What is the likely diagnosis and treatment for a pregnant woman presenting with vaginal discharge and a fishy odor?

Bacterial Vaginosis in Pregnancy: Diagnosis and Treatment

Bacterial vaginosis (BV) is the most likely diagnosis for a pregnant woman presenting with vaginal discharge and fishy odor, and oral metronidazole is the recommended treatment during pregnancy to reduce the risk of adverse pregnancy outcomes.

Diagnosis of Bacterial Vaginosis

BV is the most prevalent cause of vaginal discharge and malodor in women of reproductive age 1. The diagnosis requires meeting at least three of the following four clinical criteria (Amsel criteria):

1. Homogeneous, white discharge that smoothly coats the vaginal walls
2. Presence of clue cells on microscopic examination - a key diagnostic feature
3. Vaginal fluid pH >4.5
4. Fishy odor before or after addition of 10% KOH (positive whiff test)

Diagnostic Accuracy

• Clue cells on microscopic examination are highly specific for BV but are not the sole diagnostic criterion 1
• The fishy odor is a characteristic feature of BV, particularly noted in recent studies 2
• Gram stain of vaginal secretions (Nugent score) is an acceptable laboratory method for diagnosing BV 1

Common Pitfalls in Diagnosis

• BV is often confused with other vaginal infections such as trichomoniasis or candidiasis
• Up to 50% of women with BV may be asymptomatic 1
• Culture of G. vaginalis is not recommended as it lacks specificity 1
• Cervical Pap tests have limited utility for BV diagnosis due to low sensitivity 1

Treatment in Pregnancy

For pregnant women with BV, oral metronidazole is the drug of choice 1:

Recommended Treatment Regimens:

• Metronidazole 500 mg orally twice daily for 7 days 1

Rationale for Treatment During Pregnancy:

1. Reduces risk of adverse pregnancy outcomes including:

   • Premature rupture of membranes
   • Preterm labor and delivery
   • Postpartum endometritis 1, 3, 4

2. Relieves vaginal symptoms and signs of infection 1

3. May reduce risk for other infections (e.g., other STDs or HIV) 1

Special Considerations in Pregnancy

• BV during pregnancy is associated with significant adverse outcomes, with recent evidence showing 11.1% prevalence in the third trimester 2
• Women with previous preterm birth or abortion/miscarriage are at higher risk and may benefit most from treatment 3, 2
• All pregnant women with symptomatic BV require treatment regardless of pregnancy status 1
• High-risk pregnant women (those with previous preterm delivery) who have asymptomatic BV may be evaluated for treatment 1

Follow-up Recommendations

• Evaluate for "test of cure" one month after treatment 3
• Monitor for recurrence of symptoms
• Consider screening women with history of previous preterm birth or miscarriage 2

Important Clinical Correlations

• BV is associated with increased risk of chorioamnionitis, fetal infection, and cervical dysplasia 5, 4
• The pathology appears to result from inflammation, though the exact mechanism needs further investigation 4
• BV can co-occur with other vaginal infections such as candidiasis 5, 2

BV is not merely a nuisance infection but has significant implications for maternal and fetal health during pregnancy. Early diagnosis and appropriate treatment with metronidazole can significantly reduce these risks.