Heat and pregnancy-related emergencies: Risk of placental abruption during hot weather
Introduction
A growing number of studies suggest that environmental conditions can affect the risk of placental abruption (Mankita, 2012, Michikawa et al., 2017, Yackerson et al., 2007). Placental abruption is an obstetric emergency that in extreme cases can lead to severe maternal and fetal morbidity or mortality (Oyelese and Ananth, 2006, Tikkanen, 2011). Abruption occurs when the placenta separates prematurely from the wall of the uterus before delivery, causing hemorrhage (Oyelese and Ananth, 2006). Every 7–12 pregnancies per 1000 end in abruption in North America (Ananth et al., 2014), with data suggesting that rates may be increasing (Ananth et al., 2014, Broers et al., 2004, Oyelese and Ananth, 2006). Preventing placental abruption is difficult as its causes are not fully understood, and risk factors such as preeclampsia and substance abuse account for only a proportion of cases (Tikkanen, 2011). Recent studies suggest that exposure to air pollutants may increase the risk of abruption (Ibrahimou et al., 2017, Michikawa et al., 2017), and that unstable seasonal weather in semi-arid areas can contribute (Mankita, 2012, Yackerson et al., 2007). The possibility that elevated outdoor temperature could increase the risk of placental abruption has however not been investigated.
Elevated temperature has potential to trigger placental abruption through different routes. In normal individuals, outdoor heat stress results in diversion of blood flow to the skin surface to prevent increasing core body temperature (Wells and Cole, 2002). Pregnant women may however not be able to regulate temperature as efficiently due to the physiologic changes of gestation (Schifano et al., 2016). Heat may alter placental blood flow patterns, potentially reducing the integrity of the placenta and increasing the chance of abruption. Also, elevated temperatures have been shown to increase fetal heart rate and lead to uterine contractions (Vaha-Eskeli and Erkkola, 1991), both of which are associated with placental abruption (Tikkanen, 2011). Heat could further affect risk factors for abruption, such as preeclampsia and prolonged preterm premature rupture of membranes (Beltran et al., 2014, Yackerson et al., 2007). Related outcomes such as preterm birth, low birth weight, and stillbirth have been shown to be more frequent during high temperatures, thought to be due to the added strain that heat exerts on pregnant women (Auger et al., 2016a, Arroyo et al., 2016, Bruckner et al., 2014, Dadvand et al., 2011, Ha et al., 2017a, Ha et al., 2017b, Schifano et al., 2016). The possibility of an association with placental abruption however has not been studied, despite similarities in biologic pathways of abruption, preterm birth, and stillbirth. To fill this knowledge gap, we sought to determine the relationship between elevated outdoor temperature and the odds of placental abruption in a large population of pregnant women exposed to heat during warm months.
Section snippets
Study population
We included hospital records for all women whose pregnancies were complicated by placental abruption in Quebec, Canada from 1989 to 2012, and counted multiple pregnancies only once. We obtained the data from the Maintenance and Use of Data for the Study of Hospital Clientele registry, which contains hospital discharge information for all pregnant women who delivered in a hospital in the province (Ministry of Health and Social Services, 2017). In Quebec 99% of deliveries occur in hospital, thus
Results
There were 17,172 cases of placental abruption, including 5294 preterm and 11,878 term abruptions (Table 1). 19.2% of all abruptions occurred when the maximum weekly temperature was 30 °C or higher, while 13.7% of all weeks between May and October had temperatures that high. Slightly more term abruptions occurred at temperatures 30 °C or higher compared with preterm abruptions (19.4% vs. 18.8%). Most placental abruptions occurred among women between 25 and 34 years (63.6%), and women who had no
Discussion
In this case-crossover study of > 17,000 cases of placental abruption, heat was associated with a greater odds of placental abruption, particularly for women who were at term. Associations were stronger for pregnant women younger than 35 years of age, and women who were nulliparous or socioeconomically disadvantaged. There was no association between heat and placental abruption before term. These findings suggest that heat may trigger placental abruption in women who are at the end of gestation
Conclusions
In conclusion, this case-crossover study found that elevated temperature was associated with an increased odds of placental abruption, particularly abruption at term. Relationships were stronger for women younger than 35 years, and women who were nulliparous or socioeconomically disadvantaged. Placental abruption is an obstetric emergency with potentially serious consequences. Triggers are unclear especially for women without risk factors. The possibility that heat may increase a woman's
Funding
This work was supported by the Canadian Institutes of Health Research (MOP-130452). NA was supported by the Fonds de recherche du Québec-Santé (34695). The funders were not involved in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.
Conflicts of interest
The authors report no conflict of interest.
References (37)
- et al.
Impact of air pollution and temperature on adverse birth outcomes: Madrid, 2001–2009
Environ. Pollut.
(2016) - et al.
Cold ambient temperature in utero and birth outcomes in Uppsala, Sweden, 1915–1929
Ann. Epidemiol.
(2014) - et al.
Oxidative stress
Best Pract. Res. Clin. Obstet. Gynaecol.
(2011) - et al.
Humidity: a review and primer on atmospheric moisture and human health
Environ. Res.
(2016) - et al.
Gaining more flexibility in cox proportional hazards regression models with cubic spline functions
Comput. Methods Prog. Biomed.
(1997) - et al.
Heat and air pollution exposure as triggers of delivery: a survival analysis of population-based pregnancy cohorts in Rome and Barcelona
Environ. Int.
(2016) - et al.
The effect of short-term heat stress on uterine contractility, fetal heart rate and fetal movements at late pregnancy
Eur. J. Obstet. Gynecol. Reprod. Biol.
(1991) Thermal environment and human birth weight
J. Theor. Biol.
(2002)- et al.
An international contrast of rates of placental abruption: an age-period-cohort analysis
PLoS One
(2014) - et al.
Methods to calculate the heat index as an exposure metric in environmental health research
Environ. Health Perspect.
(2013)
Extreme heat and risk of early delivery among preterm and term pregnancies
Epidemiology
Elevated outdoor temperatures and risk of stillbirth
Int. J. Epidemiol.
Secular trends in preeclampsia incidence and outcomes in a large Canada database: a longitudinal study over 24 years
Can. J. Cardiol.
High ambient temperature and the risk of preterm delivery
Am. J. Epidemiol.
Associations of meteorology with adverse pregnancy outcomes: a systematic review of preeclampsia, preterm birth and birth weight
Chronic Dis. Can.
The occurrence of abruptio placentae in Canada: 1990 to 1997
Chronic Dis. Can.
Commentary: does air pollution confound studies of temperature?
Epidemiology
Williams Obstetrics
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