You should always check with your health care provider before starting any new medication. There is some evidence that nicotine replacement therapy, like patches, gum and lozenges, may have negative effects on a developing fetus. However, the risks of smoking are certainly greater than the risks from NRT. NRT may be the extra help you need to quit, especially if you are a heavy smoker. You will need to discuss the risks and benefits with your health care provider to make the best decision for you.
There are two non-nicotine medications that improve smoking cessation: bupropion (Zyban) and varenicline (Chantix). In animal studies of bupropion scientists have found some evidence of impact on fetal development, but no evidence of harm in studies of humans. There are no studies about fetal effects from Chantix. If you are interested in using either of these medications while you’re pregnant, talk to your health care provider.