What are the risk factors from the mother and a preterm (less than 37 weeks gestation) baby that predispose the baby to sepsis?

Risk Factors for Neonatal Sepsis from Mother and Preterm Infant

Preterm delivery (<37 weeks gestation) is the single most important risk factor for early-onset neonatal sepsis, with gestational age showing a direct inverse relationship to infection risk—the earlier the delivery, the higher the risk. 1

Maternal Risk Factors

Colonization and Infection

• Maternal GBS colonization is the primary maternal risk factor, with colonized mothers being >25 times more likely to deliver infants with early-onset GBS disease compared to non-colonized mothers 1
• GBS bacteriuria during any trimester indicates heavy maternal colonization and significantly increases neonatal sepsis risk 1
• Heavy GBS colonization (culture from direct plating rather than selective broth only) carries higher risk for early-onset disease 1
• Maternal urinary or reproductive tract infection increases sepsis risk 3.6-fold (OR = 3.61,95% CI: 2.14-6.11) 2

Intrapartum Complications

• Chorioamnionitis increases neonatal sepsis risk 4.4 to 4.6-fold (OR = 4.4-4.58) and is an independent risk factor even after controlling for other variables 1, 2, 3
• Prolonged rupture of membranes (≥18 hours) increases risk 2.6-fold (OR = 2.63,95% CI: 2.09-3.30) 1, 2
• Maternal intrapartum fever ≥100.4°F (≥38.0°C) increases risk 3.6-fold (OR = 3.59,95% CI: 2.25-5.71) 1, 2
• Multiple vaginal examinations (≥3 times) dramatically increases risk nearly 8-fold (OR = 7.95% CI: 4.04-15.64) 2
• Internal fetal monitoring >12 hours increases risk 7.2-fold (OR = 7.2,95% CI: 1.6-32.2), likely by facilitating ascending infection 3
• Postpartum endometritis is associated with 6.4-fold increased neonatal sepsis risk (OR = 6.4,95% CI: 1.2-34.2) 3

Other Maternal Factors

• Young maternal age is associated with increased early-onset GBS disease risk 1
• Black race shows higher risk for early-onset disease 1
• Low maternal GBS-specific anticapsular antibody levels increase susceptibility 1
• Previous delivery of an infant with invasive GBS disease is a significant risk factor for subsequent deliveries 1

Preterm Infant Risk Factors

Gestational Age and Birth Weight

• Gestational age <37 weeks is a critical independent risk factor, with risk increasing as gestational age decreases (OR = 1.31 per week decrease, 95% CI: 1.18-1.44) 1, 2
• Very low birth weight increases risk 3.8-fold (OR = 3.79,95% CI: 2.14-6.73) 2
• Infants born <35 weeks with high-risk delivery characteristics (cervical insufficiency, preterm labor, premature rupture of membranes, intra-amniotic infection, or nonreassuring fetal status) are at highest risk and require empiric antibiotics even after adequate intrapartum prophylaxis 1, 4

Fetal/Neonatal Complications

• Perinatal asphyxia or intrauterine distress increases risk 3-fold (OR = 3.00,95% CI: 2.18-4.13) 2
• Meconium-contaminated amniotic fluid increases risk 4.5-fold (OR = 4.51,95% CI: 2.31-8.81) 2
• Amniotic fluid index <5 cm after preterm premature rupture of membranes is independently associated with increased early-onset neonatal sepsis and chorioamnionitis 5

Immunologic Vulnerability

• Preterm infants exhibit distinct (not simply deficient) immune function with impaired innate and adaptive immunity compared to term infants, fundamentally increasing their susceptibility to infection and sepsis-related mortality 6

Critical Clinical Pitfalls to Avoid

• Do not assume cesarean delivery prevents GBS transmission—GBS can cross intact membranes, though risk is extremely low with planned cesarean before labor onset and membrane rupture 1
• Do not rely on single risk factors in isolation—women with one intrapartum risk factor but negative GBS screening have relatively low risk (0.9 per 1,000 births), while colonized women without risk factors have higher risk (5.1 per 1,000 births) 1
• Do not delay screening in threatened preterm delivery—obtain vaginal and rectal GBS cultures immediately if time permits, and initiate intrapartum prophylaxis pending results when substantial preterm delivery risk exists 1
• Recognize that adequate intrapartum antibiotic prophylaxis (≥4 hours before delivery) is 78-89% effective in preventing early-onset GBS disease in preterm deliveries, but preterm infants <35 weeks with high-risk characteristics still require empiric antibiotics regardless 1