High-altitude residence alters blood-pressure course and increases hypertensive disorders of pregnancy

Abstract

Objectives

To determine whether the full spectrum of hypertensive disorders of pregnancy (HDP) – comprising gestational hypertension; preeclampsia with or without severe features; eclampsia; and Hemolysis, Elevated Liver enzymes, and Low Platelets (HELLP) Syndrome – is increased at high (≥2500 m, 8250 ft) compared with lower altitudes in Colorado independent of maternal background characteristics, and if so their relationship to neonatal well-being.

Methods

A retrospective cohort study was conducted using statewide birth-certificate data to compare the frequency of gestational hypertension, preeclampsia (with or without severe features), eclampsia, HELLP Syndrome, or all HDP combined in 617,958 Colorado women who lived at high vs. low altitude (<2500 m) and delivered during the 10-year period, 2007–2016. We also compared blood-pressure changes longitudinally during pregnancy and the frequency of HDP in 454 high (>2500 m)- vs. low (<1700 m)-altitude Colorado residents delivering in 2013 and 2014, and matched for maternal risk factors. Data were compared between altitudes using t-tests or chi-square, and by multiple or logistic regression analyses to adjust for risk factors and predict specific hypertensive or neonatal complications.

Results

Statewide, high-altitude residence increased the frequency of each HDP disorder separately or all combined by 33%. High-altitude women studied longitudinally also had more HDP accompanied by higher blood pressures throughout pregnancy. The frequency of low birth weight infants (<2500 g), 5-min Apgar scores <7, and NICU admissions were also greater at high than low altitudes statewide, with the latter being accounted for by the increased incidence of HDP.

Conclusions

Residence at high altitude constitutes a risk factor for HDP and recommends increased clinical surveillance. The increased incidence also makes high altitude a natural laboratory for evaluating the efficacy of predictive biomarkers or new therapies for HDP.

Keywords:

• Hypoxia
• intrauterine growth restriction
• preeclampsia

Acknowledgements

We thank Jared Ahrendsen, Heather Boucher, Yasmine Dakhama, Javier Gutierrez, Pete Julian, Trenton Klimper, Bill Moore, Barbara Neistadt, and Mayi Gnofam for their help with the acquisition of the medical records data from the longitudinally studied subjects. We also thank the many physicians and staff members who also helped make the collection of these data possible.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data for this study are available from the corresponding author (LGM) upon reasonable request.

Health and Safety: All mandatory laboratory health and safety procedures have been complied within the course of conducting the studies described in this paper.

Additional information

Funding

This work was supported by the NIH Grants [HD088590, HD057022] and the Colorado Center for Women’s Health Research.