Sexually transmitted infections (STIs) present a unique consideration during pregnancy because they can affect the mother’s health, the developing fetus, or the newborn. These infections introduce bacteria or viruses into the maternal environment that can complicate the normal course of gestation. The effects range from mild, manageable conditions to severe, life-altering outcomes for the child, including stillbirth or long-term disability. Medical advancements provide clear protocols for screening and treatment, which significantly reduce the risk of transmission and harm when infections are identified and managed early. Understanding how these infections move from mother to child and the potential consequences is paramount to ensuring the best health outcomes for both.
Pathways for Transmission to the Fetus
Infections can travel from the pregnant woman to her child through several distinct routes, depending on the specific pathogen. The first pathway is in utero transmission, where the infectious agent crosses the placental barrier to infect the fetus directly during pregnancy. Syphilis and Human Immunodeficiency Virus (HIV) are examples of infections that utilize this transplacental route, with the risk of transfer increasing as pregnancy progresses.
The second, and most frequent, route is peripartum transmission, which occurs during labor and delivery. The baby contacts infected maternal blood, genital secretions, or lesions while passing through the birth canal. Gonorrhea, Chlamydia, and Herpes Simplex Virus (HSV) are typically transmitted this way. A third route is postnatal transmission, which happens after delivery, most commonly through breastfeeding, relevant for certain viral infections like HIV.
Specific Risks Posed by Common STIs
The consequences of an STI transmission to the fetus or newborn are highly dependent on the specific infection and whether the mother was treated.
Syphilis
Untreated maternal Syphilis, caused by the bacterium Treponema pallidum, is highly destructive, leading to adverse outcomes in over half of affected pregnancies. The bacteria cross the placenta, causing miscarriage, premature birth, or stillbirth, with up to 40% of infected infants facing a fatal outcome. Surviving newborns may develop congenital syphilis, which causes bone abnormalities, severe anemia, jaundice, neurological damage, and long-term vision and hearing loss.
HIV
HIV poses a risk of vertical transmission during pregnancy, delivery, or breastfeeding. Without intervention, the transmission rate can be as high as 25% to 30%. Beyond the risk of HIV infection itself, maternal HIV is also associated with adverse birth outcomes like low birth weight and preterm birth, even in infants who do not contract the virus.
Hepatitis B
Hepatitis B can lead to chronic, long-term illness if transmitted at birth. The virus causes chronic infection in the newborn, which can lead to severe liver disease, including cirrhosis or liver cancer later in life. Testing the mother allows for immediate postnatal intervention to prevent this lifelong chronic infection.
Gonorrhea and Chlamydia
Chlamydia and Gonorrhea are bacterial infections primarily transmitted during passage through the birth canal. Untreated Gonorrhea can cause severe neonatal conjunctivitis (ophthalmia neonatorum), which may lead to blindness if not treated immediately after birth. Gonorrhea can also cause life-threatening blood or joint infections in the newborn. Chlamydia exposure can also cause neonatal conjunctivitis and may result in Chlamydia pneumonia, a serious respiratory infection appearing weeks to months after birth. Untreated infections are also linked to pregnancy complications like premature rupture of membranes and preterm delivery.
Herpes Simplex Virus (HSV)
Herpes Simplex Virus (HSV) carries the risk of a rare but severe infection in the newborn, especially if the mother has a primary outbreak near delivery. Neonatal herpes can be localized to the skin, eyes, and mouth, or it can be a disseminated infection affecting multiple organs, including the brain. This can result in long-term neurological impairment or death.
Why Early Prenatal Screening is Essential
Routine prenatal screening is the most effective defense against the harmful effects of STIs. Many STIs, including Chlamydia, Gonorrhea, and Syphilis, often present with no symptoms in the mother, making universal testing necessary for detection. Early detection allows medical providers to administer curative or preventative treatment before the infection causes irreparable harm.
Current clinical guidelines recommend that all pregnant individuals be screened for HIV, Syphilis, and Hepatitis B at their first prenatal visit, typically in the first trimester. Screening for Chlamydia and Gonorrhea is also recommended for all pregnant individuals under the age of 25 and those at increased risk. Repeat testing for Syphilis and HIV is recommended in the third trimester for individuals at continued high risk, ensuring they benefit from early intervention.
Treatment Strategies to Protect the Fetus
Once an STI is diagnosed during pregnancy, specific medical interventions are available to protect the child.
Treatment for Bacterial Infections
For bacterial infections like Syphilis, treatment involves a course of Benzathine penicillin G via injection. This antibiotic crosses the placenta effectively, often curing both the mother and the fetus and preventing congenital syphilis when given early. Gonorrhea and Chlamydia are treated with pregnancy-safe antibiotics, such as Azithromycin and Ceftriaxone, which eradicate the infection and prevent transmission during delivery.
Treatment for Viral Infections
For viral infections, the goal is mitigation and risk reduction. Pregnant individuals with HIV are prescribed a combination of antiretroviral medications (ART), which dramatically lowers the viral load in the mother’s blood. An undetectable viral load reduces the transmission risk to less than 1%. In cases of active genital Herpes lesions near delivery, a Cesarean section may be performed to prevent the baby from contacting the virus.
Postnatal Interventions
Postnatal interventions provide a final layer of protection. Infants born to mothers who are Hepatitis B positive receive both the Hepatitis B vaccine and Hepatitis B immune globulin immediately after birth to prevent the establishment of chronic infection. All newborns also receive antibiotic eye ointment shortly after birth to guard against the risk of blindness from Gonorrhea infection.