Gestational exposure to organochlorine compounds and metals and infant birth weight: effect modification by maternal hardships.

BACKGROUND: Gestational exposure to toxic environmental chemicals and maternal social hardships are individually associated with impaired fetal growth, but it is unclear whether the effects of environmental chemical exposure on infant birth weight are modified by maternal hardships. METHODS: We used data from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a pan-Canadian cohort of 1982 pregnant females enrolled between 2008 and 2011. We quantified eleven environmental chemical concentrations from two chemical classes - six organochlorine compounds (OCs) and five metals - that were detected in ≥ 70% of blood samples collected during the first trimester. We examined fetal growth using birth weight adjusted for gestational age and assessed nine maternal hardships by questionnaire. Each maternal hardship variable was dichotomized to indicate whether the females experienced the hardship. In our analysis, we used elastic net to select the environmental chemicals, maternal hardships, and 2-way interactions between maternal hardships and environmental chemicals that were most predictive of birth weight. Next, we obtained effect estimates using multiple linear regression, and plotted the relationships by hardship status for visual interpretation. RESULTS: Elastic net selected trans-nonachlor, lead, low educational status, racially minoritized background, and low supplemental folic acid intake. All were inversely associated with birth weight. Elastic net also selected interaction terms. Among those with increasing environmental chemical exposures and reported hardships, we observed stronger negative associations and a few positive associations. For example, every two-fold increase in lead concentrations was more strongly associated with reduced infant birth weight among participants with low educational status (ß = -100 g (g); 95% confidence interval (CI): -215, 16), than those with higher educational status (ß = -34 g; 95% CI: -63, -3). In contrast, every two-fold increase in mercury concentrations was associated with slightly higher birth weight among participants with low educational status (ß = 23 g; 95% CI: -25, 71) compared to those with higher educational status (ß = -9 g; 95% CI: -24, 6). CONCLUSIONS: Our findings suggest that maternal hardships can modify the associations of gestational exposure to some OCs and metals with infant birth weight.

Validation of Insurance Billing Codes for Monitoring Antenatal Screening.

BACKGROUND: Prevalence statistics for pregnancy complications identified through screening such as gestational diabetes usually assume universal screening. However, rates of screening completion in pregnancy are not available in many birth registries or hospital databases. We validated screening-test completion by comparing public insurance laboratory and radiology billing records with medical records at three hospitals in British Columbia, Canada. METHODS: We abstracted a random sample of 140 delivery medical records (2014-2019), and successfully linked 127 to valid provincial insurance billings and maternal-newborn registry data. We compared billing records for gestational diabetes screening, any ultrasound before 14 weeks gestational age, and Group B streptococcus screening during each pregnancy to the gold standard of medical records by calculating sensitivity and specificity, positive predictive value, negative predictive value, and prevalence with 95% confidence intervals (CIs). RESULTS: Gestational diabetes screening (screened vs. unscreened) in billing records had a high sensitivity (98% [95% CI = 93, 100]) and specificity (>99% [95% CI = 86, 100]). The use of specific glucose screening approaches (two-step vs. one-step) were also well characterized by billing data. Other tests showed high sensitivity (ultrasound 97% [95% CI = 92, 99]; Group B streptococcus 96% [95% CI = 89, 99]) but lower negative predictive values (ultrasound 64% [95% CI = 33, 99]; Group B streptococcus 70% [95% CI = 40, 89]). Lower negative predictive values were due to the high prevalence of these screening tests in our sample. CONCLUSIONS: Laboratory and radiology insurance billing codes accurately identified those who completed routine antenatal screening tests with relatively low false-positive rates.

The effect of changing screening practices and demographics on the incidence of gestational diabetes in British Columbia, 2005-2019.

BACKGROUND: Rates of gestational diabetes are reported to be increasing in many jurisdictions, but the reasons for this are poorly understood. We sought to evaluate the relative contribution of screening practices for gestational diabetes (including completion and methods of screening) and population characteristics to risk of gestational diabetes in British Columbia, Canada, from 2005 to 2019. METHODS: We used a population-based cohort from a provincial registry of perinatal data, linked to laboratory billing records. We used data on screening completion, screening method (1-step 75-g glucose test or 2-step approach of 50-g glucose screening test, followed by a diagnostic test for patients who screen positive) and demographic risk factors. We modelled predicted annual risk for gestational diabetes, sequentially adjusted for screening completion, screening method and risk factors. RESULTS: We included 551 457 pregnancies in the study cohort. The incidence of gestational diabetes more than doubled over the study period, from 7.2% in 2005 to 14.7% in 2019. Screening completion increased from 87.2% in 2005 to 95.5% in 2019. Use of 1-step screening methods increased from 0.0% in 2005 to 39.5% in 2019 among those who were screened. Unadjusted models estimated a 2.04 (95% confidence interval [CI] 1.94-2.13) increased risk of gestational diabetes in 2019 (v. 2005). This increase was 1.89 (95% CI 1.81-1.98) after accounting for the rise in screening completion and 1.34 (95% CI 1.28-1.40) after accounting for changes in screening methods. Further accounting for demographic risk factors (e.g., age, body mass index, prenatal care) had a small impact (increase of 1.25, 95% CI 1.19-1.31). INTERPRETATION: Most of the observed increase in the incidence of gestational diabetes was attributable to changes in screening practices (primarily changes in screening methods) rather than changing population factors. Our findings highlight the importance of understanding variation in screening practices when monitoring incidence rates for gestational diabetes.

Trends in Gestational Diabetes Screening Practices in British Columbia from 2005-2019.

OBJECTIVES: To examine trends in the frequency and method (one-step vs. two-step) of gestational diabetes mellitus (GDM) screening in British Columbia (BC), Canada, across subgroups of pregnant individuals in the context of changing local and national clinical practice guidelines. METHODS: We conducted a retrospective cohort study using de-identified, linked perinatal and laboratory billing data. We included all pregnancies delivered in BC after 28 weeks gestation, with screening dates between June 2004 and May 2019. We calculated the prevalence of each screening method with 95% CI overall and over time, and we examined screening practices in subgroups and different geographic regions. In October 2010, BC began recommending a one-step method; therefore, we examined time periods relative to this and other Canadian guideline changes. RESULTS: Screening completion increased over the study period, from 88% in 2004 to 96% in 2019. After a guideline change in 2010, use of one-step screening increased sharply from 2.0% (95% CI 1.9-2.0) to 45.2% (95% CI 44.9-45.6). Following the 2013 Diabetes Canada guideline change, one-step screening decreased to 42.8% (95% CI 42.5-43.1). Of those receiving one-step screening, 18% were diagnosed with GDM compared to 9% with two-step screening. Use of one-step screening was higher in pregnant people with risk factors and in larger urban centres. CONCLUSION: GDM screening in BC demonstrated higher use of one-step screening among people with risk factors; however, there were strong regional disparities and considerable variation in screening practices over time and across subgroups.

Survey of Mode of Delivery and Maternal and Perinatal Outcomes in Canada.

OBJECTIVE: To identify determinants of cesarean delivery (CD) and examine associations between mode of delivery (MOD) and maternal and perinatal outcomes. METHODS: We conducted a retrospective analysis of a Canadian multicentre birth cohort derived from provincial data collected in 2008/2009. Maternal and perinatal characteristics and outcomes were compared between vaginal and cesarean birth and between the following MOD subgroups: spontaneous vaginal delivery (VD), assisted VD, planned cesarean delivery (CD), and intrapartum CD. Multivariate regression identified determinants of CD and the effects of MOD and previous CD on maternal and perinatal outcomes. RESULTS: The cohort included 264 755 births (72.1% VD and 27.9% CD) from 91 participating institutions. Determinants of CD included maternal age, parity, previous CD, chronic hypertension, diabetes, urinary tract infection or pyelonephritis, gestational hypertension, vaginal bleeding, labour induction, pre-term gestational age, low birth weight, large for gestational age, malpresentation, and male sex. CD was associated with greater risk of maternal and perinatal morbidity and mortality. Subgroup analysis demonstrated higher risk of adverse pregnancy outcomes with assisted VD and intrapartum CD than spontaneous VD. Planned CD reduced the risk of obstetric wound hematoma and perinatal mortality but increased maternal and neonatal morbidity. Previous CD increased the risk of maternal and neonatal morbidity among multiparous women. CONCLUSIONS: The CD rate in Canada is consistent with global trends reflecting demographic and obstetric intervention factors. The risk of adverse pregnancy outcomes with CD warrants evaluation of interventions to safely prevent nonessential cesarean birth.

Prenatal exposure to endocrine disrupting chemical mixtures and infant birth weight: A Bayesian analysis using kernel machine regression.

BACKGROUND: Pregnant women are regularly exposed to a multitude of endocrine disrupting chemicals (EDCs). EDC exposures, both individually and as mixtures, may affect fetal growth. The relationship of EDC mixtures with infant birth weight, however, remains poorly understood. We examined the relations between prenatal exposure to EDC mixtures and infant birth weight. METHODS: We used data from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a pan-Canadian cohort of 1857 pregnant women enrolled between 2008 and 2011. We quantified twenty-one chemical concentrations from five EDC classes, including organochlorine compounds (OCs), metals, perfluoroalkyl substances (PFAS), phenols and phthalate metabolites that were detected in >70% of urine or blood samples collected during the first trimester. In our primary analysis, we used Bayesian kernel machine regression (BKMR) models to assess variable importance, explore EDC mixture effects, and identify any interactions among EDCs. Our secondary analysis used traditional linear regression to compare the results with those of BKMR and to quantify the changes in mean birth weight in relation to prenatal EDC exposures. RESULTS: We found evidence that mixtures of OCs and metals were associated with monotonic decreases in mean birth weight across the whole range of exposure. trans-Nonachlor from the OC mixture and lead (Pb) from the metal mixture had the greatest impact on birth weight. Our linear regression analysis corroborated the BKMR results and found that a 2-fold increase in trans-nonachlor and Pb concentrations reduced mean birth weight by -38 g (95% confidence interval (CI): -67, -10) and -39 g (95% CI: -69, -9), respectively. A sex-specific association for OC mixture was observed among female infants. PFAS, phenols and phthalates were not associated with birth weight. No interactions were observed among the EDCs. CONCLUSIONS: Using BKMR, we observed that both OC and metal mixtures were associated with decreased birth weight in the MIREC Study. trans-Nonachlor from the OC mixture and Pb from the metal mixture contributed most to the adverse effects.

Perinatal outcomes of planned home birth after cesarean and planned hospital vaginal birth after cesarean at term gestation in British Columbia, Canada: A retrospective population-based cohort study.

BACKGROUND: The aim of this retrospective population-based cohort study was to determine whether the mode of delivery and maternal and neonatal outcomes differ between planned home VBAC (HBAC) and planned hospital VBAC. METHODS: All midwifery clients with at least one prior cesarean birth delivered between April 2000 and March 2017 (N = 4741; n = 4180 planned hospital VBAC, n = 561 planned HBAC) were included. Multivariate binomial logistic regression analyses were conducted to calculate the odds ratios adjusted for the potential covariates. The primary outcome was the mode of delivery, and the secondary outcomes were uterine rupture/dehiscence, postpartum hemorrhage, nonintact perineum, episiotomy, obstetric trauma, Apgar score <7 at 5 minutes, neonatal resuscitation requiring positive pressure ventilation, neonatal intensive care unit admission, and a composite outcome of severe neonatal mortality and morbidity and maternal mortality and morbidity. RESULTS: Planned HBAC was associated with a significant 39% decrease in the odds of having a cesarean birth (aOR 0.61, 95% CI 0.47-0.79) adjusting for the prepregnancy and pregnancy characteristics. Severe adverse outcomes were relatively rare in both settings; thus, our study did not have sufficient power to detect the true differences associated with the place of birth. CONCLUSIONS: Home births for those eligible for VBACs and attended by registered midwives within an integrated health system were associated with higher vaginal birth rates compared with planned hospital VBACs. Severe adverse outcomes were relatively rare in both settings.

Maternal Vitamin D Levels During Pregnancy and Their Effects on Maternal-Fetal Outcomes: A Systematic Review.

To synthesize and critically review the current evidence available on maternal vitamin D deficiency and its effects on maternal-fetal outcomes, this study reviewed the maternal-fetal outcomes, including prolonged labour or cesarean delivery, preeclampsia, gestational diabetes, low birth weight and small for gestational age, and preterm birth. An extensive systematic searched was performed in Medline and EMBASE, where a medical subject heading (MeSH) was used with terms "Vitamin D/25(OH)D" and "pregnancy/fetal outcomes"; these terms were combined with "and." In Web of Science and Google Scholar, a key word search was used. Nineteen articles were included for full review. This review found that the current state of the evidence is equivocal for maternal-fetal outcomes such as the risk of prolonged labour and cesarean delivery, gestational diabetes, low birth weight and small for gestational age, and preterm birth. Although some previous studies have found improvement in pregnancy outcomes with sufficient vitamin D levels, others have not shown any association with the aforementioned outcomes. This systematic review also highlights an association between the risk of preeclampsia and maternal vitamin D levels that is found to be consistent among studies.

2009 IOM guidelines for gestational weight gain: how well do they predict outcomes across ethnic groups?

Objective: To determine whether the Institute Of Medicine's (IOM) 2009 guidelines for weight-gain during pregnancy are predictive of maternal and infant outcomes in ethnic minority populations.Methods: We designed a population-based study using administrative data on 181,948 women who delivered live singleton births in Washington State between 2006-2008. We examined risks of gestational hypertension, preeclampsia/eclampsia, cesarean delivery, and extended hospital stay in White, Black, Native-American, East-Asian, Hispanic, South-Asian and Hawaiian/Pacific islander women according to whether they gained more or less weight during pregnancy than recommended by IOM guidelines. We also examined risks of neonatal outcomes including Apgar score <7 at 5 min, admission to NICU, requirement for ventilation, and a diagnosis of small or large for gestational age at birth.Results: Gaining too much weight was associated with increased odds for gestational hypertension (adjusted OR (aOR) ranged between 1.53-2.22), preeclampsia/eclampsia (aOR 1.44-1.81), cesarean delivery (aOR 1.07-1.38) and extended hospital stay (aOR 1.06-1.28) in all ethnic groups. Gaining too little weight was associated with decreased odds for gestational hypertension and delivery by cesarean section in Whites, Blacks and Hispanics. Gaining less weight or more weight than recommended was associated with increased odds for small for gestational age and large for gestational age infants respectively, in all ethnic groups.Conclusions: Adherence to the 2009 IOM guidelines for weight gain during pregnancy reduces risk for various adverse maternal outcomes in all ethnic groups studied. However, the guidelines were less predictive of infant outcomes with the exception of small and large for gestational age.Abbreviations: GWG: Gestational weight gain; IOM/NRC; Institute of Medicine and National Research Council; NICU: Neonatal intensive care need for ventilation; SGA: Small for gestational age; LGA: Large for gestational age; BERD: Birth Events Records Database; CHARS: Comprehensive Hospital Discharge Abstract Reporting System; ICD: International Classification of Disease; LMP: Last menstrual period; OR: Odds ratio.

Coal smoke, gestational cadmium exposure, and fetal growth.

BACKGROUND: Gestational cadmium exposure may impair fetal growth. Coal smoke has largely been unexplored as a source of cadmium exposure. We investigated the relationship between gestational cadmium exposure and fetal growth, and assessed coal smoke as a potential source of airborne cadmium, among non-smoking pregnant women in Ulaanbaatar, Mongolia, where coal combustion in home heating stoves is a major source of outdoor and indoor air pollution. METHODS: This observational study was nested within the Ulaanbaatar Gestation and Air Pollution Research (UGAAR) study, a randomized controlled trial of portable high efficiency particulate air (HEPA) filter air cleaner use during pregnancy, fetal growth, and early childhood development. We measured third trimester blood cadmium concentrations in 374 out of 465 participants who had a live birth. We used multiple linear and logistic regression to assess the relationships between log2-transformed maternal blood cadmium concentrations and birth weight, length, head circumference, ponderal index, low birth weight, small for gestational age, and preterm birth in crude and adjusted models. We also evaluated the relationships between log2-transformed blood cadmium concentrations and the density of coal-burning stoves within 5000 m of each participant's apartment as a proxy of coal smoke emissions from home heating stoves. RESULTS: The median (25th,75th percentile) blood cadmium concentration was 0.20 (0.15, 0.29) µg/L. A doubling of blood cadmium was associated with a 95 g (95% CI: 34, 155 g) reduction in birth weight in adjusted models. An interquartile range increase in coal stove density (from 3.4 to 4.9 gers/hectare) surrounding participants' apartments was associated with a 12.2% (95% CI: 0.3, 25.6%) increase in blood cadmium concentrations. CONCLUSIONS: Gestational cadmium exposure was associated with reduced birth weight. In settings where coal is a widely used fuel, cadmium may play a role in the putative association between air pollution and impaired fetal growth.