High altitude during pregnancy

Critical pregnancy at altitude: A look at Latin America

Critical pregnancy at high altitudes increases morbidity and mortality from 2500 m above sea level. In addition to altitude, there are other influential factors such as social inequalities, cultural, prehospital barriers, and lack the appropriate development of healthcare infrastructure. The most frequent causes of critical pregnancy leading to admission to Intensive Care Units are pregnancy hypertensive disorders (native residents seem to be more protected), hemorrhages and infection/sepsis. In Latin America, there are 32 Intensive Care Units above 2500 m above sea level. Arterial blood gases at altitude are affected by changes in barometric pressure. The analysis of their values provides very useful information for the management of obstetric emergencies at very high altitude, especially respiratory and metabolic pathologies.

Sex-biased regulatory changes in the placenta of native highlanders contribute to adaptive fetal development

Compared with lowlander migrants, native Tibetans have a higher reproductive success at high altitude though the underlying mechanism remains unclear. Here, we compared the transcriptome and histology of full-term placentas between native Tibetans and Han migrants. We found that the placental trophoblast shows the largest expression divergence between Tibetans and Han, and Tibetans show decreased immune response and endoplasmic reticulum stress. Remarkably, we detected a sex-biased expression divergence, where the male-infant placentas show a greater between-population difference than the female-infant placentas. The umbilical cord plays a key role in the sex-biased expression divergence, which is associated with the higher birth weight of the male newborns of Tibetans. We also identified adaptive histological changes in the male-infant placentas of Tibetans, including larger umbilical artery wall and umbilical artery intima and media, and fewer syncytial knots. These findings provide valuable insights into the sex-biased adaptation of human populations, with significant implications for medical and genetic studies of human reproduction.

Pain control and neonatal outcomes in 211 women under epidural anesthesia during childbirth at high altitude in Qinghai, China

Background

High altitudes are characterized by low-pressure oxygen deprivation. This is further exacerbated with increasing altitude. High altitudes can be associated with reduced oxygenation, which in turn, can affect labor, as well as maternal and fetal outcomes. Epidural anesthesia can significantly relieve labor pain. This study aimed to assess the effects of elevation gradient changes at high altitude on the analgesic effect of epidural anesthesia, labor duration, and neonatal outcomes.

Methods

We divided 211 women who received epidural anesthesia into groups according to varying elevation of their residence (76 in Xining City, mean altitude 2,200 m; 63 in Haibei Prefecture, mean altitude 3,655 m; and 72 in Yushu Prefecture, mean altitude 4,493 m). The analgesic effect was assessed using a visual analog scale (VAS). Labor duration was objectively recorded. The neonatal outcome was assessed using Apgar scores and fetal umbilical artery blood pH.

Results

VAS scores among the three groups did not differ significantly (p > 0.05). The neonatal Apgar scores in descending order were: Xining group > Haibei group > Yushu group (p < 0.05). The stage of labor was similar among the three groups (p > 0.05). Fetal umbilical artery blood pH in descending order were: Xining group > Haibei group > Yushu group (p < 0.05).

Conclusion

Elevation gradient changes in highland areas did not affect the efficacy of epidural anesthesia or labor duration. However, neonatal outcomes were affected.

[Cerebral oxygen metabolism and brain electrical activity of healthy full-term neonates in high-altitude areas: a multicenter clinical research protocol]

Further evidence is needed to explore the impact of high-altitude environments on the neurologic function of neonates. Non-invasive techniques such as cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography can provide data on cerebral oxygenation and brain electrical activity. This study will conduct multiple cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography monitoring sessions at various time points within the first 3 days postpartum for healthy full-term neonates at different altitudes. The obtained data on cerebral oxygenation and brain electrical activity will be compared between different altitudes, and corresponding reference ranges will be established. The study involves 6 participating centers in the Chinese High Altitude Neonatal Medicine Alliance, with altitude gradients divided into 4 categories: 800 m, 1 900 m, 2 400 m, and 3 500 m, with an anticipated sample size of 170 neonates per altitude gradient. This multicenter prospective cohort study aims to provide evidence supporting the impact of high-altitude environments on early brain function and metabolism in neonates.

Altered expression of nutrient transporters in syncytiotrophoblast membranes in preeclampsia placentae

INTRODUCTION

Expression of nutrient transporters in the placenta affects fetal growth. This study reports the protein expression of nutrient transporters in the syncytial membranes [microvillous membrane (MVM) and basal membrane (BM)] of normotensive control and preeclampsia placentae.

METHODS

Placentae were collected from fourteen normotensive control women and fourteen women with preeclampsia. The syncytiotrophoblast MVM and BM membranes were isolated. The protein expression of glucose transporter (GLUT1), vitamin B₁₂ transporter (CD320) and fatty acid transporters (FATP2, FATP4) was assessed in both the membranes.

RESULTS

Comparison between membranes demonstrates similar CD320 protein expression in normotensive group whereas, in preeclampsia placentae it was higher in the BM as compared to MVM (p < 0.05). FATP2&4 protein expression was higher in the BM as compared to their respective MVM fraction in both the groups (p < 0.01 for both). Comparison between groups demonstrates higher GLUT1 expression in the MVM (p < 0.05) and BM (p < 0.05) whereas lower CD320 expression in the MVM (p < 0.05) of preeclampsia placentae as compared to their respective membranes in normotensive control. Furthermore, GLUT1 protein expression was positively associated and CD320 protein expression was negatively associated with maternal body mass index (BMI) (p < 0.05 for both). No difference was observed in the FATP2&4 protein expression. However, FATP4 protein expression was negatively associated with maternal blood pressure (p < 0.05 for MVM; p = 0.060 for BM) and birth weight (p < 0.05 for both membranes).

DISCUSSION

The current study for the first time demonstrates differential expression of various transporters in the syncytiotrophoblast membranes of the preeclampsia placentae which may influence fetal growth.

Decreased Vitamin D Levels and Altered Placental Vitamin D Gene Expression at High Altitude: Role of Genetic Ancestry

High-altitude hypoxia challenges reproduction; particularly in non-native populations. Although high-altitude residence is associated with vitamin D deficiency, the homeostasis and metabolism of vitamin D in natives and migrants remain unknown. We report that high altitude (3600 m residence) negatively impacted vitamin D levels, with the high-altitude Andeans having the lowest 25-OH-D levels and the high-altitude Europeans having the lowest 1α,25-(OH)2-D levels. There was a significant interaction of genetic ancestry with altitude in the ratio of 1α,25-(OH)2-D to 25-OH-D; with the ratio being significantly lower in Europeans compared to Andeans living at high altitude. Placental gene expression accounted for as much as 50% of circulating vitamin D levels, with CYP2R1 (25-hydroxylase), CYP27B1 (1α-hydroxylase), CYP24A1 (24-hydroxylase), and LRP2 (megalin) as the major determinants of vitamin D levels. High-altitude residents had a greater correlation between circulating vitamin D levels and placental gene expression than low-altitude residents. Placental 7-dehydrocholesterol reductase and vitamin D receptor were upregulated at high altitude in both genetic-ancestry groups, while megalin and 24-hydroxylase were upregulated only in Europeans. Given that vitamin D deficiency and decreased 1α,25-(OH)2-D to 25-OH-D ratios are associated with pregnancy complications, our data support a role for high-altitude-induced vitamin D dysregulation impacting reproductive outcomes, particularly in migrants.

Elevation of Pulmonary Artery Pressure in Newborns from High-Altitude Pregnancies Complicated by Preeclampsia

We hypothesized that fetal exposure to the oxidative stress induced by the combined challenge of preeclampsia (PE) and high altitude would induce a significant impairment in the development of pulmonary circulation. We conducted a prospective study in La Paz (Bolivia, mean altitude 3625 m) in which newborns from singleton pregnancies with and without PE were compared (PE group n = 69, control n = 70). We conducted an echocardiographic study in these infants at the median age of two days. The percentage of cesarean deliveries and small for gestational age (SGA) infants was significantly higher in the PE group. Heart rate, respiratory rate, and oxygen saturation did not vary significantly between groups. Estimated pulmonary arterial pressure and pulmonary vascular resistance were 30% higher in newborns exposed to PE and high altitude compared with those exposed only to high altitude. We also detected signs of right ventricular hypertrophy in infants subjected to both exposures. In conclusion, this study provides evidence that the combination of PE and pregnancy at high altitude induces subclinical alterations in the pulmonary circulation of the newborn. Follow-up of this cohort may provide us with valuable information on the potential increased susceptibility to developing pulmonary hypertension or other pulmonary and cardiovascular disorders.

Altitude and Its Association with Low Birth Weight among Children of 151,873 Peruvian Women: A Pooled Analysis of a Nationally Representative Survey

The aim of this study was to determine the relationship between the altitude of residence and the low birth weight (LBW) of the children of pregnant Peruvian women using a nationally representative database. An analysis of individual-level data from the last 13 years (from 2009 to 2021) of the Demographic and Family Health Survey was performed. The outcome variable was LBW, defined as birth weight less than 2500 g, while the independent variable was the altitude of residence in meters above sea level (masl). To estimate the association between the two variables, the crude and adjusted generalized linear model of the Poisson family with a log link was used along with crude and adjusted prevalence ratios, which were estimated with their respective 95% confidence interval. A total of 151,873 women aged 15-49 years were included between 2009 and 2021. The pooled proportion of LBW was 7.0%. As the main finding, the children of mothers residing at an altitude from 2500 to 3499 masl and ≥3500 masl had a higher probability of LBW. It was found that the children of mothers residing at an altitude above 2500 masl were more likely to have LBW. Our results will help to strengthen the cultural practice of maternal health care and increase its coverage in women residing in high-altitude regions.

High Altitude Pregnancies and Vascular Dysfunction: Observations From Latin American Studies

An estimated human population of 170 million inhabit at high-altitude (HA, above 2,500 m). The potential pathological effects of HA hypobaric hypoxia during gestation have been the focus of several researchers around the world. The studies based on the Himalayan and Central/South American mountains are particularly interesting as these areas account for nearly 70% of the HA world population. At present, studies in human and animal models revealed important alterations in fetal development and growth at HA. Moreover, vascular responses to chronic hypobaria in the pregnant mother and her fetus may induce marked cardiovascular impairments during pregnancy or in the neonatal period. In addition, recent studies have shown potential long-lasting postnatal effects that may increase cardiovascular risk in individuals gestated under chronic hypobaria. Hence, the maternal and fetal adaptive responses to hypoxia, influenced by HA ancestry, are vital for a better developmental and cardiovascular outcome of the offspring. This mini-review exposes and discusses the main determinants of vascular dysfunction due to developmental hypoxia at HA, such as the Andean Mountains, at the maternal and fetal/neonatal levels. Although significant advances have been made from Latin American studies, this area still needs further investigations to reveal the mechanisms involved in vascular dysfunction, to estimate complications of pregnancy and postnatal life adequately, and most importantly, to determine potential treatments to prevent or treat the pathological effects of being developed under chronic hypobaric hypoxia.

Integrative Review of Exercise at Altitude during Pregnancy

Many competitive and elite athletes continue to train throughout their pregnancies and many visit or live at altitude. The purpose of this integrative review is to synthesize, analyze and critique published studies regarding the safety of serious recreational or elite athletes exercising at altitude while pregnant. Seven databases were searched, and 157 documents were located, which were screened for appropriateness and reduced to seven articles that met the criteria. The studies were analyzed based on maternal and fetal outcomes. Current recommendations for exercising at altitude were based on sedentary individuals who frequently did not have the expected physiological responses based on research on pregnancy and altitude. It is unknown whether competitive and elite athletes would have similar responses to exercise at altitude. More research on exercise at altitude on individuals with a variety of fitness levels is needed.

Pregnancy-related acute kidney injury at high altitude: a retrospective observational study in a single center

Background

Pregnancy-related acute kidney injury (Pr-AKI) is associated with maternal and fetal morbidity and mortality. There are few studies focusing on Pr-AKI at high altitude in the literature.

Objectives

to investigate the incidence, etiology, clinical features and maternal-fetal outcomes of Pr-AKI in women living at high altitude.

Methods

6,512 pregnant women attending the Department of Obstetrics & Gynecology at local hospital from January 2015 to December 2018 were screened for Pr-AKI. Patients with serum creatinine above normal range(> 70umol/L) then underwent assessment to confirm the diagnosis of Pr-AKI. AKI was diagnosed and staged based on Kidney Disease Improving Global Outcomes(KDIGO) guideline. Individuals meeting the Pr-AKI criteria were recruited. Their clinical data were recorded and retrospectively analyzed.

Results

Pr-AKI was identified in 136/6512(2.09 %) patients. Hypertensive disorders of pregnancy(HDP) was the leading cause of Pr-AKI(35.3 %). 4(2.9 %) women died and the majority(86.1 %) had recovered renal function before discharge. Fetal outcomes were confirmed in 109 deliveries with gestational age ≥ 20 weeks. Pre-term delivery occurred in 30(27.3 %) cases and perinatal deaths in 17(15.5 %). The rate of low birth weight infant(LBWI) and intrauterine growth restriction(IUGR) was 22.0 and 10.9 % respectively. 16(14.5 %) infants were admitted to NICU after birth. Patients with HDP had a higher cesarean rate(56.3 %). More IUGR(25.0 %) and LBWI(37.8 %) were observed in their infants with a higher risk of admission to NICU(22.0 %). High altitude might have an adverse impact on HDP-related Pr-AKI patients with earlier terminated pregnancy and more stillbirth/neonatal death. Logistic regression models indicated that uncontrolled blood pressure, high altitude and advanced AKI were associated with adverse fetal outcomes in HDP-related Pr-AKI patients.

Conclusions

Pr-AKI was not rare in high-altitude regions and caused severe fetal morbidities and mortalities. Uncontrolled blood pressure, high altitude and advanced AKI were all risk factors for adverse fetal outcomes in Pr-AKI patients, especially for those with hypertensive disorders of pregnancy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02418-7.

Newborn anthropometry, maternal capital, and altitude in the highland population from the province of Jujuy, Argentina

OBJECTIVE

To analyze variability in newborn (NB) anthropometry among Jujenean NBs as a function of geographic altitude (500 m to ≈4000 masl), maternal anthropometry and other maternal characteristics within the maternal capital framework.

MATERIALS AND METHODS

Data obtained from 41,371 mother/child pairs recorded in the Jujuy Perinatal Information System (SIP) between 2009 and 2014, including: NB and maternal weight, length/height and BMI; gestational age (corrected); maternal age, educational level, nutritional status, and marital status; birth interval; and planned pregnancy. Based on the declared place of residence, the prevalence of unsatisfied basic needs (% UBN) was determined and the data was split into two altitudinal groups: highlands (HL, >2500 masl) and lowlands (LL, <2500 masl). ANOVA, Chi-squared and Pearson tests were applied as needed. Statistical associations between the response variables-NB weight, length and BMI-and maternal and environmental variables were tested using a Generalized Additive Mixed Model (GAMM).

RESULTS

All NB and maternal anthropometric variables were lower in HL compared to LL; they also presented negative correlations with altitude, except NB length. Apart from gestational age and birth interval, HL and LL presented statistically significant differences in all study variables. GAMM results showed that maternal anthropometry was the main influence on NB weight and length.

DISCUSSION

Of all the maternal capital features examined, only maternal anthropometric variables were found to protect offspring against the negative impact of HL environments.

Perinatal Hypoxemia and Oxygen Sensing

The development of the control of breathing begins in utero and continues postnatally. Fetal breathing movements are needed for establishing connectivity between the lungs and central mechanisms controlling breathing. Maturation of the control of breathing, including the increase of hypoxia chemosensitivity, continues postnatally. Insufficient oxygenation, or hypoxia, is a major stressor that can manifest for different reasons in the fetus and neonate. Though the fetus and neonate have different hypoxia sensing mechanisms and respond differently to acute hypoxia, both responses prevent deviations to respiratory and other developmental processes. Intermittent and chronic hypoxia pose much greater threats to the normal developmental respiratory processes. Gestational intermittent hypoxia, due to maternal sleep-disordered breathing and sleep apnea, increases eupneic breathing and decreases the hypoxic ventilatory response associated with impaired gasping and autoresuscitation postnatally. Chronic fetal hypoxia, due to biologic or environmental (i.e. high-altitude) factors, is implicated in fetal growth restriction and preterm birth causing a decrease in the postnatal hypoxic ventilatory responses with increases in irregular eupneic breathing. Mechanisms driving these changes include delayed chemoreceptor development, catecholaminergic activity, abnormal myelination, increased astrocyte proliferation in the dorsal respiratory group, among others. Long-term high-altitude residents demonstrate favorable adaptations to chronic hypoxia as do their offspring. Neonatal intermittent hypoxia is common among preterm infants due to immature respiratory systems and thus, display a reduced drive to breathe and apneas due to insufficient hypoxic sensitivity. However, ongoing intermittent hypoxia can enhance hypoxic sensitivity causing ventilatory overshoots followed by apnea; the number of apneas is positively correlated with degree of hypoxic sensitivity in preterm infants. Chronic neonatal hypoxia may arise from fetal complications like maternal smoking or from postnatal cardiovascular problems, causing blunting of the hypoxic ventilatory responses throughout at least adolescence due to attenuation of carotid body fibers responses to hypoxia with potential roles of brainstem serotonin, microglia, and inflammation, though these effects depend on the age in which chronic hypoxia initiates. Fetal and neonatal intermittent and chronic hypoxia are implicated in preterm birth and complicate the respiratory system through their direct effects on hypoxia sensing mechanisms and interruptions to the normal developmental processes. Thus, precise regulation of oxygen homeostasis is crucial for normal development of the respiratory control network. © 2021 American Physiological Society. Compr Physiol 11:1653-1677, 2021.

Hypoxic modulation of fetal vascular MLCK abundance, localization, and function

Changes in vascular contractility are among the most important physiological effects of acute and chronic fetal hypoxia. Given the essential role of myosin light-chain kinase (MLCK) in smooth muscle contractility and its heterogeneous distribution, this study explores the hypothesis that subcellular changes in MLCK distribution contribute to hypoxic modulation of fetal carotid artery contractility. Relative to common carotid arteries from normoxic term fetal lambs (FN), carotids from fetal lambs gestated at high altitude (3,802 m) (FH) exhibited depressed contractility without changes in MLCK mRNA or protein abundance. Patterns of confocal colocalization of MLCK with α-actin and 20-kDa regulatory myosin light chain (MLC20) enabled calculation of subcellular MLCK fractions: 1) colocalized with the contractile apparatus, 2) colocalized with α-actin distant from the contractile apparatus, and 3) not colocalized with α-actin. Chronic hypoxia did not affect MLCK abundance in the contractile fraction, despite a concurrent decrease in contractility. Organ culture for 72 h under 1% O2 decreased total MLCK abundance in FN and FH carotid arteries, but decreased the contractile MLCK abundance only in FH carotid arteries. Correspondingly, culture under 1% O2 depressed contractility more in FH than FN carotid arteries. In addition, hypoxia appeared to attenuate ubiquitin-independent proteasomal degradation of MLCK, as reported for other proteins. In aggregate, these results demonstrate that the combination of chronic hypoxia followed by hypoxic culture can induce MLCK translocation among at least three subcellular fractions with possible influences on contractility, indicating that changes in MLCK distribution are a significant component of fetal vascular responses to hypoxia.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

Study of the Effect of Treatment With Atrial Natriuretic Peptide (ANP) and Cinaciguat in Chronic Hypoxic Neonatal Lambs on Residual Strain and Microstructure of the Arteries

In this study, we assessed the effects of Atrial Natriuretic Peptide (ANP) and Cinaciguat, as experimental medicines to treat neonatal lambs exposed to chronic hypoxic conditions. To compare the different treatments, the mechanical responses of aorta, carotid, and femoral arterial walls were analyzed by means of axial pre-stretch and ring-opening tests, through a study with n = 6 animals for each group analyzed. The axial pre-stretch test measures the level of shortening in different zones of the arteries when extracted from lambs, while the ring-opening test is used to quantify the degree of residual circumferential deformation in a given zone of an artery. In addition, histological studies were carried out to measure elastin, collagen, and smooth muscle cell (SMC) nuclei densities, both in control and treated groups. The results show that mechanical response is related with histological results, specifically in the proximal abdominal aorta (PAA) and distal carotid zones (DCA), where the cell nuclei content is related to a decrease of residual deformations. The opening angle and the elastic fibers of the aorta artery were statistically correlated (p < 0.05). Specifically, in PAA zone, there are significant differences of opening angle and cell nuclei density values between control and treated groups (p-values to opening angle: Control-ANP = 2 ⋅ 10-2, Control-Cinaciguat = 1 ⋅ 10-2; p-values to cell nuclei density: Control-ANP = 5 ⋅ 10-4, Control-Cinaciguat = 2 ⋅ 10-2). Respect to distal carotid zone (DCA), significant differences between Control and Cinaciguat groups were observed to opening angle (p-value = 4 ⋅ 10-2), and cell nuclei density (p-value = 1 ⋅ 10-2). Our findings add evidence that medical treatments may have effects on the mechanical responses of arterial walls and should be taken into account when evaluating the complete medical outcome.

Maternal Altitude-Corrected Hemoglobin and at Term Neonatal Anthropometry at 3400 m of Altitude

Villamonte-Calanche, Wilfredo, Nelly Lam-Figueroa, Maria Jerí-Palomino, Cleto De-La-Torre, and Alexandra A. Villamonte-Jerí. Maternal altitude-corrected hemoglobin and at term neonatal anthropometry at 3400 m of altitude. High Alt Med Biol. 21:287-291, 2020. Introduction: Fetal growth is prominent in the last trimester of pregnancy. The development of the fetus depends on the nutrient consumption and oxygen delivery of the pregnant woman. Therefore, maternal anemia has an inverse relationship with fetal growth. Consequently, the newborn has lower anthropometric measurements. Residing in places of a high altitude increases the level of hemoglobin (Hb); as a result, the World Health Organization (WHO) recommends adjusting the value of Hb in maternal blood at 3400-m altitude by reducing 2.4 g/dL to obtain the corrected Hb (HbCorr). Objective: To determine if the relationship of maternal HbCorr for high altitude is related to term neonatal anthropometry at 3400-m altitude. Material and Methods: We performed a retrospective cohort study and evaluated the neonatal anthropometric variables (weight, ponderal index, head circumference [HC], and HC for birthweight index) in 308 exposed pregnant women (HbCorr <11 g/dL) and 600 unexposed pregnant women (HbCorr ≥11 g/dL). We obtained absolute relative frequencies and measures of central tendency. Besides, we compared the qualitative and quantitative variables using the chi-square and the Student t or the Mann-Whitney or Kruskal-Wallis U test, if applicable. We also performed linear regression. Results: Of anemic pregnant women, 68.2% were mild, while only 1% were severe. There was no relationship between HbCorr and neonatal anthropometry, and none of the anemic pregnant women showed a statistical difference in the neonatal anthropometric measures evaluated compared to the unexposed women. Conclusion: There is no relationship between HbCorr and neonatal anthropometry at 3400-m altitude.

Endovascular trophoblast and spiral artery remodeling

Spiral artery remodeling, which is indispensable for successful pregnancy, is accomplished by endovascular trophoblasts that move upstream along the arterial wall, replace the endothelium, and disrupt the muscular lining. This review outlines the possible factors that could regulate endovascular trophoblast differentiation and invasion. First, high oxygen tension in the spiral artery could initiate endovascular trophoblast invasion. Second, activation of maternal decidual natural killer (dNK) cells could support perivascular invasion of interstitial trophoblasts and consequently could facilitate the endovascular trophoblast invasion. Third, maternal platelets trapped by the endovascular trophoblasts could enhance endovascular trophoblast invasion, which is in part mediated by chemokine CCL5 (C-C motif ligand 5) released from the activated platelets and chemokine receptor CCR1 (C-C chemokine receptor type 1) expressed specifically on the endovascular trophoblasts. The rat, in which trophoblast cells exhibit extensive interstitial and endovascular invasion, could be a suitable model animal for the study of human spiral artery remodeling. Apparently paradoxical results came from the rat study, i.e., exposure to hypoxia or depletion of dNK cells resulted in acceleration of the endovascular trophoblast invasion. This implies the presence of as-yet-undetermined regulator(s) whose effects on endovascular trophoblast invasion surpass the effects of surrounding oxygen tension or maternal dNK cells. In the future, clarification of the molecular differences between human interstitial and endovascular trophoblasts as well as establishment of the pregnant rat model exhibiting shallow endovascular trophoblast invasion and preeclamptic symptoms will contribute to elucidating the mechanism of spiral artery remodeling.

Prevalence and causes of cesarean births among women residing at high altitude in Lhasa, Tibet: A retrospective observational study of 7365 women

OBJECTIVE

Currently, there is paucity of data on the rate of vaginal deliveries and cesarean section among women in Tibet. In this study, we carried out an observational study of 7365 consecutive pregnant women in Lhasa, Tibet who gave birth at our tertiary care institution between 2012 and 2015.

MATERIALS AND METHODS

In this retrospective study, we reviewed the hospital records for demographic data, obstetric history, and the number of vaginal and emergency cesarean section deliveries. The overall and annual rate of vaginal and cesarean section deliveries was calculated. Causes, indications or risks for cesarean section were also analyzed.

RESULTS

During the review period, 7365 neonates were delivered at our hospital, including 1690 (23.0%) deliveries via cesarean section. The yearly rate of cesarean section progressively declined from 26.7% in 2012 to 18% in 2015 (P < 0.001). Furthermore, the annual rate of emergency cesarean section declined 53.9%between 2012 and 2015(P < 0.001). Fetal risk factors (39.9%) and maternal risk factors (40.3%) were the major causes of cesarean section in the women. Social factors as a cause of cesarean section fluctuated between 7.9% and 11.1%.

CONCLUSION

This study has demonstrated a steady decline in the annual rate of cesarean section in women in Tibet between 2012 and 2015. A decrease in the rate of emergency cesarean section contributed substantially to this decline. Moreover, approximately 10% caesarian sections were performed without clear indications, highlighting the need for strengthening prenatal counseling for pregnant women in Tibet.

Moderate altitude impacts birth weight: 30 years retrospective sibling analyses using record linkage data

OBJECTIVE

We investigated the effect of a change of altitude of maternal living address on infant birth weight.

METHOD

Data on infant birth weights of the first and second pregnancies from same women were extracted from all Austrian birth certificates between 1984 and 2016.

RESULTS

A total of 544,624 pair pregnancies were identified and analyzed. We observed a statistically significant interaction (p < .0001) between altitudes of two births and birth weight. Among women having first birth at low altitude (200 m), the estimated second mean birth weight was 3567 g for those remained at low altitudes, and reduced to 3536 g for those ascended (1200 m). In contrast, among women having first births at high altitudes, the estimated birth weight of second birth at high altitude was 3414 g, yet increased to 3499 g compared to those descended to lower altitudes.

CONCLUSION

We demonstrated a longitudinal negative effect of altitude on birth weight within the same mother from first and second birth. This association is likely to be casual. Relocation of mothers within low-to-medium altitude level may have profound effects on infants' birth weight.

Geographic altitude and prevalence of underweight, stunting and wasting in newborns with the INTERGROWTH-21st standard

OBJECTIVE

To assess the prevalence and risks of underweight, stunting and wasting by gestational age in newborns of the Jujuy Province, Argentina at different altitude levels.

METHODS

Live newborns (n=48,656) born from 2009-2014 in public facilities with a gestational age between 24⁺⁰ to 42⁺⁶ weeks. Phenotypes of underweight (<P3weight/age), stunting (<P3length/age) and wasting (<P3body mass index/age) were calculated using INTERGROWTH-21st standards. Risk factors were maternal age, education, body mass index, parity, diabetes, hypertension, preeclampsia, tuberculosis, prematurity, and congenital malformations. Data were grouped by the geographic altitude: ≥2.000 or <2.000m.a.s.l. Chi-squared test and a multivariate logistic regression analysis were performed to estimate the risk of the phenotypes associated with an altitudinal level ≥2.000m.a.s.l.

RESULTS

The prevalence of underweight, stunting and wasting were 1.27%, 3.39% and 4.68%, respectively, and significantly higher at >2.000m.a.s.l. Maternal age, body mass index >35kg/m², hypertension, congenital malformations, and prematurity were more strongly associated with underweight rather than stunting or wasting at ≥2.000m.a.s.l.

CONCLUSIONS

Underweight, stunting, and wasting risks were higher at a higher altitude, and were associated with recognized maternal and fetal conditions. The use of those three phenotypes will help prioritize preventive interventions and focus the management of fetal undernutrition.

Mechanical Ventilation in Neonatal Respiratory Distress Syndrome at High Altitude: A Retrospective Study From Tibet

Objective: To explore the characteristics of mechanical ventilation parameters and the arterial partial pressure of oxygen in neonatal respiratory distress syndrome (RDS) at high altitude. Methods: From the 1st May 2017 to the 31st December 2018, we recruited 33 neonates with severe RDS who were undergoing mechanical ventilation in the NICU of Naqu People's Hospital in Tibet (4,580 m above sea level); these neonates formed a plateau observation group. We also recruited a non-plateau control group: 66 neonates with severe RDS undergoing mechanical ventilation of Shengjing Hospital in Liaoning (51 m above sea level). Various ventilation parameters and the arterial partial pressure of oxygen were then compared between the two groups, between the survivors of the two groups, and between those who died and survived in the plateau group. Results: In terms of initial ventilator parameters, peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP), and the fraction of inspired oxygen (FiO2) in the plateau group were significantly higher than those in the non-plateau group (P < 0.01). PIP, PEEP, and FiO2 in the survivors from the plateau group were also significantly higher than those in the non-plateau group (P < 0.01). In addition, the arterial partial pressure of oxygen in the non-plateau group was higher (P < 0.05) than that in the plateau group during the early postnatal period, and the arterial partial pressure of oxygen at 6 and 12 h was lower than that in the plateau group (P < 0.05). Conclusion: Mechanical ventilation can effectively improve the arterial oxygen partial pressure and reduce the mortality of newborns with RDS in a plateau environment. It was clearly evident that ventilation parameters are closely related to altitude. It is therefore not advisable to apply mechanical ventilation parameters used in a non-plateau area as a guide for the treatment of newborns with RDS in plateau areas.

Investigation of elevation as a risk factor for hypertensive disorders of pregnancy among Colorado women between 2007 and 2015

OBJECTIVE

The purpose of this study is to determine the association between high elevation and hypertensive disorders of pregnancy (HDP).

METHODS

Retrospective cohort study using Colorado birth certificate data to compare HDP at high (≥8,000 ft), moderate (4,501-7,999 ft), or low (≤4,500 ft) elevation using logistic regression.

RESULTS

Among the cohort (n = 314,431), 3.4% of women developed a HDP. High or moderate elevation was not significantly associated with HDP relative to low elevation (adjusted odds ratio [aOR] 1.16, 95% confidence interval [CI] 0.93-1.43; aOR 1.14, 95% CI 0.98-1.31, respectively).

CONCLUSION

Women living at high or moderate elevation do not have higher odds of HDP.

Altitude and Variable Effects on Infant Mortality in the United States

Levine, Robert S., Jason L. Salemi, Maria C. Mejia de Grubb, Sarah K. Wood, Lisa Gittner, Hafiz Khan, Michael A. Langston, Baqar A. Husaini, George Rust, and Charles H. Hennekens. Altitude and variable effects on infant mortality in the United States. High Alt Med Biol. 19:265-271, 2018.

AIMS

To explore whether altitude has different effects on infant mortality from newborn respiratory distress, nontraumatic intracranial hemorrhage, and necrotizing enterocolitis.

RESULTS

Infants born in the US Mountain Census Division (AR, CO, ID, NV, NM, UT, and WY) had lower mortality from newborn respiratory distress (p < 0.001, mortality rate ratios [MRR] = 0.5 for non-Hispanic blacks and non-Hispanic whites and 0.6 for Hispanic whites) relative to infants born elsewhere in the United States, while Mountain Division non-Hispanic white infants had significantly higher mortality from nontraumatic intracranial hemorrhage (MRR = 1.3 [1.1, 1.6] p < 0.001). After adjustment for state average birth weight, gestational age, and income inequality, a statistically significant, inverse association remained between state average altitude and non-Hispanic white infant mortality from newborn respiratory distress. County altitude (3058 counties in 9 categories from ≤0 to ≥7000 feet) was negatively correlated with newborn respiratory distress (r = -0.91, p < 0.001) and necrotizing enterocolitis (r = -0.81, p = 0.006) at ≤0 to ≥7000 feet and positively correlated with nontraumatic intracranial hemorrhage at ≤0 to 6000-6999 feet (r = 0.78, p = 0.02).

CONCLUSIONS

These data show variable cause-specific effects of altitude on infant mortality. Analytic epidemiologic research is needed to confirm or refute the hypotheses generated by these descriptive data.

The Role of Uric Acid in Preeclampsia: Is Uric Acid a Causative Factor or a Sign of Preeclampsia?

PURPOSE OF REVIEW

Because of the significant discrepancies on this topic, this review will focus on the role of uric acid in PE, uric acid as a predictor of preeclampsia and fetal growth retardation. We considered eligible review and original articles relevant to the research question.

RECENT FINDINGS

Hypertensive disorders of pregnancy such as preeclampsia (PE) are a major cause of both maternal and fetal morbidity and mortality worldwide. Uric acid has been reported as a key factor contributing to the pathogenesis of PE. Some studies have indicated that serum uric acid levels increase with the severity of PE, while several studies have shown contradictory results. Some studies suggested high uric acid levels lead to PE, while others state that PE causes an increase in uric acid levels. Despite the strong association of uric acid in the pathogenesis of preeclampsia, current data is still contradictory hence genetic and high-end laboratory investigations may clarify this enigma.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Long-term high altitude hypoxia during gestation suppresses large conductance Ca2+ -activated K+ channel function in uterine arteries: a causal role for microRNA-210

KEY POINTS

Gestational hypoxia represses ten-eleven translocation methylcytosine dioxygenase 1 (TET1) expression in uterine arteries, which is recovered by inhibiting endogenous miR-210. Inhibition of miR-210 rescues BK_Ca channel expression and current in uterine arteries of pregnant animals acclimatized to high altitude hypoxia in a TET-dependent manner. miR-210 blockade restores BK_Ca channel-mediated relaxations and attenuates pressure-dependent myogenic tone in uterine arteries of pregnant animals acclimatized to high altitude.

ABSTRACT

Gestational hypoxia at high altitude has profound adverse effects on the uteroplacental circulation, and is associated with increased incidence of preeclampsia and fetal intrauterine growth restriction. Previous studies demonstrated that suppression of large-conductance Ca²⁺ -activated K⁺ (BK_Ca ) channel function played a critical role in the maladaptation of uteroplacental circulation caused by gestational hypoxia. Yet, the mechanisms underlying gestational hypoxia-induced BK_Ca channel repression remain undetermined. The present study investigated a causal role of microRNA-210 (miR-210) in hypoxia-mediated repression of BK_Ca channel expression and function in uterine arteries using a sheep model. The results revealed that gestational hypoxia significantly decreased ten-eleven translocation methylcytosine dioxygenase 1 (TET1) expression in uterine arteries, which was recovered by inhibiting endogenous miR-210 with miR-210 locked nucleic acid (miR-210-LNA). Of importance, miR-210-LNA restored BK_Ca channel β1 subunit expression in uterine arteries, which was blocked by a competitive TET inhibitor, fumarate, thus functionally linking miR-210 to the TET1-BK_Ca channel cascade. In addition, miR-210-LNA reversed hypoxia-mediated suppression of BK_Ca channel function and rescued the effect of steroid hormones in upregulating BK_Ca channel expression and function in uterine arteries, which were also ablated by fumarate. Collectively, the present study demonstrates a causative effect of miR-210 in the downregulation of TET1 and subsequent repression of BK_Ca channel expression and function, providing a novel mechanistic insight into the regulation of BK_Ca channel function and the molecular basis underlying the maladaptation of uterine vascular function in gestational hypoxia.

Hypoxia: From Placental Development to Fetal Programming

Hypoxia may influence normal and different pathological processes. Low oxygenation activates a variety of responses, many of them regulated by hypoxia-inducible factor 1 complex, which is mostly involved in cellular control of O₂ consumption and delivery, inhibition of growth and development, and promotion of anaerobic metabolism. Hypoxia plays a significant physiological role in fetal development; it is involved in different embryonic processes, for example, placentation, angiogenesis, and hematopoiesis. More recently, fetal hypoxia has been associated directly or indirectly with fetal programming of heart, brain, and kidney function and metabolism in adulthood. In this review, the role of hypoxia in fetal development, placentation, and fetal programming is summarized. Hypoxia is a basic mechanism involved in different pregnancy disorders and fetal health developmental complications. Although there are scientific data showing that hypoxia mediates changes in the growth trajectory of the fetus, modulates gene expression by epigenetic mechanisms, and determines the health status later in adulthood, more mechanistic studies are needed. Furthermore, if we consider that intrauterine hypoxia is not a rare event, and can be a consequence of unavoidable exposures to air pollution, nutritional deficiencies, obesity, and other very common conditions (drug addiction and stress), the health of future generations may be damaged and the incidence of some diseases will markedly increase as a consequence of disturbed fetal programming. Birth Defects Research 109:1377-1385, 2017.© 2017 Wiley Periodicals, Inc.

Extreme pregnancy: maternal physical activity at Everest Base Camp

High-altitude natives employ numerous physiological strategies to survive and reproduce. However, the concomitant influence of altitude and physical activity during pregnancy has not been studied above 3,700 m. We report a case of physical activity, sleep behavior, and physiological measurements on a 28-yr-old third-trimester pregnant native highlander (Sherpa) during ascent from 3,440 m to Everest Base Camp (~5,300 m) over 8 days in the Nepal Himalaya and again ~10 mo postpartum during a similar ascent profile. The participant engaged in 250-300 min of moderate to vigorous physical activity per day during ascent to altitude while pregnant, with similar volumes of moderate to vigorous physical activity while postpartum. There were no apparent maternal, fetal, or neonatal complications related to the superimposition of the large volumes of physical activity at altitude. This report demonstrates a rare description of physical activity and ascent to high altitude during pregnancy and points to novel questions regarding the superimposition of pregnancy, altitude, and physical activity in high-altitude natives.

Trophoblast lineage specification, differentiation and their regulation by oxygen tension

Development of the early embryo takes place under low oxygen tension. Under such conditions, the embryo implants and the trophectoderm, the outer layer of blastocyst, proliferate, forming the cytotrophoblastic shell, the early placenta. The cytotrophoblasts (CTBs) are the so-called epithelial 'stem cells' of the placenta, which, depending on the signals they receive, can differentiate into either extravillous trophoblast (EVT) or syncytiotrophoblast (STB). EVTs anchor the placenta to the uterine wall and remodel maternal spiral arterioles in order to provide ample blood supply to the growing fetus. STBs arise through CTB fusion, secrete hormones necessary for pregnancy maintenance and form a barrier across which nutrient and gas exchange can take place. The bulk of EVT differentiation occurs during the first trimester, before the onset of maternal arterial blood flow into the intervillous space of the placenta, and thus under low oxygen tension. These conditions affect numerous signaling pathways, including those acting through hypoxia-inducible factor, the nutrient sensor mTOR and the endoplasmic reticulum stress-induced unfolded protein response pathway. These pathways are known to be involved in placental development and disease, and specific components have even been identified as directly involved in lineage-specific trophoblast differentiation. Nevertheless, much controversy surrounds the role of hypoxia in trophoblast differentiation, particularly with EVT. This review summarizes previous studies on this topic, with the intent of integrating these results and synthesizing conclusions that resolve some of the controversy, but then also pointing to remaining areas, which require further investigation.

Gestational hypoxia disrupts the neonatal leptin surge and programs hyperphagia and obesity in male offspring in the Sprague-Dawley rat

The effect of gestational hypoxia on the neonatal leptin surge, development of hypothalamic arcuate nuclei (ARH) projections and appetite that could contribute to the programming of offspring obesity is lacking. We examined the effect of 12% O₂ from gestational days 15–19 in the Sprague-Dawley rat on post-weaning appetite, fat deposition by MRI, adipose tissue cytokine expression, the neonatal leptin surge, ARH response to exogenous leptin, and αMSH projections to the paraventricular nucleus (PVN) in response to a high fat (HFD) or control diet (CD) in male offspring. Normoxia (NMX) and Hypoxia (HPX) offspring exhibited increased food intake when fed a HFD from 5–8 weeks post-birth; HPX offspring on the CD had increased food intake from weeks 5–7 vs. NMX offspring on a CD. HPX offspring on a HFD remained hyperphagic through 23 weeks. Body weight were the same between offspring from HPX vs. NMX dams from 4–12 weeks of age fed a CD or HFD. By 14–23 weeks of age, HPX offspring fed the CD or HFD as well as male NMX offspring fed the HFD were heavier vs. NMX offspring fed the CD. HPX offspring fed a CD exhibited increased abdominal adiposity (MRI) that was amplified by a HFD. HPX offspring fed a HFD exhibited the highest abdominal fat cytokine expression. HPX male offspring had higher plasma leptin from postnatal day (PN) 6 through 14 vs. NMX pups. HPX offspring exhibited increased basal c-Fos labeled cells in the ARH vs. NMX pups on PN16. Leptin increased c-Fos staining in the ARH in NMX but not HPX offspring at PN16. HPX offspring had fewer αMSH fibers in the PVN vs. NMX offspring on PN16. In conclusion, gestational hypoxia impacts the developing ARH resulting in hyperphagia contributing to adult obesity on a control diet and exacerbated by a HFD.

High altitude and pre-eclampsia: Adaptation or protection

Adaptive genes of high altitude can also be protective in diseases like preeclampsia, hypertension, and diabetes mellitus, Alzheimer, Parkinson Disease and Cancer, which may result from deregulation of hypoxia pathway. The example of pre-eclampsia and normal pregnancy were studied to see if the hypoxia-induced disorders can be dragged towards adaptation. Here, we analyse the genetic variants that are known to be associated with adaptation to high altitude hypoxia. Our results demonstrated that the genetic variants of EPAS1, ADAM9, and EGLN1 increased approximately three-fold in the cases of preeclampsia compared to normal pregnancy. This may suggest the ability of the hypoxic cells of preeclampsia to respond to the high selective pressure of hypoxia with a higher degree of genetic variability, which can lead to adaptation. Signs of "acclimatisation" were seen both in cases and controls but with higher frequencies in controls. This can be a new approach that follows patients' genetic selection and susceptibility of individuals for adaptability, which could be enhanced by drug development.

Expression of StAR and Key Genes Regulating Cortisol Biosynthesis in Near Term Ovine Fetal Adrenocortical Cells: Effects of Long-Term Hypoxia

We previously demonstrated decreased expression of key genes regulating cortisol biosynthesis in long-term hypoxic (LTH) sheep fetal adrenals compared to controls. We also showed that inhibition of the extracellular signal-regulated kinases (ERKs) with the mitogen-activated protein kinase (MEK)/ERK inhibitor UO126 limited adrenocorticotropic (ACTH)-induced cortisol production in ovine fetal adrenocortical cells (FACs), suggesting a role for ERKs in cortisol synthesis. This study was designed to determine whether the previously observed decrease in LTH cytochrome P45011A1/cytochrome P450c17 (CYP11A1/CYP17) in adrenal glands was maintained in vitro, and whether ACTH alone with or without UO126 treatment had altered the expression of CYP11A1, CYP17, and steroidogenic acute regulatory protein (StAR) in control versus LTH FACs. Ewes were maintained at high altitude (3820 m) from ∼40 days of gestation (dG). At 138 to 141 dG, fetal adrenal glands were collected from LTH (n = 5) and age-matched normoxic controls (n = 6). Fetal adrenocortical cells were challenged with ACTH (10^-8 M) with or without UO126 (10 µM) for 18 hours. Media samples were collected for cortisol analysis and messenger RNA (mRNA) for CYP11A1, CYP17, and StAR was quantified by quantitative real-time polymerase chain reaction. Cortisol was higher in the LTH versus control ( P < .05). StAR mRNA was decreased in LTH versus control ( P < .05). U0126 alone had no effect on mRNA in either group. UO126 prevented the increase in CYP11A1 and CYP17 in control FACs. Basal CYP11A1 and CYP17 were not different in LTH versus control. ACTH increased CYP11A1 and CYP17 only in control FACs ( P < .05). U1026 attenuated the ACTH response indicative of a role for ERK in CYP11A1 and CYP17 expression. ACTH may require additional factors in FACs to fully regulate StAR expression.

Travel During Pregnancy: Considerations for the Obstetric Provider

Importance

Travel among US citizens is becoming increasingly common, and travel during pregnancy is also speculated to be increasingly common. During pregnancy, the obstetric provider may be the first or only clinician approached with questions regarding travel.

Objective

In this review, we discuss the reasons women travel during pregnancy, medical considerations for long-haul air travel, destination-specific medical complications, and precautions for pregnant women to take both before travel and while abroad. To improve the quality of pretravel counseling for patients before or during pregnancy, we have created 2 tools: a guide for assessing the pregnant patient's risk during travel and a pretravel checklist for the obstetric provider.

Evidence Acquisition

A PubMed search for English-language publications about travel during pregnancy was performed using the search terms "travel" and "pregnancy" and was limited to those published since the year 2000. Studies on subtopics were not limited by year of publication.

Results

Eight review articles were identified. Three additional studies that analyzed data from travel clinics were found, and 2 studies reported on the frequency of international travel during pregnancy. Additional publications addressed air travel during pregnancy (10 reviews, 16 studies), high-altitude travel during pregnancy (5 reviews, 5 studies), and destination-specific illnesses in pregnant travelers.

Conclusions and Relevance

Travel during pregnancy including international travel is common. Pregnant travelers have unique travel-related and destination-specific risks. We review those risks and provide tools for obstetric providers to use in counseling pregnant travelers.

Athletes at High Altitude

CONTEXT

Athletes at different skill levels perform strenuous physical activity at high altitude for a variety of reasons. Multiple team and endurance events are held at high altitude and may place athletes at increased risk for developing acute high altitude illness (AHAI). Training at high altitude has been a routine part of preparation for some of the high level athletes for a long time. There is a general belief that altitude training improves athletic performance for competitive and recreational athletes.

EVIDENCE ACQUISITION

A review of relevant publications between 1980 and 2015 was completed using PubMed and Google Scholar.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 3.

RESULTS

AHAI is a relatively uncommon and potentially serious condition among travelers to altitudes above 2500 m. The broad term AHAI includes several syndromes such as acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). Athletes may be at higher risk for developing AHAI due to faster ascent and more vigorous exertion compared with nonathletes. Evidence regarding the effects of altitude training on athletic performance is weak. The natural live high, train low altitude training strategy may provide the best protocol for enhancing endurance performance in elite and subelite athletes. High altitude sports are generally safe for recreational athletes, but they should be aware of their individual risks.

CONCLUSION

Individualized and appropriate acclimatization is an essential component of injury and illness prevention.

Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia

Vitamin D status increases during healthy mammalian pregnancy, but the molecular determinants remain uncharacterized. The first objective of this study was to determine the effects of pregnancy, and the second objective was to examine the role of chronic hypoxia on vitamin D status and metabolism in an ovine model. We analyzed the plasma levels of cholecalciferol, 25-OH-D, and 1α,25-(OH)2D in nonpregnant ewes, near-term pregnant ewes, and their fetuses exposed to normoxia (low altitude) or hypoxia (high-altitude) for 100 days. Hypoxic sheep had increased circulating levels of 25-OH-D and 1α,25-(OH)2D compared with normoxic sheep. Hypoxia increases in 25-OH-D were associated with increased expression of renal 25-hydroxylases CYP2R1 and CYP2J. Pregnancy did not increase further the plasma levels of 25-OH-D, but it significantly increased those of the active metabolite, 1α,25-(OH)2D, in both normoxic and hypoxic ewes. Increased bioactivation of vitamin D correlated with increased expression of the vitamin D-activating enzyme CYP27b1 and decreased expression of the inactivating enzyme CYP24a1 in maternal kidneys and placentas. Hypoxia increased parathyroid hormone levels and further increased renal CYP27b1. Pregnancy and hypoxia decreased the expression of vitamin D receptor (VDR) in maternal kidney and lung, with opposite effects on placental VDR. We conclude that ovine pregnancy is a model of increased vitamin D status, and long-term hypoxia further improves vitamin D status due to pregnancy- and hypoxia-specific regulation of VDR and metabolic enzymes.

Prevalence of very low birthweight, malformation, and low Apgar score among newborns in Brazil according to maternal urban or rural residence at birth

AIM

Adverse birth outcomes are a major public health issue in rural areas, where several environmental risk factors, including pesticides, may endanger the health of women of reproductive age. We investigated the prevalence of selected birth outcomes among newborns from mothers living in urban and rural areas of a Brazilian municipality.

METHODS

Information about all live births that occurred between 2004 and 2006 in the Municipality of Nova Friburgo, Brazil, was retrieved from the Live Birth Information System. Newborns were classified as rural or urban, according to the mother's residence address.

RESULTS

Newborns from rural areas had a higher prevalence of very low-birthweight, low Apgar score, and malformation. On Poisson regression with adjustment for several confounders, rural offspring were more likely to have the aforementioned outcomes.

CONCLUSIONS

Women in rural areas are at higher risk of giving birth to an infant with very low-birthweight, low 5-min Apgar score and malformations detectable at birth, regardless of socioeconomic and gestational conditions.

Wilderness Preparticipation Evaluation and Considerations for Special Populations

Children, older adults, disabled and special needs athletes, and female athletes who participate in outdoor and wilderness sports and activities each face unique risks. For children and adolescents traveling to high altitude, the preparticipation physical evaluation should focus on risk assessment, prevention strategies, early recognition of altitude-related symptoms, management plans, and appropriate follow-up. As the risk and prevalence of chronic disease increases with age, both older patients and providers need to be aware of disease and medication-specific risks relative to wilderness sport and activity participation. Disabled and special needs athletes benefit from careful pre-event planning for the potential medical issues and equipment modifications that may affect their health in wilderness environments. Issues that demand special consideration for female adventurers include pregnancy, contraceptive use, menses, and ferritin levels at altitude. A careful preparticipation evaluation that factors in unique, population- specific risks will help special populations stay healthy and safe on wilderness adventures. The PubMed and SportDiscus databases were searched in 2014 using both MeSH terms and text words and include peer-reviewed English language articles from 1977 to 2014. Additional information was accessed from Web-based sources to produce this narrative review on preparticipation evaluation for special populations undertaking wilderness adventures. Key words include children, adolescent, pediatric, seniors, elderly, disabled, special needs, female, athlete, preparticipiation examination, wilderness medicine, and sports.

Wilderness Preparticipation Evaluation and Considerations for Special Populations

Children, older adults, disabled and special needs athletes, and female athletes who participate in outdoor and wilderness sports and activities each face unique risks. For children and adolescents traveling to high altitude, the preparticipation physical evaluation should focus on risk assessment, prevention strategies, early recognition of altitude-related symptoms, management plans, and appropriate follow-up. As the risk and prevalence of chronic disease increases with age, both older patients and providers need to be aware of disease and medication-specific risks relative to wilderness sport and activity participation. Disabled and special needs athletes benefit from careful pre-event planning for the potential medical issues and equipment modifications that may affect their health in wilderness environments. Issues that demand special consideration for female adventurers include pregnancy, contraceptive use, menses, and ferritin levels at altitude. A careful preparticipation evaluation that factors in unique, population-specific risks will help special populations stay healthy and safe on wilderness adventures. The PubMed and SportDiscus databases were searched in 2014 using both MeSH terms and text words and include peer-reviewed English language articles from 1977 to 2014. Additional information was accessed from Web-based sources to produce this narrative review on preparticipation evaluation for special populations undertaking wilderness adventures. Key words include children, adolescent, pediatric, seniors, elderly, disabled, special needs, female, athlete, preparticipiation examination, wilderness medicine, and sports.

Neonatal variables, altitude of residence and Aymara ancestry in northern Chile

Studies performed in the Andean plateau, one of the highest inhabited areas in the world, have reported that reduced availability of oxygen is associated to fetal growth retardation and lower birth weight, which are established predictors of morbidity and mortality during the first year of life. To test this hypothesis, perinatal variables of neonates born at the Juan Noé Hospital of Arica, Chile, were analyzed in relation to altitude of residence and Aymara ancestry of their mothers. The study population comprised the offspring of 5,295 mothers born between February 2004 and August 2010. Information included birth weight, height, head circumference, gestational age, altitude of residence and socioeconomic status, and was obtained from medical records. Mother´s ancestry was assessed based on surnames which were linked to percentages of Aymara admixture estimates relying on 40 selected ancestry informative markers. After correcting for the effect of multicollinearity among predictor variables, neonates born to mothers with an increased component of Aymara ancestry showed significantly higher birth weight and height at sea level, a marginally significant (p-value 0.06) decrease of birth weight and a significant decrease of height with altitude in comparison with the offspring of mothers with low Aymara ancestry. Since observed tendencies are suggestive of a possible genetic adaptation to hypoxia of the Chilean Aymara, we discuss briefly preliminary evidence related to fetal oxygen transport, particularly polymorphisms in the promoters of the HBG1 and HBG2 genes that are modulators of HbF synthesis, obtained in this ethnic group.

miR455 is linked to hypoxia signaling and is deregulated in preeclampsia

Preeclampsia is a severe pregnancy-related disorder and a leading cause of maternal and fetal mortality worldwide. Early identification of patients with an increased risk for preeclampsia is thus one of the most important goals in obstetrics. Here we identify two related human microRNAs as potential biomarkers to detect at-risk pregnancies. We demonstrate that miR455-3P and miR455-5P are significantly downregulated in placentas from preeclampsia patients, whereas other placenta-specific microRNAs remain unaffected. microRNA target prediction and validation revealed a potential link of miR455-3P to hypoxia signaling. Together with our observation that expression levels of miR455-3P and miR455-5P are upregulated during trophoblast differentiation, our results suggest a model in which miR455-3P represses a hypoxia response that might otherwise prevent cytotrophoblasts from syncytiotrophoblast differentiation. In summary, our work reveals aberrant hypoxia signaling in preeclampsia that can be explained by deregulated expression of miR455. As miR455 has been found in circulating blood, the development of noninvasive prenatal tests enabling early diagnosis of preeclampsia may be possible.

The placental pursuit for an adequate oxidant balance between the mother and the fetus

The placenta is the exchange organ that regulates metabolic processes between the mother and her developing fetus. The adequate function of this organ is clearly vital for a physiologic gestational process and a healthy baby as final outcome. The umbilico-placental vasculature has the capacity to respond to variations in the materno-fetal milieu. Depending on the intensity and the extensity of the insult, these responses may be immediate-, mediate-, and long-lasting, deriving in potential morphostructural and functional changes later in life. These adjustments usually compensate the initial insults, but occasionally may switch to long-lasting remodeling and dysfunctional processes, arising maladaptation. One of the most challenging conditions in modern perinatology is hypoxia and oxidative stress during development, both disorders occurring in high-altitude and in low-altitude placental insufficiency. Hypoxia and oxidative stress may induce endothelial dysfunction and thus, reduction in the perfusion of the placenta and restriction in the fetal growth and development. This Review will focus on placental responses to hypoxic conditions, usually related with high-altitude and placental insufficiency, deriving in oxidative stress and vascular disorders, altering fetal and maternal health. Although day-to-day clinical practice, basic and clinical research are clearly providing evidence of the severe impact of oxygen deficiency and oxidative stress establishment during pregnancy, further research on umbilical and placental vascular function under these conditions is badly needed to clarify the myriad of questions still unsettled.

Integrative transcriptome analysis reveals dysregulation of canonical cancer molecular pathways in placenta leading to preeclampsia

We previously suggested links between specific XPD mutations in the fetal genome and the risk of placental maldevelopment and preeclampsia, possibly due to impairment of Transcription Factor (TF)IIH-mediated functions in placenta. To identify the underlying mechanisms, we conducted the current integrative analysis of several relevant transcriptome data sources. Our meta-analysis revealed downregulation of TFIIH subunits in preeclamptic placentas. Our overall integrative analysis suggested that, in the presence of hypoxia and oxidative stress, EGFR signaling deficiency, which can be caused by TFIIH impairment as well as by other mechanisms, results in ATF3 upregulation, inducing mediators of clinical symptoms of preeclampsia such as FLT1 and ENG. EGFR- and ATF3-dependent pathways play prominent roles in cancer development. We propose that dysregulation of these canonical cancer molecular pathways occurs in preeclampsia and delineate the relevance of TFIIH, providing etiologic clues which could eventually translate into a therapeutic approach.

Gestational hypoxia induces preeclampsia-like symptoms via heightened endothelin-1 signaling in pregnant rats

Preeclampsia is a life-threatening pregnancy disorder. However, its pathogenesis remains unclear. We tested the hypothesis that gestational hypoxia induces preeclampsia-like symptoms via heightened endothelin-1 (ET-1) signaling. Time-dated pregnant and nonpregnant rats were divided into normoxic and hypoxic (10.5% O2 from the gestational day 6-21) groups. Chronic hypoxia had no significant effect on blood pressure or proteinuria in nonpregnant rats but significantly increased blood pressure on day 12 (systolic blood pressure, 111.7 ± 6.1 versus 138.5 ± 3.5 mm Hg; P=0.004) and day 20 (systolic blood pressure, 103.4 ± 4.6 versus 125.1 ± 6.1 mm Hg; P=0.02) in pregnant rats and urine protein (μg/μL)/creatinine (nmol/μL) ratio on day 20 (0.10 ± 0.01 versus 0.20 ± 0.04; P=0.04), as compared with the normoxic control group. This was accompanied with asymmetrical fetal growth restriction. Hypoxia resulted in impaired trophoblast invasion and uteroplacental vascular remodeling. In addition, plasma ET-1 levels, as well as the abundance of prepro-ET-1 mRNA, ET-1 type A receptor and angiotensin II type 1 receptor protein in the kidney and placenta were significantly increased in the chronic hypoxic group, as compared with the control animals. Treatment with the ET-1 type A receptor antagonist, BQ123, during the course of hypoxia exposure significantly attenuated the hypoxia-induced hypertension and other preeclampsia-like features. The results demonstrate that chronic hypoxia during gestation induces preeclamptic symptoms in pregnant rats via heightened ET-1 and ET-1 type A receptor-mediated signaling, providing a molecular mechanism linking gestational hypoxia and increased risk of preeclampsia.