The impacts of excessive heat on preterm labor HOT AS BLUE BLAZES: ASHLEY WARD, PHD CLIMATE INTEGRATION AND OUTREACH ASSOCIATE CISA DEPARTMENT OF GEOGRAPHY UNIVERSITY OF NORTH CAROLINA AT CAHPEL HILL
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T h e i m p a c t s o f
excessive h e a t o n
p r e t e r m l a b o r
HOT AS BLUE BLAZES:
ASHLEY WARD, PHD CLIMATE INTEGRATIO N AND OUTREACH ASSOCIATE
C ISA DEPARTMENT OF GEOGRAPHY
UNIVERSITY OF NORTH CAROLINA AT CAHPEL HILL
Kovach, M., Konrad, C., Fuhrmann, C. (2015). Area-level risk factors for heat-related illness in rural and urban locations across North
Carolina, USA. Applied Geography. 60, 175-183.
Heat -Re la t ed Il lness Ra t e s by Zip Code, NC 2007-2012
9 oftop 10are in the Southeas t
Al l of s outheas t wi th
exception of V irginia in
top 20 & exceed
national average for
preterm births
Percent of Pre te rm Births
2011-2015
Associations with Hist ory of pret erm bi r t h
Mul t ip le bir ths
Smoking, a lcohol, or drug use
Late or no prenatal care
Diabetes or hypertens ion
Infection
P r e t e r m
Bir th
i n N C
S ources : 1 ) “B orn too s oon and too s mall in North C arolina. ” M arch of D imes F oundation, M arch 2015 ; 2 ) B erkowitz ,
G S , P apiernick E . 1993 . E pidemiology of preterm bir th. E pidemiological R eview 15 ( 2 ) : 414 -443
Pre t e rm Birth Ra t e s by Zip Code, NC 2011-2015
Previous work on excessive heat impacts
to pregnant women
Focus es on single events
Examines impact of al l t emperat ure ext remes
Western United States or overseas
Findings:
1.Heat waves associated with pre-term birth but how much
depends upon strength and length of exposure
2. Impacts range from <1% – 2% increase in risk for each
increase in degree interval (most common association with
heat index)
3. Heat Index highly correlated
1. Descr ibe t he relat ionship bet ween excessive heat days and pret erm
delivery (< 37 weeks ) in NC, 2011 -2015
- Max temp
- Min temp
- Mean temp
- Heat index
- 1-5 day lags for each
- 3 day cumulative for each
- departure f rom normal
2. Determine thres holds at whic h health impac ts occur for each
meteorolog ic al variable
A im s
1. Populat ion: al l l ive, singleton births in NC during 2011–2015 heat
seasons (May- September)
2. Expos ure: P RISM data was provided for each available variable; other
variables calculated f rom thes e provided variables (heat index, mean
temperature, lags , and cumulative variables )
3. Outcome clas si f ication: b i r th cert i f icate data from NC Vi tal Records was
obtained
4. Other variables : maternal age, maternal race, maternal ethnici ty, pr incipal
source of payment, acces s to OB/ midwife, b i r th weight, region, urban acces s
(determined from C ensus)
Methods
S tatis tic al Analys is:
- Case-cros sover study with t ime- strat i f ied referent select ion
- Cox Proport ional Hazards
Descr iptive Statis tic s:
- Individual and county- level summaries of pre- term bir th
Binomial Generalized Additive Model:
- To establ is h thres holds at which impacts are experienced
M ethods
Sum m ary
Statistics: Preterm birth, NC
Results
Threshold: two degree temperature groups of analysis
Odds Ratio: increased percent in odds of preterm birth associated with temperature threshold (upper and lower confidence interval ranges at 95% confidence interval
Percentile: placement of respective threshold temperature among regional distribution of temperature
Statistically significant associations:• Max temp• Min temp*• Mean temp• 3 day cumulative for each
• No significant differences in race, slight differences by region
Where to go
from here?
Heat Early Warning S ystem
Unders tanding changes in r isk
Engaging with pregnant women to unders tand
contextual factors around r isk
Suggested thresholds for warningsY el low: temperatures at which any impact to preterm bir th is detected
Red: t emperat ures i n t he 90t h percent i l e wi t h not ab l y hi gher impact s t o pret erm bi r t h
Where to go
from here?
Heat Early Warning S ystem
Unders tanding changes in r isk
Engaging with pregnant women to unders tand
contextual factors around r isk
*Stat ions que r i ed : Asheville, NC; Hickory, N C
Note : Asheville, N C d i d n o t reg is te r a n y even t s a t t h r e s h o l d t e m p e r a t u r e s
*Stat ions que r i ed : Raleigh, NC; G r e e n s b o r o , N C
* Sta t ions quer ied : Fayettevil le, N C
L o w t h r e s h o ld f r e q u e n c y v e r y h i g h – th is g r a p h rep re sen t s t h e p o i n t o f 4% o r grea te r increase in o d d s
o f p r e t e r m labor
Where to go
from here?
Heat Early Warning S ystem
Unders tanding changes in r isk
Engaging with pregnant women to unders tand
contextual factors around r isk
Special thanks
Co-AuthorsCharles Konrad, Director, Southeast Regional Climate Center; Professor, Department of Geography, University of North Carolina at
Chapel Hill
Jordan Clark, PhD Candidate, Department of Geography, University of North Carolina at Chapel Hill
Rachel Woodul, PhD Candidate, Department of Geography, University of North Carolina at Chapel Hill
Jordan McCleod, Climatologist, Southeast Regional Climate Center
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