To screen or not to screen for asymptomatic bacteriuria in pregnancy: a comparative three-year retrospective review between two maternity centres

Background: Current national guidance in Ireland states that asymptomatic bacteriuria (AB) should be screened for at 12-16 weeks' gestation and treated with a seven-day course of antimicrobials, due to the potential risk of preterm birth and low birth weight infants (LBWI), however, this is based on low quality evidence.

Methods: Over a three-year period (2018-2020), a retrospective review was undertaken in two neighbouring maternity hospitals; one of which screens for AB (Rotunda hospital (RH)) and one which does not (National Maternity Hospital (NMH)). Patients were included on the basis of fulfilling the IDSA definition for pyelonephritis and requiring admission for intravenous antibiotics. Rates of antenatal pyelonephritis were compared between hospitals, and between screened and unscreened populations. Secondary outcomes including rates of preterm births and LBWI were compared across sites.

Results: A total of 47,676 deliveries between the two centres (24,768 RH; 22,908 NMH) were assessed, of which 158 patients met inclusion criteria for antenatal pyelonephritis (n = 88 RH, n = 70 NMH). There was no statistically significant difference in the rate of antenatal pyelonephritis (p = 0.34) or preterm births (p = 0.21) across sites. RH had a significantly higher rate of LBWI at 6.45% versus 5.68% of all births in NMH (p=<0.004). Given the screening rate in RH was below 100%, this cohort was further subdivided into 'RH screened' and 'RH unscreened'. There was no statistically significant difference in the rate of antenatal pyelonephritis both between the 'NMH unscreened' group (n = 70) versus the 'RH screened' group (n = 62) (p = 0.53), or in the 'RH screened' group (n = 62) versus the 'RH unscreened' group (n = 26) (p = 0.53).

Conclusion: Omission of a screening programme for AB in NMH did not result in higher rates of antenatal pyelonephritis, preterm birth or LBWI. Our findings may inform decision-making on screening protocols and whether selective screening (i.e. screening in high-risk patients only) could be more cost-effective without compromising best quality of care.