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Infectious Disease in Pregnancy

By Lara A. Friel, MD, PhD, Associate Professor, Maternal-Fetal Medicine Division, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Texas Health Medical School at Houston, McGovern Medical School

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Most common maternal infections (eg, 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:

HIV infection 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 is more common during pregnancy. Listeriosis increases risk of

  • Spontaneous abortion

  • Preterm labor

  • Stillbirth

  • Premature rupture of the membranes

  • Preterm labor

Tests for these infections are done during routine prenatal evaluations or if symptoms develop.

Genital herpes can be transmitted to the neonate during delivery. Risk is high enough that cesarean delivery is preferred in the following situations:

  • When women have visible herpetic lesions

  • When women who have a known history of infection develop prodromal symptoms before labor

  • When herpes infection first occurs during the late 3rd trimester (when cervical viral shedding at delivery is likely)

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.


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 Table: Some Drugs With Adverse Effects During Pregnancy 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 wk 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: Some Drugs With Adverse Effects During Pregnancy); they are not used from the middle to the end of pregnancy.

Key Points

  • Most common maternal infections (eg, UTIs, skin and respiratory tract infections) are usually not serious problems during pregnancy.

  • Maternal infections that can damage the fetus include cytomegalovirus infection, herpes simplex virus infection, rubella, toxoplasmosis, hepatitis B, and syphilis.

  • 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.

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