1.Introduction Common viral infections during pregnancy are caused by: herpes simplex virus (HSV), cytomegalovirus (CMV), rubella virus, influenza virus, hepatitis B virus, human papillomavirus (HPV) and human immunodeficiency virus (HIV). Many of these viruses affect the growth and development of the embryo and fetus and can lead to miscarriage, fetal malformation, intrauterine growth retardation and stillbirth; some can cause vertical transmission from mother to child through the placenta. The application of antiviral drugs during pregnancy can alleviate the clinical symptoms of patients and speed up their recovery, as well as interrupt the vertical transmission between mother and child and protect the fetus. However, many antiviral drugs exert their effects by inhibiting DNA or ribonucleic acid (RNA) replication and protein synthesis in host cells, and have toxic and teratogenic effects on the embryo, so care should be taken when using them during pregnancy. This article introduces antiviral drugs commonly used in pregnancy according to the five levels of risk to pregnancy issued by the U.S. Food and Drug Administration, for clinical reference when selecting them. 2. Antiviral drugs commonly used in pregnancy At present, antiviral drugs commonly used in clinical practice can be divided into six categories according to their mechanism of action: ① inhibit DNA-type viruses: such as acyclovir, famciclovir, ganciclovir, adenosine, etc.; ② inhibit RNA-type viruses: such as ribavirin, zidovudine, etc.; ③ prevent viruses from penetrating into host cells and shedding their shells to prevent host cell infection: such as amantadine, etc.; ④ stimulate host ④ stimulate host cells to synthesize antiviral proteins, regulate host organism immune function, and inhibit virus multiplication: e.g. interferon; ⑤ inhibit the activity of neuraminidase on the surface of viral particles to prevent virus release: e.g. isoquinolines; ⑥ reverse transcriptase inhibitors, which can inhibit reverse transcriptase activity and have an inhibitory effect on the replication of human immunodeficiency virus and viral hepatitis B, e.g. lamivudine. The following is a brief introduction of some clinically used antiviral drugs. 2.1 Ribavirin Ribavirin, with FDA classification X, is a broad-spectrum antiviral drug that inhibits viral RNA synthesis and is commonly used in the treatment of influenza (flu) and epidemic B encephalitis (B encephalitis). Animal experiments found that this drug has obvious teratogenic and embryotoxic effects, and its half-life in humans is long, and the drug can still be detected in blood after 4 weeks of use. It is strictly prohibited for use during pregnancy and lactation. 2.2 Acyclovir Acyclovir, classified as Class C by the FDA, is a synthetic broad-spectrum antiviral drug that inhibits the replication of viral DNA and is commonly used to treat herpes virus and cytomegalovirus infections, such as herpes simplex, genital herpes, and herpes zoster. Animal experiments have found that the drug can affect thymus development in rats, resulting in defective immune system function. The drug has been reported to cause chromosome breakage in human cells, but clinical data show that the drug is relatively safe for use during pregnancy. A study in the United States showed that of 478 newborns whose mothers had used the drug in the first trimester, 18 (3.8%) had severe malformations. In recent years, many foreign sources have shown that the use of acyclovir during pregnancy in patients with combined genital herpes prevents vertical transmission and has no effect on the newborn. The drug can be applied topically or systemically (intravenously or orally) during pregnancy, and is a cautionary drug during pregnancy. 2.3 Vaxilovir No FDA classification is available. Vaxilovir is a precursor of acyclovir, with an oral bioavailability 3.3-5.3 times higher than that of acyclovir, and is mainly used for herpes simplex virus infection. Animal studies have not found teratogenic effects of the drug, but its safety in the fetus has not been adequately studied. One source reported that the incidence of neonatal malformations in 380 women who applied this drug in the first trimester of pregnancy was similar to the incidence of neonatal malformations in the population. 2.4 Ganciclovir Ganciclovir, classified as Class C by the FDA, is a derivative of acyclovir and has a stronger antiviral effect. However, animal studies have found teratogenic and embryotoxic effects in rodents. Its effect on the fetus is still unclear, and should not be used by pregnant women without special. 2.5 Amantadine Amantadine is classified as Class C by FDA. This drug can inhibit RNA virus nucleic acid decapitation, and prevent the virus from penetrating into the cell, which can specifically inhibit influenza A virus, but is not effective for influenza B. It is only used for the prevention and treatment of influenza A virus infection. Animal experiments have found embryotoxic and teratogenic effects after the application of large amounts of amantadine, and studies on the safety of application during pregnancy are not yet available. In another study, four pregnant women who used the drug in early pregnancy had one congenital heart disease in their four newborns. However, the number of cases is too small to make a definitive assessment. This drug should not be used during pregnancy unless the benefits of its use outweigh its risks. 2.6 Adenosine Adenosine has an FDA classification of Class C. It is an anti-DNA viral agent with in vitro activity against herpes simplex virus types I and II, varicella . Herpes zoster virus and cytomegalovirus have antiviral activity in vitro. In animal studies, the drug has been shown to have teratogenic effects. There are few safety studies for use in pregnant women. Acyclovir has been used sparingly in recent years because it is more effective than adenosine in treating herpes viruses and has a higher safety profile. It should not be used in the absence of special pregnant women. 2.7 Interferon Interferon, classified as Class C by the FDA, is a class of glycoproteins with multiple biological activities that have broad-spectrum antiviral effects and modulate immune function. Clinically, interferon is mainly used to treat viral infectious diseases such as viral hepatitis B, herpes simplex and condyloma acuminata. Foreign animal experiments have found that the application of high doses of interferon can cause embryolysis during early pregnancy and increase the rate of miscarriage. The study of the safety of the drug on the fetus in pregnant women is not sufficient. We believe that interferon should not be used in early pregnancy as much as possible, and it can be used at the discretion of middle and late pregnancy according to the condition, and it is generally used only for the adjuvant treatment of herpes simplex and cytomegalovirus infection during pregnancy. In addition, vaginal suppositories of interferon ( Olpin) are contraindicated in pregnancy. 2.8 Zidovudine Zidovudine is FDA classified as Class C. Its metabolites competitively inhibit reverse transcriptase and viral core protein synthesis and are used clinically primarily for the treatment of HIV infection. No teratogenic effects have been found in pregnant rabbits and rats, but dose-related fetotoxic effects have been found in mice. In humans, the drug has not been found to be teratogenic and may inhibit hematopoiesis when applied in large amounts. In clinical practice, zidovudine has a very important role in preventing the vertical transmission of HIV, in addition to being used for the treatment of HIV infection, and can significantly reduce the vertical transmission of HIV, which should be used with caution. 2.9 Lamivudine Lamivudine, classified as Class C by the FDA, competitively inhibits reverse transcriptase activity. It was originally used in combination with zidovudine for the treatment of HIV infection, but in recent years it has been used mainly for the treatment of hepatitis B virus infection. No teratogenic effects have been found in animal studies, but no adequate and controlled studies have been reported in humans, so the advantages and disadvantages should be weighed when using this drug. In conclusion, the current therapeutic effect of antiviral drugs is not very satisfactory and has certain toxic side effects on the human body, while some viral infections can be treated with immune agents, such as the prevention of vertical transmission of hepatitis B virus can be used to protect the fetus with viral hepatitis B immunoglobulin. Therefore, as far as obstetric clinics are concerned, not many pregnant women actually require the application of antiviral therapy, and there is little clinical experience with the application of antiviral drugs during pregnancy. Since most antivirals act on the ribonucleic acid and DNA of cells and are toxic to the host cells, the use of antivirals in pregnant women, especially when applied systemically, requires great caution.