Infections in pregnancy

• Most pregnancies are uncomplicated by infection, but a small number of infections acquired before or during pregnancy can pass from mother to baby and cause miscarriage, stillbirth, preterm birth, congenital disease or neonatal sepsis.
• The protective approach has four parts: screen the mother, treat her promptly, give prophylaxis around the time of birth, and protect the newborn with vaccines or medicines.
• Many important infections (HIV, syphilis, hepatitis B virus, hepatitis C virus) are screened for in every pregnancy; others (chlamydia, gonorrhoea, tuberculosis) are screened for only when risk factors exist.
• Group B streptococcus is managed not by treating the mother during pregnancy but by giving intravenous antibiotics in labour, because risk-based universal screening is not recommended in the United Kingdom.
• No single country's guideline is authoritative: the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), the British HIV Association (BHIVA) and the Royal College of Obstetricians and Gynaecologists (RCOG) differ on points such as screening policy and drug doses, and local protocol should be followed.

By the end of this page you should be able to:

1. List the infections that are screened for in every pregnancy and those that are screened for only when risk factors exist.
2. Explain how vertical transmission occurs and the four layers of prevention.
3. Plan first-trimester to intrapartum care for human immunodeficiency virus (HIV), syphilis, hepatitis B virus (HBV), hepatitis C virus (HCV), group B streptococcus (GBS) and the common "TORCH" infections.
4. Choose an intrapartum antibiotic prophylaxis regimen for GBS and state when it is effective.
5. Recognise red flags in pregnancy (fever with a rash, reduced fetal movements, severe headache, or a flu-like illness with risk factors) and know the initial investigations.
6. Tailor advice for women in high-transmission settings and in low-resource settings.

This page is a broad clinical guide to infections that matter in pregnancy, not a single disease. It covers screening, prevention of transmission, treatment in pregnancy and intrapartum prophylaxis. It deliberately cross-checks the infectious disease topics that cover each organism in more depth; doses and regimens here are the pregnancy-specific essentials, and local formularies should always be checked before prescribing.

Pregnancy changes immunity, physiology and the placenta in ways that make some infections more dangerous to the woman and more transmissible to the baby. Normal immune adaptation partly suppresses cell-mediated responses to tolerate the fetus; this is why infections that are mild in a healthy non-pregnant adult can become severe or can reactivate in pregnancy. The placenta is also a route of infection: organisms that reach the maternal bloodstream can cross it, especially early in gestation when the placental barrier is still developing. Early infection (first trimester) is the most likely to cause structural damage to the fetus; later infection is more likely to cause inflammation, preterm labour or neonatal sepsis. Some organisms (rubella, cytomegalovirus, toxoplasma) cause no symptoms in the mother at all, so screening and prevention rather than waiting for symptoms are essential.

The central screening timetable is set out below and in the flowchart that follows. Screen every pregnant woman for HIV, syphilis, hepatitis B virus (HBV) and hepatitis C virus (HCV) at the first prenatal visit; screen for chlamydia, gonorrhoea and tuberculosis (TB) only when risk factors or local prevalence indicate it. Re-screen later in pregnancy when risk is ongoing. ^[1][2]

The following flowchart summarises how a pregnant woman moves through screening, diagnosis and prophylaxis.

Baseline investigations for a woman with suspected infection in pregnancy include a full blood count, renal and liver function tests, inflammatory markers (C-reactive protein), blood cultures when febrile, a urine dipstick and culture, and pathogen-specific testing (polymerase chain reaction, serology, antigen tests). Imaging that is usually safe in pregnancy includes chest radiography with abdominal shielding, ultrasound and magnetic resonance imaging; computed tomography is reserved for situations where it changes management. Always involve the obstetric, infectious disease and neonatal teams early.

Group B streptococcus is the commonest cause of severe early-onset infection in newborn infants. It colonises the bowel and vagina of 20 to 40% of adults, including pregnant women, and causes early-onset disease (infection in the first 7 days of life) in roughly 0.57 per 1000 births in the United Kingdom and Ireland. ^[4] The organism is carried without symptoms, so waiting for it to cause disease does not work; prevention depends on intrapartum antibiotic prophylaxis (IAP) given to the mother during labour. ^[4][14]

Screening policy differs by country. The United Kingdom, following RCOG, uses a risk-based approach rather than universal culture screening: universal screening is not recommended, and antenatal antibiotic treatment of a vaginal swab is not recommended. ^[4][14] Many other countries (including the United States) use a universal culture-based approach at 35 to 37 weeks. Wherever the mother lives, treatment of GBS found in the urine (more than 100 000 colony-forming units per millilitre) is given at the time it is found, plus IAP in labour. ^[14]

Who needs IAP? Women with GBS in a vaginal or rectal swab in the current or a previous pregnancy, GBS bacteriuria in the current or a previous pregnancy, a previous baby affected by early- or late-onset GBS disease, or confirmed preterm labour before 37 weeks of gestation. Women with GBS in a previous pregnancy carry a 50% risk of recurrence and should be offered IAP or late pregnancy retesting. ^[14]

Regimen. Benzylpenicillin 3 g intravenously as a loading infusion over 30 minutes, then 1.8 g intravenously every 4 hours until delivery. For women allergic to penicillin, teicoplanin 12 mg per kilogram every 12 hours (rounded to the nearest 100 mg, maximum 800 mg per dose). ^[14] IAP is effective only when the first dose is given at least 4 hours before delivery. ^[14] If a dose is missed by more than 1 hour, prophylaxis has lapsed and a 3 g loading dose must be repeated rather than the routine 1.8 g dose. ^[14]

Group B streptococcus can also cause late-onset disease (7 to 90 days) in the baby; this is not prevented by IAP.

Syphilis in pregnancy is serious because Treponema pallidum crosses the placenta and can cause congenital syphilis, stillbirth and neonatal death, yet it is entirely treatable. All pregnant women should be tested at the first prenatal visit, and retested at 28 weeks and at delivery when risk factors such as substance use, multiple partners, a new partner, another sexually transmitted infection (STI) during pregnancy or residence in a high-prevalence area exist. ^[1][2][7] Test any woman with a fetal death after 20 weeks. ^[7]

Penicillin G is the only known effective antimicrobial for treating fetal infection and preventing congenital syphilis. ^[7] Pregnant women should receive the penicillin regimen appropriate to their stage of infection; for early (primary, secondary or early latent) disease a second dose of benzathine penicillin G 2.4 million units intramuscularly 1 week after the initial dose may be beneficial. ^[7] Women with a known penicillin allergy must be desensitised and treated with penicillin G; tetracyclines and doxycycline are avoided in the second and third trimesters, and erythromycin and azithromycin do not reliably cure maternal infection or treat the fetus. ^{[7] [1]}

Missed doses more than 9 days apart are not acceptable for late-latent disease; an optimal interval is 7 days, and if a woman misses a dose every effort should be made to give it within 2 days. Inadequate treatment is likely if delivery occurs within 30 days of therapy, if clinical signs of infection are present at delivery, or if the maternal antibody titre at delivery is fourfold higher than the pre-treatment titre. ^[7]

Listeriosis in pregnancy is usually a mild, flu-like or even asymptomatic illness in the mother, but Listeria monocytogenes crosses the placenta and can cause miscarriage, stillbirth, preterm labour and neonatal sepsis. In the United States about 1 in 25 000 pregnant women are infected each year, and 1 in 4 affected pregnancies end in fetal or neonatal loss. ^[10]

Prevention is dietary and behavioural: avoid unpasteurised dairy products, undercooked ready-to-eat meats and foods prepared in conditions where Listeria can grow; wash fruit and vegetables; reheat deli meats until steaming hot; and seek care promptly for fever or aches if a high-risk food was eaten in the previous two months. Management of suspected listeriosis (blood cultures, empiric ampicillin-based therapy) is directed by the local infectious disease and obstetric team. ^[10]

Asymptomatic bacteriuria is common in pregnancy and progresses to pyelonephritis in a substantial minority if untreated; both are associated with preterm birth. All pregnant women should have urine tested (culture, not just dipstick) at the first visit, and any infection should be treated promptly with a pregnancy-safe antibiotic (typically nitrofurantoin, cephalexin or amoxicillin depending on local resistance and gestation) and the urine re-cultured. Women with GBS in the urine are treated at the time and receive IAP in labour. ^[14]

Pregnancy is not a reason to delay treatment of active TB. Women with active TB disease should start treatment immediately; the medicines cross the placenta but are not known to harm the baby. ^[6] Most women diagnosed with latent TB can have treatment deferred until 2 to 3 months after delivery, although those at high risk of progression (HIV infection, recent conversion) should be treated during pregnancy. ^[6]

Screening is targeted: test women with risk factors (born in or frequent travel to a high-prevalence country, HIV, known contact with active TB). Both the TB skin test and the TB blood test (interferon-gamma release assay) are used; the skin test is safe and reliable throughout pregnancy, and the blood test, though safe, is less well evaluated. ^[6] A baby born to a woman with untreated active TB can be born with TB or acquire it through close contact after birth. ^[6]

Without antiretroviral therapy (ART), 15 to 40% of infants of HIV-positive mothers acquire the infection during pregnancy, birth or breastfeeding. ^[9] With ART started early and sustained viral suppression, the risk of perinatal transmission falls to under 2%, and in a French cohort of over 5400 women who entered pregnancy already suppressed (HIV viral load under 50 copies per millilitre near delivery) no perinatal transmissions occurred. ^[9] Despite this, about 160 000 infants were newly infected in 2021 worldwide, and roughly half of these (48%) were born to women who did not receive ART because they did not know their status; a further 22% followed acute maternal infection during pregnancy or breastfeeding, 22% followed stopping treatment and 8% followed treatment without adequate viral suppression. ^[9]

Screening and treatment. Test all pregnant women at the first visit (opt-out), retest in the third trimester when risk is present and do a rapid test at delivery if the woman has not been screened. ^[2] HIV-positive women should be started on ART as early as possible, usually two nucleoside reverse-transcriptase inhibitors plus a third agent. Evidence supports tenofovir (disoproxil fumarate or alafenamide) with emtricitabine or lamivudine plus either dolutegravir or darunavir with ritonavir as preferred when ART is initiated in pregnancy. ^[9] Women who conceive already on a suppressive regimen should generally continue it, because interruption raises the risk of viral rebound and transmission. ^[9] Women with HIV in the United Kingdom are managed under the BHIVA 2025 pregnancy guidelines, which cover screening, preventing acquisition, psychosocial care and detailed infant feeding advice. ^[8]

Intrapartum and postpartum care depend on the viral load near delivery and include mode of delivery, infant antiretroviral prophylaxis and decisions about feeding. The exact thresholds and regimens follow national practice and change; the BHIVA guidelines schedule a full review by 2030. ^[8] Where safe infant formula feeding is available it has been the standard to avoid breastfeeding; supported breastfeeding is now an option in several guidelines when the mother is virally suppressed and monitored, and the decision is a shared one. ^[9]

HBV screening (HBsAg) is offered at the first visit of every pregnancy regardless of vaccination status or prior testing. ^[1][2][3] An infant infected at birth has a 90% chance of developing chronic HBV infection, so timely infant prophylaxis matters more than almost anything else in this topic. ^[3]

Pregnant women who are HBsAg positive should be tested for HBV DNA to decide on antiviral therapy during the third trimester when the viral load is high. Infants of HBsAg-positive mothers receive hepatitis B vaccine and hepatitis B immune globulin (HBIG) at birth, complete the vaccine series and are tested at 9 to 12 months of age (or 1 to 2 months after the series if it was delayed). ^{[3] [1]}

HCV screening is offered to all pregnant women in most settings. ^[1][2] No treatment currently prevents mother-to-child transmission during pregnancy, so screening serves three purposes: identifying women for treatment after delivery, identifying infants who need testing in early infancy, and informing delivery care. A minority of infants of HCV-infected mothers acquire the infection, and the risk rises with high maternal viral load or HIV co-infection. Sexual and perinatal transmission both occur, but the dominant mode is blood. ^[1]

Place syphilis testing at the very first visit and retest at 28 weeks and delivery in women at continued risk. Penicillin G remains the only drug that reliably treats the fetus. ^[7]

Rubella is usually mild in the mother but infection in the first 8 to 10 weeks of pregnancy can cause congenital rubella syndrome (cataracts, congenital heart disease, deafness, microcephaly). The measles-mumps-rubella (MMR) vaccine is live and must not be given in pregnancy, but women who are not immune should be vaccinated after delivery and before any future pregnancy. Suspected infection in pregnancy is managed with serology (IgG and IgM) and, where needed, referral. ^[5]

CMV is the most common congenital infection and the leading infectious cause of sensorineural hearing loss and neurodevelopmental disability. Primary infection in 1 to 4% of pregnant women is most dangerous when it occurs in the first trimester, and vertical transmission rates are roughly 30 to 42% in the first trimester, 38 to 44% in the second and 59 to 73% in the third, increasing as the placenta becomes more permeable. ^[12] Congenital CMV affects an estimated 0.2 to 2.2% of all live births, and symptomatic disease occurs in 11 to 12.7% of infected infants, with up to half of those infected in early pregnancy having disease. ^[12]

Routine universal CMV screening is not yet standard in many countries, including the United Kingdom; hygienic measures are the main primary prevention: thorough handwashing after nappy changes and contact with young children's saliva, avoiding sharing food or utensils, and avoiding kissing young children on the mouth. ^[12] For women with confirmed primary CMV in early pregnancy, valaciclovir 8 g per day (given as 2 g four times daily) reduced the rate of positive amniocentesis for CMV from 30% to 11% in a randomised trial (odds ratio 0.29, 95% confidence interval 0.09 to 0.90). ^[12] Diagnosis in pregnancy uses serology (IgG, IgM, avidity) and, where needed, amniocentesis for CMV DNA at least 6 to 8 weeks after presumed infection and after 20 weeks gestation; specialist involvement is essential.

Most maternal infections are mild (slapped-cheek rash, arthralgia, fever), but the virus can infect the fetal bone marrow and cause severe anaemia and hydrops fetalis. Pregnant women exposed to or infected with parvovirus B19 are managed by serology (IgG and IgM) and serial ultrasound for fetal middle cerebral artery Doppler to detect anaemia; intrauterine transfusion is life-saving in severe fetal anaemia. ^[5]

In pregnancy, varicella can cause congenital varicella syndrome (with infection up to 28 weeks), shingles in infancy (infection between 20 and 37 weeks) and neonatal chickenpox (infection after 36 weeks). Pregnant women should avoid contact with suspected chickenpox where possible. A pregnant woman with a varicella rash is treated with oral aciclovir 800 mg five times daily or valaciclovir 1 g three times daily for 7 days; severe disease requires intravenous aciclovir. ^[5] Post-exposure measures have shifted from varicella zoster immune globulin toward oral antivirals in the United Kingdom's 2025 guidance. Non-immune women should be offered varicella vaccine after delivery. ^[5]

Influenza is more severe in pregnancy and increases the risk of preterm birth. Inactivated influenza vaccine is recommended in any trimester; live attenuated vaccines are avoided. This topic also interacts with the respiratory system directly and with the respiratory topic of pneumonia.

Toxoplasma gondii is acquired mainly from undercooked meat, from soil or from cat faeces. Primary infection just before or during pregnancy can pass to the fetus; most affected infants have no signs at birth but may later develop blindness, intracranial calcification and neurological disability, and severe disease can present at birth. ^[13] Prevention advice focuses on food and cat hygiene: have someone else change the cat litter where possible, wear gloves and wash hands if not; keep cats indoors; feed cats only commercial food, not raw meat; and avoid undercooked meat, unpasteurised foods and unwashed produce. ^[13] Treatment decisions use spiramycin (and, in confirmed fetal infection, pyrimethamine-sulfadiazine with folinic acid) directed by local specialists.

In endemic regions malaria is a major cause of maternal anaemia, low birth weight and perinatal death. The WHO recommends intermittent preventive treatment in pregnancy (IPTp) with sulfadoxine-pyrimethamine in malaria-endemic areas, with current guidance covering women of all gravidities and earlier (pre-2024) guidance targeting first and second pregnancies; dosing starts as early as possible in the second trimester (not before week 13 of pregnancy) and continues at least one month apart to achieve at least three doses. ^[11] Antifolate components are contraindicated in the first trimester. Uncomplicated malaria is treated with artemisinin-based combination therapy appropriate to trimester and species; severe malaria with parenteral artesunate. Insecticide-treated bed nets, prompt treatment of febrile illness and, where appropriate, iron and folate are the associated measures. ^[11]

Many of the infections above present in similar ways, so a structured approach is safer than pattern-matching.

Notify the health protection team promptly when measles or rubella is suspected in pregnancy, and isolate pregnant women with a suspected viral rash from other pregnant women until assessed. ^[5]

Principles supported across guidelines: screen every pregnancy for HIV, syphilis, HBV and HCV; screen for chlamydia, gonorrhoea and TB when risk exists; give seasonal influenza vaccine in any trimester; give tetanus and other indicated vaccines; advise food and animal hygiene to prevent listeria and toxoplasma; offer GBS risk-based care and IAP; and give the mother and her household postpartum vaccination where needed (MMR, varicella). ^{[1][5][11][13]}

Women living with HIV. Multidisciplinary care (HIV physician, obstetrician, paediatrician, midwife) from conception; standard pregnancy ultrasound; avoid invasive prenatal testing until the viral load is suppressed where possible; neonatal ART prophylaxis and early diagnostic testing. ^[8][9]

Women who are immunocompromised. Reactivation of CMV, toxoplasmosis and TB can occur; screening and prophylaxis (for example, against Pneumocystis and toxoplasmosis) follow local HIV or immunosuppression protocols.

Women in high-prevalence settings. Syphilis retesting late in pregnancy, third-trimester HIV retesting, TB risk assessment and malaria IPTp are the single most cost-effective interventions. ^[1][7][11]

Families and contacts. Strict food hygiene, hand hygiene after contact with small children, and vaccination of household members and older siblings protect the pregnant woman before pregnancy ends.

• Rapid HIV and syphilis point-of-care tests at the first visit (and at delivery if no prior screen) prevent the majority of vertical transmissions.
• HBV vaccine with HBIG for the infant is the single intervention that interrupts peri-natal HBV infection; even where HBIG is unavailable, birth-dose vaccine given within 24 hours reduces transmission significantly.
• Penicillin G for syphilis and antenatal corticosteroids where preterm birth is likely are usually available and cheap; the barriers are access and testing, not drugs.
• Where malaria is endemic, insecticide-treated nets and sulfadoxine-pyrimethamine IPTp should be integrated into routine antenatal care; artemisinin-based treatment is restricted in the first trimester and the first-line drugs available differ.
• Listeria and toxoplasma advice costs nothing: food hygiene and avoiding cat litter handling.
• Women with TB should be treated without delay; lack of sputum culture or radiography should not delay presumptive treatment in typical cases.

Infections in pregnancy can lead to miscarriage, stillbirth, fetal growth restriction, preterm labour and birth, neonatal sepsis and congenital infection with long-term disability. The specific complications of each infection are discussed in the relevant section above.

With modern screening and treatment, perinatal transmission rates for HIV fall below 2%, syphilis-related stillbirth is prevented in most adequately treated pregnancies, HBV transmission is prevented in the majority of infants receiving birth-dose vaccine and HBIG, and GBS early-onset disease is reduced by intrapartum antibiotics. Outcomes remain worse where access to antenatal care is limited, which is why access and testing usually matter more than drug choice.

Screening, treatment, intrapartum prophylaxis and newborn prophylaxis (vaccines, antiretroviral drugs, testing and follow-up) are the four layers. Education about food and animal hygiene and vaccination of women who are not immune (MMR, varicella, influenza) outside pregnancy complete the picture.

• Screen every pregnancy for HIV, syphilis, HBV and HCV at the first visit; add chlamydia, gonorrhoea and targeted TB screening from risk.
• Vertical transmission is prevented in four layers: screen the mother, treat her, give prophylaxis around birth and protect the newborn.
• HIV: without ART 15 to 40% of infants acquire infection; with early ART and suppression, under 2%. Regimen is two nucleoside drugs plus dolutegravir or darunavir/ritonavir.
• Syphilis: penicillin G is the only drug that reliably treats the fetus; desensitise allergic women; retest at 28 weeks and delivery when risk continues.
• HBV: birth-dose vaccine plus HBIG in the first hours prevents most perinatal transmission; 90% of infants infected at birth become chronically infected.
• HCV: no in-pregnancy prophylaxis; screen, deliver normally unless obstetric reasons, and test the infant at 2 to 6 months.
• GBS: colonises 20 to 40% of adults; intrapartum benzylpenicillin 3 g then 1.8 g every 4 hours, effective only if started at least 4 hours before delivery. ^[4][14]
• CMV: most common congenital infection; hygiene advice is the main prevention; valaciclovir 8 g per day reduces vertical transmission in early primary infection.
• Toxoplasmosis: prevention is food and cat hygiene; primary infection just before or during pregnancy risks later blindness or brain damage in the child.
• Listeriosis: a mild or absent illness in the mother can still cause miscarriage or stillbirth; food avoidance and early treatment save lives.
• Malaria: IPTp with sulfadoxine-pyrimethamine in endemic areas; start in the second trimester, never before week 13.
• Active TB in pregnancy should be treated immediately; latent TB can usually wait until after delivery.
• Suspected viral rash in pregnancy, especially measles or rubella, should be reported to health protection services and the woman isolated from other pregnant women.
• Local protocols differ: never quote a dose or screening policy without checking the guideline in use locally.

HIV infection · Syphilis · Hepatitis B · Hepatitis C · Tuberculosis · Malaria · Toxoplasmosis · Cytomegalovirus · Rubella · Varicella · Listeriosis · Urinary tract infection in pregnancy · Neonatal sepsis · Antenatal care · Intrapartum care · Fetal growth restriction · Preterm labour · Stillbirth.