Association of ambient PM(2·5) exposure with maternal bone strength in pregnant women from Mexico City: a longitudinal cohort study

BACKGROUND: Pregnancy is associated with deteriorations in maternal bone strength and heightened susceptibility to bone fractures. We aimed to investigate whether ambient particulate matter (PM)(2·5) concentrations were associated with bone strength during pregnancy. METHODS: In this longitudinal cohort study, we analysed longitudinal data from women participating in the Programming Research in Obesity, Growth, Environment and Social Stressors (PROGRESS) cohort in Mexico City, Mexico. Eligible women were aged 18 years or older, at less than 20 weeks’ gestation at the time of recruitment, planning to stay in Mexico City for the next 3 years, without heart or kidney disease, did not use steroids or anti-epileptic drugs, were not daily consumers of alcohol, and had access to a telephone. Daily ambient PM(2·5) concentrations were estimated from a spatio-temporal model that was based on the individual’s address. Trabecular bone strength was measured using quantitative ultrasound from the radius of the middle finger and cortical bone strength from the proximal phalanx of the middle finger, during the second trimester, third trimester, and 1 and 6 months post partum. Bone strength T scores were modelled with PM(2·5) concentrations using linear mixed models and distributed lag models. FINDINGS: Adjusting for multiple exposure windows, each 10 ug/m³ increase in PM(2·5) exposure concentrations in the first trimester was associated with a 0·18 SD decrease (95% CI −0·35 to −0·01; p=0·033) in ultrasound speed-of-sound (SOS) T score of trabecular bone strength from the second trimester until 6 months post partum. Similarly, each 10 μg/m³ increase in third trimester PM(2·5) exposure was associated with a 0·18 SD decrease (−0·36 to −0·01; p=0·044) in the SOS T score of trabecular bone strength from the third trimester until 6 months post partum. PM(2·5) exposure in the first month post partum was associated with a 0·20 SD decline (−0·39 to −0·01; p=0·043) in cortical bone strength until 6 months post partum. INTERPRETATION: Ambient PM(2·5) exposure during and after pregnancy was associated with diminished trabecular and cortical bone strength. Early pregnancy PM(2·5) exposure was associated with a greater decline in bone strength later during pregnancy. Late pregnancy and early post-partum exposures adversely affected the post-partum bone strength recovery. Technological and policy solutions to reduce PM(2·5) pollution could improve public health by reducing bone fracture risk.