Glezen 1992.

Methods	Pregnant women attending the Baylor Midwifery Clinic in Texas were randomised into the vaccine or placebo group depending on their hospital district number. Vaccine or placebo was administered during the prenatal visit at 34‐36 gestational weeks. Follow‐up consisted of the delivery and birth record of those delivered at Jefferson Davis Hospital. Cord blood samples were also obtained at delivery.
Participants	Pregnant women of 30‐38 gestational weeks attending the Baylor Midwifery Clinic were enrolled (n = 237), and those delivering at Jefferson Davis Hospital were followed up (n = 213).
Interventions	Group 1: capsular polysaccharide vaccine (n = 130). Group 2: placebo/saline (n = 83).
Outcomes	Preterm delivery, neonatal jaundice, fetal distress, neonatal intubation, measurements of cord sera antibodies.
Notes	Participants were mostly Hispanic and of low‐income. Exclusions: pregnant women expected to have a complicated pregnancy course or delivery.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Quote: "Women were randomised to receive PRP or placebo (saline for injection) according to the eighth digit of their hospital district number by random number table". Comment: this seems to be a non‐random process and hence a quasi‐randomised trial.
Allocation concealment (selection bias)	Unclear risk	Insufficient information.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Study states that it is double‐blinded, but does not specify further.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Study states that it is double‐blinded, but does not specify further.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition (213/237 participants were successfully followed up) was mentioned along with their reasons.
Selective reporting (reporting bias)	Unclear risk	Published protocol was not available but all the outcomes mentioned in the methods section were reported in the results.
Other bias	Unclear risk	Quote: "Participants were mostly Hispanic and of low‐income". Comment: possible selection bias.