The first thing the nurse does at virtually every prenatal visit is hand the mom-to-be a cup for a urine sample. Also known as "dipstick tests," they're easy, common, non-invasive tests. So common, in fact, most women don't even give them a second thought. But pregnancy urine tests are actually a great little warning sign that something may be not quite right.

Dr. Melissa Dugan-Kim, an OB/GYN with the Northwestern Specialists for Women in Chicago, says her practice starts urine testing with the very first visit, and that one is the most thoroughly tested sample. "We actually send that first sample out to a lab for culture to make sure we're not starting the pregnancy with a urinary tract infection (UTI)," says Dr. Dugan-Kim. "Many pregnant women won't have the typical symptoms and are already feeling uncomfortable in their abdominal region so may not recognize symptoms." After that, says Dr. Dugan-Kim, a dip is taken and read by an automated machine, although some practices still use visual comparison against a chart.

JoEllen Wynne, associate director of education for the American Academy of Nurse Practitioners, says urine testing has been the standard as long as she can remember, but it's more effective at early diagnoses of some conditions than others. These are some of the red flags the urine test is looking for:

• Ketones: Early in the pregnancy the presence of ketones means that the body is accessing your fat stores for energy rather than relying on glucose. In a normal, balanced diet, your body gets the energy it needs from the carbohydrates in your diet. If your diet doesn't contain enough carbohydrates to supply the body with glucose, stored fats are broken down and ketones are made. Sometimes the cause is severe nausea and may be a signal that IV fluids need to be given to prevent dehydration. Sometimes it's nutritional; the woman may be severely restricting her diet to avoid weight gain. In that case, the doctor will counsel the mother-to-be on proper nutrition. The worry here, says Wynne, is that the body is working so hard to nourish the mother, there may not be enough left over to nourish the baby.

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