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In the ASB-screen study, women with a healthy singleton pregnancy will be screened for the occurrence of asymptomatic bacteriuria. In the ASB-treat study we evaluate whether nitrofurantoin treatment for women with asymptomatic bacteriuria is effective in reducing the risk of preterm delivery and/or pyelonephritis (primary outcome) and bad neonatal outcome (secondary outcome). In addition, we will assess whether it is cost-effective to screen and treat for ASB.
ASB-screen: Multicenter observational cohort study
ASB-treat: Multicenter double blind randomized clinical trial
Women with a singleton pregnancy and asymptomatic bacteriuria (a positive urine culture without symptoms of a urinary tract infection) will be included. 4.400 women will be screened for the presence of ASB in the ASB-screen study, of whom 500 are expected to be screen positive, in order to include 220 women in the randomized clinical trial (ASB-treat).
Nitrofurantoin 2x100 mg/day or placebo for 5 consecutive days.
Primary outcome is a composite of the development of pyelonephritis and delivery before 34 weeks. Secondary outcome measures is adverse neonatal outcome, child growth and development at 2 years, time to delivery, preterm birth rate before 32 and 37 weeks, days of neonatal admission, maternal morbidity, and maternal admission for preterm labour and costs.
Among women positive for ASB, we anticipate the occurrence of the primary outcome (delivery before 34 weeks and/or pyelonephritis) to be 10% in the treatment group and 25% in the no treatment group. ASB results often in an UTI (25-50% and these women are more prone to shock and respiratory distress syndrome). If ASB is not treated, 20% of pregnancies will be complicated by pyelonephritis compared to 2% of pregnancies without bacteriuria 1. Treatment of ASB results in a decrease of pyelonephritis (OR 0.24; 95%-CI 0.19-0.32, NNT 7) compared to women who were not treated. Using a two sided test with an alpha 0.05 and a beta of 0.8, 220 women with bacteriuria (110 per arm) are needed in the study. Anticipating a 5% prevalence of asymptomatic bacteriuria, we need to screen 4.400 women.
The study design will enable us to compare the costs and effects of the following strategies:
1. no screening for asymptomatic bacteriuria
2. screening for asymptomatic bacteriuria, and treatment of women with
For each of these strategies, we will calculate the costs as well as the effects in terms of maternal urinary tract infection and bad neonatal outcome (mortality and severe morbidity, see above).
We will need a run-in period of six months for the study set up, and 12 months for
inclusion. After inclusion of the last patient, 30 months (6 months pregnancy and 24 months for evaluating the child at age 2) are needed for follow-up data collection and report of results.
Prof. dr. B.W.J. Mol, Gynaecologist and Epidemiologist,
Department of Gynaecology and Obstetrics, AMC Amsterdam
ZonMW – www.ZonMw.nl