Smoking

I quit smoking cigarettes right around 11 weeks, I was a pack a day. I'm now at 26 weeks and my cravings are worse than ever. I know its harmful but does a single cigarette every now and again going to cause any major issues to my baby? I'm a first time mom and dont really know what to expect. I guess what I'm asking is, is one cigarette every other day or so going to cause the same side effects to my baby as smoking full term? I feel so guilty. No doctor will say it safe at all which I understand. But has anyone been through this to tell me?