, 95% CI: 34.0-51.4) due to medical intervention. A less dramatically elevated risk of very preterm (RR = 2.1, 95% CI: 1.1-4.0) and moderately preterm (RR = 2.2, 95% CI: 1.7-2.9) birth due to medical intervention was apparent among pregnancies complicated by mild preeclampsia. Very preterm births due to membrane rupture were too rare to examine, but moderately preterm births due to membrane rupture were not associated with preeclampsia. Preeclampsia was associated with an increase in the risk of moderately preterm births due to spontaneous labor (RR = 1.9, 95% CI: 1.3-2.8), but not very preterm births (RR = 1.0, 95% CI: 0.7-1.2). Substantial variability was observed in the association between preeclampsia and preterm birth in relation to the subtypes defined by gestational age and pathway, with strong associations between hypertension and medically induced preterm births. The results indicate a need to separate preterm births into subcategories to properly evaluate the association between preeclampsia and preterm births and interventions to reduce the adverse effects of preeclampsia.

Adult↗
PubMed1997

Influence of gestational age on the time from spontaneous rupture of the chorioamniotic membranes to the onset of labor.

Our goal was to assess the influence of gestational age on the timing of labor onset following spontaneous rupture of the chorioamniotic membranes. The 24,831 patients in the Nova Scotia Atlee perinatal database from 1986 to 1992 whose membranes ruptured prior to labor onset and had live births were analyzed using life-table analysis methods. The probability of labor onset at specified intervals following rupture was markedly lower when rupture occurred earlier in gestation. Pregnancies of < 33 weeks' gestation were less than half as likely as term pregnancies to proceed to labor within 24 hours and pregnancies of 33-36 weeks' gestation were 50-75% as likely as term pregnancies to progress within that period. These data provide clear evidence that the earlier in gestation the rupture occurs, the less likely labor onset is within specified time periods. This pattern supports the contention that preterm rupture of membranes is etiologically distinct from preterm labor.

Amnion↗
PubMed1997

Regression models for ordinal responses: a review of methods and applications.

BACKGROUND: Epidemiologists are often interested in estimating the risk of several related diseases as well as adverse outcomes, which have a natural ordering of severity or certainty. While most investigators choose to model several dichotomous outcomes (such as very low birthweight versus normal and moderately low birthweight versus normal), this approach does not fully utilize the available information. Several statistical models for ordinal responses have been proposed, but have been underutilized. In this paper, we describe statistical methods for modelling ordinal response data, and illustrate the fit of these models to a large database from a perinatal health programme. METHODS: Models considered here include (1) the cumulative logit model, (2) continuation-ratio model, (3) constrained and unconstrained partial proportional odds models, (4) adjacent-category logit model, (5) polytomous logistic model, and (6) stereotype logistic model. We illustrate and compare the fit of these models on a perinatal database, to study the impact of midline episiotomy procedure on perineal lacerations during labour and delivery. Finally, we provide a discussion on graphical methods for the assessment of model assumptions and model constraints, and conclude with a discussion on the choice of an ordinal model. The primary focus in this paper is the formulation of ordinal models, interpretation of model parameters, and their implications for epidemiological research. CONCLUSIONS: This paper presents a synthesized review of generalized linear regression models for analysing ordered responses. We recommend that the analyst performs (i) goodness-of-fit tests and an analysis of residuals, (ii) sensitivity analysis by fitting and comparing different models, and (iii) by graphically examining the model assumptions.

Epidemiologic Methods↗
PubMed1997

Influence of hypertensive disorders and cigarette smoking on placental abruption and uterine bleeding during pregnancy.

OBJECTIVE: To assess the influence of hypertensive disorders in pregnancy on the subsequent risk of placental abruption and uterine bleeding of unknown aetiology, and to examine the combined effects of hypertensive disorders and cigarette smoking during pregnancy on the risk of uteroplacental bleeding disorders. DESIGN: Retrospective cohort study. SETTING: Data for this study were derived from the Nova Scotia Atlee Perinatal database, Canada, comprising of women who were delivered in the province between 1980 and 1993. POPULATION: 120,666 pregnancies resulting in singleton births, of which 13,360 pregnancies were complicated by pre-eclampsia and/or chronic hypertension. MAIN OUTCOME MEASURES: Risks and relative risks of placental abruption and uterine bleeding of unknown aetiology in pregnancies complicated by chronic hypertension, mild and severe pre-eclampsia, and chronic hypertension with superimposed pre-eclampsia, each compared with normotensive patients. Adjusted relative risks were obtained through the fit of multivariable logistic regression models based on the method of generalised estimating equations. RESULTS: Chronically hypertensive women had no increased risk of abruption (RR 1.4; 95% CI 0.5-3.6), while women whose pregnancies were complicated by severe pre-eclampsia (RR 3.8; 95% CI 2.1-6.9), and chronic hypertension with superimposed pre-eclampsia (RR 2.8; 95% CI 1.2-6.3) showed strong associations with placental abruption. However, none of the hypertensive disorders were associated with uterine bleeding of unknown aetiology. The association between placental abruption and hypertensive disorders varied by parity. Parous women with chronic hypertension and superimposed pre-eclampsia were at greater risk of placental abruption (aRR 3.8; 95% CI 1.9-7.8) than nulliparous women with chronic hypertension and superimposed pre-eclampsia (aRR 1.6; 95% CI 0.5-4.9). The joint effects of smoking and hypertension had a greater effect on the risk of placental abruption than would have been expected based on their individual effects. CONCLUSIONS: The pattern of association between placental abruption and hypertension varied in relation to the specific type of hypertensive disorder. However, uterine bleeding of unknown aetiology was not associated with hypertension. Findings from this study suggest that placental abruption and uterine bleeding of unknown origin are aetiologically distinct obstetric complications with respect to hypertensive disorders during pregnancy.

Abruptio Placentae↗
PubMed1997

Epidemiology of antepartum fetal testing.

Advances in perinatal and neonatal health care over the past few decades have resulted in a substantial reduction in perinatal mortality. Some of this improvement has been attributed to antepartum fetal surveillance techniques. The primary objective of antepartum fetal surveillance techniques is to avoid fetal deaths. An ideal secondary objective is to avoid neonatal complications related to intrauterine asphyxia. In this article, some of the difficulties in evaluating existing antepartum fetal surveillance techniques are highlighted. Some of the epidemiological methods for evaluating a screening test are reviewed and their importance discussed with reference to fetal testing procedures. Lastly, the possibility of considering indication-specific fetal testing to improve perinatal morbidity is examined.

Female↗
PubMed1996

Maternal cigarette smoking as a risk factor for placental abruption, placenta previa, and uterine bleeding in pregnancy.

The authors carried out an epidemiologic study to evaluate the role of maternal cigarette smoking as a potential risk factor for placental abruption, placenta previa, and uterine bleeding of unknown etiology in pregnancy. Data for this prospective cohort study were obtained from women seeking prenatal care at any of the two tertiary, seven regional, or 17 community hospitals in the province of Nova Scotia, Canada, between January 1, 1986, and December 31, 1993. A total of 87,184 pregnancies (among 61,667 women) were registered in the database. Women who smoked during pregnancy (33%) were compared with nonsmokers, and all women were followed until the termination of pregnancy. Placental abruption was indicated in 9.9 per 1,000 pregnancies, while placenta previa and uterine bleeding of unknown etiology were indicated in 3.6 and 58.9 per 1,000 pregnancies, respectively. Women who smoked had a twofold increase in the risk of abruption (relative risk = 2.05, 95% confidence interval (CI) 1.75-2.40) in comparison with nonsmokers, while the relative risk for placenta previa was 1.36 (95% CI 1.04-1.79). However, cigarette smoking was not found to be associated with uterine bleeding of unknown etiology (relative risk = 1.01, 95% CI 0.94-1.08). There was no evidence for an increased risk of uteroplacental bleeding disorders with increasing numbers of cigarettes smoked. All analyses were adjusted for potentially confounding factors through logistic regression models based on the method of generalized estimating equations. The study confirms a positive association between cigarette smoking and placental abruption and a weak association with placenta previa but not with other uterine bleeding. The distinct pattern of results for placental abruption, placenta previa, and uterine bleeding of unknown origin suggests that these three uteroplacental bleeding disorders do not have a common etiology in relation to cigarette smoking.

Abruptio Placentae↗
PubMed1996

Assessment of pelvic floor function: a series of simple tests in nulliparous women.

The aim of the study was to assess normal ranges, variations, test-retest reliability and correlations between tests for a battery of simple, minimally invasive tests of pelvic floor function in nulliparous asymptomatic women. Women were recruited by advertisement and underwent dipstick urinalysis, simple cystometrics, provocative tests for incontinence, Q-tip test and surface electromyography with acrylic plug electrodes. Subjects were retested at a later date. Nineteen subjects underwent initial testing and 12 were retested. A wide range of normal values was obtained. Cystometric measures of first and strong urge to void the maximum bladder capacity, Q-tip test and rectal perineometry had significant correlations between the two visits. There were no significant between-test correlation coefficients. It was concluded that the simple tests used demonstrate a mixed ability to follow pelvic floor function longitudinally.

Adolescent↗
PubMed1996

Placental abruption and its association with hypertension and prolonged rupture of membranes: a methodologic review and meta-analysis.

OBJECTIVE: To conduct a meta-analysis of published studies on placental abruption to examine its incidence, recurrence, and association with hypertensive disorders (chronic hypertension and preeclampsia) and prolonged rupture of membranes (PROM) in pregnancy. DATA SOURCES: We reviewed studies on placental abruption published since 1950, based on a comprehensive literature search using MEDLINE, and by identifying studies cited in the references of published reports. METHODS OF STUDY SELECTION: We identified 54 studies, excluding case reports on placental abruption and studies relating to placenta previa and vaginal bleeding of unknown origin. We also restricted the search to articles published in English. TABULATION, INTEGRATION, AND RESULTS: Studies chosen for the meta-analysis were categorized based on their study design (case-control or cohort), where they were conducted (United States or other countries), source of the data (vital records versus other sources), and magnitude of risk (risk of abruption greater or less than 1.0%). We used both fixed- and random-effects analysis to identify sources of heterogeneity in results among studies. There were striking differences in the incidence of placental abruption between cohort (0.69%) and case-control (0.35%) studies. United States-based studies found a somewhat higher incidence both for cohort (0.81%) and case-control (0.37%) studies compared with studies conducted outside the U.S. (0.60% and 0.26%, respectively). Abruption was more than ten times more common in pregnancies preceded by a pregnancy with abruption. Chronically hypertensive patients were more than three times as likely to develop placental abruption (odds ratio [OR] 3.13, 95% confidence interval [CI] 2.04-4.80) as normotensive patients. The OR for placental abruption was 1.73 (95% CI 1.47-2.04) for patients with preeclampsia. Similarly, women with pregnancies complicated by PROM were more than three times as likely to develop placental abruption (OR 3.05, 95% CI 2.16-4.32). United States-based studies, case-control studies, and studies with an incidence of abruption greater than 1% demonstrated stronger associations between abruption and hypertension and PROM. CONCLUSION: Risk of abruption is strongly associated with chronic hypertension, PROM, and especially abruption in a prior pregnancy, and somewhat more modestly with preeclampsia. The criteria for the diagnosis of placental abruption, hypertensive disorders, and PROM may have introduced variability among the results of these studies. More standardized definitions of these pregnancy complications would improve the comparability of the study results.

Abruptio Placentae↗
PubMed1996

Effect of maternal age and parity on the risk of uteroplacental bleeding disorders in pregnancy.

OBJECTIVE: To examine the risk of placental abruption, placenta previa, and uterine bleeding of unknown etiology in relation to advanced maternal age and parity in a large, population-based study. METHODS: Data for this study were derived from the Nova Scotia Atlee perinatal provincial data base, Canada, an ongoing project on human reproduction. Women who delivered between 1980 and 1993 (n = 123,941) in the province of Nova Scotia were included in the study, with the exception of pregnancies resulting in multiple births (n = 2859) and those missing data on maternal age or parity (n = 14). Multivariable logistic regression models based on the method of generalized estimating equations were used to generate odds ratios after adjustment for multiple confounders. RESULTS: The frequency of abruption was increased slightly among younger women (relative risk [RR] 1.3, 95% confidence interval [CI] 1.0-1.7), compared with women ages 25-29 years, but there was no increase with advancing maternal age. In contrast, the risk of placenta previa increased dramatically with advancing maternal age, with women older than 40 years having a nearly ninefold greater risk than women under the age of 20, after adjustment for potential confounders, including parity. Uterine bleeding of unknown etiology was not associated with advanced maternal age, except for a slight increase among women over 40 (RR 1.3, 95% CI 1.0-1.6). The risk of placenta previa and placental abruption was increased with higher parity among younger women only, but uterine bleeding of unknown etiology was more weakly associated with higher parity. In addition, an analysis of the joint effects of age and parity on placental abruption indicated a strong parity effect for women under 30 years, whereas the risk of placenta previa increased with increasing parity up to age 35 years. Uterine bleeding of unknown etiology also indicated a parity effect that was restricted to women under 25 years. CONCLUSION: Multiparity is associated with the risk of placenta previa and, to a lesser extent, placental abruption, but not with other uterine bleeding. Increasing maternal age is associated independently with the risk of placenta previa, but not with either of the other two conditions. Finally, the increased risks of uteroplacental bleeding disorders with advanced parity among the younger women (ie, 20-25 years, parity 3+) may reflect effects of close pregnancy spacing, or confounding by unmeasured factors that characterize women who have many pregnancies at a relatively young age. Overall, the findings suggest that the three uteroplacental bleeding disorders do not share a common etiology in relation to maternal age and parity, and that placenta previa is linked to aging of the uterus and the effects of repeated pregnancies.

Abruptio Placentae↗
PubMed1996

Effects of maternal smoking on amniotic fluid volume and fetal urine output.

The purpose of this study was to assess the effects of maternal smoking on amniotic fluid volume and fetal urine output. Seventeen women (10 smokers and 7 non-smokers) were serially assessed through pregnancy. Smoking status was determined by self-report and carbon monoxide manometry. Amniotic fluid volume was assessed by sonographically measuring the maximum vertical pocket, the amniotic fluid index, and the two dimensions of the largest pockets. The coronal area formula was used to calculate bladder volume at 5-minute intervals for 20 minutes. Urine output was calculated from serial measurements of bladder volume. The mean gestational age of the first session was 26.8 (2.7) weeks, of the second session 32.4 (1.6) weeks, and of the last session 36.9 (2.1) weeks. In the univariate analysis there were no differences between smokers and non-smokers at any of the three visits for gestational age, fetal weight, maximum vertical pocket, amniotic fluid index, two-dimensional maximum pocket, and urine output. In the regression model, while controlling for gestational age, smoking status could not predict significant differences in any parameter. Maternal smoking does not appear to affect either amniotic fluid volume or fetal urine output.

Amniotic Fluid↗
PubMed1996

Utility of antibiotic therapy in preterm premature rupture of membranes: a meta-analysis.

The optimal management of preterm premature rupture of membranes (PROM) is controversial. Maternal risks must be weighed against fetal benefit when expectant management is considered. Despite concerns about maternal harm, protocols of expectant management seem to afford the best perinatal outcomes. Given that infection often is the common pathway for delivery in preterm PROM, recent reports have explored the utility of maternal administration of antibiotics. In this paper we will summarize these results using meta-analytic techniques and assess the impact of antibiotic therapy on maternal and perinatal outcomes.

Anti-Bacterial Agents↗
PubMed1995

Intrauterine growth retardation as an endpoint in mutation epidemiology: an evaluation based on paternal age.

Czeizel recently suggested that intrauterine growth retardation might be of value as a phenotypic endpoint in mutation epidemiology. We hypothesized that if some fraction of small-for-gestational age (SGA) births are due to new germinal mutations, then an association with advanced paternal age should be present. We evaluated the relation between paternal age and SGA, low birthweight, and preterm births using a large sample of births (n = 254,892) from North Carolina. The analyses were restricted to births of mothers aged 20-34 years and adjusted for maternal age, race, education, marital status, gravidity, and smoking. No material increase in the risk of SGA, low birthweight, and preterm delivery was found for fathers in any age category. For example, odds ratios for SGA ranged from 0.87 (fathers aged 50 years or greater) to 1.13 (fathers aged 45-49 years). The results indicate no discernable relationship between SGA and related endpoints and the increase in increase of mutations that accompany advanced paternal age.

Adolescent↗
PubMed1995

Effect of hypertensive diseases in pregnancy on birthweight, gestational duration, and small-for-gestational-age births.

We measured the impact of hypertensive disorders in pregnancy (chronic hypertension, pregnancy-induced hypertension, and eclampsia) on birthweight, gestational duration, and small-for-gestational-age births. We employed a retrospective cohort design using North Carolina birth certificate data for the years 1988-1990, with the analyses based on nearly 300,000 pregnancies. Women noted to have eclampsia during pregnancy had a substantially greater risk of delivering very-low-birthweight infants (birthweight < or = 1,499 gm; risk difference (RD) = 6.7%) and moderately-low-birthweight infants (1,500-2,499 gm; RD = 14.6%), and very preterm (gestational age < 33 weeks; RD = 7.1%) and moderately preterm (33-36 weeks; RD = 9.3%) births, compared with women without hypertension. Corresponding risk differences for these outcomes were 1.9% and 5.1% for very low and moderately low birthweight, and 1.6% and 3.0% for very preterm and moderately preterm for women with chronic hypertension. Risk differences were of similar magnitude for women with pregnancy-induced hypertension for these outcomes. Hypertensive disorders in pregnancy were associated with small-for-gestational-age infants, with risk differences of 5.1%, 3.5%, and 9.2% for chronic hypertension, pregnancy-induced hypertension, and eclampsia, respectively. The patterns of risk were similar for preterm births due to spontaneous onset of labor and those due to other precipitating events. We observed similar patterns for black and white women. Control for confounders through multivariable logistic regression models did not alter the observed patterns. In spite of the limited data quality, we found that hypertensive disorders in pregnancy substantially increase the risk of low birthweight, preterm births, and small-for-gestational-age births.

Adult↗
PubMed1995

Hypertensive disorders of pregnancy and stillbirth in North Carolina, 1988 to 1991.

BACKGROUND: The objectives of this study were (i) to assess the effect of hypertensive disorders of pregnancy on the risk of stillbirth, and (ii) to characterize the relationship between hypertension and stillbirth separately by gravidity, race, 'explained' versus 'unexplained' causes of stillbirth, and antepartum versus intrapartum stillbirths. METHODS: The study was based on a retrospective cohort of approximately 400,000 pregnancies identified through the birth and fetal death certificates in North Carolina, USA, between 1988 and 1991. Multivariable polytomous logistic regression was used to generate odds ratios comparing stillbirth risk in hypertensive compared to non-hypertensive mothers, adjusted for potential confounders. RESULTS: The risk of chronic hypertension was 7.6 per 1000 pregnancies, while pregnancy-induced hypertension (PIH) and eclampsia were reported in 36.6 and 6.0 per 1000 pregnancies, respectively. Pregnancies among chronic hypertensives were more likely to result in losses after 28 weeks gestation (RR = 3.29, 95% CI: 2.43-4.43), while the risk ratio was 2.16 (95% CI: 1.45-3.22) for losses prior to 28 weeks' gestation. Pregnancies to patients with PIH were at 1.42 (95% CI: 1.15-1.79) times greater risk of terminating in late stillbirth, while the risk ratio for eclampsia was 2.23 (95% CI: 1.51-3.30). The risk ratio for 'explained' antepartum stillbirth was higher than intrapartum stillbirth for all of the hypertensive diseases. CONCLUSIONS: Hypertensive disorders were found to have a strong adverse impact on stillbirth suggesting that early diagnosis of hypertension during pregnancy and adequate medical intervention may help reduce the risk of stillbirth.

Chronic Disease↗
PubMed1994

Breast cancer mortality among female electrical workers in the United States.

BACKGROUND: Previous epidemiologic studies have suggested that exposure to electric or magnetic fields in occupational and residential environments may cause cancer. Recent experimental findings provide some support for the hypothesis that exposure to extremely low-frequency electromagnetic fields reduces the pineal gland's nocturnal production of the hormone melatonin, thereby increasing susceptibility to sex hormone-related cancers such as breast cancer. PURPOSE: Our purpose was to assess the evidence that cancer of the female breast might be associated with exposure to extremely low-frequency electromagnetic fields. METHODS: Records of women who had breast cancer as the underlying cause of their death (ICD-9 174) and control subjects (four per case) were selected from computer files of U.S. mortality data for the years 1985-1989. Women 20 years and older at the time of their death were eligible for inclusion if they were residents of and died in one of the 24 states that provided death certification records with occupation and industry codes to the National Center for Health Statistics for at least 1 year during the study interval. Data from death certificates were used to classify the case and control subjects with regard to potential occupational exposure to electric and magnetic fields. Control subjects were a random sample of women who died of any other underlying cause, excluding leukemia and brain cancer. RESULTS: The data analysis contrasted 68 women with breast cancer and 199 controls, all with electrical occupations, with 27,814 women with breast cancer and 110,750 controls, all of whom had other occupations. Electrical workers had excess mortality from breast cancer relative to other employed women [odds ratio (OR) = 1.38; 95% confidence interval (CI) = 1.04-1.82]). Adjusted ORs for specific electrical occupations were 1.73 (95% CI = 0.92-3.25) for electrical engineers, 1.28 (95% CI = 0.79-2.07) for electrical technicians, and 2.17 (95% CI = 1.17-4.02) for telephone installers, repairers, and line workers. There was no excess of breast cancer, however, in seven other occupations held more frequently by women and also involving potentially elevated electrical exposures, including telephone operators, data keyers, and computer operators and programmers. CONCLUSIONS: In light of the limitations inherent in death certification data and the design of this study, any conclusions regarding the hypothesis that exposure to extremely low-frequency electromagnetic fields causes breast cancer among women must be limited. Nevertheless, our findings are broadly consistent with that hypothesis and encourage further investigation with improvements in study design and data quality.

Adult↗
PubMed1994

Residential magnetic fields, wire codes, and pregnancy outcome.

The relationship of measured residential magnetic fields and wire codes to pregnancy outcome was examined in data collected for a study of childhood cancer in Denver. Pregnancies in homes with measured fields above 0.2 microT or high wire codes were not more likely to end in miscarriage, low birth weight, or preterm delivery. Lack of data on potential confounders and small numbers of cases limit the study's conclusions.

Abortion, Spontaneous↗
PubMed1994

Vaginal bleeding and adverse reproductive outcomes: a meta-analysis.

The objective of this paper is to characterise and quantify the association between vaginal bleeding and pregnancy outcome. A meta-analysis was performed in order to quantify the risk of adverse reproductive outcome by combining evidence from all previous studies of vaginal bleeding. The reproductive endpoints considered were low birthweight, preterm birth, stillbirth, perinatal death and congenital malformation. The meta-analysis confirms an association of vaginal bleeding with adverse pregnancy outcomes, but identified discrepancies in the reported risks of vaginal bleeding and magnitudes of association between bleeding and adverse reproductive outcomes, observed across studies. These discrepancies may be attributed to inconsistent definitions of the timing and severity of vaginal bleeding. The implications of such inconsistencies are discussed, suggesting a need for more standardised definitions of vaginal bleeding and reproductive endpoints in future studies.

Abortion, Threatened↗