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High-risk infections in pregnancy

High-risk infections in pregnancy

Key learning points

  • Not all infections have signs and symptoms but they can still cause physical and neurological problems in newborns
  • Viruses can be transmitted through unprotected sex, direct contact with infected blood, sharing infected needles, perinatal mother-to-baby contact or breastfeeding
  • Certain infections can occur at any stage of pregnancy and may result in miscarriage, pre-term labour or stillbirth

Infections in pregnancy can be transmitted to the newborn. Early detection can reduce and prevent transmission. Some infections will not have signs and symptoms but they can still cause physical and neurological problems to the newborn.

Hepatitis B, HIV and syphilis screening are part of routine antenatal screening in pregnancy in the UK. Treatment is available to prevent and reduce the risk of mother-to-child transmission.

Group B streptococcus (GBS) screening in pregnancy is not currently recommended as part of the UK National Screening Committee (NSM). Early onset GBS infection rate is increasing in the UK, and late onset infections are rising even faster. Maternal GBS bacteraemia is an indicator for intrapartum antimicrobial prophylaxis (IAP).

Hepatitis B

All pregnant women are offered screening for hepatitis B as part of routine antenatal care. 

The hepatitis B virus is an infectious inflammatory illness of the liver. Hepatitis B is very infectious and is present in all body fluids such as vaginal secretions, semen, blood and saliva.

The virus can be transmitted through unprotected sex, direct contact with infected blood, perinatal transmission from mother to baby and sharing infected needles.

An acute hepatitis B (newly acquired infection) may last up to six months with or without symptoms. Symptoms, if they exist, may include loss of appetite, joint and muscle pain, low-grade fever and stomach pain. Most people do not experience initial symptoms but develop them one to four months after exposure.

In people who acquire infection during adulthood, around 90% will clear the infection spontaneously after several weeks, will no longer be infectious to others and are immune to re-infection. Acute infection may occasionally lead to fulminant hepatic necrosis, which is often fatal.1,2

Chronic hepatitis B refers to infection that fails to clear within six months. The risk of developing chronic hepatitis B infection depends on the age at which infection is acquired. Chronic infection occurs in 90% of those infected perinatally but is less frequent in those infected as children. 

Once the infection becomes chronic it is unlikely to rectify and the affected person then becomes a lifelong carrier. Around 20-25% of individuals with chronic hepatitis B virus infection develop liver disease, leading to cirrhosis. This will increase the risk of developing hepatocellular carcinoma.2

Post-exposure immunisation is provided to infants born to hepatitis B-infected mothers. Babies who are at risk should be given the hepatitis B vaccine and immunoglobulin if required at birth.2 The first dose is given within 24 hours of birth, followed by a dose four and eight weeks later and a further dose at one year of age. 


HIV is a retrovirus which, left untreated, leads to immunosuppression and eventually to AIDS. There is no cure for HIV as yet.

HIV is present in all body fluids such as breast milk, vaginal secretions, semen and blood. HIV can be transmitted through unprotected sexual intercourse, direct contact with blood of an infected person, mother-to-child infection during pregnancy, at birth or when breastfeeding, and when sharing infected needles.

People with HIV may have a short illness soon after getting the virus, but can then feel well for a long time. Most people will only notice further symptoms of HIV after a few years. The most common symptoms of seroconversion (the period when HIV antibodies develop and become detectable) are:

  • Sore throat.
  • Fever.
  • Rash over the body.

HIV attacks the T-helper cells (CD4 cells), the white cells that play an essential part the human immune system.1 When HIV  enters the body it replicates inside the CD4 cells to produce HIV virons. 

Vertical transmission (mother to child) of HIV is rare now in the UK with routine antenatal screening, antiretroviral treatment and advice to avoid breastfeeding. Transmission rates in mothers who have been diagnosed early in pregnancy with effective antiretroviral treatment and viral suppression are now estimated to be less than 0.5%. The newborn is also given a short course of antiretroviral medication. The risk of mother-to-child transmission in an untreated mother is around 25%.1,3


Syphilis is an infectious disease caused by an infection with the spirochete bacterium Treponema pallidum. It is transmitted by direct contact with an infectious lesion or by vertical transmission (transplacental passage) during pregnancy. Site of bacterial entry is typically genital, anal or oral.4

Syphilis infection progresses in stages according to the duration of infection. Without treatment syphilis can progress through four stages:

  • Primary and secondary, where a person is symptomatic and highly infectious.
  • Latent (early/late), where the infection is found at lower levels.
  • Tertiary, where syphilis re-activates and serious health complications are common.

Syphilis screening is a part of routine antenatal screening and pregnant women are recommended to take the test.

In pregnancy syphilis may be transmitted transplacentally at any stage and may result in miscarriage, pre-term labour, stillbirth and congenital syphilis. The risk of transmission in primary syphilis ranges from 70-100%, in early latent syphilis it is 40% and in late latent syphilis the risk is 10%.1

Approximately two-thirds of babies with congenital syphilis will be asymptomatic at delivery but most will develop symptoms by five weeks. Untreated congenital syphilis can result in physical and neurological impairments affecting the infant’s teeth, vision, hearing and bones.

Pregnant women who test positive will require a complete sexual health assessment and examination by the genitourinary medicine team. This will enable the health professionals to determine the stage of the infection and identify any health problems.

Expectant mothers with acute infection or inadequately treated previous infection will need treatment. A single dose of benzathine penicillin is effective in most cases.1

Group B streptococcus (GBS)

GBS is a bacterium carried harmlessly in the vagina. It is also found in the genital and gastrointestinal tracts of both men and women. GBS carried in this way can be difficult to detect, does not cause any symptoms and is considered normal.5

It is estimated that 15-30% of pregnant women are colonised with GBS. A third to half of the babies born to these women are colonised with GBS; 2-3% of colonised babies will develop invasive GBS infection such as pneumonia, septicaemia or meningitis.

Two-thirds of invasive infections in infants occur in the first seven days after birth (early onset GBS infection, EOGBS). Most of the remainder present seven to 90 days after birth (late onset invasive GBS infections, LOGBS). Between 70% and 90% of EOGBS can be prevented by IAP.

The Royal College of Obstetricians and Gynaecologists (RCOG) Green Top Guideline 36, established in 2003, provides advice to obstetricians, midwives and neonatologists on the prevention of EOGBS disease.

The guideline recommends a risk-based prevention approach for offering IAP. However, even with this, EOGBS infections continue to rise and there is no preventive management for LOGBS.6

Expectant mothers should be given IAP if they have a previous history of a baby with GBS infection, a vaginal swab positive for GBS in current pregnancy, urinary infection with GBS in current pregnancy, chorioamnionitis or fever during labour. 

GBS screening in pregnancy is not currently recommended as part of the UK National Screening Committee. However, the National Institute for Health Research Health Technology Assessment Programme is currently inviting applicants from NHS settings to take part in a research proposal to look at the clinical and cost effectiveness of screening for GBS in pregnancy.7

In September, the Royal College of Obstetricians and Gynaecologists (RCOG) released a new guideline, stating that all women who go into labour before 37 weeks should be offered antibiotics to protect their baby against GBS.8


    1 Public Health England. NHS Infectious Diseases in Pregnancy Screening Programme Handbook 2016 to 2017 

    2 Public Health England, Department of Health. Immunisation against infection disease: Hepatitis B 2013;18:1-2

    3 De Ruiter A, Taylor G, Clayden P et al. British HIV Association guidelines for management of HIV infection in pregnant women 2012 (2014 interim review). HIV MED 2014;15 Suppl4:1-77

    4 Kingston M, French P, Higgins S et al. UK national guidelines on the management of syphilis 2015. International Journal of STD & AIDS 2016;27:421-46

    5 Roa G, Nartey G, McAree T et al. Outcome of a screening programme for the prevention of neonatal invasive early-onset group B Streptococcus infection in a UK maternity unit: an observational study. BMJ Open 2017;7:e014634

    6 Royal College of Obstetricians and Gynaecologists. The prevention of early-onset Neonatal Group B Streptococcal Disease. Green Top Guideline No 36. 2nd ed. RCOG Press 2012

    7 O’Suillivan C, Lamagni T, Efstratiou A et al. Group B Streptococcal disease in UK and Irish infants younger than 90 days, 2014-2015. Arch Dis Child 2016;101(A2)

    8 Royal College of Obstetricians and Gynaecologists. Group B Streptococcal Disease, Early-onset. Green Top Guideline No 36. 3rd edition. RCOG Press 2017


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    Infections in pregnancy can be transmitted to the newborn. Some will not have signs and symptoms but they can still create physical and neurological problems for the baby.