Identical and Nonidentical Twins: Risk and Factors Involved in Development of Islet Autoimmunity and Type 1 Diabetes

OBJECTIVE

There are variable reports of risk of concordance for progression to islet autoantibodies and type 1 diabetes in identical twins after one twin is diagnosed. We examined development of positive autoantibodies and type 1 diabetes and the effects of genetic factors and common environment on autoantibody positivity in identical twins, nonidentical twins, and full siblings.

RESEARCH DESIGN AND METHODS

Subjects from the TrialNet Pathway to Prevention Study (N = 48,026) were screened from 2004 to 2015 for islet autoantibodies (GAD antibody [GADA], insulinoma-associated antigen 2 [IA-2A], and autoantibodies against insulin [IAA]). Of these subjects, 17,226 (157 identical twins, 283 nonidentical twins, and 16,786 full siblings) were followed for autoantibody positivity or type 1 diabetes for a median of 2.1 years.

RESULTS

At screening, identical twins were more likely to have positive GADA, IA-2A, and IAA than nonidentical twins or full siblings (all P < 0.0001). Younger age, male sex, and genetic factors were significant factors for expression of IA-2A, IAA, one or more positive autoantibodies, and two or more positive autoantibodies (all P ≤ 0.03). Initially autoantibody-positive identical twins had a 69% risk of diabetes by 3 years compared with 1.5% for initially autoantibody-negative identical twins. In nonidentical twins, type 1 diabetes risk by 3 years was 72% for initially multiple autoantibody-positive, 13% for single autoantibody-positive, and 0% for initially autoantibody-negative nonidentical twins. Full siblings had a 3-year type 1 diabetes risk of 47% for multiple autoantibody-positive, 12% for single autoantibody-positive, and 0.5% for initially autoantibody-negative subjects.

CONCLUSIONS

Risk of type 1 diabetes at 3 years is high for initially multiple and single autoantibody-positive identical twins and multiple autoantibody-positive nonidentical twins. Genetic predisposition, age, and male sex are significant risk factors for development of positive autoantibodies in twins.

The accuracy of self-reported pregnancy-related weight: a systematic review

Self-reported maternal weight is error-prone, and the context of pregnancy may impact error distributions. This systematic review summarizes error in self-reported weight across pregnancy and assesses implications for bias in associations between pregnancy-related weight and birth outcomes. We searched PubMed and Google Scholar through November 2015 for peer-reviewed articles reporting accuracy of self-reported, pregnancy-related weight at four time points: prepregnancy, delivery, over gestation and postpartum. Included studies compared maternal self-report to anthropometric measurement or medical report of weights. Sixty-two studies met inclusion criteria. We extracted data on magnitude of error and misclassification. We assessed impact of reporting error on bias in associations between pregnancy-related weight and birth outcomes. Women underreported prepregnancy (PPW: -2.94 to -0.29 kg) and delivery weight (DW: -1.28 to 0.07 kg), and over-reported gestational weight gain (GWG: 0.33 to 3 kg). Magnitude of error was small, ranged widely, and varied by prepregnancy weight class and race/ethnicity. Misclassification was moderate (PPW: 0-48.3%; DW: 39.0-49.0%; GWG: 16.7-59.1%), and overestimated some estimates of population prevalence. However, reporting error did not largely bias associations between pregnancy-related weight and birth outcomes. Although measured weight is preferable, self-report is a cost-effective and practical measurement approach. Future researchers should develop bias correction techniques for self-reported pregnancy-related weight.

Gestational weight gain in twin pregnancies and maternal and child health: a systematic review

Our objective was to systematically review the data interrogating the association between gestational weight gain (GWG) and maternal and child health among women with twin gestations. We identified 15 articles of twin gestations that studied GWG in relation to a maternal, perinatal or child health outcome and controlled for gestational age at delivery and prepregnancy body mass index. A positive association between GWG and fetal size was consistently found. Evidence on preterm birth and pregnancy complications was inconsistent. The existing studies suffer from serious methodological weaknesses, including not properly accounting for the strong correlation between gestational duration and GWG and not controlling for chorionicity. In addition, serious perinatal outcomes were not studied, and no research is available on the association between GWG and outcomes beyond birth. Our systematic review underscores that GWG in twin gestations is a neglected area of research. Rigorous studies are needed to inform future evidence-based guidelines.

Educational attainment and obesity: a systematic review

Although previous systematic reviews considered the relationship between socioeconomic status and obesity, almost 200 peer-reviewed articles have been published since the last review on that topic, and this paper focuses specifically on education, which has different implications. The authors systematically review the peer-reviewed literature from around the world considering the association between educational attainment and obesity. Databases from public health and medicine, education, psychology, economics, and other social sciences were searched, and articles published in English, French, Portuguese and Spanish were included. This paper includes 289 articles that report on 410 populations in 91 countries. The relationship between educational attainment and obesity was modified by both gender and the country's economic development level: an inverse association was more common in studies of higher-income countries and a positive association was more common in lower-income countries, with stronger social patterning among women. Relatively few studies reported on lower-income countries, controlled for a comprehensive set of potential confounding variables and/or attempted to assess causality through the use of quasi-experimental designs. Future research should address these gaps to understand if the relationship between educational attainment and obesity may be causal, thus supporting education policy as a tool for obesity prevention.

Excessive gestational weight gain over multiple pregnancies and the prevalence of obesity at age 40

Objective

While several studies have found an association between excessive gestational weight gain and obesity later in life, to the best of our knowledge, no studies have explored the role of gestational weight gain events across the life course.

Design and Methods

We describe how the prevalence of mid-life obesity (BMI≥30 at age 40 or 41) among women varies by life course patterns of gestational weight gain (using 2009 IOM guidelines) in the USA’s National Longitudinal Survey of Youth 1979 cohort.

Results

Among women who reported 1–3 births before age 40, the prevalence of mid-life obesity increased with a rising number of excessive gestational weight gain events: from none (23.4%, n=875), to one (37.6%, n=707), to two (46.8%, n=427), and to three (54.6%, n=108), p<0.00005 for trend. Obesity prevalence was similar for the same number of excessive gestational weight gain events, regardless of parity. No clear pattern emerged for the sequencing of excessive gestational weight gain event(s) and later obesity.

Conclusions

In our descriptive exploratory study, excessive gestational weight gain events appear to be associated with increased prevalence of obesity for parous women, suggesting the importance of preventive interventions regardless of timing of pregnancy-related weight changes over the life course.

Bacterial safety of flash-heated and unheated expressed breastmilk during storage

Heat-treated breastmilk is one infant-feeding option recommended by the WHO to reduce mother-to-child transmission of HIV in developing countries. Flash-heat, a simple pasteurization method that a mother could perform in her home, has been shown to inactivate cell-free HIV-1. Since heating may affect the naturally occurring antimicrobial properties found in breastmilk, storing heated breastmilk may present a safety issue in resource-poor settings due to lack of refrigeration and potential contamination. To address this, we investigated the ability of flash-heat to eliminate bacteria and to prevent growth over time compared with unheated breastmilk. We collected breastmilk samples from 38 HIV positive mothers in South Africa and aliquoted them to flash-heated and unheated controls. Samples were stored at room temperature for 0, 2, 6 and 8 h and then plated and incubated for 24 h at 37 degrees C in CO(2). We performed total colony counts and identified Escherichia coli, Staphylocuccus aureus and Group A and Group B streptococci. Unheated samples had a significantly higher number of samples positive for bacterial growth at each time point (p < 0.0001), as well as mean colony-forming units (CFU)/ml in those samples that were positive at each time point (p < 0.0001). In addition, unheated samples had a significantly higher rate of bacterial propagation over time than flash-heated samples when comparing log values of CFU/ml across 0-8 h (p < 0.005). No pathogenic growth was observed in the flash-heated samples, while the unheated samples showed growth of E. coli (n = 1) and S. aureus (n = 6). Our data suggest that storage of flash-heated breastmilk is safe at room temperature for up to 8 h.

Disparities in reported prenatal care advice from health care providers among women of Mexican origin in California

Poorer birth outcomes have been documented among U.S.-born women of Mexican descent when compared with Mexican immigrant women. Behavioral changes that are associated with acculturation may contribute to these deteriorating outcomes. Prenatal health promotion advice can alter prenatal risk behaviors. The growing diversity of the U.S. population during the 1990s heightens the importance of examining the cultural relevance of current health promotion practices. This study examines disparities in the reported receipt of health behavior advice during pregnancy among U.S.-born women of Mexican origin and Mexican immigrant women in California. Data for the analysis are from the 1994-95 California Pregnancy Risk Assessment Monitoring System. The study sample includes 1,423 women of Mexican descent. All participants had a live birth in California between January 1994 and December 1995. Women were interviewed about the prenatal counseling they received related to diet, smoking, and alcohol use. Logistic regression was used to analyze the likelihood of reporting advice after controlling for sociodemographic and health system characteristics. Immigrant women were more likely than the U.S.-born to report receipt of prenatal advice on smoking, alcohol, and diet (OR = 1.83, p < .05) despite evidence of the lower prevalence of related health risks among Mexican-born women. Culturally appropriate prenatal counseling would emphasize the maintenance of traditional protective behaviors among less acculturated foreign-born women, and the prevention or cessation of those risk behaviors among the more acculturated women.

Tolerance of high-dose (3,000 mg/day) coenzyme Q10 in ALS

An open-label dose-escalation trial was performed to assess the safety and tolerability of high doses of coenzyme Q10 (CoQ10) in ALS. CoQ10, a cofactor in mitochondrial electron transfer, may improve the mitochondrial dysfunction in ALS. In this study, CoQ10 was safe and well tolerated in 31 subjects treated with doses as high as 3,000 mg/day for 8 months.

Preterm birth among African American and white women: a multilevel analysis of socioeconomic characteristics and cigarette smoking

STUDY OBJECTIVE

Research shows that neighbourhood socioeconomic factors are associated with preterm delivery. This study examined whether cigarette smoking and individual socioeconomic factors modify the effects of neighbourhood factors on preterm delivery.

DESIGN

Case-control study.

SETTING

Moffit Hospital in San Francisco, California.

PARTICIPANTS

417 African American and 1244 white women, including all preterm and a random selection of term deliveries 1980-1990, excluding non-singleton pregnancies, congenital anomolies, induced deliveries, and women transported for special care. US census data from 1980 and 1990 were used to characterise the women's neighbourhoods, defined as census tracts.

RESULTS

Cigarette smoking increased the risk of preterm delivery among both African American (OR=1.77, 95% confidence intervals (CI) (1.12 to 2.79)) and white women (OR=1.25, 95% CI (1.01 to 1.55)). However, cigarette smoking did not attenuate or modify the association of neighbourhood factors with preterm delivery. Among African American women, having public insurance modified the relation between neighbourhood unemployment and preterm delivery; among women without public insurance, the risk of preterm delivery was low in areas with low unemployment and high in areas with high unemployment, while among women with public insurance the risk of preterm delivery was highest at low levels of neighbourhood unemployment.

CONCLUSIONS

Cigarette smoking was associated with preterm delivery, especially among African Americans. Adverse neighbourhood conditions had an influence on preterm delivery beyond that of cigarette smoking. The effects of some neighbourhood characteristics were different depending on individual socioeconomic status. Examining socioeconomic and behavioural/biological risk factors together may increase understanding of the complex causes of preterm delivery.

The relationship of neighborhood socioeconomic characteristics to birthweight among 5 ethnic groups in California

OBJECTIVES

This study sought to examine relationships between neighborhood socioeconomic characteristics and birthweight, accounting for individual socioeconomic characteristics, among 5 ethnic groups.

METHODS

Birth records were linked to census block-group data for 22 304 women delivering infants at 18 California hospitals during 1994-1995. Information on income and additional factors was obtained from a surveyed subset of 8457 women. Neighborhood levels of poverty, unemployment, and education were examined.

RESULTS

After adjustment for mothers' individual socioeconomic characteristics and other risk factors, less-favorable neighborhood socioeconomic characteristics were associated with lower birthweight among Blacks and Asians. No consistent relationship between neighborhood socioeconomic characteristics and birthweight was found among Whites, US-born Latinas, or foreign-born Latinas overall, but birthweight increased with less-favorable neighborhood socioeconomic characteristics among foreign-born Latinas in high-poverty or high-unemployment neighborhoods. These findings were not explained by measured behavioral or cultural factors.

CONCLUSIONS

In addition to individual socioeconomic characteristics, living in neighborhoods that are less socioeconomically advantaged may differentially influence birthweight, depending on women's ethnicity and nativity.

Body mass index in mid-life women: relative influence of menopause, hormone use, and ethnicity

OBJECTIVE

To assess the relative influence of menopausal status and hormone use on body mass index (BMI) among a multiethnic sample of mid-life women.

DESIGN

Cross-sectional telephone survey conducted at seven sites where each site targeted an ethnic minority group and Caucasians as part of Study of Women's Health Across the Nation (SWAN).

SUBJECTS

A total of 7181 Caucasians, 3949 African-Americans, 1660 Hispanics, 562 Chinese Americans, and 803 Japanese Americans between ages of 40 and 55 y residing in or near Boston, Chicago, Detroit, Los Angeles, Newark, NJ, Oakland, CA, and Pittsburgh, PA.

MEASUREMENTS

Self-reported BMI based on weight in kg divided by height in m(2) menopausal status, physical inactivity, postmenopausal hormone use, ethnicity, and age in years.

RESULTS

Compared to premenopausal women (covariate adjusted M=27.3), women reporting a surgical menopause (M=28.2) or being in the perimenopausal transition (M=27.7 for early and 27.9 for late perimenopause) had higher BMI. Women reporting a natural menopause (M=27.4) did not have a higher BMI than premenopausal women, after adjusting for chronological age and other covariates. Hormone use was associated with lower BMI (M=26.5 vs 27.3). A comparison of effect sizes showed that menopausal status (F=13.1), followed by chronological age (F=24.0), were the least powerful predictors of BMI, whereas the more powerful predictors were physical activity level (F=1377.1) and ethnicity (F=400.5).

CONCLUSIONS

The menopausal transition affects body mass index in mid-life, but the effect is small relative to other influences. Interventions to increase physical activity are highly recommended to prevent increases in adiposity common in mid-life.

Does the pattern of postpartum weight change differ according to pregravid body size?

OBJECTIVES

To examine differences in the pattern of weight changes during and after pregnancy among four pregravid body mass index (BMI) groups.

STUDY DESIGN

Prospective cohort study of women who had two consecutive births at the University of California, San Francisco (UCSF) between 1980 and 1990.

MEASUREMENTS

Maternal body weights were available before conception and delivery, and at 6 weeks postpartum for the first (index) pregnancy, and before conception for the second study pregnancy. Height and two pregravid weights were self-reported. Weights at delivery and 6 weeks postpartum were measured. Net delivery weight was defined as delivery weight minus infant birth weight. Three non-overlapping sequential weight changes were constructed: (1) net gestational gain (net delivery weight minus pregravid weight at the index pregnancy); (2) early net postpartum weight change (6-week postpartum weight minus net delivery weight); and (3) late postpartum weight change (pregravid weight at the second pregnancy minus 6-week postpartum weight).

SUBJECTS

A total of 985 healthy women (age 18-41 y) from four race/ethnicity groups (Asian, Hispanic, black and white) who had a singleton, full-term, live birth for the index pregnancy followed by a second consecutive birth.

RESULTS

Four race/ethnicity groups were combined (no interaction) to contrast average weight changes among pregravid BMI groups. Means adjusted for eight covariates (parity, race/ethnicity, education, mode of delivery, smoking, hypertension of pregnancy, age, height) and time intervals were not altered appreciably. Early net postpartum weight losses were similar for all pregravid BMI groups. Late (median of 2 y) postpartum weight losses were 4 kg higher in the low and average BMI groups compared with the highest BMI group. About half of the net gestational gain was lost by 6 weeks postpartum, and the percentage that was lost decreased over time.

CONCLUSIONS

This study suggests that early postpartum weight loss does not vary by maternal pregravid BMI group, but late postpartum weight change does. Serial weight measurements are needed in epidemiologic studies to differentiate retention of gestational gain from weight gain during the late postpartum period.

The relative importance of gestational gain and maternal characteristics associated with the risk of becoming overweight after pregnancy

OBJECTIVES

To assess the relationships between gestational gain, race/ethnicity, reproductive history, age, education and the risk of becoming overweight after pregnancy.

STUDY DESIGN

Prospective cohort study of adult women from four race/ethnicity groups who had two consecutive births between 1980 and 1990 at the University of California, San Francisco (UCSF).

MEASUREMENTS

Height and pregravid weights for each pregnancy were self-reported. Women were classified as overweight or not overweight according to the Institute of Medicine (IOM) criteria for pregnancy. Gestational gain was defined as the difference between the pregravid weight and the last weight before delivery of the first study pregnancy.

SUBJECTS

1300 healthy women aged 18-41 y who had a singleton, full-term, live birth (index or first study pregnancy) followed by a second birth. Self-reported pregravid weights and heights were used to calculate body mass index (BMI). Women with a pregravid BMI below 26.0 kg/m2 before the index pregnancy were classified as not overweight (n = 1128). Overweight status following the index pregnancy was based on pregravid BMI for the second pregnancy.

RESULTS

Seventy-two women (6.4%) became overweight following the index pregnancy. Statistically significant independent predictors of the risk of becoming overweight included: maternal age 24-30 vs above 30 y, high gestational gain, short interval from menarche to first ever birth ( < 8 y), and young age at menarche ( < 12 y). The risk of becoming overweight was increased 2.5-3 times for each of these risk factors. Whites were 4.5 times more likely to become overweight than Asians, but blacks and Hispanics did not appear to differ from whites. Parity, time interval, smoking habit, education, marital status and other factors were not associated with the risk of becoming overweight.

CONCLUSIONS

These findings suggest that young age at menarche, maternal age and short time from menarche to first ever birth may be as important as high gestational weight gain in determining the risk of becoming overweight after pregnancy.

Conversion of psoriasis patients from the conventional formulation of cyclosporin A to a new microemulsion formulation: a randomized, open, multicentre assessment of safety and tolerability

OBJECTIVE

To assess the safety, tolerability and efficacy of a new cyclosporin A (CyA) microemulsion formulation, Sandimmun Neoral (Neoral), in patients with severe psoriasis that was stable on CyA administered as Sandimmun (SIM).

METHODS

In this 24-week, open, randomized, prospective, multicentre trial, 28 patients continued on the same dosage of SIM, while 30 converted to Neoral at 2.5 mg/kg/day or a dosage equivalent to their pre-conversion SIM dosage. During the study, dosages could be adjusted to maintain efficacy, because of adverse events or after disease stabilization. The maximum permitted dosage for either formulation was 5.0 mg/kg/day. Primary efficacy criteria were change in Psoriasis Area and Severity Index (PASI) from baseline and time to relapse.

RESULTS

The dosage was increased to maintain efficacy in 22 patients (Neoral 13; SIM 9) and 20 dose reductions for safety were required (Neoral 14, SIM 6). In both groups, PASI scores remained stable throughout and relapses were primarily a result of dosage reduction after disease stabilization. No significant difference was found between groups in the proportion of patients remaining relapse-free. Adverse events were recorded in 20 patients receiving Neoral and 14 receiving SIM. Most drug-related events were of mild or moderate severity and reflected the known CyA side-effect profile. Dose titration guidelines ensured that mean blood pressure and serum creatinine concentrations remained stable in both groups.

CONCLUSIONS

If the guidelines for CyA use are followed and the Neoral dosage does not exceed 5 mg/kg/day, conversion of stable patients with severe psoriasis from SIM to Neoral should present no clinically relevant safety or tolerability problems and efficacy of treatment is maintained.

Defining preterm delivery--the epidemiology of clinical presentation

It is possible that preterm delivery is not a single entity but a cluster of conditions with different aetiologies that ultimately result in the delivery of an infant before 37 completed weeks of gestation. Whereas some researchers have reported aetiological heterogeneity, others have found no differences between subtypes or have disputed the desirability and utility of classifying preterm birth into subtypes. This study explores the relationship of maternal risk factors to type of preterm delivery in a cohort of over 7000 black and white women delivering singleton infants at the University of California, San Francisco's Moffitt Hospital between 1980 and 1990. Although the magnitude of the effect of individual risk factors differed between preterm delivery subtypes, the set of risk factors significantly associated with both categories of spontaneous preterm delivery was identical, while that associated with medically indicated preterm births was different. This study indicates that whereas the distinction between spontaneous preterm deliveries and those that are medically indicated seems valid, distinguishing between types of spontaneous preterm births may not lead to useful aetiological inferences.

Pregnancy weight gain: still controversial

During the 20th century, recommendations for maternal weight gain in pregnancy were controversial, ranging from rigid restriction to encouragement of ample gain. In 1990, the Institute of Medicine (IOM) recommended weight-gain ranges with the primary goal of improving infant birth weight. These guidelines were widely adopted but not universally accepted. Critics have argued that the IOM's recommendations are unlikely to improve perinatal outcomes and may actually increase the risk of negative consequences to both infants and mothers. We systematically reviewed studies that examined fetal and maternal outcomes according to the IOM's weight-gain recommendations in women with a normal prepregnancy weight. These studies showed that pregnancy weight gain within the IOM's recommended ranges is associated with the best outcome for both mothers and infants. However, weight gain in most pregnant women is not within the IOM's ranges. All of the studies reviewed were observational and there is a compelling need to conduct experimental studies to examine interventional strategies to improve maternal weight gain with the objective of optimizing health outcomes.

Determination of CD4 antigen density on cells: role of antibody valency, avidity, clones, and conjugation

The number of R-phycoerythrin (R-PE)-conjugated antibodies bound to a cell can be quantitated on a flow cytometer by using beads with known numbers of attached R-PE molecules (QuantiBRITE PE). Using these reference beads, we have observed that a number of factors affect the accuracy of the quantitation and conclusions about epitope density. These factors include valence of antibody binding, the use of antibody fragments (Fab's) versus intact monoclonal antibodies (mAb's), fixation, the purity of the conjugate (i.e., percentage of 1:1 ratios), dissociation rate, the use of washed versus unwashed preparations, and the location of epitope on target antigen. We used CD4 on T cells as a model to explore these challenges in detail. We conclude that CD4+ T cells bind approximately 49,000 CD4 (Leu 3a) antibody molecules, that this binding is bivalent, and therefore that there are approximately 98,000 CD4 antigen molecules on the surface of these cells.

Staining of cell surface human CD4 with 2'-F-pyrimidine-containing RNA aptamers for flow cytometry

We have used recombinant human CD4 presented on beads as an affinity matrix to screen a 2'-F-pyrimidine-containing RNA library with a complexity of approximately 10(14) molecules. Affinity-selected aptamers bind recombinant CD4 with low nanomolar equilibrium dissociation constants. These high-affinity aptamers conjugated to different fluorophores such as fluorescein and phycoerythrin were used to stain cells, expressing human CD4 on cell surface, for analysis by flow cytometry. Aptamers, conjugated to fluorophores, stained mouse T cells that express human CD4 on the surface, but not the control mouse T cells lacking human CD4. The control cells, however, do express mouse CD4 whose extracellular domain has 55% sequence identity to the human form. These human CD4-specific aptamers selectively stained CD4(+) T cells in a preparation of human peripheral blood mononuclear cells. These results and others suggest that aptamers are emerging as a versatile class of molecules that can be used for various diagnostic applications performed under different formats or platforms.

The pattern of maternal weight gain in women with good pregnancy outcomes

OBJECTIVES

This study describes the pattern of maternal weight gain in women with good pregnancy outcomes and provides data to fill in the provisional weight-gain charts published by the Institute of Medicine (IOM) in 1990.

METHODS

We selected 7002 women with good outcomes (defined by factors related to maternal and infant health) from the University of California, San Francisco, Perinatal Database. For each body mass index category, we compared percentiles of weight gain by trimester in women who achieved the IOM recommendations for total gain and those who did not.

RESULTS

Trimester rates of gain varied by body mass index category and exceeded IOM guidelines in all groups. Forty percent of these women with good outcomes had total gains within the guidelines and provided data to complete the IOM weight-gain charts.

CONCLUSIONS

Most women in this good-outcome sample would have been suspected of being at increased risk for poor outcome on the basis of their weight gain. This confirms the IOM recommendation that evaluation of the underlying causes of excessively high or low weight gain during pregnancy is necessary before appropriate interventions can be applied.

The association of pattern of maternal weight gain with length of gestation and risk of spontaneous preterm delivery

Monitoring weight gain during pregnancy may be useful in detecting pregnancies that are at increased risk of early delivery. This study examines 7259 deliveries that occurred at the University of California, San Francisco's Moffitt Hospital from 1980 to 1990. Obese women, women with diabetes or hypertension during pregnancy, deliveries with congenital malformations and non-spontaneous preterm deliveries were excluded. Pattern of gain was assessed by fitting a quadratic curve to each woman's series of weight and date measurements, using simple regression techniques. The parameters from this curve were used to develop a variable for pattern of gain that reflects how much an individual's pattern of gain differs from a linear pattern of gain. Multivariable linear and logistic regression analyses indicate that patterns of gain that deviate greatly from the average pattern of gain (i.e. patterns that show a marked speeding up or slowing down of gain towards the end of pregnancy) are associated with significantly shorter gestational age and confer a significantly increased risk of spontaneous preterm delivery. The results suggest that monitoring weight gain during pregnancy is important, although more specific studies are needed to understand the mechanisms by which weight gain pattern relates to preterm delivery before appropriate interventions can be developed.

A critical review of the relationship between gestational weight gain and preterm delivery

OBJECTIVE

To review the relationship between gestational weight gain and preterm delivery.

DATA SOURCES

We identified published studies through Medline searches (for the period 1980-1996), and we reviewed bibliographies from published articles.

METHODS OF STUDY SELECTION

We excluded non-English-language articles and articles that used total weight gain, unadjusted for gestational age. Thirteen articles were identified for review.

TABULATION, INTEGRATION AND RESULTS

Eleven of the 13 studies reported a significant association between maternal weight gain and risk of preterm delivery, and most reported that inadequate rate of maternal weight gain was associated with an increased risk (approximately 50-100%) of preterm delivery. Studies examining pattern of gain noted that a low rate of gain during the latter part of pregnancy (but not early pregnancy) was associated with an increased risk of preterm delivery (also approximately 50-100%). The studies' findings were relatively consistent, despite the use of diverse samples, study designs, and analytic strategies.

CONCLUSION

The evidence suggests that a lower rate of weight gain during pregnancy is associated with an increased risk of preterm delivery, and that a slow rate of gain during the latter part of pregnancy may be particularly important. To improve our understanding of the mechanisms of these relationships, future studies should examine pattern of gain; they should stratify analyses on the different subtypes of preterm delivery and provide more detailed descriptions of methods for assessing gestational duration.

Analysing the relationship between maternal weight gain and birthweight: exploration of four statistical issues

Four statistical issues concerning the analysis of birthweight and maternal weight gain during pregnancy are discussed: (1) Part-whole correlation is described (e.g. the correlation between total maternal weight gain and her infant's birthweight). (2) The choice between a ratio or two separate explanatory variables is explored (e.g. body mass index or using maternal weight and height separately). (3) Two statistical properties (bias and power) when a binary variable replaces a continuous variable are discussed (e.g. consequences of using low birthweight instead of reported birthweight). (4) A model selection procedure is presented to provide a way to select a useful subset of variables from a large number of available explanatory variables to model an outcome variable (e.g. birthweight). These issues are illustrated with a set of 4017 births from Moffitt Hospital at the University of California, San Francisco. Furthermore, these four issues arise in a number of applications of statistical methods to data collected to study the epidemiology of newborn infants.

Use of a high affinity DNA ligand in flow cytometry

To investigate the feasibility of using oligonucleotides in flow cytometry we describe a model system consisting of human neutrophil elastase (HNE) coated on 3.3 micro beads and a high affinity DNA ligand for HNE isolated by in vitro selection (SELEX). In this system the fluoresceinated DNA ligand was equally effective as an anti- HNE antibody in detecting HNE on beads. The location on and the chemistry of attachment of fluorescein to the DNA ligand is critical for the sensitivity of detection. DNA constructs in which fluorescein was conjugated via an ethylene glycol tether to either the 5'-end or near the 3'-end gave much higher signals than did probes with fluorescein directly conjugated to either end. Second-step staining with strepavidin-conjugated phycoerythrin was accomplished using a biotinylated DNA ligand in the initial staining of HNE beads. These data suggest that instead of, or in addition to, antibodies high affinity oligonucleotide probes can be useful in diagnostic applications based on flow cytometry.

Factors associated with the pattern of maternal weight gain during pregnancy

OBJECTIVE

To examine the pattern of maternal weight gain using maternal characteristics and pregnancy outcome.

METHODS

We used maternal weight data measured prospectively from all deliveries between 1980-1990 at the University of California, San Francisco. Piecewise linear regression was used to estimate the rate of maternal weight gain in each trimester. Bivariate techniques were used to examine associations between maternal weight gain per trimester and maternal characteristics and pregnancy outcomes. We also used multiple regression analysis to examine the relationship between maternal characteristics and trimester weight gain.

RESULTS

Weight data for at least one trimester were available for 10,418 women. The average rate of weight gain (kg/week) was lowest during the first trimester (0.169 +/- 0.268, n = 7587), peaked during the second trimester (0.563 +/- 0.236, n = 8000), and slowed slightly in the third trimester (0.518 +/- 0.234, n = 10,052). Maternal height, hypertension, cesarean delivery, and fetal size correlated positively with the rate of gain in each trimester, but pre-pregnancy body size, age, parity, smoking status, race-ethnicity, and diabetes were associated differently with gain, depending on which trimester was examined. The most important maternal predictors of weight gain per trimester were age and Asian race-ethnicity in the first trimester; pre-pregnancy body mass, parity, and height in the second; and hypertension, age, and parity in the third.

CONCLUSION

Maternal weight gain per trimester is associated with a number of maternal characteristics and pregnancy outcomes, and these relationships vary according to which trimester is being examined.

Maternal weight gain pattern and birth weight

OBJECTIVES

To determine the relationship between maternal weight gain pattern and birth weight.

METHODS

All nonobese, white women delivered at the University of California, San Francisco, between 1980-1990 were eligible for this study. Our study group included 2994 uncomplicated pregnancies with complete data. All recorded prenatal weight gain measurements were used to estimate maternal trimester weight gain, pattern of gain (based on low versus not-low gain at each trimester), and total gain at delivery. Multiple linear regression analysis was used to assess the relationship between these weight gain measurements and fetal birth weight.

RESULTS

After adjustment for seven covariates, each kilogram of maternal gain in the first, second, and third trimesters was associated with statistically significant increases in fetal birth weight of 18.0, 32.8, and 17.0 g, respectively. When compared with the pattern of gain that was not low in any trimester, patterns with low gain in the first and second trimesters or in the second and third trimesters were associated with significant decreases in birth weights of 133.0 and 88.5 g, but no important change in birth weight was seen for the group whose gains were low in the first and third trimesters. These findings were not due to differences in total weight gain, which averaged approximately 11 kg in these three pattern groups.

CONCLUSION

The results suggest that specific patterns of maternal weight gain, particularly weight gain during the second trimester, are related to fetal birth weight.

Dietary intake among Mexican-American women: generational differences and a comparison with white non-Hispanic women

OBJECTIVES

Although Mexican Americans consume diets that may protect them against adverse health, dietary advantages may disappear with increased acculturation. This study examined whether the nutrient intake of second-generation Mexican-American women of childbearing age deteriorates compared with that of first-generation Mexican-American women and approximates that of White non-Hispanic women.

METHODS

Data on the absolute and relative intake of eight nutrients were obtained from a 24-hour recall and compared among 475 first-generation and 898 second-generation Mexican-American women, and among 2326 White non-Hispanic women.

RESULTS

Although first-generation Mexican-American women were of lower socioeconomic status than were second-generation or White non-Hispanic women, they had a higher average intake of protein; vitamins A, C, and folic acid; and calcium than the other two groups. Whereas the mean adequacy ratio of the eight nutrients studied was highest in first-generation Mexican women, it was lowest in their second-generation counterparts.

CONCLUSIONS

First-generation Mexican women stand a markedly lower risk of eating a poor diet than second-generation Mexican women, whose nutrient intake resembles that of White non-Hispanic women.

Weight gain and energy intake during pregnancy

The ideal weight gain or energy intake for an individual woman cannot be determined from research studies. Current guidelines for maternal gain, however, combined with individualized assessment and follow-up, can provide the clinician and the pregnant women with a meaningful target and plan for achieving a healthy weight gain. For some women, increased amounts of maternal weight gain may improve fetal growth prenatally and therefore improve fetal health. For other women, high gains, or even gains within the recommended range, may enhance fetal growth to the point where labor complications, operative deliveries, permanent maternal obesity, and other health problems may occur. Balancing the health benefits and risks of maternal weight gain is a challenge that we will continue to face in the future.

Dietary, alcohol, and tobacco intake among Mexican-American women of childbearing age: results from HANES data

PURPOSE

Dietary intake and substance abuse are important predictors of pregnancy outcome yet little is known about these behaviors in Mexican Americans. Dietary, tobacco, and alcohol intake of Mexican-American and non-Hispanic white women were compared across the reproductive cycle.

DESIGN

Four cross-sectional groups--interconceptional, pregnant, lactating, and postpartum non-lactating--were compared within and between ethnic groups.

SUBJECTS

A stratified sample of 682 women, 16 to 44 years old, of Mexican birth or origin from the Hispanic HANES was contrasted with a similarly stratified sample of 1,396 white non-Hispanic women from the NHANES:

MEASURES

Demographic, behavioral and health characteristics, food practices, and fluid intake were examined. Data on food servings were combined into five major food groups.

RESULTS

Compared with white non-Hispanics, Mexican-American women had lower socioeconomic status and worse perceived health. However, Mexican Americans reported lower consumption of tobacco, alcohol, diet soda, and caffeine, particularly during pregnancy and lactation. Although portion sizes for the foods consumed were not assessed, frequency of consumption of fruits and vegetables and milk was lower and meat higher among Mexican Americans.

CONCLUSIONS

Despite socioeconomic disadvantages, Mexican-American women have better health habits than white non-Hispanic women. From these data it is unclear how diet affects pregnancy outcomes in Mexican Americans.

A prospective study of dietary intake and acquired immune deficiency syndrome in HIV-seropositive homosexual men

We prospectively studied the relationship between dietary intake at baseline and the development of AIDS over 6 years in a population-based sample of 296 human immunodeficiency virus (HIV)-seropositive men. Nutrient intake was assessed before HIV serostatus was known. Subjects diagnosed with AIDS at baseline or during the 1st year were excluded. After adjustment for baseline CD4 T-lymphocyte count, HIV symptoms, and other risk factors, no nutrients were significantly associated with AIDS. However, when the continuous CD4 count and HIV symptom variables were replaced with a single binary health status variable, the hazard of AIDS decreased as consumption increased for all 11 micronutrients; this relationship was statistically significant for iron, vitamin E, and riboflavin and approached significance for vitamins C, thiamine, and niacin. Higher intake of all 11 micronutrients was associated with higher CD4 counts at baseline, and was significantly so for six of them. Daily multivitamin use was associated with a reduced hazard of AIDS [hazard ratio (HR) = 0.7; 95% confidence interval (CI) = 0.5, 1.0] and a significantly reduced risk for low CD4 counts at baseline (HR = 0.6, 95% CI = 0.4, 0.9). Additional studies are needed to determine whether dietary intake modifies the rate of developing AIDS in those who are HIV seropositive.

Differences in postpartum weight retention between black and white mothers

OBJECTIVE

To determine whether the overall retention of weight gained during pregnancy and the factors affecting postpartum weight retention differ by race.

METHODS

Data from the 1988 National Maternal and Infant Health Survey were analyzed to examine postpartum weight retention of 20 lb or more among 990 black and 1129 white women who began pregnancy with normal weight for height. The impact of various maternal characteristics on both weight retention and the association between weight retention and race was tested by multivariate methods.

RESULTS

Black mothers were twice as likely to retain at least 20 lb than white mothers (adjusted odds ratio 2.20, 95% confidence interval 1.50-3.22). This black-white difference did not differ substantially by socioeconomic status. However, many factors affecting postpartum weight retention differed by maternal race. For example, whereas unmarried status was associated with weight retention among white mothers, high parity was associated with weight retention among black mothers. Low socioeconomic status and high prenatal weight gain were associated with an increased risk of weight retention for both black and white mothers.

CONCLUSION

These data suggest that population-specific strategies may be needed to help mothers return to their pre-pregnancy weight.

Supportive nurse-midwife care is associated with a reduced incidence of cesarean section

OBJECTIVE

Our purpose was to examine whether care by a certified nurse-midwife, including personal labor support, was associated with a reduced risk of cesarean delivery.

STUDY DESIGN

A retrospective cohort study comparing 3551 physician-managed patients with 1056 certified nurse-midwife-managed patients in a university hospital with a mixed socioeconomic and ethnic population was performed. Regression analysis was used to estimate the risk of labor abnormalities, diagnosis of fetal distress, and cesarean delivery in patients delivered by a certified nurse-midwife vs a physician and to control for maternal age, race, parity, fetal size, and delivery year. Subjects included were women having at least five prenatal visits who were delivered of term, singleton, liveborn infants without congenital anomalies with occiput presentation.

RESULTS

Odds ratio for cesarean section for women delivered by certified nurse-midwives versus those delivered by physicians was 0.71 (95% confidence interval 0.55, 0.91). Midwifery care was associated with a lower risk of abnormal labor (adjusted odds ratio 0.70, 95% confidence interval 0.60, 0.83) and diagnosis of fetal distress (adjusted odds ratio 0.50, 95% confidence interval 0.32, 0.77).

CONCLUSION

This work demonstrates that labor abnormalities and diagnosis of fetal distress are less frequent in patients cared for by nurse-midwives, and there is an association with a lower incidence of cesarean section.

Vitamin and mineral status of women of childbearing potential

Increasing data suggest a role for micronutrients in pregnancy outcome, and in some cases nutritional status must be adequate in the first weeks of pregnancy. We examined nationally representative survey data on women of childbearing age: the NHANES II data for serum measures of iron status and the CSFII four-day data for dietary measures of intake of protein, iron, zinc, folic acid, and vitamins A, C, and B6. For those nutrients, women below or near poverty had consistently lower levels, with median intakes below the RDA for all but protein (e.g., folic acid, 150 micrograms in contrast with the RDA of 180 for nonpregnant and 400 for pregnant women; for B6, 0.96 mg instead of 1.6 or 2.2). Even among women with incomes as high as three times the poverty level or more, large segments of the population had very low intakes. For example, the 25th percentile in that group was only 142 micrograms/day of folic acid, 4.6 alpha-tocopherol equivalents of vitamin E, 6.7 mg zinc, and 433 mg of calcium. Approximately 15% of women had low transferrin saturation.

Lactate Measured in Diluted and Undiluted Whole Blood and Plasma: Comparison of Methods and Effect of Hematocrit

We evaluated a new analyzer that measures lactate in undiluted whole blood by direct (or undiluted) amperometry [Nova Stat Profile 7 Analyzer (SP7); Nova Biomedical, Waltham, MA] by comparing it with two other analyzers, one for measuring lactate in whole blood by indirect (or diluted) amperometry [Model 2300; Yellow Springs Instrument Co. (YSI), Yellow Springs, OH] and another for measuring lactate in plasma by enzymatic colorimetry (aca; Du Pont Co., Wilmington, DE). All between-method comparisons of the three methods showed that the results for plasma were comparable (Sy/x = 0.24-0.33 mmol/L). Within-method comparisons by the YSI differed substantially between plasma and whole blood (Sy/x = 0.48 mmol/L), but within-method comparisons by the SP7 produced better agreement between plasma and whole blood (Sy/x = 0.18 mmol/L). The difference between whole blood and plasma by YSI is related to hematocrit, with the greatest differences noted for samples with the highest hematocrit. Serum lactate measured by SP7 had between-day imprecision (CV) ranging from 12% at 0.5 mmol/L to 4.2% at 3.7 mmol/L, showed a linear standard curve to at least 11.5 mmol/L, and was independent of hematocrit. There was a mean bias of approximately 0.4 mmol/L for results in the reference range for both plasma and whole blood by SP7 compared with plasma results by either aca or YSI.

Lactate measured in diluted and undiluted whole blood and plasma: comparison of methods and effect of hematocrit

We evaluated a new analyzer that measures lactate in undiluted whole blood by direct (or undiluted) amperometry [Nova Stat Profile 7 Analyzer (SP7); Nova Biomedical, Waltham, MA] by comparing it with two other analyzers, one for measuring lactate in whole blood by indirect (or diluted) amperometry [Model 2300; Yellow Springs Instrument Co. (YSI), Yellow Springs, OH] and another for measuring lactate in plasma by enzymatic colorimetry (aca; Du Pont Co., Wilmington, DE). All between-method comparisons of the three methods showed that the results for plasma were comparable (Sy/x = 0.24-0.33 mmol/L). Within-method comparisons by the YSI differed substantially between plasma and whole blood (Sy/x = 0.48 mmol/L), but within-method comparisons by the SP7 produced better agreement between plasma and whole blood (Sy/x = 0.18 mmol/L). The difference between whole blood and plasma by YSI is related to hematocrit, with the greatest differences noted for samples with the highest hematocrit. Serum lactate measured by SP7 had between-day imprecision (CV) ranging from 12% at 0.5 mmol/L to 4.2% at 3.7 mmol/L, showed a linear standard curve to at least 11.5 mmol/L, and was independent of hematocrit. There was a mean bias of approximately 0.4 mmol/L for results in the reference range for both plasma and whole blood by SP7 compared with plasma results by either aca or YSI.

Prenatal weight gain advice: an examination of the recent prenatal weight gain recommendations of the Institute of Medicine

The Institute of Medicine (IOM) recently published new guidelines for maternal weight gain during pregnancy. Using data collected at Moffitt Hospital, University of California at San Francisco, we examined the associations between maternal weight gain outside the recommendations of the IOM and three pregnancy outcomes (small for gestational age [SGA] infants, large for gestational age [LGA] infants, and cesarean delivery). These analyses were repeated using population-specific weight gain ranges derived from a subgroup of women in this cohort with healthy pregnancy outcomes. The purpose of the study was to compare the national guidelines of the IOM with hospital standards. Both the recommendations of the IOM and the hospital ranges were associated with fewer SGA infants, LGA infants, and cesarean deliveries. The overall associations were similar for the population-derived and national ranges. Although the IOM ranges should be examined in other populations and with other birth outcomes, our results validated their recommendations. Maternal weight gain within the IOM recommendations reduced the risk of the outcomes studied; furthermore, these ranges performed as well as those derived from the target population.

Obstetric complications with GDM. Effects of maternal weight

Obstetric complications recorded prospectively were assessed retrospectively in 150 women with gestational diabetes mellitus (GDM) and 305 control subjects matched for age, parity, and ethnicity. Intensive diet therapy and self-monitoring of capillary blood glucose were used to obtain postprandial euglycemia; 22% of GDM subjects required insulin. GDM and control subjects were grouped by body mass index to detect any influence of maternal prepregnancy weight on outcome. Polyhydramnios, preterm labor, and pyelonephritis were not more frequent in GDM, but hypertension without proteinuria (7.3 vs. 3.3%) and preeclampsia (8 vs. 3.9%) were more frequent in GDM. The frequency of hypertensive complications in GDM was not totally attributable to being overweight. Abnormalities of labor, birth trauma, and fetal macrosomia were not more common in GDM; 6.7% of the infants of mothers with GDM weighed greater than 4200 g at birth compared with 3.6% of control infants (NS), and 10% were large for gestational age and sex compared with 6.6% of control infants (NS). Despite this, cesarean delivery was more common in GDM (35.3 vs. 22%, P less than 0.01), mostly due to significantly more cesarean births without labor.