Lab Test

Intrapartum Group B

GBS, Intrapartum, Vaginal, Prenatal, Group B Strep, Streptococcus

Test Codes



  • This test is ONLY for intrapartum screening when the Group B Streptococcus (GBS) status of the mother is unknown at the time of delivery.
  • Universal antepartum screening for GBS at 36-37 weeks of gestation is the standard of care for preventing neonatal GBS disease, order Strep Screen, Group B

Specimen Collection Criteria

Collect: Vaginal-rectal specimen as described below.

  • It is recommended to use only one swab to screen for colonization with Group B Streptococcus (GBS) in women.
  • Use this swab to first sample the vaginal introitus and then the anorectum. Place the swab into Amies transport medium. 

Physician Office/Draw Specimen Preparation

Maintain swab specimen at room temperature (20-26°C or 68-78.8°F).

Preparation for Courier Transport

Transport: Swab in Amies transport medium at room temperature (20-26°C or 68-78.8°F).

Rejection Criteria

  • Specimens received at room temperature greater than 24 hours after collection.
  • Swabs on which the specimen appears to have dried.
  • Specimens not in bacterial transport medium.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 6 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Room Temperature (20-26°C or 68-78.8°F): 7 days


Farmington Hills sent to Royal Oak Microbiology Laboratory for testing.
Grosse Pointe sent to Royal Oak Microbiology Laboratory for testing.
Royal Oak Microbiology Laboratory
Troy sent to Royal Oak Microbiology Laboratory for testing.


Sunday – Saturday, 24 hours a day.
STAT results available within 2 hours of receipt in the Laboratory.

Routine results available within 24 hours.

Reference Range

No Group B Streptococcus recovered.

Test Methodology

Nucleic Acid Amplification (FDA Approved; Xpert GBS); antimicrobial susceptibility testing performed only if GBS is isolated.


The presence of Group B Streptococcus in vaginal-rectal specimens obtained from pregnant women at the time of delivery has been associated with invasive perinatal disease.

Clinical Utility

Routine antepartum GBS screening requires incubation in enrichment broth media prior to testing, which results in a 2-3 day turnaround time for results. For women who have had no prenatal care, preterm delivery, or unknown GBS test results, intrapartum testing can provide results in time to administer antibiotics before delivery, if required.

The intrapartum screening test is ONLY for detecting Group B Streptococcus in women with unknown GBS test results at the time of delivery. For routine GBS screening, providers should order Strep Screen, Group B.

Clinical Disease

Group B Streptococcus (Streptococcus agalactiae) is a major cause of perinatal bacterial infections. It causes endometritis, amnionitis, and urinary tract infections in parturient women and systemic and focal infections in infants from birth until 3 or more months of age. Two distinct forms of invasive disease occur in neonates. Early-onset disease is often characterized by respiratory distress, apnea, shock, pneumonia, and, occasionally, meningitis, and its onset usually occurs within the first 24 hours of life (range, 0 to 6 days). Late-onset disease, which typically occurs after one week of age (range, 7 days to 3 months), is frequently manifested as occult bacteremia or meningitis; other focal infections, such as osteomyelitis, septic arthritis, and cellulitis, can also occur. Group B Streptococcus also cause infections in adults, particularly the elderly, those with diabetes, malignancy, or other immunocompromising conditions.


Incubation Period

The incubation period of early-onset disease is less than 6 days. In late-onset disease the incubation period from GBS acquisition to disease is unknown. Onset usually occurs from 7 days to 3 months of age.


Transmission from mother to infant occurs in utero shortly before delivery or during delivery. After delivery, person-to-person transmission can occur. Although uncommon, GBS can be acquired in the nursery from colonized infants or hospital personnel (probably via hand contamination), or in the community. The risk of early-onset disease is increased in pre-term infants born at less than 37 weeks gestation, in those born after the amniotic membranes have been ruptured for more than 18 hours and in infants born of women with intrapartum fever or chorioamnionitis, multiple births (such as twins), or GBS bacteriuria. Low or absent concentration of type-specific serum antibody also appears to be a predisposing factor. The period of communicability is unknown, but it may extend throughout the duration of colonization or of disease. Infants can remain colonized for several months after birth and after treatment of symptomatic infections.


  1. CDC. 2010. Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC.MMWR: Recommendations and Reports. 59(RR11); 1-36.

CPT Codes



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This directory currently reflects information only for specimens collected and/or processed at the
Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.