The housing renovation activities in China have rapidly developed over the past two decades. Various kinds of renovation materials have been produced to improve the status of living. Housing decoration materials usually contain oil paints, dyes, laminate board, solid wood, marble, wallpaper, resin glue and plywood. A large number of environmental pollutants have been detected within these renovation materials. For example, organic solvents, heavy metals, and volatile organic compounds (VOCs), such as benzene, toluene, xylene, styrene and aldehyde, may be emitted from paints or dyes. Formaldehyde, trichloroethylene and VOCs can be found in boards or plywood. While radioactive substances such as radon may be emitted from marbles [17, 24, 25]. Large volumes of the contaminants may be released into the atmosphere during or after the indoor renovations. One Chinese study tested newly renovated houses and showed that only 20.75% of them met formaldehyde concentration level health standards. In addition, the passing rate was only 16.67% for VOCs in those houses . Another study on the indoor detection showed that formaldehyde in as much as 80.96% of carpentry jobs and benzene in 35.71% of painting jobs were exceeded the standards for a renovation work environment . Low-quality decoration materials may release much more pollutants into air; for example, excessive lead has been found in some brands of paints . The indoor pollution phenomenon is widespread in China and some other countries [28, 29]. Interior renovation contaminants, polluting indoor environments, are a new great threat to human health. However, there is a lack of evidence on the association between indoor renovation during the periconceptional time and the risk of adverse pregnancy outcomes, including CHD in offspring.
We found that maternal exposure to renovations may have an increased risk of giving birth to fetuses with CHD, which, to our knowledge, is the first view on housing renovation exposure showing an association with CHD in fetuses. This finding may be attributed to organic pollutants and other volatile contaminants being released from decoration materials. Maternal occupational exposure to organic solvents, such as Stoddard or Chlorinated solvents potentially increased the incidence rate of selected types of CHDs [30, 31]. Some studies verified that trichloroethylene (TCE) can cause the developmental abnormalities in the hearts of avian embryos and mouse embryos [32, 33]. In addition, epidemiological studies showed that exposure to benzene, TCE, and formaldehyde may increase the prevalence of CHD in offspring [32, 34, 35]. The increased risks for CHD occurrence from exposure to renovation activity may be due to those harmful substances being released from the decoration materials. Moreover, maternal exposure to organic dyes, lacquers, pigments and paints during the first trimester of pregnancy was found to be related to a higher incidence of cardiac malformations in fetuses [18, 19]. Except for the occupational exposure, a DNBC study indicated that maternal non-occupational exposure to paint fumes may also be related to congenital abnormalities .
Because of the variety of confounding factors related to housing renovation, we first needed to determine the factors included in multivariate equations. We selected confounders based on the literature retrieval. Many studies have indicated that using folic acid before or during pregnancy may protect fetuses from some birth defects, including CHD [36, 37]. A higher maternal education level and residence in a city have been shown to be protective elements for CHD . Other factors such as maternal smoking or exposure to ETS [39, 40], and factory or landfill nearby [40, 41] are associated with the appearance of CHD in fetuses. In addition, the quality of air ventilation may also link to CHD. The structural characteristics, indoor temperature, absolute humidity and air-exchange rate of a building were shown to greatly affect the dynamic VOC emission rates  which may influence the concentration of air pollutants. The confounders with significant difference or contributing to the change of main effect were therefore recruited as covariate factors in the model.
Different phenotypes of CHDs showed different sensitivity to renovation exposure. Our result found that indoor renovations may increase the risk of the occurrence of conotruncal heart defects and anomalous venous return, which was confirmed by other studies. Just as the previous studies by Shaw and Tikkanen described earlier, mothers' occupational exposure to organic dyes (OR: 5.0) or pigments “end-use” (OR: 2.0) can increase the risk of conotruncal heart disease in offspring . Exposure to certain chemicals like dyes, lacquers, pigments and paints, during the first trimester of pregnancy was found to be related to a higher incidence of conal malformations such as TGA, tetralogy of Fallot and truncus arteriosus [18, 19]. Occupational exposure to Stoddard solvent may be associated with D-transposition of the great arteries (OR: 2.0) . While benzene usage around the time conception/organogenesis increased the risk for neural crest malformations including double-outlet ventricle, Tetralogy of Fallot, and VSD (OR: 5.3; 95%CI: 1.4 to 21.1) . Although we did not find an increased risk for septal defects and obstructions in our study, other research has shown maternal history of organic solvent exposure early in pregnancy may be associated with a slight increased risk for VSD (OR: 1.8) ; exposure was also associated with pure coarctation of the aorta (OR: 3.2) , aortic stenosis (OR: 2.1) and pulmonary valve stenosis (OR: 2.1) . The different results may be due to sample sizes, different definitions of exposure, and different diagnostic abilities.
Our study showed a clear influence of time on the critical exposure windows of renovation activity for CHD occurrence. We can see that a shorter the interval between renovation and moving-in was associated with a greater risk that the offspring will suffer from CHD. Mothers who moved into a month-old redecorated house during the first trimester or 3 months before conception seemed to have an increased risk of giving birth to a baby with CHD. Similar results have not yet been reported in previous studies. Perhaps this finding can be explained by the dynamics of organic contaminants emission and elimination . Heart is the first organ to form and function in the embryo. The first trimester is the critical window for heart development [47–49], so any risk factors that occur during this time may increase the risk of CHD. The concentration of VOCs released from the redecoration materials seemed to be the highest level in the newly renovated houses. The time at which VOCs from water-based paints, dry building materials and solvent-based paints are completely emitted is only approximately hundreds of seconds . Over time, VOCs will slowly evaporate and the concentration will be gradually reduced [50, 51]. In Howard’s test, the amount of formaldehyde emitted from conversion varnish coatings was 2.3-8.1 times higher than the amount of free formaldehyde applied . The emission rate drops quickly in the first eight days, and then declines much more slowly over a longer period . In addition, the elimination rates are strongly associated with air ventilation rates in houses .
In this article, we first reported the relationship between housing renovations and CHD occurrence. Maternal exposure to interior housing renovation activity may be associated with an increased risk of CHD in offspring. Moreover, different from the previous case–control study that investigated pregnant exposure during infancy or childhood period; our study started the epidemiologic investigation during pregnancy which may reduce errors in reporting exposure as much as possible. However, there were also some limitations to this study. First, like many epidemiological investigations, self-reported information from pregnant women would bring some bias. It is possible that case and control mothers may misclassify their exposure behaviors. In addition, a hospital-based study may introduce selection bias that influences the results. Therefore, further studies should be applied to test for the biomarkers on pollutions in biological samples of cases and controls in population. Second, due to a relatively small sample size, it was difficult to divide the CHD types and complexity factors into specific classifications. The number of cases was too small to have a high statistical power to assess the associations between renovations and CHD occurrence, especially for some selected phenotypes. A larger-scale prospective survey is needed in further investigations to enhance the efficacy of analysis. Finally, the relationship between renovation and indoor environmental pollution is complex. For example, new furniture is an important source of VOC, but this factor was not considered due to the low exposure rate. The types and qualities of renovation materials also have not been analyzed in this study. All of these problems should be considered in further studies.