Vertical Transmission
Passing of infection from mother to baby before, during, or after birth
Quick Facts
- Type: Mode of disease transmission
- Timing: Pregnancy, delivery, or breastfeeding
- Common examples: HIV, hepatitis B, syphilis, group B strep
- Largely preventable: Yes, with prenatal care and treatment
Overview
Vertical transmission describes the spread of an infection or condition from a pregnant person to their baby. It is contrasted with horizontal transmission, in which infections spread between unrelated people. The term most often refers to infections, but some genetic and immune conditions can also pass from parent to child.
Transmission can happen at three main points: across the placenta during pregnancy (transplacental), through contact with blood and fluids during labor and delivery, or through breast milk after birth. Many of the most serious infections that travel this route, including HIV, hepatitis B, and syphilis, can be greatly reduced or prevented with routine prenatal screening and treatment, which is why early and regular pregnancy care matters so much.
Signs in the Baby
Vertical transmission itself is a process rather than a single illness, so what is seen depends on the infection involved. Some babies appear healthy at birth and develop problems later, while others show signs right away.
- Low birth weight or being small for gestational age
- Jaundice (yellowing of the skin and eyes)
- Enlarged liver or spleen
- Rash, skin sores, or eye discharge
- Poor feeding, irritability, or unusual sleepiness
- Hearing or vision problems detected on screening
Because some infections are silent at first, newborns are screened and monitored when a transmissible infection is known or suspected in the mother.
Causes
Many infections can be passed vertically. Common and important examples include:
- Viruses: HIV, hepatitis B and C, cytomegalovirus (CMV), rubella, herpes simplex, and Zika.
- Bacteria: group B streptococcus and the organism that causes syphilis.
- Parasites: Toxoplasma (toxoplasmosis).
The route varies by organism. Some cross the placenta during pregnancy, some are acquired as the baby passes through the birth canal, and a few can be passed in breast milk. The risk of passing each infection depends on the type of organism, how active the infection is, and whether the mother is receiving treatment.
Risk Factors
- An untreated or undiagnosed infection during pregnancy
- A high level of virus or bacteria in the mother's body
- Limited or no prenatal care
- Prolonged rupture of membranes (water breaking long before delivery)
- Invasive procedures during labor
- Breastfeeding when certain untreated infections are present
Diagnosis
The first step is identifying infections in the mother. Standard prenatal care includes blood tests for HIV, hepatitis B, and syphilis, and screening for group B strep late in pregnancy. When transmission is a concern, testing of the baby may include:
- Blood tests for the specific infection, sometimes repeated over weeks to months
- Physical examination for signs such as jaundice, rash, or organ enlargement
- Hearing and vision screening
- Imaging of the brain or other organs if a congenital infection is suspected
Some infections require follow-up testing because a newborn can carry the mother's antibodies for a time, which can blur early results.
Treatment
Treatment is directed at the specific infection and aims both to protect the baby and to lower the chance of transmission in the first place.
- Antiviral medicines: Treating HIV during pregnancy can lower transmission to very low levels; antivirals are also used for hepatitis B and herpes.
- Antibiotics: Penicillin treats syphilis in pregnancy; antibiotics given during labor reduce group B strep transmission.
- Immunization and immune globulin: Hepatitis B vaccine and immune globulin given to the newborn shortly after birth are highly effective at preventing infection.
- Delivery planning: In some situations a cesarean birth or avoiding breastfeeding is advised to reduce risk.
Babies who become infected receive treatment and long-term follow-up tailored to the condition.
Prevention
- Begin prenatal care early and attend all scheduled visits
- Complete recommended prenatal infection screening
- Take prescribed treatment for any infection found during pregnancy
- Stay up to date on recommended vaccines before or during pregnancy
- Discuss safe feeding choices with your care team when an infection is present
- Ensure the newborn receives recommended post-birth vaccines and medicines
When to See a Doctor
Anyone who is pregnant or planning a pregnancy should seek prenatal care promptly so that any transmissible infection can be found and treated. Contact your care team if you develop a fever, rash, flu-like illness, or possible exposure to an infection during pregnancy. After birth, seek urgent care if a newborn has poor feeding, unusual sleepiness, a high fever, a spreading rash, or difficulty breathing, as these can be signs of serious infection that needs immediate attention.
Frequently Asked Questions
What does vertical transmission mean?
Vertical transmission means an infection or condition passes from a mother to her baby. It can happen during pregnancy across the placenta, during labor and delivery, or after birth through breast milk.
Can vertical transmission be prevented?
Many forms can be greatly reduced or prevented. Routine prenatal screening, treating infections during pregnancy, vaccinating the newborn, and planning the safest delivery and feeding method all lower the risk substantially.
Which infections are most commonly passed this way?
Common examples include HIV, hepatitis B, syphilis, group B streptococcus, cytomegalovirus, herpes, and toxoplasmosis. Standard prenatal care screens for several of these so they can be addressed early.
Does a mother with an infection always pass it to her baby?
No. Transmission is not guaranteed and depends on the specific infection, how active it is, and whether treatment is given. For many infections, proper care during pregnancy and birth brings the risk down to a very low level.
Why are newborns sometimes tested more than once?
A baby can carry the mother's antibodies for weeks to months, which can make early test results hard to interpret. Repeating tests over time helps confirm whether the baby is actually infected.
References
- Centers for Disease Control and Prevention (CDC). Mother-to-Child Transmission of Infections.
- World Health Organization (WHO). Mother-to-child transmission of HIV and other infections.
- MedlinePlus, U.S. National Library of Medicine. Infections and Pregnancy.
- American College of Obstetricians and Gynecologists (ACOG). Prenatal Infection Screening.