Meters also store the readings, so that doctors can track patients’ diabetes - and how well they are managing it with insulin and meals - every time they go in for an appointment.

If the measurements are inaccurate, women may give themselves doses of insulin that are higher or lower than what they should be receiving, or doctors may not have the best information to counsel and treat their patients.

And using the devices isn’t straightforward either, said Metzger, who was not involved in the current study.

“We give them a meter and teach them how to do it and then try to use that information (from the meter) right away,” he said. “There’s a significant learning curve for ... this kind of technology.”

Sacks said the new study may underestimate the problems with glucose meters, because all the readings were done by trained nurses - which is very different from when patients use them for the first time.

Women may also be hesitant to redo a measurement even if they worry it could be wrong, because the strips they are done on cost about 50 cents each. The meters themselves start at around 15 dollars.

Despite the inaccuracies, Sacks said the meters are still the best tool there is to manage diabetes on a day-to-day basis.

“What pregnant women should do is follow the directions very, very carefully,” he said. “Make sure that the technique is as good as can be.”

And if something seems off - such as a low reading right after a big meal - “they should repeat the test,” he advised.

SOURCE: Diabetes Care, online January 7, 2010.