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Sexually transmitted infections (STIs) include syphilis, gonorrhea, chlamydial and trichomonal infections, and infections caused by human immunodeficiency virus (HIV), herpes simplex virus (HSV), human papillomavirus (HPV), and hepatitis B and C viruses. In describing their pathogenesis, horizontal transmission is transfer to a contemporary. Instead, vertical transmission refers to passage of an infectious agent from the mother to her fetus through the placenta, during labor or delivery, or by breastfeeding. Many STIs can harm the mother or fetus. Thus, these are sought through both asymptomatic screening and symptomatic diagnostic testing and then treated. For this, the Centers for Disease Control and Prevention (CDC) provides guidelines, which are described throughout this chapter.

For STI screening and diagnosis, serological testing is recommended in some cases and identifies antibodies formed by the patient against the pathogen. In others, direct detection of an infectious agent by culture or by a nucleic acid amplification test (NAAT) of body fluids or lesions is suitable. NAATs include any molecular method used to detect the presence of DNA or RNA of a pathogen. NAATs may be polymerase chain reaction (PCR) tests (most common), transcription-mediated amplification (TMA) tests, or others. NAATs may be qualitative (detecting presence or absence only) or quantitative depending on the specific test. The terms NAAT and PCR may be used interchangeably in some cases when appropriate.

If one STI is identified, patients are offered screening for all STIs, because these infections are commonly comorbid. Treatment of most STIs is associated with improved pregnancy outcome and prevention of perinatal morbidity. Logically, education, screening, treatment, and prevention are essential components of prenatal care.


This infection remains a major threat for both mother and fetus. Since 2001, the combined rate of primary and secondary syphilis has risen almost yearly, and among women in 2019, the rate was 4 cases per 100,000 persons (Centers for Disease Control and Prevention, 2021b). For congenital syphilis, the rate in 2019 was 48 cases per 100,000 live births. This is a nearly 300 percent rise since 2015. Of risks, higher congenital syphilis rates are linked to inadequate prenatal care, substance use during pregnancy, African American race, and lack of screening and treatment (Smullin, 2021). The CDC also includes sex work, multiple or new sexual partners, incarceration, or homelessness (Workowski, 2021). Syphilis remains a significant global health problem (Korenromp, 2019).


Syphilis is caused by the spirochetal bacterium Treponema pallidum. With horizontal transmission, minute abrasions on the vaginal mucosa provide entry, and cervical eversion, hyperemia, and friability raise this risk. Spirochetes replicate and disseminate through lymphatic channels and then hematogenously if untreated.

During vertical transmission, spirochetes readily cross the placenta. This is the most common route, but neonatal infection may result from contact with spirochetes from lesions at delivery or across the placental membranes. Fetal infection develops in ...

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