Infection Screening in Pregnancy

Question 1

What is the #1 cause of congenital abnormality?

Answer 1

CMV

Question 2

What is vertical transmission?

Answer 2

Passage of virus from mother to fetus

Question 3

How can vertical transmission occur?

Answer 3

1) During pregnancy
2) During delivery
3) Postnatally i.e close contact with mother, breast milk

Question 4

What are the maternal determinants of vertical transmission?

Answer 4

1) Anatomical changes in genital tract
2) Hormonal changes - direct effects on viral replication?

Question 5

What are the viral determinants of vertical transmission?

Answer 5

1) Dose of virus
* increased risk of transmission primary CMV, HSV
* high viral loads, HIV, Hep C

2) Increased risk of transmission
* HepBeAg positive

3) Strain specific effects e.g CMV

4) Immunomodulating effects of the virus on the host’s immune response (CMV, HSV, HIV)

Question 6

What are the fetal determinants of vertical transmission of viruses?

Answer 6

1) Clever ways of getting across the placenta
* transplacental trafficking of maternal lymphocytes: CMV, HIV, Hep C
* transplacental trafficking of free virus (when the virus does not replicate but can still get into the foetel cells)
* Ascending infection e.g HSV through the cervix and into the uterine cavity
* Specific receptors on the placenta/growing foetus which are used by the virus to infect specific cells

2) Effect of transplacental maternal antibody
* may be insufficient or ineffective

3) Fetal immune response to the virus

Question 7

What are neonatal determinants of perinatal infection?

Answer 7

1) Exposure to large viral dose during delivery/postnatally

2) Lack of maternal Ab (transplacental and in breast milk)

3) Immature immune response of newborn to some viruses

Question 8

Which layers does the virus need to cross to get to the fetus?

Answer 8

Maternal lacunae, stromal layer, syncytiotrophoblast, endothelial cells

Question 9

What are some of the key clinical manifestations of congenital infections?

Answer 9

1) Jaundice
* CMV, toxo, rubella, HSV, syphillis, Hep B

2) Purpura
* usually appears on the first day
* CMV, toxo, rubella, HSV, syphillis

3) Hepatosplenomegaly
* CMV, toxo, HSV, syphillis, coxsackle

Question 10

What are some congenital eye abnormalities?

Answer 10

1) Cataracts
* Rubella, VZV, toxo, CMV & HSV (rare)

2) Chorioretinitis
* Rubella (generalised), toxo, CMV, HSV, VZV, syphilis

3) Glaucoma
* Rubella, syphilis

4) Keratoconjunctivitis
* HSV

Question 11

What are some orthopaedic/cardiac signs of congenital abnormality?

Answer 11

1) Bone lesions
* Rubella (radiolucencies), syphillis (osteitis), toxo

2) Congenital heart disease
* Rubella
* CMV
* Mumps (not proven)

Question 12

What are some CNS signs?

Answer 12

1) Seizures, encephalitis
* HSV
* Enterovirus

2) Cerebral calcification (CT)
* CMV
* VZV
* HSV
* Toxoplasmosis

Question 13

What are some maternal indications for testing the newborn?

Answer 13

History:
* maternal illness
* maternal exposure (work, child in day care)
* premature infant
* parents with STD
* parent with high risk behaviour
* adolescent mother
* no antenatal care

Question 14

What are some physical examination (early life) indications for testing?

Answer 14

• Prematurity
• Microcephaly
• SGA
• Unexplained hydrocephalus
• Ocular findings
• Unexplained jaundice

Question 15

What are some appropriate specimens for testing?

Answer 15

• Urine
• Throat swab
• Neonatal serum (paired)
• Maternal serology
• CSF
• Skin lesions
• Stool
• Placenta

Question 16

What are the ways of diagnosing congenital infection?

Answer 16

1) Direct
* NAT (Nucleic Acid Testing)
* IFA (immunofluorescence)
* Culture

2) Indirect
* Serology IF, CFT, EIA
* EM (electron microscopy)

Question 17

Other than urine, what else is sampled?

Answer 17

Saliva, self-administered swabs, dried blood spots (CMV DNA) and air dried swabs