Fetal Thyroid Function, Birth Weight, andin UteroExposure to Fine Particle Air Pollution: A Birth Cohort Study.
Thyroid hormones are critical for fetal development and growth. Whether prenatal exposure to fine particle air pollution (≤ 2.5 μm; PM2.5) affects fetal thyroid function and what the impact is on birth weight in normal healthy pregnancies have not been studied yet.



We studied the impact of third-trimester PM2.5exposure on fetal and maternal thyroid hormones and their mediating role on birth weight.



We measured the levels of free thyroid hormones (FT3, FT4) and thyroid-stimulating hormone (TSH) in cord blood (n= 499) and maternal blood (n= 431) collected after delivery from mother-child pairs enrolled between February 2010 and June 2014 in the ENVIRONAGE birth cohort with catchment area in the province of Limburg, Belgium.



An interquartile range (IQR) increment (8.2 μg/m3) in third-trimester PM2.5exposure was inversely associated with cord blood TSH levels (-11.6%; 95% CI: -21.8, -0.1) and the FT4/FT3ratio (-62.7%; 95% CI: -91.6, -33.8). A 10th-90th percentile decrease in cord blood FT4levels was associated with a 56 g decrease in mean birth weight (95% CI: -90, -23). Assuming causality, we estimated that cord blood FT4mediated 21% (-19 g; 95% CI: -37, -1) of the estimated effect of an IQR increment in third-trimester PM2.5exposure on birth weight. Third-trimester PM2.5exposure was inversely but not significantly associated with maternal blood FT4levels collected 1 day after delivery (-4.0%, 95% CI: -8.0, 0.2 for an IQR increment in third-trimester PM2.5).



In our study population of normal healthy pregnancies, third-trimester exposure to PM2.5air pollution was associated with differences in fetal thyroid hormone levels that may contribute to reduced birth weight. Additional research is needed to confirm our findings in other populations and to evaluate potential consequences later in life.
Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.
Bram G
BG
Janssen
Nelly D
ND
Saenen
Harry A
HA
Roels
Narjes
N
Madhloum
Wilfried
W
Gyselaers
Wouter
W
Lefebvre
Joris
J
Penders
Charlotte
C
Vanpoucke
Karen
K
Vrijens
Tim S
TS
Nawrot
D000328:Adult; D000393:Air Pollutants / Q000633:toxicity*; D000397:Air Pollution / Q000706:statistics & numerical data*; D001530:Belgium / Q000453:epidemiology; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005312:Fetal Blood; D047109:Fetal Development / Q000187:drug effects*; D006801:Humans; D008297:Male; D018811:Maternal Exposure / Q000706:statistics & numerical data*; D052638:Particulate Matter / Q000633:toxicity*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D013961:Thyroid Gland / Q000502:physiology; D013963:Thyroid Hormones; D013972:Thyrotropin / Q000097:blood
D000393:Air Pollutants; D052638:Particulate Matter; D013963:Thyroid Hormones; D013972:Thyrotropin