Biomedical subjects

Anna Maria Siega-Riz

Publications and source records attributed to Anna Maria Siega-Riz.

At least 19 recordsLinked to original sources

PubMed2006

The relationship between pregnancy weight gain and glucose tolerance status among black and white women in central North Carolina.

OBJECTIVE: The objective of the study was to examine weight and its relationship to glucose intolerance during pregnancy. STUDY DESIGN: Women were classified into mutually exclusive glucose tolerance groups; impaired glucose tolerance of pregnancy defined as 1 high value on the oral glucose tolerance test, gestational diabetes mellitus as 2 high values, and normal glucose tolerance as a normal value on the universal screen test. Logistic regression was used to examine the relationship between prepregnancy body mass index and weight gain, and glucose tolerance status and predicted probabilities were calculated. RESULTS: Weight gain ratio (observed/expected) was significantly higher for women with gestational diabetes mellitus, compared with women with normal glucose tolerance. The likelihood of developing gestational diabetes mellitus was significantly increased by both prepregnancy overweight (odds ratio 2.2, 95% confidence interval 1.1-4.3) and obese status (odds ratio 3.7, 95% confidence interval 2.2-6.3) but only marginally by weight gain ratio. In contrast, the likelihood of developing impaired glucose tolerance was increased by weight gain ratio for women who started pregnancy overweight. CONCLUSION: Prepregnancy weight was strongly associated with gestational diabetes mellitus, whereas weight gain during pregnancy was associated with impaired glucose tolerance only among overweight women.

Adult↗

PubMed2006

Fat intake and the risk of gastroschisis.

BACKGROUND: Young age has been associated with an increased risk of gastroschisis. It has been suggested that the pathogenesis of gastroschisis may be related to vascular disruption. Nutrients that may be associated with vasoconstriction include dietary fat and its subtypes. The objective of this study was to examine the association between dietary fats and gastroschisis and whether maternal age modified this association. METHODS: Data came from the National Birth Defects Prevention Study (NBDPS), which included 304 isolated gastroschisis cases and 3313 controls. Dietary intake in the year prior to conception was ascertained using a food frequency questionnaire, and included total, saturated, monosaturated, and polyunsaturated fat and cholesterol. Unconditional logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for confounders. Age and smoking were tested as effect modifiers. RESULTS: Higher mean intakes of total energy, total fat, and cholesterol as well as the subtypes of fats were found for gastroschisis cases compared to controls. Cases were more likely to be in the middle (adjusted OR [AOR], 1.3; 95% CI, 0.9-1.9) and highest (AOR, 1.2; 95% CI, 0.8-1.7) tertile of total fat intake compared to controls. This pattern was also true for saturated fat intake. No association was found for mono or polyunsaturated fat. Cases were less likely to be in the middle (AOR, 0.6; 95% CI, 0.4-0.9) and highest (AOR, 0.8; 95% CI, 0.6-1.2) tertiles for cholesterol. There was no evidence of effect modification. CONCLUSIONS: A possible weak effect of increased risk of gastroschisis associated with higher intakes of total fat or saturated fat was found in the NBDPS; however, this did not help to explain why younger aged women are at greater risk of having an infant with this type of birth defect.

Adolescent↗

PubMed2006

The effects of prophylactic iron given in prenatal supplements on iron status and birth outcomes: a randomized controlled trial.

OBJECTIVE: The hypothesis that daily use of a prenatal supplement with iron from enrollment to third trimester to initially iron-replete, nonanemic pregnant women would reduce third-trimester anemia and improve birth outcomes was tested. STUDY DESIGN: Eight hundred sixty-seven women in Raleigh, North Carolina, who were at < 20 weeks of gestation were enrolled; 429 of these women had hemoglobin levels of > or = 110 g/L and ferritin levels of > or = 40 microg/L and were assigned randomly to receive prenatal supplements with 30 mg of iron as ferrous sulfate (n = 218 women) or 0 mg of iron (n = 211 women) until 26 to 29 weeks of gestation. Intent-to-treat analysis was used for the outcomes of third-trimester iron status, birth weight, preterm birth, and small-for-gestational age. RESULTS: Mean birth weight was higher by 108 g (P = .03), and the incidence of preterm delivery was lower (8% vs 14%; P = .05) in the 30-mg group compared with the control group, respectively. Iron supplementation did not affect the prevalence of small-for-gestational age infants or third-trimester iron status. CONCLUSION: Prophylactic iron supplementation that is begun early in pregnancy among low income women in the United States may have benefits beyond the reduction of iron deficiency anemia during pregnancy.

Adolescent↗

PubMed2006

Polymorphisms in folate metabolizing genes and risk for spontaneous preterm and small-for-gestational age birth.

OBJECTIVE: Variants in the folate metabolism pathway affect the accumulation of homocysteine are modified by nutrient levels and have been linked to adverse birth outcomes. STUDY DESIGN: We examined the relationship among MTHFR(677), MTHFR(1298), MTR(2756), MTRR(66), and SHMT1(1420), dietary folate intake, and preterm and small-for-gestational-age (SGA) birth in a nested case-control study of black and white women. RESULTS: White carriers of SHMT1(1420)T or MTRR(66)A had an increased risk of spontaneous preterm birth (odds ratio [OR] = 1.9, 95% CI 1.1-3.1; OR = 2.0, 95% CI 1.1-3.6 respectively). In black women, there appeared to be an interaction between dietary folate intake and the SHMT1(1420)T variant allele, such that only carriers who also were in the lowest quartile of dietary folate intake had higher risk of spontaneous preterm birth (OR = 2.6, 95% CI 0.8-8.0) and SGA (OR = 2.9, 95% CI 0.9-8.9). CONCLUSION: Our results suggest the possibility of a direct or indirect role for the SHMT1(1420)T variant in spontaneous preterm or SGA births.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗

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

Psychosocial factors and socioeconomic indicators are associated with household food insecurity among pregnant women.

Household food insecurity has been associated with several negative health outcomes, yet little is known about the prevalence and correlates of household food insecurity during pregnancy. This study was conducted as part of the Pregnancy, Infection, and Nutrition prospective cohort study to identify risk factors of preterm birth. The USDA 18-item scale was used to assess the prevalence of food insecurity among pregnant women with incomes <or= 400% of poverty. Descriptive statistics and logistic regression were used to identify socioeconomic, demographic, and psychosocial predictors of household food insecurity. Among 606 pregnant women, 75% were from fully food-secure, 15% from marginally food-secure, and 10% from food-insecure households. Women from marginally food-secure and food-insecure households had significantly less income, less education, and were older than women from fully food-secure households. In bivariate analysis, all psychosocial factors were significantly associated with household food insecurity and showed a dose-response relation with increasing food insecurity. Socioeconomic and demographic predictors for household food insecurity were income, black race, and age. After controlling for socioeconomic and demographic variables, psychosocial indicators of perceived stress, trait anxiety, and depressive symptoms, and a locus of control attributed to chance were positively associated with any household food insecurity. Conversely, self-esteem and mastery were inversely associated with any household food insecurity. Psychosocial factors as well as socioeconomic and demographic indicators are associated with household food insecurity among pregnant women; however, the direction of causation between psychosocial indicators and food insecurity cannot be determined in these data.

Adolescent↗

PubMed2006

Correction for errors in measuring adherence to prenatal multivitamin/mineral supplement use among low-income women.

Adherence to prenatal multivitamin/mineral supplement use is often measured by self-reports or pill counts. Although both measures were shown to overestimate adherence, measurement error is rarely considered. In this study, we examined measurement error in adherence to prenatal supplement use among pregnant women and demonstrated a calibration method to adjust for error. In a validation subsample (n=51) from a larger clinical study of supplementation, adherence was assessed by self-reports, pill counts, and a Medication Event Monitoring System (MEMS) bottle cap that recorded the date and time of each opening of the pill bottle. Mean adherence in the validation sample as measured by the MEMS (the gold standard) was 68%; thus, adherence measured by self-report (77%) and pill count (84%) reflected overestimation. The Pearson correlation coefficients of self-reports and pill counts to MEMS were 0.35 and 0.62, respectively. When adherence was defined as taking >or=75% of the pills prescribed, sensitivity and specificity were greater for pill counts (93 and 52%, respectively) than for self-reports (88 and 44%). The regression coefficient for pill count adherence from a linear regression on MEMS adherence was applied to pill counts from a larger sample (n=244). The adjustment significantly lowered the estimate of adherence from 74 to 64% (P<0.001) in this larger sample. In conclusion, our data show that both self-reports and pill counts overestimate adherence and that linear regression in comparison to an external standard such as MEMS can be used to correct for measurement error in adherence.

Adolescent↗

PubMed2006

Methodological challenges in studying labour progression in contemporary practice.

In the 1950s, Emanuel Friedman described the first comprehensive method of evaluating labour in clinical practice. In this landmark work, Friedman described the relationship between the duration of labour and cervical dilation as a sigmoid curve and outlined a tool for following labour progression and for identifying abnormal labour. His definitions of labour protraction and arrest continue to be applied in contemporary obstetric practice, although there have been considerable changes since in the clinical management of labour and delivery. This paper provides an overview of Friedman's work, addresses various methodological challenges in studying labour progression, and describes the utility of more advanced statistical methods for studying labour progression, such as survival analysis, compared with other approaches. Additional research that utilises and refines such methods will provide greater insight into labour progression and may assist in updating the diagnostic criteria for labour protraction and arrest disorders in contemporary obstetric practice. Moreover, such detailed information could have important clinical implications towards reducing the rate of primary caesarean delivery in the United States.

Cesarean Section↗

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↗

PubMed2005

Genetic variation in the sodium-dependent vitamin C transporters, SLC23A1, and SLC23A2 and risk for preterm delivery.

Vitamin C has been the focus of epidemiologic investigation in preterm delivery (<37 weeks' gestation), which is a leading cause of neonatal mortality and birth-related morbidity. There are two sodium-dependent membrane transporters encoded by SLC23A1 and SLC23A2, which have key roles in human vitamin C metabolism and which control dietary uptake, reabsorption, and tissue distribution of vitamin C. Using maternal DNA, the authors evaluated common single-nucleotide polymorphisms (SNPs) in SLC23A1 and SLC23A2 in a nested case-control analysis of the Pregnancy, Infection, and Nutrition Study (1995-2000) cohort. Of the associations observed for both haplotypes in SLC23A1 and individual SNPs in SLC23A2, the most robust finding is with an intron 2 variant in SLC23A2. Heterozygotes and homozygotes for this variant had a 1.7-fold (95% confidence interval: 0.9, 3.3) and a 2.7-fold (95% confidence interval: 1.2, 6.3) elevation in the risk of spontaneous preterm birth, respectively. Semi-Bayesian hierarchical regression analysis, which simultaneously adjusted for multiple SNPs within the same gene, gave comparable results. The authors' findings link genetic variants in the vitamin C transporters to spontaneous preterm birth, which may explain previous dietary associations. If the findings from this study are confirmed, they may serve as the foundation for genetic risk assessment of nutritional pathways in preterm birth.

Adult↗

PubMed2005

Maternal pre-pregnancy overweight and obesity and the risk of cesarean delivery in nulliparous women.

PURPOSE: To examine the effect of maternal pre-pregnancy overweight and obesity on the risk of term cesarean delivery in nulliparous women. METHODS: The authors examined data from 641 nulliparous women with a term pregnancy that participated in the Pregnancy, Infection, and Nutrition Study from 1995 to 2002. Unadjusted and adjusted risk ratios and 95% confidence intervals (CI) were computed for normal weight (BMI 19.8-26.0 kg/m(2)), overweight (BMI 26.1-29.0 kg/m(2)), and obese (BMI>29.0 kg/m(2)) women. Normal weight women served as the referent population. RESULTS: The unadjusted risk ratio for cesarean delivery for overweight women compared with normal weight women was 1.4 (95% CI, 0.97, 2.1) and for obese women compared with normal weight women was 1.4 (95% CI, 1.03, 2.0). After controlling for maternal height, education, weight gain during pregnancy, and labor induction, the adjusted risk ratio for cesarean delivery among overweight women was 1.2 (95% CI, 0.8, 1.8). The adjusted risk ratio for obese women was 1.5 (95% CI, 1.05, 2.0). CONCLUSION: Our analysis confirms that there is a moderate association between maternal pre-pregnancy obesity and an unplanned term cesarean delivery. However, the risk is not as large as previously reported.

Adolescent↗

PubMed2005

Dietary fiber intake by American preschoolers is associated with more nutrient-dense diets.

OBJECTIVE: To illustrate and discuss implications of the new Diet Reference Intakes for fiber, relative to a nationally representative sample of American preschoolers. DESIGN: Cross-sectional study using the Continuing Survey of Food Intake by Individuals 1994-1996, 1998. SUBJECTS: Children 2 through 5 years of age who provided 2 days of dietary intake data (N=5,437) were grouped and 2- and 3-year-olds (n=2,805) were compared with 4- and 5-year-olds. STATISTICAL ANALYSIS: Descriptive analysis (mean+/-standard error) was used to describe the sample and to rank children into quartiles of dietary fiber intake. Nonparametric test for trend was employed to examine significance level of observed changes in nutrient and food group consumption by increasing fiber intake quartiles. RESULTS: Main contributors to dietary fiber intakes were low-fiber fruits and legumes. Children in the high-fiber quartile consumed diets with higher nutrient and fiber density and increased number of servings of Food Guide Pyramid food groups. Many children in this population did not meet intake recommendations of "age plus five," and most lacked the 14 g/1,000 kcal of energy consumed, even after considering a hypothetical estimated average of 5 g/day functional fiber. CONCLUSIONS: Children would benefit from diets higher in fiber. Newly recommended intake levels are only met by a few and further studies need to be conducted to provide evidence for a recommended intake level of fiber in children. Average consumption of functional fiber in children has to be examined.

Age Distribution↗

PubMed2005

Adverse effect of high added sugar consumption on dietary intake in American preschoolers.

OBJECTIVES: To assess the effect of Dietary Reference Intakes (DRI)-recommended added sugar intake levels on nutrient and food group consumption by preschoolers. STUDY DESIGN: This was a cross-sectional study of 2- to 5-year-olds in the United States Department of Agriculture Continuing Survey of Food Intake by Individuals (CSFII), 1994 to 1996, and 1998 (n = 5437). Main food sources of added sugar were established. For five categories (< or =10% energy from added sugar, 11% to 15%, 16% to 20%, 21% to 25%, and >25%), mean nutrient and food group consumption and proportion of children not meeting the DRI were ascertained. The nonparametric test for trend indicated significance of changes. Analysis was stratified by age (2- to 3-year-olds versus 4- to 5-year-olds), and survey design corrected to maintain the nationally representative character of the data. RESULTS: The majority of children consumed less than 25% of energy from added sugar; the main sources were fruit and or soft drinks and desserts. Increasing added sugar consumption was paralleled by decreasing nutrient and food group intakes and increasing proportions of children with intakes below the DRI. Calcium intake was insufficient in large proportions of children consuming 16% or more from added sugar. CONCLUSIONS: In preschoolers, the new DRI for added sugar are reason for concern. Further research is needed to investigate the effects of the DRI on diet quality, body weight, and health status in young children.

Child Nutritional Physiological Phenomena↗

PubMed2005

Pill count adherence to prenatal multivitamin/mineral supplement use among low-income women.

In the United States, the prevalence of third trimester anemia among low-income pregnant women is 29% and has not improved since the 1980s. Although low adherence has been linked to the ineffectiveness of iron supplementation programs, data regarding adherence to supplementation in low-income women are currently lacking. Hence this study was conducted to better understand the factors associated with adherence to the use of iron-containing prenatal multivitamin/mineral supplements among low-income pregnant women. Adherence to supplement use was assessed by pill counts among 244 pregnant women of 867 women who were initially randomized to receive 1 of 3 prenatal supplements. All women received care at a public prenatal clinic. Maternal characteristics associated with adherence were identified using predictive modeling. Women took 74% of supplements as prescribed. Adherence was higher among non-Hispanic white women than among non-Hispanic black women (79% vs. 72%, P </= 0.01). Interactions of ethnicity with age group, smoking status, and prior supplement use were significant. Multivariate regression analysis stratified by ethnicity revealed that among the white women education beyond high school, unmarried status, nulligravidity, and smoking were positively associated with adherence. In contrast, among the black women, supplement use 3 mo prior to current pregnancy and no loss of appetite were positively associated with adherence. Further research investigating the influence of cultural factors is necessary to better understand adherence to supplement use and the differences in adherence among ethnic groups.

Adolescent↗

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↗

PubMed2004

Multivitamin use and the risk of preterm birth.

Previous research suggests that multivitamin use before and during pregnancy can diminish diet-related deficiencies of certain micronutrients and potentially prevent preterm birth. To assess this association, the authors performed an analysis by using data from the Pregnancy, Infection, and Nutrition Study (n = 2,010). Women were recruited at 24-29 weeks of pregnancy from four prenatal care clinics in North Carolina from August 1995 to June 2000. For women who took multivitamins prior to pregnancy, compared with nonusers, the adjusted risk ratio was 0.50 (95% confidence interval: 0.20, 1.25) for delivering preterm (<37 weeks). In contrast, prenatal and periconceptional use, compared with nonuse, were not related to preterm birth, with adjusted risk ratios of 1.1. Preconceptional multivitamin use was inversely associated with both early (<35 weeks; adjusted odds ratio = 0.59, 95% confidence interval: 0.12, 2.76) and late (35-36 weeks; adjusted odds ratio = 0.40, 95% confidence interval: 0.12, 1.40) preterm birth; findings were based on only two and three exposed cases, respectively. These results suggest that, compared with nonusers, women who take multivitamin supplements prior to conception may have a reduced risk of preterm birth, but further studies are needed with a larger sample of preconceptional users.

Adult↗

PubMed2004

Marginal structural models for analyzing causal effects of time-dependent treatments: an application in perinatal epidemiology.

Marginal structural models (MSMs) are causal models designed to adjust for time-dependent confounding in observational studies of time-varying treatments. MSMs are powerful tools for assessing causality with complicated, longitudinal data sets but have not been widely used by practitioners. The objective of this paper is to illustrate the fitting of an MSM for the causal effect of iron supplement use during pregnancy (time-varying treatment) on odds of anemia at delivery in the presence of time-dependent confounding. Data from pregnant women enrolled in the Iron Supplementation Study (Raleigh, North Carolina, 1997-1999) were used. The authors highlight complexities of MSMs and key issues epidemiologists should recognize before and while undertaking an analysis with these methods and show how such methods can be readily interpreted in existing software packages, including SAS and Stata. The authors emphasize that if a data set with rich information on confounders is available, MSMs can be used straightforwardly to make robust inferences about causal effects of time-dependent treatments/exposures in epidemiologic research.

Adult↗