Sexually transmitted infections (STIs) pose a serious health risk to a pregnant woman, but the potential consequences for her developing fetus or newborn infant can be especially severe. These infections are caused by various pathogens transmitted through sexual contact, and they can lead to significant health problems for both the mother and the baby if left untreated. Pregnancy does not protect a woman from acquiring an STI, and the body’s natural changes during gestation can sometimes complicate an existing infection. Having an STI while pregnant introduces a considerable risk of transmitting the pathogen to the fetus or newborn, which can result in long-term health issues or even death for the child.
How Transmission Occurs During Pregnancy and Birth
A pathogen can cross from the mother to the infant through three distinct mechanisms, depending on the specific infection and the timing of exposure. The first pathway is transplacental transmission, where the infectious agent, such as the bacterium causing syphilis, crosses the placental barrier and infects the fetus while it is still in the uterus. This route allows the infection to affect the fetus early in development and can lead to congenital disease.
The second mechanism is an ascending infection, where organisms from the lower genital tract, like Chlamydia trachomatis or Neisseria gonorrhoeae, travel upward from the cervix or vagina into the amniotic fluid. This can occur before the rupture of membranes, potentially causing inflammation of the fetal membranes or infecting the fetus directly.
The third and most common route for many STIs is perinatal contact, which occurs when the infant passes through the birth canal during delivery. The baby is exposed to high concentrations of the pathogen present in the mother’s cervical and vaginal secretions. Viral infections like Herpes Simplex Virus and bacterial infections like gonorrhea and chlamydia are frequently transmitted this way.
General Risks to Fetal Development and Delivery
Maternal STIs, particularly those that cause inflammation or systemic infection, are associated with a range of poor outcomes for the pregnancy itself. An untreated infection can increase the risk of spontaneous abortion (miscarriage), particularly if the pathogen invades the placenta early in gestation.
Infections can also lead to severe complications later in pregnancy, including stillbirth (loss of the fetus at or after 20 weeks of gestation). Inflammation caused by the infection may trigger the premature rupture of membranes, which significantly increases the danger of preterm birth.
Preterm birth (delivery before 37 weeks of pregnancy) carries substantial risks for the infant, including low birth weight and difficulty with organ development. Chronic infection can hinder the fetus’s ability to grow normally, resulting in intrauterine growth restriction (IUGR) and a baby that is small for its gestational age.
Consequences of Specific Neonatal Infections
Congenital Syphilis
Congenital Syphilis, caused by the bacterium Treponema pallidum, crosses the placenta and often leads to severe multi-system damage. If the mother has primary or secondary syphilis and is untreated, the risk of transmission is extremely high, resulting in severe adverse events in up to 80% of cases, including stillbirth and neonatal death. Surviving infants may develop a wide array of symptoms, including bone abnormalities, severe anemia, enlarged liver and spleen, and neurological complications like meningitis and hydrocephalus.
Human Immunodeficiency Virus (HIV)
HIV can be transmitted to the infant during pregnancy, labor, delivery, or through breastfeeding (vertical transmission). Without intervention, the risk of transmission is 15% to 45%, but treatment with antiretroviral therapy (ART) during pregnancy can reduce this risk to less than 1%. Infants who acquire HIV face a progressive weakening of their immune system, leading to susceptibility to life-threatening opportunistic infections and developmental delays.
Neonatal Herpes Simplex Virus (HSV)
Neonatal HSV infection is usually acquired during passage through the birth canal if the mother has an active genital lesion. The most serious forms involve the central nervous system, causing herpes encephalitis with potential for severe brain damage, or disseminated disease affecting multiple organs like the liver and lungs. Even localized disease, which presents as skin, eye, and mouth lesions, requires prompt antiviral treatment to prevent progression to more severe forms.
Chlamydia and Gonorrhea
Infections with Chlamydia trachomatis and Neisseria gonorrhoeae are often acquired during delivery and primarily cause localized disease in the newborn. Gonorrhea can lead to severe neonatal conjunctivitis (ophthalmia neonatorum), which can result in corneal scarring and permanent blindness if not treated immediately after birth. Chlamydia can also cause conjunctivitis, but it is a common cause of neonatal pneumonia, which can manifest several weeks after birth and requires specific antibiotic therapy.
Screening and Treatment Protocols for Expectant Mothers
Preventing adverse outcomes begins with universal prenatal screening, which is recommended for all expectant mothers at the first prenatal care visit. Screening for HIV, syphilis, and Hepatitis B is a standard part of this initial testing, regardless of the woman’s perceived risk factors. Prompt detection is paramount because many bacterial STIs, such as syphilis, chlamydia, and gonorrhea, can be cured with specific antibiotic regimens that are safe for use during pregnancy.
For syphilis, treatment with benzathine penicillin G is highly effective and can prevent congenital infection if administered early in the pregnancy, ideally before the second trimester. For viral infections like HIV, the focus is on management using highly active antiretroviral therapy (ART) throughout pregnancy to suppress the maternal viral load, thereby minimizing the chance of vertical transmission.
A woman with a history of genital herpes may be offered suppressive antiviral medication starting at 36 weeks of gestation to reduce the likelihood of an active outbreak during delivery. If a mother has active genital herpes lesions or symptoms of an impending outbreak at the time of labor, a Cesarean section is recommended to prevent the infant from coming into contact with the virus in the birth canal.