Antenatal Exposure to UV-B Radiation and Preeclampsia: A Retrospective Cohort Study

Effects of ambient temperature and relative humidity on preterm birth during early pregnancy and before parturition in China from 2010 to 2018: a population-based large-sample cohort study

Background

The progression of global warming and increase in instances of extreme weather have received considerable attention. We conducted a cohort study on women of childbearing age in Yunnan Province, examined the association between ambient temperature and humidity on preterm birth and evaluated the effects of extreme weather during early pregnancy and before parturition on preterm birth.

Methods

We conducted a population-based cohort study on women of childbearing age 18-49 years who participated in National Free Preconception Health Examination Project (NFPHEP) in Yunnan Province from January 1, 2010, to December 31, 2018. Meteorological data, namely daily average temperature (°C) and daily average relative humidity (%), were obtained from China National Meteorological Information Center. Four exposure windows were explored: 1 week of pregnancy, 4 weeks of pregnancy, 4 weeks before delivery, and 1 week before delivery. We used a Cox proportional hazards model and adjusted the potential risk factors for preterm birth to obtain the effects of exposure to temperature and humidity on preterm birth among the stages of pregnancy.

Results

At 1 week of pregnancy and at 4 weeks of pregnancy, the association between temperature and preterm birth was U-shaped. The correlation between relative humidity and the risk of preterm birth was n-type at 1 week of pregnancy. The correlation between preterm birth and temperature and relative humidity at 4 weeks before delivery and at 1 week before delivery is J-shaped. Low temperature and low humidity were protective factors against preterm birth, whereas high temperature and high humidity were risk factors for preterm birth.The effects of high temperature and extremely high temperature were the strongest at 4 weeks before delivery, with HRs of 1.417 (95% CI: 1.362-1.474) and 1.627 (95% CI: 1.537-1.722), respectively. The effects of extremely low humidity and low humidity were strongest at 1 week before delivery, with HRs of 0.681 (95% CI: 0.609-0.761) and 0.696 (95% CI: 0.627-0.771), respectively.

Conclusion

Temperature and relative humidity affect preterm birth differently for each pregnancy stage. The effects of meteorological factors on pregnancy outcomes such as premature birth should not be ignored.

Antenatal Exposure to UV-B Radiation and Preeclampsia: A Retrospective Cohort Study

Background

Risk of preeclampsia varies by month of delivery. We tested whether this seasonal patterning may be mediated through maternal vitamin D concentration using antenatal exposure to UV‐B radiation as an instrumental variable.

Methods and Results

Scottish maternity records were linked to antenatal UV‐B exposure derived from satellites between 2000 and 2010. Logistic regression analyses were used to explore the association between UV‐B and preeclampsia, adjusting for the potential confounding effects of month of conception, child's sex, gestation, parity, and mean monthly temperature. Of the 522 896 eligible singleton deliveries, 8689 (1.66%) mothers developed preeclampsia. Total antenatal UV‐B exposure ranged from 43.18 to 101.11 kJ/m² and was associated with reduced risk of preeclampsia with evidence of a dose‐response relationship (highest quintile of exposure: adjusted odds ratio, 0.57; 95% CI, 0.44–0.72; P<0.001). Associations were demonstrated for UV‐B exposure in all 3 trimesters.

Conclusions

The seasonal patterning of preeclampsia may be mediated through low maternal vitamin D concentration in winter resulting from low UV‐B radiation. Interventional studies are required to determine whether vitamin D supplements or UV‐B–emitting light boxes can reduce the seasonal patterning of preeclampsia.