Have studies of urinary tract infection and preterm delivery used the most appropriate methods?

Association between ambient particulate matter and preterm birth stratified by temperature: A population-based pregnancy cohort study

A growing body of literature reports associations between exposure to particulate matter with aerodynamic diameters ≤2.5 μm (PM2.5) and 2.5-10 μm (PM10-2.5) during pregnancy and preterm birth (PTB). However, the role of ambient temperature in PM-PTB associations was rarely investigated. In Israel, we used Maccabi Healthcare Services data to establish a population-based cohort of 381,265 singleton births reaching 24-42 weeks' gestation and birth weight of 500-5000 g (2004-2015). Daily PM and ambient temperature predictions from a satellite-based spatiotemporal model, at a 1 × 1 km spatial resolution, were linked to the date of birth and maternal residence. Mixed effects Cox regression models, adjusted for covariates, with a random intercept at the mother level were used to assess associations between mean exposure during pregnancy and PTB. We found that exposure to PM2.5 was positively associated with PTB when the average exposure during pregnancy was either low (first quintile) or high (fifth quintile), compared to exposure in the 2nd-4th quintiles, with hazard ratios (HRs) 1.18 (95% confidence interval [CI], 1.13-1.24) and 1.07 (95% CI, 1.02-1.12), respectively. The results revealed effect modification of temperature. For mothers exposed to low (below median) average temperature during pregnancy, HRs of PTB were 0.93 (95% CI, 0.87-1.00) and 1.21 (95% CI, 1.14-1.29) for the first and fifth PM2.5 quintiles, respectively, when compared to the 2nd-4th quintiles. However, a reverse trend was indicated for high-temperature pregnancies, where the corresponding HRs were 1.48 (95% CI, 1.39-1.58) and 0.92, (95% CI, 0.96-0.98). In conclusion, consideration of climatic factors can provide new insights into the risk of PTB as a result of exposure to PM2.5 during pregnancy.

Residential greenness and birth outcomes: Evaluating the mediation and interaction effects of particulate air pollution

BACKGROUND

The few studies that examined the association between residential greenness and birth outcomes have produced inconsistent results, and the underlying mechanisms of these associations remain unclear.

OBJECTIVES

We examined the mediation and interaction effects of particulate matter (PM) air pollution on the relationship between greenness exposure during the first and third trimesters of pregnancy and birth outcomes, including preterm birth (PTB), term low birth weight (TLBW), small for gestational age (SGA), birth weight (BW), and head circumference (HC).

METHODS

We conducted a retrospective cohort study on 16,184 singleton live births between 2010 and 2012 in Taiwan. Residential greenness was estimated based on the normalized difference vegetation index (NDVI), and the PM information during the first and third trimesters was estimated through hybrid kriging land use regression and ordinary kriging interpolation methods. Multiple regression analyses were performed to evaluate the associations between greenness exposure and birth outcomes. We estimated the mediating effects of PM associated with greenness exposure on birth outcomes through causal mediation analyses. We also examined the potential multiplicative and additive interactions between greenness exposure and PM and their effects on birth outcomes.

RESULTS

The first trimester NDVI exposure was associated with reduced risks for PTB, TLBW, and SGA, which had an adjusted OR (aOR) of 0.93 (95% CI: 0.89-0.97), 0.91 (95% CI: 0.83-0.99), and 0.95 (95% CI: 0.91-1.00), respectively, per 0.1 unit increase in multi-pollutant models. The causal mediation analysis showed that PM mediated approximately 5-19% of the association between first and third trimester greenness and PTB and mediated approximately 15-37% of the association between greenness and SGA. We identified multiplicative interactions in log scale between first trimester PM₁₀ and NDVI exposure for SGA (aOR_interaction = 0.92, p = 0.03) and HC (estimate_interaction = 1.47, p = 0.04).

CONCLUSIONS

This study revealed beneficial associations between residential greenness and birth outcomes, including PTB, TLBW, and SGA. The associations were partly mediated by a reduction in exposure to PM air pollution.

SUMMARY

The beneficial effects of greenness on PTB and SGA are partly mediated by a reduction in exposure to PM air pollution.

Prenatal exposure to ambient air temperature and risk of early delivery

BACKGROUND

Preterm birth is a major determinant of adverse health consequences, and early term births are also associated with increased risk of various outcomes. In light of climate change, the effect of ambient temperature on earlier delivery is an important factor to consider. Several studies have focused on associations of ambient air temperature (Ta) on preterm birth, but few have examined associations with early term births.

AIMS

To investigate the association of prenatal exposure to Ta with preterm birth (<37 completed gestation weeks) and with early-term birth (<39 completed gestation weeks) in a semi-arid climate.

METHODS

All singleton deliveries at the Soroka Medical Center from the Southern district of Israel, with estimated conception dates between May 1, 2004 and March 31, 2013 (N = 62,547) were linked to prenatal Ta estimates from a spatiotemporally resolved model, with daily 1 km resolution. We used time-dependent Cox regression models with weekly mean Ta throughout gestation, adjusted for calendar month and year of conception, ethnicity, census-level socio-economic status and population density.

RESULTS

Ta was positively associated with late preterm birth (31 + 0/7 - 36 + 6/7 weeks), with increased risk in the upper Ta quintile as compared to the third quintile, hazard ratio (HR) = 1.31, 95% confidence interval (CI) = 1.11-1.56. Ta also associated with early term birth (37 + 0/6 - 38 + 6/7), with increased risk in the upper Ta quintile as compared to the third quintile, HR = 1.24, 95% CI = 1.13-1.36.

CONCLUSION

Exposure to high ambient temperature during pregnancy is associated with a higher risk of preterm and early term birth in southern Israel.

Impacts of high temperature on adverse birth outcomes in Seoul, Korea: Disparities by individual- and community-level characteristics

BACKGROUND

Few studies have examined temperature's effect on adverse birth outcomes and relevant effect modifiers.

OBJECTIVES

We investigated associations between heat and adverse birth outcomes and how individual and community characteristics affect these associations for Seoul, Korea, 2004-2012.

METHODS

We applied logistic regression to estimate associations between heat index during pregnancy, 4 weeks before delivery, and 1 week before delivery and risk of preterm birth and term low birth weight. We investigated effect modification by individual (infant's sex, mother's age, and mother's educational level) and community characteristics (socioeconomic status (SES) and percentage of green areas near residence at the gu level, which is similar to borough in Western countries). We also evaluated associations by combinations of individual- and community-level SES.

RESULTS

Heat exposure during whole pregnancy was significantly associated with risk of preterm birth. An interquartile (IQR) increase (5.5 °C) in heat index during whole pregnancy was associated with an odds ratio (OR) of 1.033 (95% CI 1.005, 1.061) with NO2 adjustment, and 1.028 (95% CI 0.998, 1.059) with PM10 adjustment, for preterm birth. We also found significant associations with heat exposure during 4 weeks before delivery and 1 week before delivery on preterm birth. We did not observe significant associations with term low birth weight. Higher risk of heat on preterm birth was associated with some individual characteristics such as infants with younger or older mothers and lower community-level SES. For combinations of individual- and community-level SES, the highest and most significant estimated effect was found for infants with low educated mothers living in low SES communities, with suggestions of effects of both individual-and community-level SES.

CONCLUSIONS

Our findings have implications for evaluating impacts of high temperatures on birth outcomes, estimating health impacts of climate change, and identifying which subpopulations and factors are most relevant for disparities in this association.

Reflux nephropathy and the risk of preeclampsia and of other adverse pregnancy-related outcomes: a systematic review and meta-analysis of case series and reports in the new millennium

BACKGROUND

Reflux nephropathy is a common urinary tract malformation, and a substantial cause of morbidity in women of childbearing age. While recent studies provide further new information on pregnancy-related outcomes, their results are heterogeneous and a systematic meta-analysis may help the interpretation. The aim of this review was to analyze pregnancy-related outcomes in the recent literature on reflux nephropathy (2000-2016), to perfect the estimation of risks, and to identify specific research needs.

METHODS

We searched Medline, EMBASE and the Cochrane review databases for the period 2000-2016 (PROSPERO registration no. 42016042713).

SELECTION CRITERIA

all case series and case reports dealing with reflux nephropathy and reporting on at least one pregnancy outcome. Data were extracted from eligible case series (≥ 6 cases). For the outcomes preeclampsia (PE), pregnancy-induced hypertension (PIH), preterm birth, and newborns small for gestational age, we employed as a control group the low-risk pregnancies from a multicenter database including 1418 live-born singletons. Case reports were analyzed narratively.

RESULTS

The search retrieved 2507 papers, of which 7 case series and 4 case reports were retained. The series report on 434 women with 879 pregnancies; no study reported controls. Compared to the low-risk controls, the meta-analysis showed an increased risk of PIH (odds ratio, OR 5.55; confidence interval, CI 3.56-8.66), PE (OR 6.04; CI 2.41-15.13), and all hypertensive disorders combined (OR 10.43; CI 6.90-15.75). No difference was observed in preterm delivery and caesarean sections. A higher incidence of stillbirth was reported in one paper. Conversely, the 4 case reports (on 10 pregnancies) alert us to a potentially severe complication, hydro(uretero)nephrosis with or without infection.

CONCLUSION

Reflux nephropathy is associated with an increased risk of PIH and PE, but not of preterm delivery, suggesting the occurrence of late 'maternal' PE. The finding of a higher incidence of stillbirths in one series requires further analysis. Strict follow-up of these women is needed, in particular in late pregnancy stages, to avoid and manage in particular hypertensive pregnancy complications.

The Relationship Between 2009 Pandemic H1N1 Influenza During Pregnancy and Preterm Birth: A Population-based Cohort Study

BACKGROUND

Previous studies of maternal influenza illness and preterm birth have yielded inconsistent results. Our objective was to assess the association between 2009 pandemic H1N1 (pH1N1) influenza during pregnancy and preterm birth in a large obstetrical population.

METHODS

We linked a province-wide birth registry with health administrative databases to identify influenza-coded hospitalizations, emergency department visits, or physician visits among pregnant women during the 2009 H1N1 pandemic (our proxy for clinical pH1N1 influenza illness). Using Cox regression, we estimated adjusted hazard ratios (aHR) for preterm birth and spontaneous preterm birth treating influenza as a time-varying exposure.

RESULTS

Among 192,082 women with a singleton live birth, 2,925 (1.5%) had an influenza-coded health care encounter during the 2009 H1N1 pandemic. Compared with unexposed pregnancy time, there was no association between exposure to the pandemic, with or without clinical influenza illness, and preterm birth (no pH1N1 diagnosis: aHR = 1.0; 95% confidence interval [CI] = 0.98, 1.1; pH1N1 diagnosis: aHR = 1.0; 95% CI = 0.88, 1.2). Among women with preexisting medical conditions, influenza was associated with increased preterm birth (aHR = 1.5; 95% CI = 1.1, 2.2) and spontaneous preterm birth (aHR = 1.7; 95% CI = 1.1, 2.6), and these associations were strongest in the third trimester and when data were analyzed to allow for a transient acute effect of influenza.

CONCLUSIONS

In the general obstetrical population, there was no association between pH1N1 influenza illness and preterm birth, but women with preexisting medical conditions known to increase the risk of influenza-associated morbidity were at elevated risk.

The Influence of Meteorological Factors and Atmospheric Pollutants on the Risk of Preterm Birth

Atmospheric pollutants and meteorological conditions are suspected to be causes of preterm birth. We aimed to characterize their possible association with the risk of preterm birth (defined as birth occurring before 37 completed gestational weeks). We pooled individual data from 13 birth cohorts in 11 European countries (71,493 births from the period 1994-2011, European Study of Cohorts for Air Pollution Effects (ESCAPE)). City-specific meteorological data from routine monitors were averaged over time windows spanning from 1 week to the whole pregnancy. Atmospheric pollution measurements (nitrogen oxides and particulate matter) were combined with data from permanent monitors and land-use data into seasonally adjusted land-use regression models. Preterm birth risks associated with air pollution and meteorological factors were estimated using adjusted discrete-time Cox models. The frequency of preterm birth was 5.0%. Preterm birth risk tended to increase with first-trimester average atmospheric pressure (odds ratio per 5-mbar increase = 1.06, 95% confidence interval: 1.01, 1.11), which could not be distinguished from altitude. There was also some evidence of an increase in preterm birth risk with first-trimester average temperature in the -5°C to 15°C range, with a plateau afterwards (spline coding, P = 0.08). No evidence of adverse association with atmospheric pollutants was observed. Our study lends support for an increase in preterm birth risk with atmospheric pressure.

Invited Commentary: Influenza, Influenza Immunization, and Pregnancy-It's About Time

Immunization of pregnant women against influenza has the potential to reduce adverse fetal outcomes by reducing prenatal exposure to influenza illness. However, as touched on by Fell et al. (Am J Epidemiol. 2016;184(3):163-175) and Vazquez-Benitez et al. (Am J Epidemiol. 2016;184(3):176-186) in this issue of the Journal, observational studies in which the causal effect of maternal influenza illness and influenza immunization on fetal health are evaluated are prone to bias because of the complex temporal nature of influenza illness seasonality, influenza immunization schedules, and gestation itself. Immortal time bias is introduced by an "anytime-in-pregnancy" exposure definition because the shortened pregnancy duration associated with many adverse fetal outcomes limits the opportunity to become exposed, whereas including follow-up time during which pregnancies are no longer at risk of an adverse outcome (e.g., gestational time after 37 weeks in studies of preterm birth) can lead to overestimation of any true benefits of immunization (or harms from influenza illness). We present a framework to avoid time-related biases in the study of influenza illness and immunization in pregnancy and advise that investigations of fetal benefit from maternal influenza immunization should only be undertaken when information is available on the calendar time of influenza virus circulation and the gestational age at which maternal influenza immunization occurred.

Risk of Preterm or Small-for-Gestational-Age Birth After Influenza Vaccination During Pregnancy: Caveats When Conducting Retrospective Observational Studies

Vaccines are increasingly targeted toward women of reproductive age, and vaccines to prevent influenza and pertussis are recommended during pregnancy. Prelicensure clinical trials typically have not included pregnant women, and when they are included, trials cannot detect rare events. Thus, postmarketing vaccine safety assessments are necessary. However, analysis of observational data requires detailed assessment of potential biases. Using data from 8 Vaccine Safety Datalink sites in the United States, we analyzed the association of monovalent H1N1 influenza vaccine (MIV) during pregnancy with preterm birth (<37 weeks) and small-for-gestational-age birth (birth weight < 10th percentile). The cohort included 46,549 pregnancies during 2009-2010 (40% of participants received the MIV). We found potential biases in the vaccine-birth outcome association that might occur due to variable access to vaccines, the time-dependent nature of exposure to vaccination within pregnancy (immortal time bias), and confounding from baseline differences between vaccinated and unvaccinated women. We found a strong protective effect of vaccination on preterm birth (relative risk = 0.79, 95% confidence interval: 0.74, 0.85) when we ignored potential biases and no effect when accounted for them (relative risk = 0.91; 95% confidence interval: 0.83, 1.0). In contrast, we found no important biases in the association of MIV with small-for-gestational-age birth. Investigators conducting studies to evaluate birth outcomes after maternal vaccination should use statistical approaches to minimize potential biases.

Air Pollution and Preterm Birth in the U.S. State of Georgia (2002-2006): Associations with Concentrations of 11 Ambient Air Pollutants Estimated by Combining Community Multiscale Air Quality Model (CMAQ) Simulations with Stationary Monitor Measurements

BACKGROUND

Previous epidemiologic studies suggest associations between preterm birth and ambient air pollution.

OBJECTIVE

We investigated associations between 11 ambient air pollutants, estimated by combining Community Multiscale Air Quality model (CMAQ) simulations with measurements from stationary monitors, and risk of preterm birth (< 37 weeks of gestation) in the U.S. state of Georgia.

METHODS

Birth records for singleton births ≥ 27 weeks of gestation with complete covariate information and estimated dates of conception between 1 January 2002 and 28 February 2006 were obtained from the Office of Health Indicators for Planning, Georgia Department of Public Health (n = 511,658 births). Daily pollutant concentrations at 12-km resolution were estimated for 11 ambient air pollutants. We used logistic regression with county-level fixed effects to estimate associations between preterm birth and average pollutant concentrations during the first and second trimester. Discrete-time survival models were used to estimate third-trimester and total pregnancy associations. Effect modification was investigated by maternal education, race, census tract poverty level, and county-level urbanicity.

RESULTS

Trimester-specific and total pregnancy associations (p < 0.05) were observed for several pollutants. All the traffic-related pollutants (carbon monoxide, nitrogen dioxide, PM2.5 elemental carbon) were associated with preterm birth [e.g., odds ratios for interquartile range increases in carbon monoxide during the first, second, and third trimesters and total pregnancy were 1.005 (95% CI: 1.001, 1.009), 1.007 (95% CI: 1.002, 1.011), 1.010 (95% CI: 1.006, 1.014), and 1.011 (95% CI: 1.006, 1.017)]. Associations tended to be higher for mothers with low educational attainment and African American mothers.

CONCLUSION

Several ambient air pollutants were associated with preterm birth; associations were observed in all exposure windows.

CITATION

Hao H, Chang HH, Holmes HA, Mulholland JA, Klein M, Darrow LA, Strickland MJ. 2016. Air pollution and preterm birth in the U.S. state of Georgia (2002-2006): associations with concentrations of 11 ambient air pollutants estimated by combining Community Multiscale Air Quality Model (CMAQ) simulations with stationary monitor measurements. Environ Health Perspect 124:875-880; http://dx.doi.org/10.1289/ehp.1409651.

Immortal time bias in drug safety cohort studies: spontaneous abortion following nonsteroidal antiinflammatory drug exposure

OBJECTIVE

Experimental research of drug safety in pregnancy is generally not feasible because of ethical issues. Therefore, most of the information about drug safety in general and teratogenicity in particular is obtained through observational studies, which require careful methodologic design to obtain unbiased results. Immortal time bias occurs when some cases do not "survive" sufficient time in the study, and as such, they have reduced chances of being defined as "exposed" simply because the durations of their follow-ups were shorter. For example, studies that examine the risk for spontaneous abortions in women exposed to a drug during pregnancy are susceptible to immortal time bias because the chance of drug exposure increases the longer a pregnancy lasts. Therefore, the drug tested may falsely be found protective against the outcome tested. The objective of the current study was to illustrate the extent of immortal time bias using a cohort study of pregnancies assessing the risk for spontaneous abortions following nonsteroidal antiinflammatory drug exposure.

STUDY DESIGN

We assembled 3 databases containing data on spontaneous abortions, births and drug dispensions to create the present study's cohort. The risk for spontaneous abortion was assessed using 2 statistical analysis methods that were compared for 2 definitions of exposure (dichotomous, exposed vs unexposed, regular Cox regression vs Cox regression with time-varying exposure).

RESULTS

Significant differences were found in the risk for spontaneous abortions between the 2 statistical methods, both for groups and for most specific nonsteroidal antiinflammatory drugs (nonselective Cox inhibitors - hazard ratio, 0.70; 95% confidence interval, 0.61-0.94 vs hazard ratio, 1.10; 95% confidence interval, 0.99-1.22 for dichotomous vs time-varying exposure analyses, respectively). Furthermore, a significant correlation was found between the median misclassified immortal time for each drug and the extent of the bias.

CONCLUSION

Immortal time bias can easily occur in cohort studies assessing the risk for adverse pregnancy outcomes following exposure to drugs. One way to prevent such a bias is by defining exposure only from the time of exposure during follow-up onward using a time-varying exposure analysis.

Seasonal influenza vaccination during pregnancy and the risks of preterm delivery and small for gestational age birth

BACKGROUND

Influenza vaccination is routinely recommended for pregnant women, yet information on perinatal outcomes is sparse.

METHODS

We investigated the associations between trivalent (seasonal) influenza vaccination during pregnancy and the risks of preterm delivery (PTD, live birth <37 weeks gestation) and small for gestational age birth (SGA, <10th percentile in weight for sex-specific gestational age) during the influenza seasons 2006-07 through 2009-10. The study population included 1619 mothers of live-born, non-malformed singleton infants interviewed as part of the Slone Epidemiology Center's Birth Defects Study. Associations between influenza vaccination and PTD and SGA were assessed using Cox and logistic regression models, respectively, with propensity scores used to adjust for confounding. Women vaccinated against pandemic H1N1 were excluded from the analysis.

RESULTS

Influenza vaccination during pregnancy showed a near null association with PTD for influenza seasons 2006-07 through 2008-09 compared with unvaccinated women [adjusted hazard ratios (aHR) ranged from 0.79 [95% confidence interval (CI) 0.28, 2.21] in 2007-08 to 1.08 [95% CI: 0.40, 2.95] in 2008-09]. For 2009-10, the risk of PTD was higher in vaccinated women (aHR, 7.81 [95% CI: 2.66, 23.0]). Influenza vaccination was not associated with appreciable risks for SGA for all seasons with sufficient numbers of exposed SGA.

CONCLUSION

Though limited by study size, these findings add support to previous observations of little or no increased risk of PTD or SGA associated with seasonal influenza vaccination for three of the four influenza seasons in our study. The increased risk of PTD observed for the 2009-10 influenza season warrants further investigation.

Influenza vaccination and fetal and neonatal outcomes

As pregnant women are considered a high-risk group for severe influenza illness, current recommendations advise vaccination of all pregnant women with inactivated influenza vaccine. Nevertheless, rates of maternal influenza vaccination have historically been low, possibly reflecting ongoing concerns about vaccine safety. Until recently, the majority of evidence concerning safety of influenza vaccination during pregnancy was limited to post-marketing pharmacovigilance studies; however, in the past 5 years, one randomized clinical trial and a number of observational studies reflecting seasonal trivalent inactivated influenza vaccines and monovalent H1N1 influenza vaccines have been published. This review summarizes the evidence pertaining to fetal and neonatal outcomes following influenza vaccination during pregnancy for comparative analytic studies published between 2008 and August 2013. Since the majority of these studies are observational in nature, issues related to study quality are also addressed.

Maternal influenza vaccine and risks for preterm or small for gestational age birth

OBJECTIVE

To study the impact of influenza vaccine administered to pregnant women during all trimesters on the rates of preterm and small for gestational age (SGA) births, evaluating both increased and decreased risk.

STUDY DESIGN

This retrospective observational matched cohort study involved 7 Vaccine Safety Datalink sites across the US for the 2004-05 through 2008-09 influenza seasons. Cohort eligibility and outcomes were determined from administrative, claims, medical records, and birth data. In propensity score- and vaccine exposure time-matched analyses, ORs for preterm and SGA births were calculated.

RESULTS

Among 57 554 matched vaccinated and unvaccinated pregnant women, including 16 240 women in the first trimester, maternal vaccination was not associated with increased or decreased risk for preterm birth (OR for delivery at <37 weeks gestation, 0.97 [95% CI, 0.93-1.02]; for delivery at ≤32 weeks gestation, 0.98 [95% CI, 0.86-1.12]; and for delivery at ≤34 weeks gestation, 0.96 [95% CI, 0.88-1.04]) or SGA birth (OR for <5th percentile weight for gestational age, 1.02 [95% CI, 0.96-1.09], and for <10th percentile weight for gestational age, 1.00 [95% CI, 0.96-1.04]). Similarly, first trimester vaccination was not associated with increased or decreased risk for preterm or SGA birth.

CONCLUSION

Receipt of trivalent inactivated influenza vaccine during pregnancy was not associated with increased or decreased risk of preterm or SGA birth. These findings support the safety of vaccinating pregnant women against influenza during the first, second, and third trimesters, and suggest that a nonspecific protective effect of the influenza vaccine for these outcomes does not exist.

Time-dependent propensity score for assessing the effect of vaccine exposure on pregnancy outcomes through pregnancy exposure cohort studies

Women are advised to be vaccinated for influenza during pregnancy and may receive vaccine at any time during their pregnancy. In observational studies evaluating vaccine safety in pregnancy, to account for such time-varying vaccine exposure, a time-dependent predictor can be used in a proportional hazards model setting for outcomes such as spontaneous abortion or preterm delivery. Also, due to the observational nature of pregnancy exposure cohort studies and relatively low event rates, propensity score (PS) methods are often used to adjust for potential confounders. Using Monte Carlo simulation experiments, we compare two different ways to model the PS for vaccine exposure: (1) logistic regression treating the exposure status as binary yes or no; (2) Cox regression treating time to exposure as time-to-event. Coverage probability of the nominal 95% confidence interval for the exposure effect is used as the main measure of performance. The performance of the logistic regression PS depends largely on how the exposure data is generated. In contrast, the Cox regression PS consistently performs well across the different data generating mechanisms that we have considered. In addition, the Cox regression PS allows adjusting for potential time-varying confounders such as season of the year or exposure to additional vaccines. The application of the Cox regression PS is illustrated using data from a recent study of the safety of pandemic H1N1 influenza vaccine during pregnancy.

Air pollution and preterm premature rupture of membranes: a spatiotemporal analysis

Preterm premature rupture of membranes (PROM) is the leading identifiable predisposing factor for preterm birth. Although maternal exposure to air pollution can potentially have an impact on preterm PROM, there is no available evidence on such an impact. In this study, based on 5,555 singleton births occurring in Barcelona, Spain (2002-2005), we investigated the associations of maternal exposure to nitrogen dioxide, nitrogen oxides, and particulate matter with aerodynamic diameters of ≤2.5 µm (PM2.5), 2.5 µm-10 µm, and ≤10 µm and PM2.5 light absorption with preterm PROM and gestational age at the rupture of membranes (ROM). We utilized temporally adjusted land-use regression models to predict pollutant levels at each subject's home address during each week of her pregnancy. We conducted matched (according to the length of exposure) case-control analyses to estimate the preterm PROM risk associated with 1 interquartile-range increase in exposure levels during the entire pregnancy and during the last 3 months prior to ROM. We found an increase in preterm PROM risk of up to 50% (95% confidence interval: 4, 116) and a 1.3-day (95% confidence interval: -1.9, -0.6) reduction in gestational age at ROM associated with PM2.5 absorbance, nitrogen dioxide exposure, and nitrogen oxide exposure during the entire pregnancy and the last 3 months prior to ROM.

Epidemiologic tools to study the influence of environmental factors on fecundity and pregnancy-related outcomes

Adverse pregnancy outcomes entail a large health burden for the mother and offspring; a part of it might be avoided by better understanding the role of environmental factors in their etiology. Our aims were to review the assessment tools to characterize fecundity troubles and pregnancy-related outcomes in human populations and their sensitivity to environmental factors. For each outcome, we reviewed the possible study designs, main sources of bias, and their suggested cures. In terms of study design, for most pregnancy outcomes, cohorts with recruitment early during or even before pregnancy allow efficient characterization of pregnancy-related events, time-varying confounders, and in utero exposures that may impact birth outcomes and child health. Studies on congenital anomalies require specific designs, assessment of anomalies in medical pregnancy terminations, and, for congenital anomalies diagnosed postnatally, follow-up during several months after birth. Statistical analyses should take into account environmental exposures during the relevant time windows; survival models are an appropriate approach for fecundity, fetal loss, and gestational duration/preterm delivery. Analysis of gestational duration could distinguish pregnancies according to delivery induction (and possibly pregnancy-related conditions). In conclusion, careful design and analysis are required to better characterize environmental effects on human reproduction.

Ambient air pollution and preeclampsia: a spatiotemporal analysis

BACKGROUND

Available evidence concerning the association between air pollution and preeclampsia is limited, and specific associations with early- and late-onset preeclampsia have not been assessed.

OBJECTIVES

We investigated the association, if any, between preeclampsia (all, early-, and late-onset) and exposure to nitrogen dioxide, nitrogen oxides, particulate matter with aerodynamic diameter ≤ 2.5 μm (PM2.5; fine particles), ≤ 10 μm, and 2.5-10 μm, and PM2.5 light absorption (a proxy for elemental carbon) during the entire pregnancy and during the first, second, and third trimesters.

METHODS

This study was based on 8,398 pregnancies (including 103 cases of preeclampsia) among women residing in Barcelona, Spain (2000-2005). We applied a spatiotemporal exposure assessment framework using land use regression models to predict ambient pollutant levels during each week of pregnancy at the geocoded residence address of each woman at the time of birth. Logistic and conditional logistic regression models were used to estimate unadjusted and adjusted associations.

RESULTS

We found positive associations for most of our evaluated outcome-exposure pairs, with the strongest associations observed for preeclampsia and late-onset preeclampsia in relation to the third-trimester exposure to fine particulate pollutants, and for early-onset preeclampsia in relation to the first-trimester exposure to fine particulate pollutants. Among our investigated associations, those of first- and third-trimester exposures to PM2.5 and third-trimester exposure to PM2.5 absorbance and all preeclampsia, and third-trimester PM2.5 exposure and late-onset preeclampsia attained statistical significance.

CONCLUSION

We observed increased risk of preeclampsia associated with exposure to fine particulate air pollution. Our findings, in combination with previous evidence suggesting distinct pathogenic mechanisms for early- and late-onset preeclampsia, support additional research on this topic.

Air pollution, inflammation and preterm birth in Mexico City: study design and methods

Preterm birth is one of the leading causes of perinatal mortality and is associated with long-term adverse health consequences for surviving infants. Preterm birth rates are rising worldwide, and no effective means for prevention currently exists. Air pollution exposure may be a significant cause of prematurity, but many published studies lack the individual, clinical data needed to elucidate possible biological mechanisms mediating these epidemiological associations. This paper presents the design of a prospective study now underway to evaluate those mechanisms in a cohort of pregnant women residing in Mexico City. We address how air quality may act together with other factors to induce systemic inflammation and influence the duration of pregnancy. Data collection includes: biomarkers relevant to inflammation in cervico-vaginal exudate and peripheral blood, along with full clinical information, pro-inflammatory cytokine gene polymorphisms and air pollution data to evaluate spatial and temporal variability in air pollution exposure. Samples are collected on a monthly basis and participants are followed for the duration of pregnancy. The data will be used to evaluate whether ambient air pollution is associated with preterm birth, controlling for other risk factors. We will evaluate which time windows during pregnancy are most influential in the air pollution and preterm birth association. In addition, the epidemiological study will be complemented with a parallel toxicology invitro study, in which monocytic cells will be exposed to air particle samples to evaluate the expression of biomarkers of inflammation.

Correcting for exposure misclassification using survival analysis with a time-varying exposure

PURPOSE

Survival analysis is increasingly being used in perinatal epidemiology to assess time-varying risk factors for various pregnancy outcomes. Here we show how quantitative correction for exposure misclassification can be applied to a Cox regression model with a time-varying dichotomous exposure.

METHODS

We evaluated influenza vaccination during pregnancy in relation to preterm birth among 2267 non-malformed infants whose mothers were interviewed as part of the Slone Birth Defects Study during 2006 through 2011. The hazard of preterm birth was modeled using a time-varying exposure Cox regression model with gestational age as the time-scale. The effect of exposure misclassification was then modeled using a probabilistic bias analysis that incorporated vaccination date assignment. The parameters for the bias analysis were derived from both internal and external validation data.

RESULTS

Correction for misclassification of prenatal influenza vaccination resulted in an adjusted hazard ratio (AHR) slightly higher and less precise than the conventional analysis: Bias-corrected AHR 1.04 (95% simulation interval, 0.70-1.52); conventional AHR, 1.00 (95% confidence interval, 0.71-1.41).

CONCLUSIONS

Probabilistic bias analysis allows epidemiologists to assess quantitatively the possible confounder-adjusted effect of misclassification of a time-varying exposure, in contrast with a speculative approach to understanding information bias.

Maternal exposure to ambient temperature and the risks of preterm birth and stillbirth in Brisbane, Australia

Almost 10% of all births are preterm, and 2.2% are stillbirths. Recent research has suggested that environmental factors may be a contributory cause of these adverse birth outcomes. The authors examined the relation between ambient temperature and preterm birth and stillbirth in Brisbane, Australia, between 2005 and 2009 (n = 101,870). They used a Cox proportional hazards model with livebirth and stillbirth as competing risks. They also examined whether there were periods in pregnancy where exposure to high temperatures had a greater effect. Higher ambient temperatures in the last 4 weeks of the pregnancy increased the risk of stillbirth. The hazard ratio for stillbirth was 0.3 at 12°C relative to the reference temperature of 21°C. The temperature effect was greatest at less than 36 weeks of gestation. There was an association between higher temperature and shorter gestation, as the hazard ratio for livebirth was 0.96 at 15°C and 1.02 at 25°C. This effect was greatest at later gestational ages. These results provide strong evidence of an association between increased temperature and increased risk of stillbirth and shorter gestation.

The impact of different causal models on estimated effects of disinfection by-products on preterm birth

BACKGROUND

Previous epidemiologic studies of preterm birth and drinking water disinfection by-products (DBP) reported inconsistent results especially for third trimester exposures. These inconsistencies may have been due to differences in the underlying causal model assumed and methodological issues, including the method of analysis (cumulative vs. density-sampling of controls and matching on gestational age) and appropriate control of confounding.

METHODS

We use data from previously published research to illustrate how different causal models, methods of analysis, and the choice of covariates to control impact results.

RESULTS

Exposure at high measured TTHM levels (≥ 60 μg/l) during the last trimester - with cumulatively sampled controls - corresponded to negative effect estimates when comparing preterm to term births and averaging exposure over different length periods. In contrast, density-sampling of controls with an exposure truncated at 36 weeks gestation and adjustment for possible confounding by exposures experienced in prior trimesters led to moderate changes in risk at the highest level of exposure averaged over the four weeks prior to birth.

CONCLUSIONS

We recommend that future research on an exposure to DBPs and risk of preterm birth explore the sensitivity of their findings to different model specifications, specifically: (1) cumulative vs. density-sampling of controls when evaluating third trimester or whole pregnancy exposures, taking into account exposure-averaging length; (2) short-term peak exposures vs. long-term exposures; and (3) adjustment for exposure during prior pregnancy periods when evaluating later trimester exposures to account for possible 'priming' effects of early exposures.

The diagnosis of urinary tract infection: a systematic review

BACKGROUND

Urinary tract infections (UTI) are among the leading reasons for treatment in adult primary care medicine, accounting for a considerable percentage of antibiotic prescriptions. Because this problem is so common and so significant in routine clinical practice, a high level of diagnostic accuracy is essential. Antibiotics should not be prescribed excessively, particularly in view of the increasing prevalence of antibiotic resistance.

METHOD

Systematic review of relevant articles that were retrieved by a search of the Medline, Embase, and Cochrane Library databases. The recommendations of selected international guidelines were also taken into account, as were the German national quality standards for microbiological diagnosis.

RESULTS

The diagnosis of UTI by clinical criteria alone has an error rate of approximately 33%. The use of refined diagnostic algorithms does not completely eliminate uncertainty.

CONCLUSION

With the aid of a small number of additional diagnostic criteria, antibiotic treatment for UTI can be provided more specifically and thus more effectively. Differentiating UTI from asymptomatic bacteriuria, which usually requires no treatment, can lower the frequency of unnecessary antibiotic prescriptions.

Methodological issues in studies of air pollution and reproductive health

In the past decade there have been an increasing number of scientific studies describing possible effects of air pollution on perinatal health. These papers have mostly focused on commonly monitored air pollutants, primarily ozone (O(3)), particulate matter (PM), sulfur dioxide (SO(2)), carbon monoxide (CO), and nitrogen dioxide (NO(2)), and various indices of perinatal health, including fetal growth, pregnancy duration, and infant mortality. While most published studies have found some marker of air pollution related to some types of perinatal outcomes, variability exists in the nature of the pollutants and outcomes associated. Synthesis of the findings has been difficult for various reasons, including differences in study design and analysis. A workshop was held in September 2007 to discuss methodological differences in the published studies as a basis for understanding differences in study findings and to identify priorities for future research, including novel approaches for existing data. Four broad topic areas were considered: confounding and effect modification, spatial and temporal exposure variations, vulnerable windows of exposure, and multiple pollutants. Here we present a synopsis of the methodological issues and challenges in each area and make recommendations for future study. Two key recommendations include: (1) parallel analyses of existing data sets using a standardized methodological approach to disentangle true differences in associations from methodological differences among studies; and (2) identification of animal studies to inform important mechanistic research gaps. This work is of critical public health importance because of widespread exposure and because perinatal outcomes are important markers of future child and adult health.

Different effects of PM10 exposure on preterm birth by gestational period estimated from time-dependent survival analyses

PURPOSE

We conducted this study to determine if the preterm risks due to PM(10) exposure vary with the exposure periods during pregnancy. This study was also conducted to estimate the different effects of PM(10) exposure on preterm birth by exposure periods using the extended Cox model with PM(10) exposure as a time-dependent covariate.

METHODS

We studied birth data obtained from the Korea National Statistical office for 374,167 subjects who were delivered between 1998 and 2000 in Seoul, South Korea. We used PM(10) data that was measured hourly to give 24-h averages at 27 monitoring stations in Seoul. The extended Cox model with time-dependent exposure was used to determine if the risk of preterm delivery could be associated with PM(10) exposures for each trimester during pregnancy.

RESULTS

Effect of PM10 exposure prior to the 37 weeks of gestational period was stronger on the risk of premature birth than that posterior to the 37 weeks of gestational weeks. This trend was consistent for each trimester; however, the hazard ratios for preterm delivery associated with PM(10) exposure in the first and third trimester were slightly higher than those of the second trimester.

CONCLUSIONS

The risk of preterm birth associated with exposure to PM(10) differed with the exposure period of the neonates. Therefore, when studying the impact of air pollution exposure during pregnancy, the exposure period during pregnancy should be considered.

Meeting report: atmospheric pollution and human reproduction

BACKGROUND

There is a growing body of epidemiologic literature reporting associations between atmospheric pollutants and reproductive outcomes, particularly birth weight and gestational duration.

OBJECTIVES

The objectives of our international workshop were to discuss the current evidence, to identify the strengths and weaknesses of published epidemiologic studies, and to suggest future directions for research.

DISCUSSION

Participants identified promising exposure assessment tools, including exposure models with fine spatial and temporal resolution that take into account time-activity patterns. More knowledge on factors correlated with exposure to air pollution, such as other environmental pollutants with similar temporal variations, and assessment of nutritional factors possibly influencing birth outcomes would help evaluate importance of residual confounding. Participants proposed a list of points to report in future publications on this topic to facilitate research syntheses. Nested case-control studies analyzed using two-phase statistical techniques and development of cohorts with extensive information on pregnancy behaviors and biological samples are promising study designs. Issues related to the identification of critical exposure windows and potential biological mechanisms through which air pollutants may lead to intrauterine growth restriction and premature birth were reviewed.

CONCLUSIONS

To make progress, this research field needs input from toxicology, exposure assessment, and clinical research, especially to aid in the identification and exposure assessment of feto-toxic agents in ambient air, in the development of early markers of adverse reproductive outcomes, and of relevant biological pathways. In particular, additional research using animal models would help better delineate the biological mechanisms underpinning the associations reported in human studies.

Maternal urinary tract infection and related drug treatments during pregnancy and risk of congenital abnormalities in the offspring

OBJECTIVE

The association between urinary tract infection (UTI) of pregnant women and preterm birth/low birthweight is known, but the possible association between UTI and congenital abnormalities (CAs) was evaluated rarely. Only one study showed an association with atrial septal defect, thus we decided to check this possible association.

DESIGN

The population-based large data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (HCCSCA); most maternal UTIs were based on medically recorded data. SETTING The HCCSCA, 1980-1996, contained 22 843 newborns or fetuses with CAs and 38 151 matched controls, i.e. newborn infants without any HCAs.

POPULATION

Hungarian informative offspring: live births, stillbirths and prenatally diagnosed malformed fetuses.

METHODS

Case-control pair analysis.

MAIN OUTCOME MEASURES

Twenty-five CA groups.

RESULTS

A total of 1542 (6.75%) mothers in the case group had UTI during entire pregnancy compared with 2188 (5.74%) mothers in the control group (adjusted prevalence odds ratios [POR] with 95% CI: 1.15, 1.06-1.24). We did not find a higher prevalence of UTI during the second and/or third months of pregnancy in total case group (adjusted POR with 95% CI: 1.1, 0.9-1.2) and in any group of CAs including atrial septal defect type II.

CONCLUSIONS

No evidence for the teratogenic effect of maternal UTI and related drug treatments during early pregnancy.