Tracking Fracking for Poor Birth Outcomes

Fracking (hydraulic fracturing) is shorthand for the underground injection of water and chemicals into sedimentary rock, forcing out trapped natural gas. The process creates “produced water,” which is a combination of the water and chemicals injected plus previously existing groundwater and other substances that might be underground. Although there are plenty of potential problems with other parts of the process, produced water is particularly problematic, as it is often full of carcinogensheavy metalsradioactive elements and a wide variety of other toxic materials. Evidence exists associating multiple significant adverse health outcomes with people who live near fracking wells.

Researchers in Alberta, Canada examined this by studying infants born to parents living in rural regions within 10 kilometers of fracking activity.1 Between 2013 and 2018, Alberta was home to 4871 active fracking wells and during that time 26,193 people who lived in rural locations had a total of 34,873 pregnancies. Researchers identified 9158 individuals who gave birth within 10 kilometers of at least 1 fracking site during preconception and/or pregnancy. Urban locations were excluded. The parents were assessed for socioeconomic status, age at delivery, comorbidities, and other risk factors for adverse outcomes. The infants born from these pregnancies then had data collected and various problems were recorded, including major congenital anomalies, severe morbidity/mortality, prematurity, and small for gestational age (SGA) status, defined as weight <10% of expected for gestational age.

Associations were found between proximity during preconception and pregnancy to any well for SGA (adjusted risk ratio [aRR] 1‌.12, 95% CI 1‌‌.03-1.23) and major congenital abnormalities (aRR 1.33, 95% CI 1.01-1.69). Being conceived or being pregnant within 10 km of >100 fracking sites increased the risk of preterm labor to 1.64 (95% CI 1.04-2.60) and SGA to 1.65 (95% CI 1‌‌.1-2.48). Sensitivity analysis demonstrated that neither fracking exposure during preconception or pregnancy alone had a significant association, but exposure during both periods did, suggesting a dose response.

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Observational cohorts and case studies are subject to a lot of confounding, and proving causality due to an environmental exposure is notoriously difficult. The Bradford-Hill viewpoints, one of the founding documents of causal inference theory, listed temporality and dose-response as issues to consider when arguing for causation. Although there is plenty more evidence to be gathered about the likelihood of fracking causing harm, this study does its best to adjust for confounding by taking into account socioeconomic factors and significantly strengthens the case for dose-response and temporality, as pregnancy and conception are very well-defined time-sensitive phenomena compared to development of most cancers. These data support that being around more fracking wells and having a longer period of exposure both significantly increased the risk of adverse outcomes. This study provides another piece of the “evidence pie” of so-called sufficient components that suggest fracking may contribute to a variety of bad health outcomes.

A New CHAPter for Treating Chronic Hypertension in Pregnancy

Chronic hypertension in pregnancy is associated with an increased risk of maternal and perinatal death as well as preeclampsia, placental abruption, and preterm birth or small-for gestational age. While there is a consensus for the treatment of pregnant women with severe hypertension, the best strategy for the treatment of mild chronic hypertension during pregnancy remains unclear.

The recently published open-label randomized CHAP trial2 conducted in the United States evaluated the efficacy of an antihypertensive therapy initiated at a systolic blood pressure (SBP) ≥ 140 mm Hg or diastolic blood pressure (DBP) ≥ 90 mm Hg compared with standard treatment with initiation at either ≥ 160 mm Hg SBP or ≥ 105 mm Hg DBP. CHAP enrolled pregnant patients who were less than 23 weeks of gestation with a viable singleton fetus and a diagnosis of new or known mild chronic hypertension. Hypertension was defined as SBP ≥ 140 mm Hg, DBP of ≥ 90 mm Hg, or both, measured on at least 2 occasions before 20 weeks of gestation.

The patients were randomized to immediate therapy initiation (active therapy group) or initiation only after an episode of severe hypertension (control group). Preferred antihypertensive agents for both groups were labetalol or nifedipine. Once initiated, the therapy target for both groups was a blood pressure lower than 140/90 mm Hg. The primary efficacy outcome was a composite of severe preeclampsia, medically indicated preterm birth occurring before 35 weeks of gestation, placental abruption, or fetal/neonatal death.

Among 2408 patients assessed at baseline, the mean age was 32 years and 47.5% identified as Black, 27.9% as White, and 20.3% as Hispanic. Fifty-six percent had prior chronic hypertension and were receiving medication, 22% had prior chronic hypertension but were not taking medication, and 22% had a new diagnosis of chronic hypertension. The ninety-six percent of the patients who completed the follow-up at 6 weeks after birth were included in the analysis.

The active therapy group had a lower incidence of the primary efficacy composite outcome compared with the control group (30.2% vs. 37%, P < 0.001). In particular, the incidences of preeclampsia with severe features (23.3% vs. 29.1%, P < 0.05) and medically indicated preterm birth before 35 weeks’ gestation (12.2% vs. 16.7%, P < 0.05) were significantly lower in the active therapy group, whereas abruption and fetal or neonatal death were similar in both groups. Poor fetal growth — the primary safety outcome of the trial — was not statistically different between the 2 groups (11.2% vs. 10.4%, P = 0.56). Analyses of the secondary outcomes suggested that active therapy may decrease the risk of severe maternal hypertension (36.1% vs. 44.2%, P < 0.05), any preeclampsia (24.4% vs. 31.1%, P < 0.05), preterm birth (27.5% vs. 31.4%, P < 0.05), and low birth weight (19.2% vs. 23.1%, P < 0.05). The total number of serious adverse events was similar in both groups (155 vs. 178).

The findings of this study differ from a prior smaller randomized trial that found targeting a lower diastolic goal did not improve patient-oriented outcomes. This larger, multicenter trial in a diverse, at-risk population has already garnered support from physician organizations. This trial does demonstrate improvement in meaningful outcomes, but we must give some consideration to limitations including lack of blinding and difficulties in generalizability given that a large number of patients were excluded because they did not meet inclusion criteria, such as adherence to medication at baseline.

In conclusion, the CHAP trial convincingly suggests that active antihypertensive therapy for mild chronic hypertension in pregnancy reduces the risk of adverse outcomes without compromising fetal growth.

Seeing Clearly: Eye Surgery is Low Risk

Surgery is a known generator of stress on the body. However, not all procedures are equally stressful to the body and traditionally ophthalmic surgery has been considered low risk. The European Society of Cardiology considers the cardiovascular risk of eye surgery to be less than 1%. A 2019 Cochrane review found no benefit of routine preoperative testing before cataract surgery compared to selective or no testing. The American Academy of Ophthalmology recommends against routine preoperative testing before cataract surgery, but does suggest targeted evaluation such as an electrocardiogram in someone with known heart disease.

To further investigate the short-term risk of eye surgery, researchers from Norway and Sweden used national patient registries to examine whether there was an increased risk of acute myocardial infarction (AMI) in the week following ophthalmic surgery.3 The study protocol involved identifying AMI patients and then looking retrospectively to identify those who had had eye surgery either during days 0 to 7 prior to the AMI, or during an 8-day period 1 month earlier.

There were 353,031 patients identified with a first AMI, of whom 806 had eye surgery. Most of these individuals had no relevant comorbidities. There were 344 patients who had eye surgery in the week before the AMI and 462 had eye surgery in the comparable period a month earlier. The risk of AMI was lower in the 8-day window following eye surgery than it was a month before the procedure (odds ratio 0.83, 95% CI 0.75-0.91). The results were consistent in analyses based on the type of eye surgery. In subgroup analyses that included length of surgery, type of anesthesia, and the presence of comorbidities, there was no group that had significantly increased risk in the 8 days following eye surgery.

These results support the categorization of eye surgery as low risk. There did not appear to be an increase in risk of AMI in the time-frame when risk would be anticipated to be increased due to surgery. However, this retrospective observational study has some limitations. First of all, as patients typically have routine preoperative evaluation (whether with testing or not), those who are most at risk for complications will likely have their surgeries delayed until their medical status has been optimized. Also, it is possible that in the month after surgery, there are factors that start to increase risk, such as reduced activity due to the need to recover from surgery. Finally, most patients did not have relevant cardiovascular, pulmonary, or renal comorbidities so it is uncertain whether similar results would be seen in a population with such comorbidities. Nonetheless, these findings are reassuring and support the current recommendations that suggest little to no preoperative testing for eye surgery is needed.

Alan Ehrlich, MD, is a deputy editor for DynaMed, Ipswich, Massachusetts, and assistant clinical professor in family medicine, University of Massachusetts Medical School, Worcester.

DynaMed is a database that provides evidence-based information on more than 3000 clinical topics and is updated daily through systematic surveillance covering more than 500 journals.


1. Cairncross ZF, Couloigner I, Ryan MC, et al. Association between residential proximity to hydraulic fracturing sites and adverse birth outcomes. JAMA Pediatr. 2022;176(6):585-592. doi:10.1001/jamapediatrics.2022.0306

2. Tita AT, Szychowski JM, Boggess K, et al Treatment of mild chronic hypertention during pregnancy. N Engl J Med. 2022;386(19):1781-1792. doi: 10.1056/NEJMoa2201295

3. Sen A, Gemes K, Stalhammer G, et al. Risk of acute myocardial infarction after ophthalmologic procedures. Ann Intern Med. 2022;175(5):628-633. doi:10.7326/M20-6618