Antenatal Infections and their Consequences

Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

See also: Rubella (German Measles) and Pregnancy written for patients

Certain maternal infections can have serious long-term consequences for the fetus.

Rubella is a viral infection causing a pink rash, with swelling of lymph glands behind the ears and at the back of the head. There are mild constitutional symptoms and occasionally joint pain in adults.


With a rubella-like rash, test for rubella and parvovirus B19 (even if reported to be immune); test serum for IgG and IgM and repeat if results are equivocal. Rising levels suggest recent infection (consult a virologist).

Evidence of infection should be discussed with the patient with a view to considering termination.

Prevention is by measles, mumps and rubella (MMR) vaccine in the second year of life plus a pre-school booster, with antenatal screening for rubella susceptibility.


If rubella is contracted within the first 11 weeks of pregnancy there is a 90% chance of the fetus being affected. This falls to 20% during weeks 11-16. In weeks 16-20 there is a slight risk of deafness and, after that, no increased risk.

Fetal defects associated with fetal rubella syndrome include:

Chickenpox is characterised by fever, malaise and a pruritic rash that develops into crops of maculopapules, which become vesicular and crust over before healing. The incubation period is 7-21 days and the disease is infectious 48 hours before the rash appears and continues to be infectious until the vesicles crust over (usually within 5-6 days of onset of illness).[2]

More than 90% of the antenatal population are seropositive for varicella IgG antibody, so although contact with chickenpox is common in pregnancy, primary infection is uncommon. It is estimated to complicate three in every 1,000 pregnancies.[3]


Of exposure to chickenpox:

  • Establish whether the mother is immune. Immunity can be assumed if there is history of chickenpox or shingles.
  • If there is any doubt, request antibody levels urgently (varicella-zoster IgG antibodies).
  • Liaise with local microbiology for advice and to expedite results.
  • Varicella-zoster immunoglobulin (VZIG) may be indicated.

Of chickenpox in pregnancy:

  • Seek specialised advice urgently about the need for counselling on the risk of fetal complications, antiviral treatment and follow-up.
  • Monitor the patient closely for complications. Admit if they are systemically unwell or if they develop complications.


  • In adults, chickenpox is associated with greater morbidity - pneumonia (10% of pregnant women), hepatitis and encephalitis.
  • It may also cause fetal varicella syndrome (FVS), previously known as congenital varicella syndrome or varicella infection of the newborn.

Before 20 weeks of gestation

  • Chickenpox in the first trimester does not increase the risk of spontaneous miscarriage.[3]
  • FVS is characterised by one or more of the following:
    • Skin scarring in a dermatomal distribution.
    • Microphthalmia, chorioretinitis and cataracts.
    • Hypoplasia of the limbs.
    • Neurological abnormalities - eg, microcephaly, cortical atrophy, intellectual disability, and dysfunction of bowel and bladder sphincters.
  • The risk of FVS if a mother develops chickenpox is approximately 0.2% under 13 weeks of gestation, and 2% at 13-20 weeks of gestation.[4]

20-36 weeks of gestation

  • This does not appear to be associated with adverse effects in the fetus.
  • It may present as shingles in the first few years of infant life.

After 36 weeks

  • Up to 50% of babies are infected, and approximately 23% of these develop clinical varicella despite high titres of passively acquired maternal antibody.
  • The most severe chickenpox occurs if the infant is born within seven days of onset of the mother's rash.

Cytomegalovirus (CMV) is a common viral infection, which is usually mild or asymptomatic in healthy individuals. It may cause a febrile illness or have complications, and congenital CMV is the most common congenitally acquired infection in infants. There is no vaccination, and because it is such a common virus, the only precaution is normal good hygiene advice.


  • CMV is estimated to affect 1,800 births per year in England and Wales.
  • There is a 30-40% risk of intrauterine transmission, and a 20-25% risk of postnatal sequelae if the fetus has been infected. Because there is a good chance the baby will be unharmed, termination is not usually advised.
  • The diagnosis can be made antenatally by amniocentesis at least seven weeks after infection and after 21 weeks of gestation. If infection is confirmed, ultrasound is performed regularly to monitor for complications.
  • The effect on the fetus is more severe from a primary infection.
  • Congenital CMV can be treated with some benefit with ganciclovir.
  • Effects on the neonate include:
    • Intrauterine growth restriction and low birth weight
    • Hepatosplenomegaly
    • Jaundice
    • Thrombocytopenia
    • Anaemia
    • Petechiae and/or purpura
    • Microcephaly
    • Intracranial calcifications
    • Choroidoretinitis
    • Deafness
    • Speech defects
    • Mental impairment, which may appear later
    • Psychomotor delay
    • Visual impairment
  • At birth, babies may appear normal, but hearing defects and intellectual disability may become apparent later in life.

Parvovirus B19 is common with an estimated 50-60% of adults having been infected. Infection with parvovirus B19 has a number of manifestations including:

  • Minor febrile illness
  • Slapped cheek disease
  • Generalised rash similar to rubella
  • Arthropathy

Parvovirus IgM and IgG testing should be done if there is suspicion of exposure or infection, and specialised advice sought.


  • Infection in the first 20 weeks of pregnancy carries an increase of 9% in the risk of intrauterine death, and a 3% risk of hydrops fetalis. Of these, 50% die. Intrauterine transfusion reduces mortality rate.
  • These events usually occur 3-5 weeks after the onset of maternal infection.
  • Very rarely, permanent congenital abnormalities and anaemia have been identified. Generally the neonate is unaffected.

Measles became rare in the UK with the introduction of the MMR vaccine, but incidence has risen in recent years due to reduced vaccine uptake following adverse media coverage.

Clinical features include a disseminated maculopapular rash, coryza and conjunctivitis. Complications include pneumonia, otitis media and encephalitis.


Measles is uncommon in pregnancy, but may be associated with increased risk of maternal morbidity, intrauterine death, premature labour, and (rarely) neonatal subacute sclerosing panencephalitis (SSPE).


If exposure is suspected, and there is no history of vaccination or immunity against measles, testing of measles IgG is advised. If not detected, human normal immunoglobulin (HNIG) can be given. This may not prevent measles but it may attenuate the illness. It is not known if it protects against intrauterine death or preterm delivery.

Infection with the parasite Toxoplasma gondii, with the cat as its definitive host.

Primary infection with toxoplasmosis is often subclinical, but there may be a nonspecific illness (fatigue, headaches, muscle pains, low-grade fever), or isolated lymphadenopathy. It can be confirmed through serological testing, and presence of intrauterine spread tested by amniocentesis.


This is by a specialist. Spiramycin throughout pregnancy is used for fetal prophylaxis, with regular ultrasound examination of the fetus. Where infection is confirmed, pyrimethamine, sulfadiazine and folinic acid are used.


The greatest risk of transmission is in the third trimester, but consequences are most severe if acquired in the first trimester. There are many different forms of presentation:

  • Systemic disease of the neonate:
  • Neurological disease:
    • Hydrocephalus; due to stenosis of the duct of Sylvius requiring shunt
    • Microcephaly
    • Microphthalmia
    • Retinochoroiditis
    • Cerebral calcification
  • Mild disease; a small area of retinochoroiditis or slight cerebral calcification without signs of brain damage.
  • Subclinical.
  • Relapsing; retinochoroiditis as flare-ups can occur at any age, most cases in a previously intact retina.

Pelvic inflammatory disease (PID) includes infections of the upper genital tract and is commonly caused by sexually transmitted infections. Chlamydia trachomatis and Neisseria gonorrhoeae have been identified as causative agents, but only account for a quarter of cases in the UK. Gardnerella vaginalis, anaerobes and other organisms may be involved.

PID presents with lower abdominal pain and tenderness. It may also present with dyspareunia, abnormal vaginal bleeding and/or discharge. Many cases are asymptomatic.


Pregnant women with PID should be admitted for IV antibiotics:

  • None of the evidence-based antibiotic regimens are of proven safety in pregnancy. Benefit may outweigh risk.
  • Ceftriaxone has not specifically been studied during pregnancy. However, the risk associated with use of cephalosporins during pregnancy is thought to be low and, although data are limited for individual agents such as ceftriaxone, the cephalosporins as a class are considered to be an appropriate choice during pregnancy.
  • Doxycycline is contra-indicated beyond the 15th week of gestation because, from the 16th week of pregnancy, it causes tooth and bone discolouration and inhibits bone growth. However, it can be used in the first trimester. Inadvertent first-trimester use of tetracyclines occurs frequently and has not been associated with an increased risk of congenital malformations.
  • Metronidazole has been in clinical use for a long time, and experience suggests that it is not teratogenic in humans.
  • Ofloxacin has only limited pregnancy-exposure data.
  • There are fewer published data on the use of azithromycin rather than erythromycin during pregnancy and breast-feeding. The limited published data do not demonstrate an increased risk of congenital malformations following exposure to azithromycin in human pregnancy.
  • Current British Association for Sexual Health and HIV (BASHH) guidelines suggest following local antibiotic policy taking into account local antibiotic sensitivities, but possibly ceftriaxone plus erythromycin +/- metronidazole.


Genital herpes simplex produces patches of small, fluid-filled vesicles that burst to form shallow, painful ulcers. Initial infection is followed by recurrences and both occur as self-limiting episodes. All cases in pregnancy should be referred to a genitourinary medicine specialist for advice.[8]


  • Oral or IV aciclovir should be considered in primary infection in the first or second trimester. Daily suppression with oral aciclovir may be used from 36 weeks of gestation to reduce the chances of lesions being present at delivery.
  • Where herpes simplex virus (HSV) is contracted during the third trimester, delivery by caesarean section may be advised
  • In recurrent HSV infection, aciclovir may not be indicated. Delivery by caesarean section should be considered.


  • The risk of adverse consequences to the fetus is significantly higher in primary HSV infection than in recurrent infection.
  • Neonatal herpes is rare in the UK.
  • Congenital infection in the first half of pregnancy can cause miscarriage, stillbirth or congenital abnormalities. The perinatal mortality in this group is 50%.
  • There is, however, a greater risk of transmission when the infection is contracted in the second half of pregnancy. Infection may cause skin vesicles or scarring, eye lesions (chorioretinitis, microphthalmia, cataract), neurological damage (intracranial calcifications, microcephaly, seizures), intrauterine growth restriction or psychomotor impairment.
  • Infection contracted in labour or postnatally may cause eye, skin or mouth lesions, HSV encephalitis, or disseminated HSV with multisystem disease.

Human immunodeficiency virus (HIV) affects T lymphocytes, macrophages and monocytes with the CD4 receptor. It attacks the immune system, usually over many years, and reduces its effectiveness until an AIDS-defining illness occurs. HIV transmission to the baby is a significant problem, especially in the developing world. All pregnant women are now screened for HIV.
Maternal transmission can occur via the following routes:

  • In utero by passage of virus across the placenta
  • During delivery, from blood and placental fluids
  • From breast milk


Management is multidisciplinary, involving an HIV physician, obstetrician, paediatrician, and specialist midwife.

Transmission can be reduced by:

  • Maternal treatment with antiretrovirals
  • Appropriate management of delivery. Caesarean section may be advised, but women with low viral load may be safe to deliver vaginally.
  • Avoidance of breast-feeding.
  • Neonatal treatment with antiretroviral therapy from birth, followed by a series of HIV tests.


Vertically acquired HIV infection has decreased in recent years (now around 2%), and with treatment, mortality rates have also declined. HIV infection nevertheless has serious lifelong consequences.

Asymptomatic bacteriuria is very common in pregnant women because of the altered dynamics of the urinary tract. If untreated, this frequently progresses to urinary tract infection (UTI) - either acute cystitis (1-2%) and/or pyelonephritis.[13]The symptoms of acute cystitis are the same as in non-pregnant women:

  • Frequency
  • Urgency
  • Cloudy, smelly urine
  • Dysuria

Those of acute pyelonephritis are:

  • Pyrexia
  • Rigors
  • Flank pain
  • Nausea and vomiting
  • Headache
  • Frequency and dysuria


  • Urine should be tested by dipstick at the first antenatal visit. Confirmation if positive is with urine microscopy and culture.
  • Both asymptomatic bacteriuria and symptomatic UTI should be treated with antibiotics.
  • Refer to local guidelines for choice of antibiotic. This would usually be nitrofurantoin, trimethoprim, amoxicillin or cefalexin. Use a seven-day course and test for resolution one week after completion of treatment. Manufacturers recommend avoiding trimethoprim in the first trimester because of a theoretical teratogenic risk.[15]
  • Admission is advised for pregnant women with pyelonephritis, due to the risk of premature labour and maternal renal complications.


UTI increases the risk of premature labour and low birth weight.

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Further reading & references

  1. Rubella (German measles); Public Health England
  2. Chickenpox; NICE CKS, November 2012
  3. Chickenpox in pregnancy; Royal College of Obstetricians and Gynaecologists (September 2007)
  4. Guidance on Viral Rash in Pregnancy; Health Protection Agency (January 2011)
  5. Yinon Y, Farine D, Yudin MH, et al; Cytomegalovirus infection in pregnancy. J Obstet Gynaecol Can. 2010 Apr 32(4):348-54.
  6. Paquet C, Yudin MH; Toxoplasmosis in pregnancy: prevention, screening, and treatment. J Obstet Gynaecol Can. 2013 Jan 35(1):78-9.
  7. Management of Pelvic Inflammatory Disease; British Association for Sexual Health and HIV (2011)
  8. Herpes simplex - genital; NICE CKS, September 2012 (UK access only)
  9. Management of genital herpes; British Association for Sexual Health and HIV (2007)
  10. Straface G, Selmin A, Zanardo V, et al; Herpes simplex virus infection in pregnancy. Infect Dis Obstet Gynecol. 2012 2012:385697. Epub 2012 Apr 11.
  11. Management of HIV in Pregnancy; Royal College of Obstetricians and Gynaecologists (June 2010)
  12. Guidelines for the management of HIV infection in pregnant women (2014 interim review); British HIV Association
  13. Urinary tract infection (lower) - women; NICE CKS, October 2009
  14. Management of suspected bacterial urinary tract infection in adults; Scottish Intercollegiate Guidelines Network - SIGN (updated guidelines 2012)
  15. British National Formulary
Original Author:
Dr Hayley Willacy
Current Version:
Dr Mary Harding
Peer Reviewer:
Dr John Cox
Document ID:
4034 (v26)
Last Checked:
15 January 2014
Next Review:
14 January 2019

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.