Jonathan A. Mayo

Maternal prepregnancy body mass index and risk of spontaneous preterm birth.

BACKGROUND Findings from studies examining risk of preterm birth associated with elevated prepregnancy body mass index (BMI) have been inconsistent. METHODS Within a large population-based cohort, we explored associations between prepregnancy BMI and spontaneous preterm birth across a spectrum of BMI, gestational age, and racial/ethnic categories. We analysed data for 989,687 singleton births in California, 2007-09. Preterm birth was grouped as 20-23, 24-27, 28-31, or 32-36 weeks gestation (compared with 37-41 weeks). BMI was categorised as <18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0-34.9 (obese I); 35.0-39.9 (obese II); and ≥ 40.0 (obese III). We assessed associations between BMI and spontaneous preterm birth of varying severity among non-Hispanic White, Hispanic, and non-Hispanic Black women. RESULTS Analyses of mothers without hypertension and diabetes, adjusted for age, education, height, and prenatal care initiation, showed obesity categories I-III to be associated with increased risk of spontaneous preterm birth at 20-23 and 24-27 weeks among those of parity 1 in each race/ethnic group. Relative risks for obese III and preterm birth at 20-23 weeks were 6.29 [95% confidence interval (CI) 3.06, 12.9], 4.34 [95% CI 2.30, 8.16], and 4.45 [95% CI 2.53, 7.82] for non-Hispanic Whites, non-Hispanic Blacks, and Hispanics, respectively. A similar, but lower risk, pattern was observed for women of parity ≥ 2 and preterm birth at 20-23 weeks. Underweight was associated with modest risks for preterm birth at ≥ 24 weeks among women in each racial/ethnic group regardless of parity. CONCLUSIONS The association between womens prepregnancy BMI and risk of spontaneous preterm birth is complex and is influenced by race/ethnicity, gestational age, and parity.

Interpregnancy interval after live birth or pregnancy termination and estimated risk of preterm birth: a retrospective cohort study

We assessed whether interpregnancy interval (IPI) length after live birth and after pregnancy termination was associated with preterm birth (PTB).

Cross-Country Individual Participant Analysis of 4.1 Million Singleton Births in 5 Countries with Very High Human Development Index Confirms Known Associations but Provides No Biologic Explanation for 2/3 of All Preterm Births.

Background Preterm birth is the most common single cause of perinatal and infant mortality, affecting 15 million infants worldwide each year with global rates increasing. Understanding of risk factors remains poor, and preventive interventions have only limited benefit. Large differences exist in preterm birth rates across high income countries. We hypothesized that understanding the basis for these wide variations could lead to interventions that reduce preterm birth incidence in countries with high rates. We thus sought to assess the contributions of known risk factors for both spontaneous and provider-initiated preterm birth in selected high income countries, estimating also the potential impact of successful interventions due to advances in research, policy and public health, or clinical practice. Methods We analyzed individual patient-level data on 4.1 million singleton pregnancies from four countries with very high human development index (Czech Republic, New Zealand, Slovenia, Sweden) and one comparator U.S. state (California) to determine the specific contribution (adjusting for confounding effects) of 21 factors. Both individual and population-attributable preterm birth risks were determined, as were contributors to cross-country differences. We also assessed the ability to predict preterm birth given various sets of known risk factors. Findings Previous preterm birth and preeclampsia were the strongest individual risk factors of preterm birth in all datasets, with odds ratios of 4.6–6.0 and 2.8–5.7, respectively, for individual women having those characteristics. In contrast, on a population basis, nulliparity and male sex were the two risk factors with the highest impact on preterm birth rates, accounting for 25–50% and 11–16% of excess population attributable risk, respectively (p<0.001). The importance of nulliparity and male sex on population attributable risk was driven by high prevalence despite low odds ratios for individual women. More than 65% of the total aggregated risk of preterm birth within each country lacks a plausible biologic explanation, and 63% of difference between countries cannot be explained with known factors; thus, research is necessary to elucidate the underlying mechanisms of preterm birth and, hence, therapeutic intervention. Surprisingly, variation in prevalence of known risk factors accounted for less than 35% of the difference in preterm birth rates between countries. Known risk factors had an area under the curve of less than 0.7 in ROC analysis of preterm birth prediction within countries. These data suggest that other influences, as yet unidentified, are involved in preterm birth. Further research into biological mechanisms is warranted. Conclusions We have quantified the causes of variation in preterm birth rates among countries with very high human development index. The paucity of explicit and currently identified factors amenable to intervention illustrates the limited impact of changes possible through current clinical practice and policy interventions. Our research highlights the urgent need for research into underlying biological causes of preterm birth, which alone are likely to lead to innovative and efficacious interventions.

Swedish and American studies show that initiatives to decrease maternal obesity could play a key role in reducing preterm birth

Maternal obesity is a major source of preventable perinatal morbidity, but studies of the relationship between obesity and preterm birth have been inconsistent. This review looks at two major studies covering just under 3.5 million births, from California, USA, and Sweden.

Assessing Differences in Mortality Rates and Risk Factors Between Hispanic and Non-Hispanic Patients With Cystic Fibrosis in California

BACKGROUND Over the past 30 years, therapeutic advances have extended the median lifespan of patients with cystic fibrosis (CF). Hispanic patients are a vulnerable subpopulation with a high prevalence of risk factors for worse health outcomes. The consequences of these differences on health outcomes have not been well described. The objective of this study was to characterize the difference in health outcomes, including mortality rate, between Hispanic and non-Hispanic patients with CF. METHODS This study is a retrospective analysis of CF Foundation Patient Registry data of California residents with CF, diagnosed during or after 1991, from 1991 to 2010. Ethnicity was self-reported. The primary outcome was mortality. Hazard ratios were estimated from a Cox regression model, stratified by sex, and adjusted for socioeconomic status, clinical risk factors, and year of diagnosis. RESULTS Of 1,719 patients, 485 (28.2%) self-identified as Hispanic. Eighty-five deaths occurred, with an overall mortality rate of 4.9%. The unadjusted mortality rate was higher among Hispanic patients than among non-Hispanic patients (9.1% vs 3.3%, P < .0001). Compared with non-Hispanic patients, Hispanic patients had a lower survival rate 18 years after diagnosis (75.9% vs 91.5%, P < .0001). Adjusted for socioeconomic status and clinical risk factors, Hispanic patients had an increased rate of death compared with non-Hispanic patients (hazard ratio, 2.81; 95% CI, 1.70-4.63). CONCLUSIONS Hispanic patients with CF have a higher mortality rate than do non-Hispanic patients, even after adjusting for socioeconomic status and clinical severity. Further investigation into the mechanism for the measured difference in lung function will help inform interventions and improve the health of all patients with CF.

Women's prepregnancy underweight as a risk factor for preterm birth: a retrospective study

To investigate the distribution of known factors for preterm birth (PTB) by severity of maternal underweight; to investigate the risk‐adjusted relation between severity of underweight and PTB, and to assess whether the relation differed by gestational age.

Prepregnancy Obesity and Risks of Stillbirth

Background We examined the association of maternal obesity with risk of stillbirth, focusing on whether the pattern of results varied by gestational age or maternal race-ethnicity or parity. Methods Analyses included 4,012 stillbirths and 1,121,234 liveborn infants delivered in California from 2007–2010. We excluded stillbirths due to congenital anomalies, women with hypertensive disorders or diabetes, and plural births, to focus on fetuses and women without these known contributing conditions. We used Poisson regression to estimate relative risks (RR) and 95% confidence intervals (CI). Separate models were run for stillbirths delivered at 20–23, 24–27, 28–31, 32–36, 37–41 weeks, relative to liveborn deliveries at 37–41 weeks. Results For stillbirth at 20–23 weeks, RRs were elevated for all race-ethnicity and parity groups. The RR for a 20-unit change in BMI (which reflects the approximate BMI difference between a normal weight and an Obese III woman) was 3.5 (95% CI 2.2, 5.6) for nulliparous white women and ranged from 1.8 to 5.0 for other sub-groups. At 24–27 weeks, the association was significant (p<0.05) only for multiparous non-Hispanic whites; at 28–31 weeks, for multiparous whites and nulliparous whites and blacks; at 32–36 weeks, for multiparous whites and nulliparous blacks; and at 37–41 weeks, for all groups except nulliparous blacks. The pattern of results was similar when restricted to stillbirths due to unknown causes and somewhat stronger when restricted to stillbirths attributable to obstetric causes. Conclusion Increased risks were observed across all gestational ages, and some evidence of heterogeneity of the associations was observed by race-ethnicity and parity.

Population-level correlates of preterm delivery among black and white women in the U.S.

Objective This study examined the ability of social, demographic, environmental and health-related factors to explain geographic variability in preterm delivery among black and white women in the US and whether these factors explain black-white disparities in preterm delivery. Methods We examined county-level prevalence of preterm delivery (20–31 or 32–36 weeks gestation) among singletons born 1998–2002. We conducted multivariable linear regression analysis to estimate the association of selected variables with preterm delivery separately for each preterm/race-ethnicity group. Results The prevalence of preterm delivery varied two- to three-fold across U.S. counties, and the distributions were strikingly distinct for blacks and whites. Among births to blacks, regression models explained 46% of the variability in county-level risk of delivery at 20–31 weeks and 55% for delivery at 32–36 weeks (based on R-squared values). Respective percentages for whites were 67% and 71%. Models included socio-environmental/demographic and health-related variables and explained similar amounts of variability overall. Conclusions Much of the geographic variability in preterm delivery in the US can be explained by socioeconomic, demographic and health-related characteristics of the population, but less so for blacks than whites.

Effects of race/ethnicity and BMI on the association between height and risk for spontaneous preterm birth

OBJECTIVE Short height and obesity have each been associated with increased risk for preterm birth (PTB). However, the effect of short height on PTB risk, across different race/ethnicities and body mass index (BMI) categories, has not been studied. Our objective was to determine the influence of maternal height on the risk for PTB within race/ethnic groups, BMI groups, or adjusted for weight. STUDY DESIGN All California singleton live births from 2007 through 2010 were included from birth certificate data (vital statistics) linked to hospital discharge data. Prepregnancy BMI (kg/m(2)) was categorized as underweight (<18.5), normal (18.5-24.9), overweight (25.0-29.9), or obese (≥30.0). Maternal race/ethnicity was categorized as: non-Hispanic white, non-Hispanic black, Hispanic, and Asian. Maternal height was classified into 5 categories (shortest, short, middle, tall, tallest) based on racial/ethnic-specific height distributions, with the middle category serving as reference. Poisson regression models were used to estimate relative risks for the association between maternal height and risk of spontaneous PTB (<37 weeks and <32 weeks). Models were stratified on race/ethnicity and BMI. Generalized additive regression models were used to detect nonlinearity of the association. Covariates considered were: maternal age, weight, parity, prenatal care, education, medical payment, previous PTB, gestational and pregestational diabetes, pregestational hypertension, preeclampsia/eclampsia, and smoking. RESULTS Among 1,655,385 California singleton live births, 5.2% were spontaneous PTB <37 weeks. Short stature (first height category) was associated with increased risk for PTB for non-Hispanic whites and Hispanics across all BMI categories. Among obese women, tall stature (fifth category) was associated with reduced risk for spontaneous PTB for non-Hispanic whites, Asians, and Hispanics. The same pattern of association was seen for height and risk for spontaneous PTB <32 weeks. In the generalized additive regression model plots, short stature was associated with increased risk for spontaneous PTB of <32 and <37 weeks of gestation among whites and Asians. However, this association was not observed for blacks and Hispanics. CONCLUSION Maternal shorter height is associated with a modest increased risk for spontaneous PTB regardless of BMI. Our results suggest that PTB risk assessment should consider race/ethnicity-specific height with respect to the norm in addition to BMI assessment.

Residential agricultural pesticide exposures and risks of preeclampsia

&NA; We investigated risks of preeclampsia phenotypes from potential residential pesticide exposures, including 543 individual chemicals and 69 physicochemical groupings that were applied in the San Joaquin Valley of California during the study period, 1998–2011. The study population was derived from birth certificate data linked with Office of Statewide Health Planning and Development maternal and infant hospital discharge data. The following numbers of women with preeclampsia phenotypes were identified: 1045 with superimposed (pre‐existing hypertension with preeclampsia) preeclampsia (265 with gestational weeks 20–31 and 780 with gestational weeks 32–36); 3471 with severe preeclampsia (824 with gestational weeks 20–31 and 2647 with gestational weeks 32–36); and 2780 with mild preeclampsia (207 with gestational weeks 20–31 and 2573 with gestational weeks 32–36). The reference population for these groups was 197,461 women who did not have diabetes (gestational or pre‐existing), did not have any hypertensive disorder, and who delivered at 37 weeks or later. The frequency of any exposure was lower or about the same in each preeclampsia case group (further delineated by gestational age), and month time period, relative to the frequency in reference population controls. Nearly all odds ratios were below 1.0 for these any vs no exposure comparisons. This study showed a general lack of increased risks between a range of agriculture pesticide exposures near womens residences and various preeclampsia phenotypes. HighlightsPesticides and preeclampsia have been rarely investigated.Studied were >200,000 births and exposures to >500 pesticides.There was a general lack of association between pesticide exposures and preeclampsia.It is possible that unobserved early fetal loss may have biased risk estimates.