Page created on December 21, 2021. Not updated since.
There was never a lecture on this and so much of this topic is based on Norwegian sources and UpToDate.
Group B streptococcus
Definition and epidemiology
Group B streptococci (GBS), technically streptococcus agalactiae, is a bacteria found in normal flora (GI tract, vagina) but is the most common cause of neonatal infection. 10 – 35% of pregnant women are colonised with GBS, and colonised women can transmit the bacterium to offspring. GBS bacteriuria is a sign of significant maternal GBS colonisation of the genital tract and is associated with increased risk of neonatal GBS infection, pregnancy loss, and preterm delivery.
GBS may also cause maternal infection, including cystitis or pyelonephritis. This is called GBS infection to distinguish it from simple GBS colonisation.
Which pregnant women should be screened for GBS colonisation, and whether asymptomatic GBS colonised pregnant women should receive antibiotic therapy is controversial. This is because many colonised pregnant women never transmit the bacterium to their offspring, and because eradication does not guarantee that the bacterium re-colonises the mother, among other reasons.
GBS may cause simple asymptomatic colonisation of the maternal GI tract or genital tract, or it can cause frank cystitis or pyelonephritis.
Diagnosis and screening
GBS colonisation of the genital tract and bacteriuria can be diagnosed by culture. Cystitis is defined as bacteriuria with typical cystitis symptoms, but without fever. Pyelonephritis is cystitis + fever.
Pregnant women should be screened for GBS bacteriuria. However, screening for genital and rectal colonisation (vaginal swab) is controversial and usually not performed.
Treatment and prevention
Maternal GBS infection should be treated with antibiotics. Penicillin or ampicillin are effective.
Intrapartum antibiotic prophylaxis to prevent neonatal GBS infection is indicated in case of:
- Previous neonate with GBS-infection
- GBS bacteriuria in current pregnancy
- Intrapartum fever
Other infectious diseases
Screening for several infectious diseases, including viral hepatitis, HIV, toxoplasmosis, and syphilis, is recommended during pregnancy. Untreated viral hepatitis and HIV may transmit vertically to the foetus during delivery, and toxoplasmosis and syphilis causes birth defects.
Presence of any of these infectious diseases may also affect the decision to perform invasive tests (foetal scalp electrode for CTG, foetal scalp blood sampling) as these tests may increase the risk of vertical transmission. They may also affect the decision of how labour should undergo.
Screening for these infectious diseases is recommended during routine prenatal care, especially in risk groups. More specifically, screening involves:
- Hepatitis B serology (HBsAG)
- HIV serology (antibodies, HIV antigen)
- Syphilis serology (treponemal or nontreponemal test)
- (Screening for toxoplasmosis is not recommended)
Screening should take place early in the pregnancy, to allow for plenty of time to initiate treatment and plan preventive measures.
Maternal hepatitis B infection is managed by giving the neonate HBV vaccine and passive immunisation (immunoglobulins). These reduce the risk of vertical transmission by > 95%. In case of high viral load the mother may also receive antiviral (tenofovir) to further decrease the risk.
Maternal hepatitis C infection is more difficult to handle, as there are no measures which are known to reduce the risk of vertical transmission. Ideally, hepatitis C positive women should undergo HCV eradication therapy before attempting pregnancy. Because a known diagnosis of HCV doesn’t impact any decisions in pregnancy, it’s not screened for.
Maternal HIV infection should be managed with HAART during the whole pregnancy. Most antiretroviral drugs are safe during pregnancy. Untreated pregnant women must initiate HAART as soon as possible. The mode of delivery depends on the level of HIV viraemia. If high, C-section is recommended. If low, vaginal birth is recommended. Invasive procedures should be minimised to reduce risk. HIV positivity is a contraindication to lactation.
Peripartum, HIV positive women should continue their HAART regimen as usual. Intrapartum, women with high viral levels should receive IV zidovudine as well. All infants born to mothers with HIV should receive antiretroviral postexposure prophylaxis to reduce the risk of HIV infection.
Maternal toxoplasmosis increases the risk for birth defects. As the “T” in “TORCH”, it may cause a variety of birth defects, including chorioretinitis, intracranial calcifications, hydrocephalus, epilepsy, intellectual disability, and hearing loss. If the mother is infected during pregnancy, transplacental infection of the foetus may occur.
However, the risk for transplacental transmission varies throughout the pregnancy. Maternal infection early in the pregnancy is rarely transmitted to the foetus, but when it is, the risk for serious defects is high. Maternal infection late in the pregnancy is more frequently transmitted, but the risk for serious defects is low.
Cats are the final hosts of toxoplasma gondii. Parasite cysts or eggs are found in cat faeces, which can contaminate soil, dirt, and sand. The eggs can also be ingested by other animals, forming cysts in their muscles which may end up on a plate as meat to eat.
Maternal infection is mostly asymptomatic but may cause non-specific flu-like symptoms and cervical lymphadenitis. Screening for toxoplasmosis isn’t recommended, but serology should be taken in pregnant women with typical symptoms. In case maternal toxoplasmosis is suspected, ultrasound of the foetus may show cerebral calcifications or ventricular dilation, as well as other findings.
After week 15, amniocentesis and PCR of the amniotic fluid can give the diagnosis of foetal intrauterine infection.
Maternal toxoplasmosis can be avoided by the following:
- Avoid raw meat, meat not properly heated, and unpasteurised milk
- Vegetables and fruit should be properly washed
- Avoid work with soil, dirt, and sand
- Avoiding handling cat faeces
Maternal infection is managed with antibiotics. The exact choice depends on local guidelines. The following guidelines are Norwegian (I couldn’t find Hungarian ones):
- Foetal infection not (yet) discovered or gestational week < 14: azithromycin or spiramycin
- Foetal infection documented and gestational week > 14: Combination therapy with pyrimethamine + sulphadiazine + folinic acid
Pyrimethamine and sulphadiazine are teratogenic in the first trimester and therefore not given until approx. week 14.
Syphilis is always the worst infectious disease to study, but I’ll try to keep this short and relevant.
Syphilis (Treponema pallidum infection) causes a whole range of clinical features in the untreated adult but carries risk for the foetus as well. Transmission can occur transplacentally or perinatally during birth. The risk for foetal infection is higher with early-stage than late-stage syphilis. Clinical features of congenital syphilis include:
- Spontaneous abortion
- Rash on palms and soles
- Skeletal abnormalities
- Saddle nose
- Hutchinson teeth
- Etc. (the list is endless as you know)
Screening tests for syphilis already have a high false positive rate, and this rate is even higher in pregnancy. Confirmatory tests must always be performed following a positive screening test. Ultrasound findings of congenital syphilis include hepatomegaly, placentomegaly, ascites, and hydrops. Presence of these in a syphilis-positive mother is a sign of foetal infection.
Treatment with penicillin within week 16 – 18 treats the maternal infection, reduces the risk for foetal infection, and treats any established foetal infection.
Treatment of syphilis may precipitate the Jarisch-Herxheimer reaction in any person treated for the disease. In pregnant women in the second half of pregnancy, this reaction may precipitate uterine contraction, preterm labour, or non-reassuring foetal heart rate on CTG.