Exposure to suboptimal ambient temperature during specific gestational periods and adverse outcomes in mice

The influence of high-speed train's transient pressure change on the fetal growth of SD rats

This research aims to explore the influence of transient pressure fluctuation inside high-speed trains passing throught tunnels on the fetal growth of Sprague - Dawley (SD) rats. A pressure variation simulation system was designed and exposure experiments were performed on SD rats. Forty-eight SD rats are divided into two control groups and two experimental groups, and are then exposed to transient pressure alternation (-1200 Pa ~1200 Pa) from gestation day 0 to gestation day 5 (GD 0-5). Fetal growth and development indicators on GD12 and GD18 between experimental and control groups were compared. Statistical results showed that, compared to the control group, the key indicators in the experimental group, including placental weight, placental diameter, fetal weight, and crown-to-rump length have decreased by 4.77%, 3.38%, 6.20%, and 3.75% respectively on GD18. The findings imply that the pressure fluctuation environment of high-speed trains has potential effects on the fetal growth of SD rats.

The gut microbiota facilitate their host tolerance to extreme temperatures

BACKGROUND

Exposure to extreme cold or heat temperature is one leading cause of weather-associated mortality and morbidity in animals. Emerging studies demonstrate that the microbiota residing in guts act as an integral factor required to modulate host tolerance to cold or heat exposure, but common and unique patterns of animal-temperature associations between cold and heat have not been simultaneously examined. Therefore, we attempted to investigate the roles of gut microbiota in modulating tolerance to cold or heat exposure in mice.

RESULTS

The results showed that both cold and heat acutely change the body temperature of mice, but mice efficiently maintain their body temperature at conditions of chronic extreme temperatures. Mice adapt to extreme temperatures by adjusting body weight gain, food intake and energy harvest. Fascinatingly, 16 S rRNA sequencing shows that extreme temperatures result in a differential shift in the gut microbiota. Moreover, transplantation of the extreme-temperature microbiota is sufficient to enhance host tolerance to cold and heat, respectively. Metagenomic sequencing shows that the microbiota assists their hosts in resisting extreme temperatures through regulating the host insulin pathway.

CONCLUSIONS

Our findings highlight that the microbiota is a key factor orchestrating the overall energy homeostasis under extreme temperatures, providing an insight into the interaction and coevolution of hosts and gut microbiota.

The effects of heat stress on intrauterine development, reproductive function, and ovarian gene expression of F1 female mice as well as gene expression of F2 embryos†

Exposure to heat stress (HS) in utero was postulated to trigger an adaptive molecular response that can be transmitted to the next generation. Hence, this study assessed the impact of HS exposure at different stages of the gestational period of mice on the female F1 population and their offspring. Heat stress exposure (41°C and 65% relative humidity-RH) occurred during the first half (FP), the second half (SP), or the entire pregnancy (TP). A control group (C) was maintained in normothermic conditions (25°C, 45% RH) throughout the experiment. Heat stress had a significant negative effect on intrauterine development, mainly when HS exposure occurred in the first half of pregnancy (FP and TP groups). Postnatal growth of FP and TP mice was hindered until 4 weeks of age. The total number of follicles per ovary did not vary (P > 0.05) between the control and HS-exposed groups. Mean numbers of primordial follicles were lower (P < 0.05) in the sexually mature FP than those in SP and TP F1 females. However, the mean number of viable embryos after superovulation was lower (P < 0.05) in TP compared with C group. The expression of genes associated with physiological and cellular response to HS, autophagy, and apoptosis was significantly affected in the ovarian tissue of F1 females and F2 in vivo-derived blastocysts in all HS-exposed groups. In conclusion, exposure to HS during pregnancy compromised somatic development and reproductive parameters as well as altered gene expression profile that was then transmitted to the next generation of mice.

The mediation of the placenta on the association between maternal ambient temperature exposure and birth weight

Studies have indicated that exposure to low and high temperatures during pregnancy negatively affects fetal development. The placenta plays vital functions in fetal development and could also be impacted by suboptimal temperatures. However, whether the placenta mediates the association between suboptimal temperature and birth weight is unknown. Our study aims to evaluate the association between ambient temperature and birth weight as well as the mediation effect of the placenta. A prospective birth cohort study was conducted during 2017-2020 in Guangzhou, China (n = 3349 participants). We defined extreme temperature exposure during the whole pregnancy by using different thresholds, including low temperatures (< 25th, < 15th, < 10th, < 5th percentiles), and high temperatures (> 75th, > 85th, > 90th, > 95th percentiles). Three different approaches (generalized linear model, inverse probability weighting, and doubly robust model) were applied to estimate the effects of low/high temperatures on birth weight and placental indicators, including placental weight, placental volume, and placental-to-birth weight ratio (PFR), respectively. We observed that both low and high ambient temperatures during the whole pregnancy were associated with lower birth weight and negative changes in placental indicators. The estimated lower mean birth weight ranged from -158 g (95 % CI: -192 g, -123 g) to -363 g (95 % CI: -424 g, -301 g) for low temperatures and from -97 g (95 % CI: -135 g, -59 g) to -664 g (95 % CI: -742 g, -585 g) for high temperatures. In mediation analyses, placental weight mediated 28.79 % to 40.47 % and 48.22 % to 54.38 % of the association of low and high temperatures with birth weight, respectively. The findings suggest that placental weight may mediate the association between ambient temperature exposure and birth weight.

Association between low ambient temperature during pregnancy and adverse birth outcomes: A systematic review and meta-analysis

BACKGROUND

Extreme temperature events, including extreme cold, are becoming more frequent worldwide, which might be harmful to pregnant women and cause adverse birth outcomes. We aimed to investigate the association between exposure to low ambient temperature in pregnant women and adverse birth outcomes, such as preterm birth, low birth weight, and stillbirth, and to summarize the evidence herein.

METHODS

Relevant studies were searched in PubMed, Cochrane, and Embase electronic databases until November 2021. Studies involving low ambient temperature, preterm birth, birth weight, and stillbirth were included. The guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-analyses were followed to conduct this study risk of bias and methods for data synthesis.

RESULTS

A total of 34 studies were included. First, pregnant women exposed to low ambient temperature had an increased risk of preterm birth (risk ratio [RR] 1.08; 95% confidence interval [CI] 1.04-1.13). Subgroup analyses revealed that exposure during late pregnancy was more likely to induce preterm birth. In addition, only pregnant women exposed to <1st percentile of the mean temperature suffered increased risk of preterm birth. Moreover, pregnant women living in medium or hot areas were more prone to have preterm births than those in cold areas when exposed to low ambient temperatures. Asians and Blacks were more susceptible to low ambient temperatures than Caucasians. Second, pregnant women exposed to low ambient temperature had an increased risk of low birth weight (RR 1.07; 95% CI 1.03-1.12). Third, pregnant women had an increased risk of stillbirth while exposed to low ambient temperature during the entire pregnancy (RR 4.63; 95% CI 3.99-5.38).

CONCLUSIONS

Exposure to low ambient temperature during pregnancy increases the risk of adverse birth outcomes. Pregnant women should avoid exposure to extremely low ambient temperature (<1st percentile of the mean temperature), especially in their late pregnancy. This study could provide clues for preventing adverse outcomes from meteorological factors.

REGISTRATION

No. CRD42021259776 at PROSPERO ( https://www.crd.york.ac.uk/PROSPERO/ ).

Climate change and pregnancy complications: From hormones to the immune response

Pregnant women are highly vulnerable to adverse environments. Accumulating evidence highlights that increasing temperatures associated with the ongoing climate change pose a threat to successful reproduction. Heat stress caused by an increased ambient temperature can result in adverse pregnancy outcomes, e.g., preterm birth, stillbirth and low fetal weight. The pathomechanisms through which heat stress interferes with pregnancy maintenance still remain vague, but emerging evidence underscores that the endocrine system is severely affected. It is well known that the endocrine system pivotally contributes to the physiological progression of pregnancy. We review – sometimes speculate - how heat stress can offset hormonal dysregulations and subsequently derail other systems which interact with hormones, such as the immune response. This may account for the heat-stress related threat to successful pregnancy progression, fetal development and long-term children’s health.

The Association of Ambient Temperature with Extremely Preterm Births

INTRODUCTION

Extremely preterm births (EPT), require complex decision making and significant medical interventions. While environmental factors such as ambient temperature extremes have been associated with preterm births, little is known of the environmental associations with EPT births. The objective of this study is to explore whether ambient temperature is associated with increased risk of EPT birth.

METHODS

Birth records for 315,226 infants born in Queensland Australia (2007-2015) were matched to average maximum and minimum temperature for the last month of pregnancy. Odds ratios and 95% confidence intervals were calculated using a generalised linear model. Population attributable risk was calculated for a 5% reduction in maximum temperature.

RESULTS

Each one degree increase in maximum [aOR 1.03 (95% CI 1.01, 1.05)] and minimum temperature [aOR 1.02 (95% CI 1.01, 1.04)] was associated with an increase in odds for EPT birth. Increased odds for EPT births was found for maternal smoking [aOR 1.46 (95% CI 1.23, 1.72)], increasing plurality [OR 6.38 (95% CI 5.48, 7.42)] and stillbirth [aOR 342.99 (95% CI 295.53, 398.06)]. When stratified by birth status, the association was only found for live births.

DISCUSSION

Higher temperatures are associated with small increases in the odds of delivering an infant in the EPT period. The risk may be enhanced for women who smoke during pregnancy. Women at an increased risk of preterm births should be counselled around methods to reduce their exposure to excessive heat.

Preconception ambient temperature and preterm birth: a time-series study in rural Henan, China

Changes in the preconception ambient temperature (PAT) can affect the gametogenesis, disturbing the development of the embryo, but the health risks of PAT on the developing fetus are still unclear. Here, based on the National Free Preconception Health Examination Project in the rural areas of Henan Province, we evaluate the effects of PAT on preterm birth (PTB). Data of 1,231,715 records from self-reported interviews, preconception physical examination, early gestation follow-up, and postpartum follow-up were collected from 1 January 2013 to 31 December 2016. Generalized additive models were used to assess the cumulative and lag effects of PAT upon PTB. The significant cumulative effects of mean temperature within 2 weeks and 3 weeks on the risk of PTB, especially upon late PTB (34-36 weeks) (P < 0.05), were observed. Exposure to extreme heat (> 90th percentile) within 2 weeks (RR = 1.470) and 3 weeks (RR = 1.375) before conception could increase the risk of PTB. After stratifying PTB, exposure to extreme heat within 2 weeks before conception can increase the risks of early (< 34 weeks) and late PTB (P < 0.05). Besides, exposure to extreme cold (< 10th percentile) within 3 weeks or longer before conception can elevate the risk of PTB, especially late PTB. The significant lag effects of temperature changes on the risk of early PTB (lag-8 days or earlier) were observed. In conclusion, the risk of PTB was susceptible to PAT changes within 2 weeks or longer before conception. Our findings provide (i) guidance for rural couples to make pregnancy plans and (ii) scientific evidence for the government to formulate policies to prevent PTB.