Infections in Pregnancy

Bacteriuria and pyelonephritis

Why pregnancy changes the rules. Progesterone relaxes ureteral smooth muscle and the enlarging uterus compresses the ureters, producing hydroureter and urinary stasis, worse on the right because the uterus is dextrorotated. Bacteria ascend easily, so a quarter to a third of women with untreated asymptomatic bacteriuria develop pyelonephritis.

Screening. Every pregnant woman has a urine culture at the first prenatal visit. Asymptomatic bacteriuria (≥100,000 CFU/mL of one organism without symptoms, most often E. coli) is always treated, and a repeat culture confirms cure because recurrence is common. Group B streptococcus (GBS) in the urine at any count qualifies the woman for intrapartum GBS prophylaxis without the routine 36–37-week swab.

Pyelonephritis. Fever, flank pain, costovertebral angle tenderness and vomiting warrant admission. Give IV ceftriaxone (or ampicillin plus gentamicin) until afebrile for 24–48 hours, then an oral agent to complete 10–14 days, followed by nightly nitrofurantoin or cephalexin suppression for the rest of the pregnancy because recurrence is common.

Gram-negative endotoxin can cause septic shock and ARDS or pulmonary edema from capillary leak, made worse by aggressive IV fluids and tocolytics. Hemolytic anemia, transient renal dysfunction and preterm contractions are the other classic complications.

Intraamniotic infection

What it is. Intraamniotic infection (chorioamnionitis, or "triple I") is ascending polymicrobial infection of the fluid, membranes, placenta or decidua by GBS, E. coli, anaerobes and genital mycoplasmas. Risk factors: prolonged membrane rupture or labor, many digital examinations, internal monitors and GBS colonization.

Diagnosis. Intrapartum fever (≥39.0°C once, or 38.0–38.9°C that persists on repeat) plus fetal tachycardia >160/min, maternal WBC >15,000/μL without recent steroids, or purulent cervical fluid. Uterine tenderness, foul fluid and maternal tachycardia support it; fever beginning only after delivery suggests postpartum endometritis instead.

Complications. Infected myometrium contracts poorly, so atony with postpartum hemorrhage, endometritis and wound infection follow more often; neonates face sepsis, pneumonia, meningitis and cerebral palsy. Antibiotics only bridge; emptying the uterus removes the source.

HIV and herpes simplex virus

Testing and ART. HIV testing is opt-out at the first visit, and a laboring woman with unknown status gets a rapid test. Every pregnant woman with HIV takes combination ART as early as possible, regardless of CD4 count or viral load; the viral load around 34–36 weeks guides the delivery plan.

Delivery. Viral load >1,000 copies/mL or unknown near term → scheduled cesarean at 38 weeks, before labor and membrane rupture (after which its benefit is uncertain), with IV zidovudine starting about 3 hours before surgery. With suppression, vaginal delivery proceeds and cesarean follows usual obstetric indications. Avoid artificial rupture of membranes, scalp electrodes, forceps or vacuum and episiotomy when possible. The newborn starts zidovudine ideally within 6 hours. In the United States formula feeding eliminates postnatal transmission; a suppressed mother who wishes to breastfeed receives individualized counseling.

Herpes simplex. Neonatal transmission is 30–50% when herpes is first acquired near delivery (no protective maternal IgG yet) versus <1% with a history of recurrences. Any woman with prior genital herpes starts acyclovir or valacyclovir suppression at 36 weeks, cutting term recurrences, shedding and cesareans. Genital lesions or prodromal burning or tingling at labor mean cesarean; lesions on the buttock or thigh are covered and vaginal delivery proceeds. Avoid scalp electrodes. Neonatal herpes (skin-eye-mouth, encephalitis or disseminated disease) is treated with IV acyclovir.

Hepatitis B and syphilis

Hepatitis B. Test HBsAg in every pregnancy, even after vaccination. If positive, check HBV DNA; above 200,000 IU/mL, start tenofovir at 28–32 weeks, because a high viral load overwhelms neonatal immunoprophylaxis. Every exposed newborn gets hepatitis B vaccine plus HBIG within 12 hours (if maternal HBsAg positivity is found after birth, HBIG can still be given up to 7 days of age) and serologic testing after the series. Without prophylaxis an HBeAg-positive mother infects up to ~90% of infants, and ~90% of infected newborns become chronic carriers. Breastfeeding is allowed and cesarean does not help. Hepatitis C screening is also universal, with treatment deferred until after delivery.

Syphilis screening. RPR or VDRL confirmed by a treponemal test (FTA-ABS or TP-PA), or the reverse sequence, at the first visit, 28 weeks and delivery, and after any stillbirth at ≥20 weeks. Penicillin crosses the placenta and treats the fetus.

Within 24 hours of penicillin, lysed treponemes trigger cytokine release: fever, chills, myalgia and headache (the Jarisch-Herxheimer reaction). In the second half of pregnancy it can cause contractions, preterm labor or fetal heart rate abnormalities. Counsel beforehand, give antipyretics and monitor the fetus, but never delay or withhold penicillin.

Congenital syphilis. Untreated infection causes stillbirth, hydrops and preterm birth; early signs include hepatosplenomegaly, snuffles, a palm and sole rash and periostitis, and late signs include Hutchinson teeth, saddle nose, saber shins, interstitial keratitis and deafness.

Exposures and congenital infections

Varicella. Chickenpox, especially pneumonia, is more severe in pregnancy. An exposed woman unsure of her history gets a varicella IgG; if nonimmune, VariZIG is given as soon as possible, up to 10 days after exposure. Maternal chickenpox is treated with oral acyclovir or valacyclovir, and pneumonia with admission and IV acyclovir. Congenital varicella syndrome follows infection before 20 weeks (about 2% at 13–20 weeks). A maternal rash from 5 days before to 2 days after delivery means the antibody-free newborn gets VariZIG. The live vaccine waits until postpartum.

Parvovirus B19. The slapped-cheek virus of children causes arthropathy in adults and enters fetal erythroid precursors through the P antigen, producing aplastic anemia, high-output failure and nonimmune hydrops, mostly with infection before 20 weeks; it does not cause malformations. An exposed woman, often a teacher, gets IgG and IgM. IgG alone means immunity; a positive IgM triggers middle cerebral artery peak systolic velocity Doppler every 1–2 weeks for 8–12 weeks, and a rising value leads to cordocentesis and intrauterine transfusion.

Toxoplasmosis. Primary infection from cat feces or undercooked meat threatens the fetus; transmission rises with gestational age while severity falls. Acute infection is confirmed at a reference laboratory (IgM plus IgG avidity; high avidity early in pregnancy means infection predated conception), and fetal infection by amniotic fluid PCR at ≥18 weeks. Spiramycin concentrates in the placenta and reduces transmission but does not treat the fetus; confirmed fetal infection gets pyrimethamine, sulfadiazine and leucovorin, avoiding pyrimethamine in the first trimester. Prevention: someone else changes the litter, and meat is cooked thoroughly.

Cytomegalovirus. CMV affects about 1 in 200 newborns and is the leading nongenetic cause of sensorineural hearing loss. Primary maternal infection carries the highest risk, but reactivation can also transmit. Findings include periventricular calcifications, microcephaly, chorioretinitis, petechiae and growth restriction, though many newborns look normal and lose hearing later. With no vaccine and no routine screening, prevention is hygiene: handwashing after diaper changes and no sharing utensils or mouth kisses with young children. Symptomatic newborns receive valganciclovir.

Listeria. Listeria monocytogenes, a gram-positive rod with tumbling motility, grows at refrigerator temperatures in unpasteurized soft cheese, deli meats, hot dogs and smoked seafood; pregnancy raises the risk about 10-fold. The mother has a mild febrile flu-like illness, but the fetus suffers preterm labor, stillbirth and neonatal sepsis or meningitis. A febrile exposed woman gets blood cultures and IV ampicillin, often with gentamicin; cephalosporins have no activity. Asymptomatic exposure needs no testing.

Influenza and vaccines

Influenza. Pregnancy and the first 2 weeks postpartum raise the risk of severe influenza. Inactivated vaccine is given in any trimester and protects infants younger than 6 months through transplacental antibody; live vaccines (intranasal influenza, MMR, varicella) wait until after delivery. Any pregnant or recently postpartum patient with suspected influenza starts oseltamivir immediately, without waiting for testing and even beyond 48 hours.

Fever itself harms the fetus: first-trimester hyperthermia is associated with neural tube defects, so treat fever with acetaminophen.