Seasonal Variation in Gestational Blood Pressure

Universal Thermal Climate Index (UTCI) and adverse pregnancy outcomes in Ahvaz, Iran

Background

Climate change may jeopardize the health of mothers and their offspring. There are few studies on the association between increasing temperature and pregnancy outcomes. The aim of this study was to investigate the relation between Universal Thermal Climate Index (UTCI) and adverse pregnancy outcomes including stillbirth, low birth weight (LBW), preterm labor (PTL), spontaneous abortion (SA), preeclampsia and hypertension in Ahvaz, Iran.

Methods

Distributed Lag Non-linear Models (DLNM) combined with quasi-Poisson regression were used to research the effect of UTCI on adverse pregnancy outcomes. The effect of time trend, air pollutants (NO₂, SO₂ and PM₁₀), and weekdays were adjusted.

Results

The results showed that the low values of UTCI index (11.6 °C, in lags 0–6, 0–13) caused significant increase in the risk of preterm labor. However, hot thermal stress (high UTCI) significantly increased the risk of stillbirth in lag 0–13. We did not observe any significant relation between UTCI and other pregnancy outcomes in this study.

Conclusions

It seems like both hot and cold weathers can be associated with adverse pregnancy outcomes.

Scientists have found that climate change has adverse effects on human health. Because pregnant women are one of the most vulnerable groups, these negative impacts may affect their fetuses, which make up the next generation. In this study, we examined the effect of temperature on some pregnancy outcomes, including low birth weight, preterm labor, spontaneous abortion, preeclampsia and gestational hypertension in Ahvaz city, which is one of the hottest cities in the world.

One way to assess temperature impact on humans is by using temperature indicators. In this study we used the Universal Thermal Climate Index (UTCI) for this purpose. The data at different time intervals were collected and evaluated with specific models.

Our results showed that low values of UTCI, which is equivalent to cold weather, significantly increase the risk of preterm labor. But, high levels of UTCI, which means hot weather, significantly increase the risk of stillbirth.

In conclusion; both hot and cold weather can be associated with adverse pregnancy outcomes in Ahvaz city. Therefore, pregnant women should protect themselves from exposure to hot and cold weather.

Association between Physiological Equivalent Temperature (PET) with adverse pregnancy outcomes in Ahvaz, southwest of Iran

Background

There are few epidemiological studies on the relation between temperature changes and adverse pregnancy outcomes. The purpose of this study was to determine the relation between Physiological Equivalent Temperature (PET) with adverse pregnancy outcomes including stillbirth, low birth weight (LBW), preterm labor (PTL), spontaneous abortion (SA), preeclampsia and hypertension in Ahvaz, Iran.

Methods

Distributed Lag Non-linear Models (DLNM) combined with quasi-Poisson regression were used to investigate the effect of PET on adverse pregnancy outcomes. In this study the effect of time trend, air pollutants (NO₂, SO₂ and PM₁₀), and weekdays were adjusted.

Results

High PET (45.4 C°, lag = 0) caused a significant increase in risk of stillbirth. Also, high levels of PET (45.4, 43.6, 42.5 C°, lag = 0–6) and low levels of PET (9.9, 16.9 C°, lags = 0, 0–13, 0–21) significantly increased the risk of LBW. But, low levels of PET (6.4, 9.9, 16.9 C°, lags = 0–6, 0–13) reduced the risk of gestational hypertension.

Conclusion

The results of this study showed that hot and cold thermal stress may be associated with increased risk of stillbirth, and LBW in Ahvaz.

Seasonal variation in the hypertensive disorders of pregnancy in Denmark

INTRODUCTION

Hypertensive disorders of pregnancy, including gestational hypertension and preeclampsia, are leading causes of morbidity and mortality for both mother and fetus. It has been proposed that vitamin D affects a number of biological processes involved in the pathogenesis of hypertensive disorders of pregnancy. Therefore, a seasonal variation in the risk of these disorders might be expected in areas such as Denmark with marked seasonal variation in sunlight exposure. In this study, we aimed to evaluate the existence of this association.

MATERIAL AND METHODS

We used information from a cohort of 50 665 previously healthy, nulliparous women with singleton pregnancies. All women gave birth between 1989 and 2010 at Aarhus University Hospital, Denmark. Logistic regression analyses combined with the cubic spline method were used to estimate the seasonal variation for each outcome: gestational hypertension and preeclampsia, after adjusting for calendar time.

RESULTS

Of the 50 665 women included, 8.5% were diagnosed with a hypertensive disorder of pregnancy. The overall tendency was towards increasing risk when conceiving during spring and early summer, peaking midsummer, and subsequently decreasing steadily during late summer and fall to reach the nadir by winter. Seasonal variation was found for; gestational hypertension (P = .01); preeclampsia (P = .001) and early-onset preeclampsia (P = .014).

CONCLUSIONS

We found a seasonal variation in the risk of the hypertensive disorders of pregnancy in a large cohort of Danish nulliparous women. The highest risk was seen in women with the estimated date of conception in June and August, that is, during summer. Seasonal variation in vitamin D status may explain this association.

Adverse Effects of Exposure to Fine Particulate Matters and Ozone on Gestational Hypertension

Gestational hypertension (GH) is a common complication during pregnancy. GH is regarded as a potential public health challenge for pregnant women and infants. Limited evidence has linked ambient air pollution to an increased GH risk. However, most of the studies were conducted in developed countries, with inconsistent results obtained. The present study was performed to explore whether exposure to particulate matters with an aerodynamic diameter < 2.5 (PM_2.5) and ozone (O₃) was related to elevated odds of GH in a Chinese population. This population-based cohort study involved 38 115 pregnant women in Wuhan, China. All information was collected from the Wuhan Maternal and Child Health Management Information System, using standardized quality control. The daily air pollutant data for PM_2.5 and O₃ were obtained from the 20 monitoring stations of the Wuhan Environmental Monitoring Center during 2014. The nearest monitor approach was applied to individual exposure assessment of PM_2.5 and O₃ for each participant. After adjusting for major confounders and other air pollutants, a 10 µg/m³ increase in PM_2.5 and O₃ concentrations was found to correlate to a 1.14-fold [95% confidence interval (95% CI): 1.09, 1.20] and a 1.05-fold (95% CI: 1.02, 1.07) increase in GH risk, respectively. Additionally, stronger relationships between GH risk and PM_2.5 and O₃ exposure were observed in women who conceived in winter and summer, respectively. These findings suggest that air pollutants may contribute to the development of GH.

Acute effects of temperature exposure on blood pressure: An hourly level panel study

BACKGROUND

Several epidemiological studies have shown that blood pressure changes with temperature based on the daily temperature and linear relationship assumption. However, little is known about the true curve shape of the relationship between temperature and blood pressure.

OBJECTIVES

The objective of this study was to investigate the non-linear relationship between hourly temperature and blood pressure.

METHODS

This is a prospective panel study comprising 100 participants in Suzhou, China. The blood pressure of each participant was measured >50 times between October 2013 and January 2016. Hourly temperature data were derived from the nearest monitoring station owned by the China Meteorological Administration. A Distributed Lag Nonlinear Model (DLNM) was used to investigate the relationship between hourly temperature and blood pressure.

RESULTS

We found that the relationship between hourly temperature and blood pressure was parabolic. Short-term exposure to hourly temperatures had significant cold and heat effects on systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), and mean arterial pressure (MAP). The hourly temperature had a significant lag effect on blood pressure, with a lag time of 0-5 h. Alcohol users were more sensitive to the cold effects of hourly temperature, and the diabetic population was more sensitive to the heat effects of hourly temperature on PP.

CONCLUSION

Temperature imparts short-term effects on blood pressure. Therefore, timely protective measures during cold waves or cold weather are beneficial to maintain stable blood pressure levels to reduce the risk of blood pressure related diseases.

Seasonality of hypertensive disorders of pregnancy - A South Australian population study

OBJECTIVES

To investigate the seasonal variation of hypertensive disorders of pregnancy (HDP) in South Australia.

STUDY DESIGN

Retrospective population study including all 107,846 liveborn singletons during 2007-2014 in South Australia. Seasonality in incidence of HDP in relation to estimated date of conception (eDoC) and date of birth (DoB) were examined using Fourier series analysis.

MAIN OUTCOME MEASURES

Seasonality of HDP in relation to eDoC and DoB.

RESULTS

During 2007-2014, the incidence of HDP was 7.1% (n = 7,612). Seasonal modeling showed a strong relationship between HDP and eDoC (p < .001) and DoB (p < .001). Unadjusted and adjusted models (adjusted for maternal age, body mass index, ethnicity, parity, type of health care, smoking and gestational diabetes mellitus) demonstrated the presence of a peak incidence (7.8%, 7.9% respectively) occurring among pregnancies with eDoC in late Spring (November) and a trough (6.4% and 6.3% respectively) among pregnancies with eDoC in late Autumn (May). Both unadjusted and adjusted seasonal modelling showed a peak incidence of HDP for pregnancies with DoB in August (8.0%, 8.1% respectively) and a nadir among pregnancies with eDoB in February (6.2%).

CONCLUSION

The highest incidence of HDP was associated with pregnancies with eDoC during late spring and summer and birth in winter, while the lowest incidence of HDP was associated with pregnancies with eDoC during late autumn and early winter and birth in summer. Nutrient intake, in particular vitamin D, sunlight exposure and physical activity may affect maternal, fetal and placental adaptation to pregnancy and are potential contributors to the seasonal variation of HDP.

Ambient Temperature and Risk of Preeclampsia: Biased Association?

BACKGROUND

Preeclampsia is associated with conception during warm months and delivery during cold months. We sought to determine whether season of conception and shorter gestation bias the associations.

METHODS

We used hospital discharge summaries to identify 65 273 pregnancies with and 1 825 438 without preeclampsia in Quebec, Canada between 1989 and 2012. We obtained data on mean temperature for the month following conception and the month before hospital admission. We used cubic splines in log-binomial models to estimate the association between temperature and preeclampsia (risk ratios, RR; 95% confidence interval, CI). To assess the potential for bias, we compared models progressively adjusted for baseline maternal characteristics, season of conception, and length of gestation at admission.

RESULTS

With adjustment for baseline maternal characteristics only, risk of preeclampsia was higher for hot temperatures at conception and cold temperatures at end of pregnancy. Adjusting for season at conception removed the association between preeclampsia and temperature at conception. Adjustment for length of gestation removed the association between preeclampsia and temperature at end of pregnancy.

CONCLUSIONS

This study demonstrates that associations between ambient temperature and preeclampsia may be biased by short gestation, because preeclampsia commonly occurs earlier in pregnancy. Temperatures during gestation change with time for all women, and temperatures early in pregnancy frequently differ from temperatures later in pregnancy. Variation in temperature over gestation may lead to a coincidental association with preeclampsia.

Hypertension, pregnancy and weather: is seasonality involved?

OBJECTIVE

The present study aimed at assessing the association between environmental temperature and the relative humidity of the air with frequency of hypertensive disorders of pregnancy.

METHODS

A prospective and retrospective, descriptive, ecological study was held at a teaching maternity in Recife, Brazil. Data from all 26.125 pregnant women admitted between 2000 and 2006 were analysed and 5.051 had the diagnosis of hypertensive disorder of pregnancy. The incidence percentages were calculated monthly per deliveries. Data on mean monthly temperature and relative humidity of the air were collected and monthly comparisons were conducted. February was chosen as the reference month due to its lowest incidence of the disease. The relative chance of hypertensive disorders of pregnancy for each other month was estimated by odds ratio and Pearson's correlation coefficient was used to calculate the relation between the incidence of hypertensive disorders of pregnancy and the mean monthly temperature and relative air humidity.

RESULTS

February presented the lowest mean monthly incidence (9.95%) and August the highest (21.54%). Pearson correlation coefficient revealed a higher incidence of hypertensive disorders of pregnancy in the cooler months (r= -0.26; p=0.046) and no significant effect of relative air humidity (r=0.20; p=0.128).

CONCLUSION

The incidence of hypertensive disorders of pregnancy may be affected by variations in temperature, increasing during cooler periods.

First trimester vitamin D status and placental epigenomics in preeclampsia among Northern Plains primiparas

AIMS

As maternal vitamin D status has been associated with preeclampsia, the purpose of this study was to determine variations in DNA methylation patterns and associated protein expression in placental genes regulating vitamin D metabolism.

MAIN METHODS

A convenience sample of 48 pregnant nulliparous women, including 11 later diagnosed with preeclampsia, were recruited in this prospective study. Using a case-control design in two groups of women, we administered a food frequency questionnaire to determine vitamin D dietary intake. Laboratory measures included serum vitamin D levels (25[OH]D), DNA methylation patterns and protein expression in placental genes regulating vitamin D metabolism (1α-hydroxylase, CYP27B1; vitamin D receptor, VDR; retinoid X receptor, RXR) from placental tissue collected at delivery among those diagnosed with preeclampsia and those who remained normotensive throughout pregnancy.

KEY FINDINGS

There were no significant differences in vitamin D dietary intake or mean serum 25[OH]D levels, although the proportion of women with deficient 25[OH]D levels was higher in the preeclampsia group (46%) than the normotensive group (20%). Placenta samples from women with preeclampsia also had increased DNA methylation of CYP27B1, VDR and RXR genes with lower protein expression levels limited to RXR.

SIGNIFICANCE

Hypermethylation of key placental genes involved in vitamin D metabolism suggests uncoupling of processes that may interfere with placentation and availability of vitamin D at the maternal-fetal interface.

Associations of meteorology with adverse pregnancy outcomes: a systematic review of preeclampsia, preterm birth and birth weight

The relationships between meteorology and pregnancy outcomes are not well known. This article reviews available evidence on the relationships between seasonality or meteorology and three major pregnancy outcomes: the hypertensive disorders of pregnancy (including preeclampsia, eclampsia and gestational hypertension), gestational length and birth weight. In total 35, 28 and 27 studies were identified for each of these outcomes. The risks of preeclampsia appear higher for women with conception during the warmest months, and delivery in the coldest months of the year. Delivery in the coldest months is also associated with a higher eclampsia risk. Patterns of decreased gestational lengths have been observed for births in winter, as well as summer months. Most analytical studies also report decreases in gestational lengths associated with heat. Birth weights are lower for deliveries occurring in winter and in summer months. Only a limited number of studies have investigated the effects of barometric pressure on gestational length or the effects of temperature and sunshine exposure on birth weight, but these questions appear worth investigating further. Available results should encourage further etiological research aiming at enhancing our understanding of the relationships between meteorology and adverse pregnancy outcomes, ideally via harmonized multicentric studies.

Season, temperature and blood pressure: a complex interaction

An increase in blood pressure values measured during winter either in the office, at home, or at ambulatory blood pressure monitoring was consistently observed. Besides potentially contributing to increase the risk for cardiovascular events during the cold season, long term blood pressure variations can influence results of clinical trials, epidemiological surveys, and require personalized management of antihypertensive medications in the single patient. Those variations are often considered as an effect of climate, due to the close correlation observed in various countries and in different settings between temperature and blood pressure among children, adults, and specially the elderly. However, obtaining true measurements of exposition is a main problem when investigating the effects of climate on human health especially when the aim is to disentangle the effects of climate from those of seasonality. The aim of the present note is not to provide a complete review of the literature demonstrating the implications of seasonal blood pressure changes in the clinical and experimental setting; rather it is to consider methodological aspects useful to investigate the interaction between seasonality and temperature on blood pressure and to make health care providers aware of the implications of environmental factors on blood pressure in clinical and research settings.

Blood pressure rises more in pre-eclampsia than normal pregnancy when acral skin is locally cooled

OBJECTIVE

Investigate blood pressure response to acral skin vasoconstriction in healthy and pre-eclamptic pregnancies.

METHODS

Healthy women were investigated from gestational week 8 to 52 weeks postpartum and pre-eclampsia subjects at diagnosis. Finger artery ultrasound Doppler, forearm laser Doppler fluximetry and photoplethysmographic blood pressure were recorded. Hand cooling to 19 °C induced vasoconstriction.

RESULTS

Acral skin vasoconstriction increases blood pressure from 16 weeks until 12 weeks postpartum (p ≤ 0.01), with greatest responses in pre-eclampsia (p=0.047). Forearm skin perfusion is higher in pre-eclampsia (p=0.04).

CONCLUSION

Acral skin vasoconstriction raises blood pressure in pregnancy, particularly in pre-eclampsia. Pregnancy accentuates important functional differences within skin.

Association of seasonality with hypertension in pregnancy: a systematic review

A systematic literature review was conducted to examine all academic, peer-reviewed studies of seasonal or monthly variation in the prevalence of gestational hypertension, preeclampsia, or eclampsia. The objective was to test the hypothesis that prevalence rates are highest during the winter months in non-tropical regions and during wet or humid periods in tropical climates. The authors searched the epidemiological literature indexed in PubMed, cross-referenced bibliographic materials, and reviewed personal archives. Of 60 abstracts and articles screened, 20 met the final inclusion criteria. Studies included were published between 1938 and 2010. Despite differences in setting, data sources, study design, outcome definitions, and control of known risk factors, 16 separate studies (11 non-tropical and 5 tropical) concurred that prevalence rates were higher for winter delivery in non-tropical regions or delivery during wet or humid periods in tropical climates. Although the reasons for these patterns are unknown, seasonal variation in infectious diseases, environmental triggers of asthma, vitamin D levels, physiological responses to cold temperatures, healthcare access, and nutritional intake may all play a role.

Ethnic differences in the monthly variation of preeclampsia among Bedouin and Jewish parturients in the Negev

OBJECTIVE

To assess seasonal patterns and monthly variations in the incidence of preeclampsia in the Jewish and Bedouin population in Israel, assuming that ethnicity and environmental factors may have a role in the causal mechanism.

METHODS

A retrospective population-based study comparing all singleton pregnancies of patients with and without preeclampsia was performed. The study included all deliveries between and including 1988 and 2007. For each month, the percentage of births complicated by preeclampsia was calculated. The relative risks of preeclampsia by month of delivery were estimated as odds ratios, using the month of August as the reference category.

RESULTS

During the study period, 203,461 deliveries took place, of which 8,421 (4.1%) were complicated with preeclampsia (either mild or severe). Significantly higher incidence of preeclampsia was demonstrated in the Jewish population: 4.7% (n = 4,783 deliveries) versus 3.6% in the Bedouin population (n = 3,683), (p < 0.001). A similar U shaped trend in the incidence of preeclampsia was noted in both populations: the incidence was highest in the winter months and reached its nadir in August, with subsequent increase through the fall months (p < 0.001). Using August as the reference month, odds ratios were 1.32 (95% CI 1.19-1.48) for January, 1.38 (95% CI 1.24-1.54) for February and 1.33 (95% CI 1.19-1.48) for March. Time series analysis demonstrated a difference in the behavior of the 2 populations. Whereas the Jewish population had demonstrated a Gregorian-month cycle, the Bedouin population had demonstrated a lunar-month cycle.

CONCLUSION

Preeclampsia is significantly more common in the Jewish population. However, both populations demonstrate the same seasonal pattern, with higher incidence of preeclampsia in the winter months. Our findings suggest that climate and environmental exposure may have an important role in the pathophysiology of preeclampsia.

Racial/ethnic differences in the monthly variation of preeclampsia incidence

OBJECTIVE

The purpose of this study was to assess monthly patterns in preeclampsia risk separately by race/ethnicity.

STUDY DESIGN

We conducted a cohort study of 20,794 white women and 18,916 black women who received care at 12 hospitals in the United States.

RESULTS

Among white women, there was a significant U-shaped trend in the incidence of preeclampsia: the incidence was highest in winter months, reached its nadir in mid August, and subsequently increased through the fall months (P < .05). When compared with occurrences in January, the adjusted odds ratios were 0.65 (0.43, 0.99) for May, 0.76 (95% CI, 0.51, 1.13) for June, 0.64 (95% CI, 0.43, 0.97) for July, and 0.64 (95% CI, 0.42, 0.96) for August. Among black women, there was no association between month of delivery and preeclampsia risk (P = .81).

CONCLUSION

Our finding that the incidence of preeclampsia decreases in white women during the summer months and that no pattern exists in black women suggests that, in each subgroup, different or competing environmental exposures may be important for the pathogenesis of preeclampsia.