hi Miistii, welcome to the forum!
The major low-carb programs advise AGAINST strict lowcarbing - ie, weight-loss levels - during pregnancy. You can check them out -
It's recommended that you keep carb intake above ketosis levels, at least 50 grams a day, probably closer to 100 would be ideal. Atkins and Protein Power suggest following the Maintenance Level of their programs. I've read on other lowcarb sites, where women have successfully followed a lower carb program like Sugar Busters or The Zone during their pregnancies, and they found they lost the weight much quicker and easier after delivery. The important thing is to keep blood sugar and insulin levels stable. Make sure you're getting plenty of protein and FIBER. Eat your daily carb allowance in the form of veggies and more veggies, maybe some lowcarb fruits like berries and melon, and small portions of whole grains and starchy veggies like peas, lentils and yams. Lots of water too!!
If you're planning to nurse, it should be safe to resume lower carb levels soon after delivery. But again, keep to above ketosis level (minimum 40g per day). Ketones do pass into the breastmilk, and though they are not harmful - the baby is producing her own ketones - it's best not to overload the system. Make sure you get plenty of protein, and if your Ob/Gyn hasn't already prescribed them for you, get yerself on a good Prenatal vitamin and mineral supplement with iron, folate and calcium.
As for artificial sweeteners, avoid anything with aspartame / nutrasweet --- it will cross the placenta, and the phenylalanine in it can harm the baby. Splenda / sucralose is safe to use during pregnancy and nursing. If you'd rather not use an artificial sweetener, you should be able to find Stevia (an herbal sweetener) at a health food store. It comes in liquid or powder form.
Good luck to you for a happy healthy pregnancy, and happy healthy baby! ..
Doreen