Background: Pregnancy is the fertilization and development of one or more offspring. It is a period of significant importance, during the time of which, health status of the mother could have profound impact on that of the fetus. Due to the one child policy in Mainland China, ensuring the baby’s health is of the utmost priority. In the past two years the incidence rate of miscarriage has been gradually increasing. It has an impact on mothers both physically and psychologically. Formaldehyde can be released for a long time from compound and furniture products in newly decorated houses and have become a chronic source of pollution. We are interested in whether there is any association between miscarriage and formaldehyde exposure. If the association exists, the evidence could be applied to support further research to identify the sources of formaldehyde and to support formulation of environmental public health policy to reduce formaldehyde exposure. Objectives: (1) To estimate whether the serum formaldehyde concentrations were different between miscarriage women and normal pregnant women at the same stage. (2) To investigate the normal serum formaldehyde concentration in pregnant women; and (3) to identify exposure factors in miscarriage patients. Setting：Guangzhou Women and Children’s Medical Centre Method: A case-control study was carried out to estimate the association between serum formaldehyde concentrations and miscarriage. 309 pregnant women who fulfilled the inclusion criteria participated in this study, 191 normal pregnant women at term delivery as the control group and 118 women who were diagnosed with miscarriage as the case group. The main outcome was miscarriage confirmed by ultrasound and physicians. The main exposure variable was serum formaldehyde concentration. Binary logistic regression was used to estimate the crude and adjusted odds ratios for a diagnosis of miscarriage for each independent variable. The odds ratio (OR) would be used to estimate the relative risk of the serum formaldehyde concentration in miscarriage women compared with those women who were not diagnosed miscarriage. We also categorized the values of formaldehyde into quartile, and put them into logistic regression as continuous variable to test the linear dose-response relationship. Then we tested whether there would be a significant linear trend that the increasing of serum formaldehyde concentration level leads to the increased risk of miscarriage. Chi-squared tests were performed to test the association between diagnosis of miscarriage and various independent variables. And Chi-squared tests for linear trend were also used for ordinal independent to study any dose-response relationship. Results：The mean serum formaldehyde concentration was 0.0944 in the case group and 0.0239 in the control group. The difference was statistically significant. All characteristics between case group and control group were quite similar. After adjusting for age, occupation，education level, household income, home decoration situation, the following factors remained having independent impact on the miscarriage. They were formaldehyde and second-hand smoke (crude ORs=7.87 [95%CI: 4.96, 12.49]; 3.20[95%CI: 1.86, 5.52] respectively, adjusted ORs=8.06 [95%CI: 4.96, 13.09]; 3.60[95%CI: 1.58, 8.20] respectively). Exposure to formaldehyde and second-hand smoke were significantly associated with higher risk of miscarriage. The liner dose response association between formaldehyde level and miscarriage was presented with P value for trend less than 0.001. Conclusions：Our study provided some evidence of the association between the serum formaldehyde level and miscarriage. A significant linear trend was found that the increasing of serum formaldehyde concentration level lead to the increase the risk of miscarriage. And we also found that second-hand smoking was contributive to miscarriage. This association did not confound by age, occupation, education level, household income, or home decoration situation. / published_or_final_version / Public Health / Master / Master of Public Health