Can I maintain my current weight while pregnant?

No. Pregnancy is not a time for dieting and you would have to diet in order to not gain weight during the nine months you are pregnant. This is a time for revamping your eating habits if they aren't already the best they can be. Read Pregnancy and weight loss.
As far as how much weight you will put on, expect to gain the average 20-30 pounds (just over two stone) by the end of your pregnancy, most of which you will gain in the last two trimesters.

 Here’s what those extra stones consist of: About seven of these pounds are the foetus, the enlarged uterus accounts for another two pounds and the placenta and amniotic fluid contribute about one pound each.

About four to eight pounds consists of extra blood and extra-cellular fluid, plus about four pounds of body fat. Please remember that these are general figures, and may vary from person to person.
The way you eat during pregnancy may have a greater effect on the health of the baby you're bringing into the world than almost anything else you do. Pregnancy is not a time to try and lose weight, especially on the silly ‘super-low fat’ diets that are thankfully being re-examined. For example, the long chain omega-3 fat DHA, found in cold water fish like salmon, is a big part of your baby's developing brain.

Pregnancy is a time to eat more healthily and better than you ever have in your life. The results will be well worth it, and you can work on getting your body back to where you want it after your baby is born.