Gestational diabetes occurs when women who are not otherwise diabetic develop temporary diabetes (have above normal blood sugar level) while pregnant. When that happens the woman needs to follow a specific diet and may take insulin injections to control her blood sugar. Most of the time this type of diabetes goes away after the pregnancy but in some cases it may continue for longer or you could develop Type 2 diabetes later in life.
In general you don't really need to worry about gestational diabetes since, according to the American Diabetes Association, only about 4% of pregnant women are diagnosed with gestational diabetes during their pregnancy.
If you do develop gestational diabetes however, don't panic, but do work with your doctor to make sure you're taking good care of yourself and follow the guidelines given.
If you'd like more information about gestational diabetes please refer to the following ADA website: http://www.diabetes.org/gestational-diabetes.jsp
Good luck and take care!