Most common maternal infections (eg, urinary tract infection [UTIs], skin and respiratory tract infections) are usually not serious problems during pregnancy, although some genital infections (bacterial vaginosis and genital herpes) affect labor or choice of delivery method. Thus, the main issue is usually use and safety of antimicrobial drugs.
However, certain maternal infections can damage the fetus, as may occur in the following:
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Congenital cytomegalovirus infection Congenital and Perinatal Cytomegalovirus Infection (CMV) Cytomegalovirus infection may be acquired prenatally or perinatally and is the most common congenital viral infection. Signs at birth, if present, are intrauterine growth restriction, prematurity... read more
HIV infection Human Immunodeficiency Virus (HIV) Infection in Infants and Children Human immunodeficiency virus (HIV) infection is caused by the retrovirus HIV-1 (and less commonly by the related retrovirus HIV-2). Infection leads to progressive immunologic deterioration and... read more 
can be transmitted from mother to child transplacentally or perinatally. When the mother is not treated, risk of transmission at birth is about 25 to 35%.
Listeriosis Listeriosis Listeriosis is bacteremia, meningitis, cerebritis, dermatitis, an oculoglandular syndrome, intrauterine and neonatal infections, or rarely endocarditis caused by Listeria species. Symptoms vary... read more is more common during pregnancy. Listeriosis increases risk of
Listeriosis Neonatal Listeriosis Neonatal listeriosis is acquired transplacentally or during or after delivery. Symptoms are those of sepsis. Diagnosis is by culture or polymerase chain reaction testing of mother and infant... read more can be transmitted from mother to child transplacentally or perinatally.
Bacterial vaginosis Bacterial Vaginosis (BV) Bacterial vaginosis is vaginitis due to a complex alteration of vaginal flora in which lactobacilli decrease and anaerobic pathogens overgrow. Symptoms include a gray, thin, fishy-smelling vaginal... read more 
and possibly genital chlamydial infection Chlamydial, Mycoplasmal, and Ureaplasmal Mucosal Infections Sexually transmitted urethritis, cervicitis, proctitis, and pharyngitis not due to gonorrhea are caused predominantly by chlamydiae and infrequently by mycoplasmas or Ureaplasma sp. Chlamydiae... read more 
predispose to
Tests for these infections are done during routine prenatal evaluations or if symptoms develop.
Genital herpes Genital Herpes Genital herpes is a sexually transmitted disease caused by human herpesvirus 1 or 2. It causes ulcerative genital lesions. Diagnosis is clinical with laboratory confirmation by culture, polymerase... read more 
can be transmitted to the neonate during delivery. Risk is high enough that cesarean delivery is preferred in the following situations:
If visible lesions or prodrome is absent, even in women with recurrent infections, risk is low, and vaginal delivery is possible. If women are asymptomatic, serial antepartum cultures do not help identify those at risk of transmission. If women have recurrent herpes infections during pregnancy but no other risk factors for transmission, labor can sometimes be induced so that delivery occurs between recurrences. When delivery is vaginal, cervical and neonatal herpesvirus cultures are done. Acyclovir (oral and topical) appears to be safe during pregnancy.
Antibacterials
It is important to avoid giving antibacterials to pregnant patients unless there is strong evidence of a bacterial infection. Use of any antibacterial during pregnancy should be based on whether benefits outweigh risk, which varies by trimester (see Drugs With Adverse Effects During Pregnancy Drugs for Arrhythmias The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more for specific adverse effects). Severity of the infection and other options for treatment are also considered.
Aminoglycosides may be used during pregnancy to treat pyelonephritis and chorioamnionitis, but treatment should be carefully monitored to avoid maternal or fetal damage.
Cephalosporins are generally considered safe.
Chloramphenicol, even in large doses, does not harm the fetus; however, neonates cannot adequately metabolize chloramphenicol, and the resulting high blood levels may lead to circulatory collapse (gray baby syndrome). Chloramphenicol is rarely used in the US.
Fluoroquinolones are not used during pregnancy; they tend to have a high affinity for bone and cartilage and thus may have adverse musculoskeletal effects.
Macrolides are generally considered safe.
Metronidazole use during the 1st trimester used to be considered controversial; however, in multiple studies, no teratogenic or mutagenic effects were seen.
Nitrofurantoin is not known to cause congenital malformations. It is contraindicated near term because it can cause hemolytic anemia in neonates.
Penicillins are generally considered safe.
Sulfonamides are usually safe during pregnancy. However, long-acting sulfonamides cross the placenta and can displace bilirubin from binding sites. These drugs are often avoided after 34 weeks gestation because neonatal kernicterus is a risk.
Tetracyclines cross the placenta and are concentrated and deposited in fetal bones and teeth, where they combine with calcium and impair development (see table Drugs With Adverse Effects During Pregnancy Some Drugs With Adverse Effects During Pregnancy Drugs are used in over half of all pregnancies, and prevalence of use is increasing. The most commonly used drugs include antiemetics, antacids, antihistamines, analgesics, antimicrobials, diuretics... read more ); they are not used from the middle to the end of pregnancy.
Key Points
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Most common maternal infections (eg, UTIs, skin and respiratory tract infections) are usually not serious problems during pregnancy.
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Maternal infections that can damage the fetus include cytomegalovirus infection, herpes simplex virus infection, rubella, toxoplasmosis, hepatitis B, and syphilis.
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Give antibacterials to pregnant patients only when there is strong evidence of a bacterial infection and only if benefits of treatment outweigh risk, which varies by trimester.
