top of page

Lab Investigations

Assess for GBS status. In a woman who has had preterm birth, screening for bacterial vaginosis is indicated.

 

Rupture of membranes may be assessed in a number of ways via sterile speculum exam:

 

Visual inspection includes looking for pooling in the posterior fornix. Asking the woman to cough (Valsalva maneuver) may allow visualization of amniotic fluid leaking from the cervical os.

 

Ferning

Sample fluid from posterior fornix and place on slide; let air dry for 10 minutes and examine, unstained, under a microscope.

 

Nitrazine swabs

Sample fluid from posterior fornix. Normal vaginal pH is 4.5- 6.0. Amniotic fluid pH is 7.1 - 7.3. False positive tests can occur with blood, vaginal infections, alkaline urine, and semen. High negative predictive value

 

Fetal fibronectin

Helpful between 24-34 weeks to predict risk of preterm labour.

Place in the posterior fornix for 10 seconds. Wait 30-120 minutes for result.

Predictor of preterm deliver in 7-14 days.

  • high NPV

  • low PPV

Contraindications:

  • anything in the vagina within 24 hours (including sexual intercourse and digital exam)

  • GA above 34 weeks

  • bleeding

  • cervix dilated greater than 3 cm

CBC

A high WBC count with dominance of neutrophils may suggest intra-uterine infection, eg chorioamnionitis. The evidence to support the use of CRP for the early diagnosis of chorioamnionitis remain unclear, but a high CRP level may give weight to this diagnosis.

bottom of page