Part 1 Science Notes
MRCOG Part 1
Microbiology
Microbiology and Infections in Obstetrics and Gynaecology
TORCH Infections
| Infection | Organism | Key Fetal Effects | Diagnosis | Prevention/Treatment |
|---|---|---|---|---|
| Toxoplasma | Toxoplasma gondii (protozoan) | Hydrocephalus, intracranial calcification, chorioretinitis; risk increases with gestation (but severity decreases) | Maternal IgM/IgG seroconversion; PCR of amniotic fluid | Avoid undercooked meat, cat litter; spiramycin (reduces transmission); pyrimethamine + sulfadiazine (if fetal infection) |
| Rubella | Rubella virus | Congenital rubella syndrome: deafness, cataracts, cardiac defects (PDA, pulmonary stenosis), microcephaly; highest risk <12 weeks (>80% affected) | IgM/IgG; rubella-specific IgM | MMR vaccination (pre-conception); avoid in pregnancy (live vaccine); no treatment available |
| CMV | Cytomegalovirus | Most common congenital infection; sensorineural hearing loss, microcephaly, hepatosplenomegaly, petechiae, periventricular calcification; 90% asymptomatic at birth but 10-15% develop late sequelae | Maternal seroconversion (IgM/IgG avidity); PCR of amniotic fluid; neonatal urine PCR | No vaccine; hygiene measures; valaciclovir may reduce transmission (emerging evidence) |
| HSV | Herpes simplex virus (1 and 2) | Neonatal herpes: skin/eye/mouth disease, encephalitis, disseminated infection; highest risk with primary maternal infection at delivery (~40%) | Clinical + viral PCR of lesions | Primary in 3rd trimester: caesarean delivery + IV aciclovir; recurrent: oral aciclovir from 36 weeks, vaginal delivery usually safe |
| Syphilis | Treponema pallidum (spirochaete) | Congenital syphilis: stillbirth, hydrops, hepatosplenomegaly, rash, snuffles, Hutchinson's teeth, saddle nose, sabre shins | Screening: EIA/TPHA/TPPA; confirmed RPR/VDRL + specific test | Penicillin (benzathine penicillin G IM); Jarisch-Herxheimer reaction possible |
| Parvovirus B19 | Erythrovirus | Fetal anaemia → hydrops fetalis → intrauterine death; aplastic crisis; highest risk 9-20 weeks | Maternal IgM; fetal USS for hydrops; MCA Doppler for anaemia | No vaccine; intrauterine transfusion for severe anaemia; self-limiting in immunocompetent adults |
| VZV | Varicella zoster virus | <20 weeks: congenital varicella syndrome (skin scarring, limb hypoplasia, eye defects, CNS) — risk ~1%; peripartum: severe neonatal varicella (5 days before to 2 days after delivery) | Clinical diagnosis; IgM/IgG if uncertain | VZIG for non-immune exposed pregnant women within 10 days; aciclovir for maternal chickenpox; avoid contact with active varicella/zoster |
Group B Streptococcus (GBS)
- Streptococcus agalactiae; carried in vagina/rectum by 20-30% of women
- Neonatal GBS disease: early-onset (<7 days, usually <48h) — septicaemia, pneumonia, meningitis
- UK does NOT have universal screening (RCOG guideline); risk-factor based approach:
- GBS bacteriuria in current pregnancy
- Previous infant with GBS disease
- Preterm labour (<37 weeks)
- Prolonged rupture of membranes (≥18 hours)
- Maternal pyrexia in labour (≥38C)
- Intrapartum antibiotic prophylaxis: IV benzylpenicillin (first-line) or clindamycin (penicillin allergy)
- Give at onset of labour; redose every 4 hours until delivery
Sexually Transmitted Infections in Pregnancy
Chlamydia (Chlamydia trachomatis)
- Most common bacterial STI in UK; often asymptomatic
- Neonatal: ophthalmia neonatorum (conjunctivitis), pneumonia
- Treatment in pregnancy: azithromycin 1g single dose (first-line) or erythromycin
- Avoid doxycycline in pregnancy (teeth staining, bone growth inhibition)
Gonorrhoea (Neisseria gonorrhoeae)
- Neonatal: ophthalmia neonatorum (purulent, severe — can cause blindness)
- Treatment: IM ceftriaxone 1g single dose
- Test of cure required
HIV
- Vertical transmission rate: ~25% without intervention; <1% with optimal management
- Management: combination antiretroviral therapy (cART) throughout pregnancy
- Viral load <50 copies/ml at 36 weeks: vaginal delivery safe
- Viral load >400 copies/ml: planned caesarean at 38 weeks
- Avoid breastfeeding in UK (different in resource-limited settings)
- Neonatal: PEP (post-exposure prophylaxis) with zidovudine for 4 weeks
Hepatitis B
- Routine antenatal screening (HBsAg)
- High infectivity: HBeAg positive, high viral load
- Neonatal: HBV vaccine + HBIG within 12 hours of birth
- Consider maternal tenofovir if high viral load (>200,000 IU/ml) from 28-32 weeks
- Breastfeeding safe if baby vaccinated
Bacterial Vaginosis (BV)
- Overgrowth of anaerobic organisms (Gardnerella vaginalis, Mycoplasma hominis) replacing normal lactobacilli
- Diagnosis:
- Amsel criteria (3 of 4): thin grey homogeneous discharge, clue cells on wet mount, positive whiff test (amine odour with KOH), vaginal pH >4.5
- Nugent score: Gram stain scoring system (0-10; ≥7 = BV)
- Association with preterm birth, PPROM, second-trimester miscarriage, post-surgical infection
- Treatment: metronidazole (oral or vaginal); safe in pregnancy (avoid alcohol)
- Screening and treatment of asymptomatic BV in pregnancy: NOT routinely recommended (evidence for reducing preterm birth is inconsistent)
Sepsis in Obstetrics
- Leading cause of direct maternal death in the UK
- Common organisms: Group A Streptococcus (Strep pyogenes — most dangerous), E. coli, GBS, Staphylococcus aureus, anaerobes
- MEOWS (Modified Early Obstetric Warning Score): adapted for pregnancy; tracks pulse, BP, temperature, respiratory rate, consciousness
- Sepsis recognition: tachycardia, hypotension, pyrexia (or hypothermia), tachypnoea, altered consciousness, reduced urine output
- Management: Sepsis Six within 1 hour — oxygen, blood cultures, IV antibiotics, IV fluids, lactate measurement, urine output monitoring
- Source identification: genital tract, urinary tract, breast, wound, respiratory
Important Facts for MRCOG
- CMV: most common congenital infection; sensorineural hearing loss
- Rubella: highest risk <12 weeks; deafness, cataracts, cardiac defects
- Parvovirus B19: fetal anaemia and hydrops; treat with IUT
- GBS prophylaxis: IV benzylpenicillin in labour (risk-factor based in UK — no universal screening)
- Chlamydia: azithromycin in pregnancy (NOT doxycycline)
- HIV: cART + viral load <50 → vaginal delivery safe; avoid breastfeeding in UK
- BV: Amsel criteria or Nugent score; associated with preterm birth
- Group A Strep: most dangerous cause of puerperal sepsis
- Sepsis Six within 1 hour: oxygen, cultures, antibiotics, fluids, lactate, urine output
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