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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive April 9, 2014

 

Specifically targeting summer births, scientists found nearly 20,000 deliveries
occurred following a day when the mercury reached 32°C [89.6°F] or higher.






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Pregnancy ends sooner during heat waves

Extreme summer heat in Montreal may generate early deliveries.

When temperatures reach 32°C - [89.6° F] - or higher over a period of four to seven days, the risk of early-term delivery is 27% higher than on typical summer days, according to a study led by Nathalie Auger of the University of Montreal's Department of Social and Preventive Medicine. The work is published in the journal Epidemiology.

The study involved data from 300,000 births that took place in Montreal between 1981 to 2010 with summer temperatures recorded by Environment Canada during this period. Auger is also affiliated with the university's CHUM Superhospital Research Centre.


The research team sought to identify, from June through September, the probability of preterm (less than 37 gestational weeks), early-term (37-38 weeks), and full-term (39 weeks or more) deliveries during a heat wave.

Specifically targeting summer births, Auger found that nearly 20,000 deliveries occurred in the week following a day when the mercury reached 32°C  [89.6° F] or higher.


After adjusting for certain variables, including age of mother, birth order, and humidity during heat waves, Auger found that extreme heat did not seem to increase the number of preterm births. "We observed only a negligible increase in the rate of preterm births between days when the temperature was below 20°C - [68° F] and those when it was above 28°C - [82.4° F] — from 5.4% to 5.8%," Auger explained.


In women who reached 37 or 38 weeks of pregnancy, the risk of early-term delivery increased by 17% following a three-day episode of 32°C [89.6° F] or more, compared to days without a heat wave.

When the extreme heat episode lasted from 4 to 7 days, the risk reached 27%.


According to Auger, the adverse effects of high temperatures on the elderly are well documented, but little research has dealt with the impact of heat on pregnant women.


"Small-scale studies suggest that heat-induced stress increases uterine contractions during that period of pregnancy when a mother's ability to regulate her body temperature is less effective.

"We also suspect that dehydration resulting from high temperatures reduces blood supply to the uterus, increasing the release of pituitary hormones that induce labour."

Nathalie Auger, University of Montreal's Department of Social and Preventive Medicine


Auger believes that the increased risk of early-term delivery due to high temperatures may result in increased morbidity in newborns. "Studies have shown that children born at 37 or 38 weeks suffer more respiratory problems compared with children born full term [39 weeks or more]," Auger said. "Early-term newborns are also at greater risk of death."

Abstract
Background: The relationship between ambient temperature and risk of delivery is poorly understood. We examined the association between heat and risk of delivery among preterm and term pregnancies with the use of a time-to-event design to minimize bias from seasonal variation in conception rates.

Methods: We used data on 206,929 term and 12,390 preterm singleton live births for Montreal, Canada, from June through September, 1981-2010. The exposure variables were (1) maximum daily temperatures in the week preceding birth and (2) number of consecutive days with temperatures of 32[degrees]C or above during the preceding week. We estimated hazards of delivery among preterm (<37 gestational weeks), early-term (37-38 weeks), and full-term (>=39 weeks) pregnancies for both exposures in Cox regression models, adjusting for maternal characteristics. Sensitivity analyses were carried out adjusting for markers of air pollution.

Results: Maximum temperatures reached at least 32[degrees]C during the preceding week for 19,829 births (9.0%). Relative to a maximum of 20[degrees]C, the hazard of delivery within term was 4% higher for maximum temperatures of 32[degrees]C or higher, but no association was found for preterm delivery. Associations were stronger with early-term than with full-term delivery. Extreme heat episodes with 4 to 7 days of maximum temperature of at least 32[degrees]C were associated with a 27% greater hazard of delivery among early-term pregnancies relative to other days.

Conclusion:
High ambient temperature and extreme heat episodes may trigger earlier delivery among term births.

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