1st order laboratory parameters – obligatory laboratory tests.
- Determination of the vaginal pH
- Microbiological smear collection for clarification of infections.
- Urinalysis – to rule out possible cystitis (urinary bladder infection).
- A rapid test for nitrite detects nitrite-forming bacteria in the urine, if necessary. [Nitrate detection in urinary tract infection (UTI): 95% with positive nitrate test have positive cultures, however, also 45% with negative test, this especially in infants]
- Likewise, leukocyturia (increased number of white blood cells in the urine) may be detectable. [according to German S3 guidelines, a urinary tract infection (UTI) is considered likely if nitrite or leukocyte esterase test positive].
- Urine pH values > 7.0 in the pH daily profile = indication of a urinary tract infection with urease-forming bacteria (risk of infection stone formation).
- If necessary, also a urine sediment or a urine culture (pathogen detection and resistogram, that is, testing of suitable antibiotics for sensitivity / resistance) from midstream urine or catheter urine.
Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Fibronectin test (fetal fibronectin (fFN; biochemical marker of cervical maturation) – The test is used to predict impending preterm birth. If the test is negative in the case of clinical signs of an impending premature birth, it can be stated with a certainty of about 99% that no birth will take place within the next 14 days. This can avoid hospitalization, pulmonary ripening induction with corticosteroids, and any planned tocolytic therapy (labor inhibition). While a positive test may be coupled with an increased risk of preterm delivery, prediction is uncertain. Fetal fibronectin from vaginal secretions is measured. The test can be performed during the 22-35th SSW. If the pregnancy is intact, fetal fibronectin should not be secreted during this time.
- Amniotic fluid test (biochemical test for amniotic fluid proteins to verify premature rupture of the membranes; amniotic fluid proteins detectable in vaginal secretions after premature rupture of the membranes are measured). – Determining whether premature rupture of the membranes is present can be very difficult in individual cases, but it is clinically relevant. This is because in cases of preterm labor and premature rupture of membranes, the administration of antibiotics is indicated.They lead to a reduction in amniotic infection syndrome (infection of the egg cavity, placenta/uterine placenta, membranes and possibly the fetus/unborn child during pregnancy or birth with risk of sepsis (blood poisoning) for the child) and premature birth rate. If there is only preterm labor or cervical insufficiency (cervical weakness), antibiotics are generally not indicated, unless there is a vaginal infection (vaginitis).
- Inflammatory parameters: CRP (C-reactive protein) and leukocytes.
Other notes
- Cervical length measurement and fibronectin testing were of low predictive value in a large prospective observational study, including combined use:
- Preterm birth was indicated by cervical length shortening in only 8.0% (35 of 439 women) at first sonography and 23.3% (94 of 403 women) at second examination (specificities were 97.8% and 93.6%, respectively; “number needed to be screened”: 247 women would need sonography (ultrasonography) to detect impending preterm birth).
- The fibronectin test was even less useful as a screening measure: Preterm birth was indicated in only 7.3% (30 of 410 women on the second test) and 8.1% (31 of 384 women on the third test), respectively (specificities were 96 and 96.8%; “number needed to be screened”: 680 women would need fibronectin testing to detect impending preterm birth)