Pregnancy-Associated Infections

An important consideration in pregnancy is the relationship between infection in the mother and the developing foetus. Infections can indirectly impact the foetus through effects on the mother, for example, maternal urinary tract infection is associated with preterm birth, or can infect the foetus. Routes of infection can be ascending from the birth canal through the cervical os, transplacentally, or rarely, contiguously. The effect on the mother is also important: pregnancy is considered an immunosuppressive state and the growing foetus causes significant mechanical and physiological changes. Although the first trimester is the key developmental phase for the growing foetus, during the third trimester the mother is more susceptible to severe respiratory infection and some viral infections such as varicella zoster virus (VZV), due to the mechanical changes produced by the growing foetus. There is a paucity of evidence supporting the safety of drugs in pregnancy. Use of any medicinal drug in pregnancy, including antibiotics, requires good reasons. The optimum choice of antibiotics depends on the trimester of the pregnancy. In general, beta-lactams are safe and tetracyclines should be avoided throughout pregnancy. Nitrofurantoin is safe until after thirty-five weeks gestation and trimethoprim should be avoided in the first trimester but is safe otherwise (perhaps with folic acid supplementation if < 20 weeks). Specific patterns of colonization and infection of the genitourinary tract can be associated with an increased risk of an adverse pregnancy outcome, particularly preterm birth. Sexually transmitted diseases such as gonorrhoea and chlamydia are associated with an increased risk of spontaneous preterm birth, which may extend to infection in the pre-conception period. Bacterial vaginosis is an abnormal pattern of vaginal colonization and is also linked with an increased risk of preterm birth. The US Center for Disease Control recommends screening all pregnant women for chlamydia, gonorrhoea, syphilis, HIV, and hepatitis B, symptomatic women for trichomonas and genital herpes, women considered at high risk of preterm birth for bacterial vaginosis, and women at high risk of blood-borne virus infection for hepatitis C. Treatment is administered to reduce the risk of an adverse pregnancy outcome (syphilis, gonorrhoea, chlamydia, trichomonas, and bacterial vaginosis) or to prevent transmission to the infant (herpes, HIV, hepatitis B, and C).