The time for pregnant women to inhale formaldehyde to cause fetal malformation is related to the concentration of inhaled formaldehyde, if in an environment with high formaldehyde concentration, it can lead to fetal malformation in a few months, and when the concentration is low, there is a possibility of malformation in more than half a year. Formaldehyde is a teratogenic chemical substance, pregnant women living in a formaldehyde environment for a long time, will lead to fetal malformation, especially during early pregnancy, that is, the first trimester of pregnancy, is the critical period of fetal neurological development, at this time, the fetus is susceptible to the influence of the external environment. If in the environment of high formaldehyde concentration, about 1 month can lead to fetal malformation, long-term in the environment of low formaldehyde concentration, half a year and above can lead to fetal malformation. In addition, exposure to formaldehyde during preparation for pregnancy and during all periods of pregnancy can lead to fetal malformations. It is recommended that pregnant women do not live in newly renovated houses, long-term exposure to this environment will not only cause fetal malformations, but also lead to a variety of lesions in the pregnant women themselves.