Viral Infections in Pregnancy

When you are pregnant, you need to careful about infections and infectious diseases. Unborn and newborn babies have weak immune systems compared with older children and adults, and therefore are very susceptible to infection.


Chickenpox is caused by infection with the varicella-zoster virus. If a woman contracts the chickenpox in early pregnancy, the virus may cross the placental barrier and cause birth defects in the developing baby. These birth defects may include leg deformities, abnormalities of the retina in the eye, cell loss in the cerebral cortex of the brain, and a problem with the kidneys called hydronephrosis. Exposure of the baby to the chickenpox virus just before or during delivery is a serious threat to the newborn baby, and can cause central nervous system disease.

Women who have had chickenpox in the past are immune and will not develop the disease again during pregnancy. For people who have never had chickenpox, there is a vaccine available. However, this vaccine is not recommended for women who are pregnant. If you are not yet pregnant, you may want to consider getting the vaccine before you become pregnant. The vaccine may be given up to one month before the beginning of pregnancy.


Cytomegalovirus (CMV) is a very common infectious disease. CMV is transmitted through sexual intercourse and contact with saliva and urine. CMV can also be passed from mother to baby during pregnancy.

About 1% to 4% of pregnant women become infected with CMV. In a little less than half of these women, the infection may pass from the mother to her unborn baby. Of the babies who become infected during pregnancy, 10% show symptoms of congenital abnormalities at birth, and up to 15% develop problems later. The brain, eyes, liver, spleen, blood, and skin are at risk, especially if the mother contracts CMV before the 20 th week of pregnancy. Long-term effects include the following:

  • hearing loss
  • intellectual disability
  • developmental delay
  • visual impairment

Currently, there is no accepted vaccine or therapy for CMV. If you have contracted the disease, there are several ways to determine if CMV has infected your unborn baby. Amniocentesis can determine the presence of infection but not how severe the infection is. If visible signs of developmental delay are present, they may show up on ultrasound. Blood tests on the unborn baby can be used to assess his actual condition.

CMV exposure is especially risky for child care and health care workers. To prevent CMV, wash your hands frequently. People who are at risk should also use gloves to prevent being infected by the disease.

Enterovirus infections

Enteroviruses are a subgroup of viruses that include hepatitis, coxsackievirus, and poliovirus. These can cause widespread infections of the central nervous system, skin, heart, and lungs.

Hepatitis A

Hepatitis A is a very common, usually mild virus that is transmitted through contact with contaminated stool. The symptoms of hepatitis A include jaundice, fatigue, abdominal pain, loss of appetite, nausea, diarrhea, and fever. However, many people with hepatitis A do not experience symptoms. There is no long-term infection and it is not known to pass from the mother to her unborn baby. To prevent hepatitis A, always wash hands after using the bathroom, after changing a diaper, and before eating, and consider getting the hepatitis A vaccine.

Hepatitis B

Hepatitis B is a serious disease that attacks the liver. Signs and symptoms include jaundice, fatigue, abdominal pain, loss of appetite, nausea, vomiting, and joint pain. Long-term complications of hepatitis B can include lifelong infection, scarring of the liver, liver cancer, liver failure, and death.

Hepatitis B is transmitted through sexual contact, sharing needles, and from mother to baby during childbirth. Ninety per cent of infants who are infected at birth will develop chronic hepatitis B infection. Of the people who develop chronic infection, 15% to 20% will die from liver disease.

General ways to reduce the risk of contracting hepatitis B include:

  • taking the hepatitis B vaccine
  • using latex condoms when having sex
  • not sharing needles
  • not sharing personal care items such as toothbrushes and razors
  • avoiding tattoos and body piercings, or making sure that the artist or piercer is following good health practices

All pregnant women should be screened for hepatitis B and consider getting the hepatitis B vaccine. The vaccine can be given during pregnancy. Infants who are born to women with hepatitis B should be given both hepatitis B immunoglobulin and the hepatitis B vaccine within 12 hours after birth. This can help reduce the rate of transmission of the disease to the baby. There are a number of drugs that can be used to treat hepatitis B, but none of them are approved for use during pregnancy.


A coxsackie infection during pregnancy is serious because it can be fatal to the unborn baby while only causing minor symptoms in the mother. The presence of this virus may lead to hepatitis, an inflammation of the heart muscle called myocarditis, and an inflammation of the brain and spinal cord called encephalomyelitis, which can cause death of the unborn baby. Coxsackie infection itself can damage the unborn baby and lead to birth defects.


Most poliovirus infections are mild. However, pregnant women have been shown to be more susceptible to polio, with a higher chance of dying from the disease. Poliovirus affects the central nervous system, and can range from mild symptoms like headaches to severe symptoms like paralysis. Polio is rare in the developed world. However, pregnant women travelling to parts of the world with high polio rates are encouraged to get an inactive polio vaccination.

Herpes simplex virus

Herpes simplex virus, or herpes for short, is a sexually transmitted disease that can be passed from mother to baby during childbirth.

Symptoms of herpes include sores on the genitals, itching, painful urination, vaginal discharge, and sore lumps on the groin. Other symptoms may include fever and general aches. The outbreaks come and go over time. Some women have herpes only on their cervix, in which case there are few or no symptoms. While the mother may have relatively mild symptoms, a herpes infection can be very serious in newborn babies because of their immature immune system. Women with a history of herpes may be offered preventative drug therapy in the month before their due date to reduce the chance of transmission to the baby.

When a woman has active herpes lesions around the time of delivery, a caesarean delivery will greatly reduce the chances of the infection passing from mother to baby. Also, if a woman’s fetal membranes rupture and she does not go into labour with six hours, a caesarean section will be done. This is because the amniotic sac provides protection for the unborn baby, and if that protection is gone because the sac has ruptured, there is a higher risk of infection.

Newborn babies born to mothers with herpes are usually isolated from other newborn babies to prevent the possible spread of infection. If an infection does occur, the newborn can be given an antiviral drug to treat the herpes simplex virus infection.

HIV: human immunodeficiency virus

HIV is the virus that causes acquired immune deficiency syndrome (AIDS). AIDS is a serious disease in which the immune system breaks down and does not respond normally to infection. People with AIDS develop recurrent, severe infections such as pneumonia. HIV is transmitted through sexual contact, blood transfusions, sharing needles, and from a mother to her unborn baby. A baby can get HIV from his mother during pregnancy, during childbirth, and through breastfeeding.

It is now possible to offer women with HIV a high likelihood of giving birth to a healthy baby. First and foremost, though, it is crucial that the disease be identified and diagnosed. All pregnant women are encouraged to undergo screening for HIV, whether or not they are at high risk for the disease. It is important to determine your HIV status as soon as possible after you find out you are pregnant.

The first step in care is careful monitoring of the woman’s immune status using “viral load” blood tests to determine the amount of virus in the blood. A strategy for pharmaceutical therapy is then determined for the patient. This involves a number of different drugs, which serve different purposes, and is referred to as highly active antiretroviral therapy (HAART). It is very important to remain compliant with drug therapy. Forgetting to take the drugs as prescribed could cause the HIV virus to become drug-resistant. When putting together the strategy for drug therapy, the doctor will take into consideration the risks that each drug poses to the unborn baby. Some drugs are more dangerous than others.

After therapy has begun, the viral load is tested once per month until the virus is no longer detectable in the blood. This should take about six months. If, after that amount of time, the virus remains in the blood, a new therapy will need to be determined. Once there is no virus remaining in the blood, the viral load tests are done once every two to three months.

Mother-to-baby transmission rates of the disease are linked to the viral loads. The higher the viral load, the higher the rate of transmission. The goal in pregnancy is to maintain a viral load under 1000. If the mother has a viral load of over 1000, there is a higher chance of transmission in a vaginal delivery, and a caesarean section may be required. Some drugs may need to be given to the baby during labour and after childbirth.

Mothers with HIV have a 14% rate of transmission with breastfeeding. The World Health Organization has the following recommendations with regard to breastfeeding with HIV:

  • When replacement feeding is acceptable, feasible, affordable, sustainable, and safe, avoidance of all breastfeeding by HIV-infected mothers is recommended.
  • Otherwise, exclusive breastfeeding is recommended during the first months of life.
  • To minimize HIV transmission risk, breastfeeding should be discontinued as soon as feasible, taking into account local circumstances, the individual woman’s situation, and the risks of replacement feeding, including infections other than HIV and malnutrition.
  • When HIV-infected mothers choose not to breastfeed from birth or stop breastfeeding later, they should be provided with specific guidance and support for at least the first two years of the child’s life to ensure adequate replacement feeding. Programs should strive to improve conditions that will make replacement feeding safer for HIV-infected mothers and families.


Influenza, or “the flu,” is caused by viruses from the Orthomyxoviridae family. The flu is not usually serious. However, sometimes it can lead to pneumonia, which may be a serious threat to the mother. There is no firm evidence showing that the flu causes birth defects.

If you are pregnant and you have a chronic underlying medical condition, it is recommended that you receive a vaccine for influenza, called a flu shot. The flu shot is considered safe for use during any stage of pregnancy.


Most adults are immune to measles, meaning that they have either had measles in the past or they have been vaccinated against the disease. However, if you are not immune to measles, there is a small chance that you might develop the disease during pregnancy. There is an increased risk of having a low birth weight baby if you have measles while you are pregnant. If you develop measles shortly before birth, there is a high risk that your newborn baby will also get the disease, especially if the baby is premature.

Vaccination against measles is not done during pregnancy. Like chickenpox, it is best if you make sure to get vaccinated against the disease before you become pregnant.

Fifth disease

The human B19 parvovirus causes fifth disease. One typical symptom of this disease is a bright red rash on the face. Other symptoms include mild fever, sore throat, flu-like symptoms, and joint pains. This virus can cross the placental barrier and, rarely, can cause miscarriage or stillbirth. Infection with fifth disease in the unborn baby can lead to an inflammation of the heart called myocarditis. It can also stop the bone marrow from making red blood cells, leading to anemia, in which case the baby will need blood transfusions. Fifth disease can also lead to a condition called hydrops, where the tissues within the baby are filled with fluid, which can lead to death of the baby.

You can have a blood test done to determine whether you have had fifth disease in the past, in which case you would be immune to it now. At this time, there are no vaccines or medications to prevent or treat fifth disease. If you acquire fifth disease while you are pregnant, you can have an ultrasound done to check for hydrops. A series of ultrasounds may be done over a few months to monitor the situation and determine whether the unborn baby needs a transfusion.


Immunization in the developed world has led to near disappearance of rubella, also known as German measles. However, rubella does still exist to a small extent. Rubella is a risk factor for miscarriage and stillbirth, and it is considered a major teratogen in pregnancy. About 80% of women with rubella and its associated rash during the first 12 weeks of pregnancy have a baby with a congenital infection. At 14 weeks, this incidence is reduced to 52%, and by the end of the second trimester, the incidence drops to 25%. Rubella is a very difficult disease to diagnose because its symptoms are similar to other illnesses. Diagnosis via blood testing can sometimes be complicated.

The following birth defects or congenital abnormalities can occur in the unborn baby when the mother is infected with rubella:

  • eye lesions such as cataracts and glaucoma
  • heart disease
  • deafness
  • central nervous system defects
  • fetal growth restriction
  • thrombocytopenia, which is an unusually low number of platelets
  • anemia, which is an unusually low amount of red blood cells
  • hepatitis
  • jaundice
  • a chronic inflammation of the lung called pneumonitis
  • bone changes
  • chromosomal abnormalities

Newborn babies who have acquired rubella during pregnancy are contagious for months after birth. Thus, they may pass the infection on to other infants and susceptible adults that they come in contact with.

Rubella vaccine should be given to all females of childbearing age unless they already have proof of immunity. The rubella vaccine should be avoided shortly before or after pregnancy because the vaccine is a live virus. Since up to one-third of congenital infection with rubella occurs in second and later pregnancies, all women found to be susceptible to rubella during pregnancy should be given the vaccine as soon as possible after childbirth.

Nicolette Caccia, MEd, MD, FRCSC

Rory Windrim, MB, MSc, FRCSC