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.

Figure 1.

High-(≥2500 m) compared to low-(<1700 m) altitude residents matched for risk factors had higher mean arterial blood pressures (MAPs) throughout pregnancy (repeated measures ANOVA, F for full sample group effect=3.59, p=.03) due, in turn, to the lack of the mid-pregnancy blood-pressure fall seen at low altitude (panel A). Sample sizes (n) are cases with MAP data on at least four occasions. Shown are mean ± standard error of the mean (sem) values for MAP binned by gestational age groups for all longitudinally-studied high- vs. low-altitude residents (panel A), all women whose MAP remained normal (panel B), and the women with HDP (panel C). Sample sizes were not sufficient to compare the subsamples of normotensive or the women with HDP alone between altitudes, but the direction of the altitudinal differences was similar to that seen in all women.