Fetal Infections

A fetal infection is an infection that occurs in a developing fetus during pregnancy. Fetal infections can be caused by viruses, bacteria, fungi, parasites, or other germs and can lead to various complications, including congenital anomalies, poor fetal growth, and preterm birth.

One group of fetal infections that can cause congenital conditions (meaning present at birth) is known as TORCH:

• Toxoplasmosis
• Other (such as syphilis, varicella, mumps, parvovirus, and HIV)
• Rubella
• Cytomegalovirus
• Herpes simplex virus (HSV)

At Boston Children’s Hospital, our Fetal Care and Surgery Center works with your prenatal and obstetric care team to assess and treat a fetal infection as early as possible.

In most cases, a pregnant person won’t experience any symptoms of a fetal infection. Occasionally, depending on the type of infection, they may present with nonspecific symptoms such as fever, rash, or fatigue.

Signs of possible fetal infection may also appear during fetal monitoring. These can include changes in fetal heart rate or reduced fetal movement. Additionally, abnormal levels of amniotic fluid — either too much (polyhydramnios) or too little (oligohydramnios) — may raise concern for an underlying infection.

It’s important to note that the symptoms of fetal infection can vary widely depending on the cause of the infection, the gestational age when it occurs, and its severity. Prompt diagnosis and management of fetal infections are essential to providing the best care possible for both the fetus and the pregnant person.

Infections can be passed from the pregnant person to the fetus in two main ways:

• Through the bloodstream (hematogenous spread): Spread to the fetus through the pregnant person’s blood via the placenta.
• From the lower genital tract (such as the vagina) into the uterus (ascending infection): Spreads upward, potentially exposing the fetus to the infection.

Several factors can increase the risk of fetal infection during pregnancy, including:

• Certain infections, particularly those that can be transmitted to the fetus, such as sexually transmitted infections (STIs), influenza, or pneumonia, can increase the risk of a fetal infection, especially if left untreated or treated improperly.
• Conditions that weaken the pregnant person’s immune system, such as HIV/AIDS, autoimmune disorders, or immunosuppressive therapy.
• Timing of maternal infection at later stages of pregnancy increases the risk of transmitting the infection to the fetus.
• Advanced maternal age (over 35 years).
• Lifestyle factors such as smoking, drug use, or excessive alcohol consumption during pregnancy can weaken the immune system and increase susceptibility to infections.
• If the fetus’ immune system is not fully developed, it’s more susceptible to infections transmitted from the pregnant person.
• Pregnancies with multiples (twins, etc.) are at increased risk of complications, including fetal infections, due to factors such as restricted fetal growth, placental abnormalities, or increased maternal immune response.
• Travel to regions with a high prevalence of infectious diseases, such as malaria or Zika virus.

Identifying and mitigating risk factors through appropriate and routine prenatal care, screening, and preventive measures are key to reducing the risk of fetal infection.

Fetal infections can be diagnosed in different ways:

• Routine prenatal imaging including ultrasounds and fetal MRI that detect a fetal infection, such as abnormal growth patterns, excess amniotic fluid (hydrops), or structural anomalies.
• Blood tests on the pregnant person to detect antibodies or other markers of infection.
• Amniocentesis to collect a sample of amniotic fluid, which is then analyzed for infections.
• On rare occasions fetal blood sampling to check for evidence of fetal anemia and confirm fetal infection.
• Fetal monitoring during labor and delivery to help identify signs of fetal distress or infection-related complications.

If there are any concerns after delivery, doctors will evaluate the infant to confirm an infection and guide appropriate treatment. The evaluation could include a physical exam, blood tests, or imaging studies.

How we treat fetal infections depends on the type of infection and the stage of the pregnancy. In some cases, medication is given to the pregnant person to help prevent the infection from spreading to the fetus. In other cases, we deliver medication to the fetus directly through procedures such as an injection into the amniotic fluid or a fetal blood transfusion. Other treatments include:

• Continuous fetal monitoring to assess fetal well-being and the progression of the infection.
• Preterm delivery to speed up treatment and minimize exposure in cases where the infection poses a severe risk to the fetus.
• Specialized medical care, such as intravenous fluids, respiratory support, and medication after delivery, to manage the infection and any associated complications.

The long-term outlook for a fetal infection depends on the type of infection, the gestational age on which it occurred, its severity, and how quickly the infection is treated or resolved. Severe infections can lead to developmental issues if not treated early while other infections can cause congenital anomalies. Regular prenatal care and screenings are essential for detecting infections early so they can be properly managed and treated.

At the Boston Children’s, we care for fetal infections as a team. Our fetal surgeons, maternal-fetal medicine specialists, neonatologists, radiologists, cardiologists, and others work closely with the Obstetrical Infectious Disease Clinic and your prenatal care team to diagnose, monitor, and treat suspected or confirmed fetal infections. We also work with pediatric infectious disease experts to care for your baby after delivery, if needed.