Herpes simplex virus has an effect on the fetus, which may result in fetal developmental abnormalities, fetal arrest, and preterm delivery. 1. Fetal developmental malformation: In the first trimester of pregnancy, which is the period of major differentiation of the fetus, if the fetus is infected by herpes simplex virus at this time, and then medication is applied for symptomatic treatment, the effect of virus and medication is likely to lead to developmental malformation. If the virus violates the embryo, developmental malformations such as recessive spina bifida, congenital heart disease, cleft lip and palate, anencephaly and other developmental malformations may occur. 2 Fetal Arrest: Infection with herpes simplex virus in early pregnancy may lead to fetal arrest. This is because when the virus invades the embryo, it affects the differentiation and development of the embryo, and even the toxins released by the virus reproduction may cause the death of the embryo, resulting in fetal demise. Therefore, it can also cause fetal arrest. 3. Preterm labor: When herpes simplex virus infections occur in the second trimester of pregnancy, preterm labor is also likely to occur. This is because the herpes virus attacks the uterus and affects the development of the fetus, and the detection rate of herpes simplex virus in preterm babies is significantly higher than that of full-term babies. It is recommended to seek immediate medical attention when infected with the herpes simplex virus during pregnancy to avoid delaying the condition and thus affecting the pregnancy.