A 32-year-old G2P1 woman at 34 weeks’ gestation presents to the labor and delivery floor with the chief complaint of regular contractions, bloody show, and a gush of fluids. A 2.3 kg (5 Ib 1 oz) boy is delivered by spontaneous vaginal delivery without further complication 1 hour after presentation. Twenty-four hours later, the infant has developed irritability, fever, and respiratory distress. He is diagnosed with sepsis secondary to pneumonia. The mother has no complaints other than anxiety regarding the condition of her child. She denies rigors, chills, sweats, nausea, or vomiting. The mother’s pulse is 60/min, blood pressure is 125/80 mm Hg, and temperature is 37degC (98.6degF). Physical examination reveals lungs that are clear to auscultation bilaterally, and no murmurs, rubs, or gallops are present on cardiac examination. The suprapubic region is not tender to palpation. Vaginal and cervical examination reveals no significant tears or bleeds.Which prenatal test would have provided the most useful information in preventing this condition:

**Core Concept**
The case highlights the risk of Group B Streptococcus (GBS) transmission from mother to infant during birth, leading to neonatal sepsis. GBS is a gram-positive bacterium that colonizes the genitourinary and gastrointestinal tracts of women, posing a significant risk to newborns.

**Why the Correct Answer is Right**
The correct prenatal test would have been Group B Streptococcus (GBS) screening. This test involves a vaginal and rectal swab culture to detect the presence of GBS in the mother's vagina and rectum. Women at 35-37 weeks' gestation are typically screened for GBS colonization. If the mother is found to be colonized with GBS, she is offered intrapartum antibiotic prophylaxis (IAP) to reduce the risk of transmission to the infant.

**Why Each Wrong Option is Incorrect**
**Option A:** Fetal fibronectin (fFN) testing is used to detect the risk of preterm labor and delivery, not GBS colonization.
**Option B:** Non-stress test (NST) and biophysical profile (BPP) are used for fetal well-being assessment, not GBS screening.
**Option C:** Amniocentesis is used for genetic testing and diagnosis of fetal infections, not GBS screening.

**Clinical Pearl / High-Yield Fact**
GBS colonization is common in 10-30% of pregnant women, and the risk of transmission to the infant is highest in the presence of prolonged rupture of membranes (PROM) or preterm labor. A positive GBS culture in the mother is a strong predictor of neonatal sepsis.

**Correct Answer:** D. Group B Streptococcus (GBS) screening.

✓ Correct Answer: D. Rectovaginal group B streptococcal culture