First-trimester screening of pregnant women for elevated bacteria levels in urine

First-trimester screening of pregnant women for asymptomatic bacteriuria—higher than normal bacteria levels without symptoms of a bladder infection—is recommended by the Canadian Task Force on Preventive Health Care in an updated guideline in CMAJ (Canadian Medical Association Journal).

"As the data underlying this long-standing screening practice have not been revisited in decades, the task force saw the need for an updated guideline looking at the evidence on potential harms and benefits of screening while considering women's values and preferences around screening and treatment," says Dr. Ainsley Moore, a family physician and associate professor of family medicine, McMaster University, Hamilton, Ontario.

Current practice in Canada is to screen via urine culture in the first trimester, regardless of whether there are symptoms of a urinary tract infection, and to treat elevated bacteria levels with antibiotics.

The recommendation to continue screening is based only on low-quality evidence that showed a small reduction in kidney infections in pregnant women and in the number of babies with a low birth weight. The task force calls upon researchers to apply new methods to evaluate such entrenched standards of care to inform the care of pregnant women in Canada.

For women with recurrent urinary tract infections, diabetes, kidney issues or sickle cell disease, doctors should follow high-risk screening recommendations from authorities such as the Society of Obstetricians and Gynaecologists of Canada (SOGC), which, for example, advises screening for asymptomatic bacteriuria once during each trimester of pregnancy in women with recurrent urinary tract infections.

Kidney infection has been associated with bacterial blood infection (septicemia) and kidney disfunction in mothers, and with low birth weight and preterm birth in infants.

This guideline updates a 1994 guideline from the Canadian Task Force on the Periodic Health Examination that recommended routine prenatal screening.

In creating the guideline, the task force engaged women across Canada (aged 21-41 years) for their views on the potential benefits and harms of screening. The participants viewed screening as beneficial, although some were concerned about antibiotic use if they screened positive.

"We saw considerable variation in women's values and preferences when presented with evidence of the benefits and harms," says Dr. Brett Thombs, Chair of the task force. "Women who are interested in small potential reductions in the risk of kidney infection and low birth weight may choose to screen, while others who are more concerned about the potential risks of antibiotics may decide not to screen. It ultimately comes down to patient preferences and a discussion between the clinician and patient to determine these."

This clinical practice guideline has been endorsed by the Canadian Association of Midwives/Association canadienne des sages-femmes (CAM/ACSF) and the Nurse Practitioner Association of Canada (NPAC).