From the Guidelines

The most effective method for smoking cessation during pregnancy is behavioral counseling.

According to the US Preventive Services Task Force recommendation statement 1, quitting smoking early in pregnancy can reduce or eliminate the adverse effects of smoking on fetal growth.
Behavioral counseling is the recommended approach for smoking cessation during pregnancy, as evidence for other options, such as Nicotine Replacement Therapy (NRT), is limited 1.
Few clinical trials have evaluated the effectiveness of NRT for smoking cessation in pregnant women, and although most studies were in the direction of benefit, no statistically significant increase in cessation was seen 1.
There is also limited evidence on the harms of NRT from trials in pregnant persons, with potential adverse maternal events reported, including slightly increased diastolic blood pressure and skin reactions to the patch 1.
The USPSTF identified no studies on bupropion SR or varenicline pharmacotherapy for tobacco smoking cessation during pregnancy, and therefore, cannot recommend their use 1.
E-cigarettes are not recommended for smoking cessation during pregnancy, as the USPSTF could not determine whether they are effective in helping persons quit smoking cigarettes, nor could it determine what the potential long-term harms of e-cigarette use are 1.

From the Research

The most effective method for smoking cessation during pregnancy involves a combination of strategies. Key points to consider include:

Nicotine replacement therapy (NRT) is often recommended as the agent of choice for smoking cessation in pregnancy, due to the potential risks of pharmacotherapy 2.
A combination of cognitive-behavioural therapy and counselling with NRT is considered the most effective strategy to achieve smoking cessation during pregnancy 3.
Pregnant women with a moderate or high level of addiction may use NRT under the supervision of their physician, while those who smoke 5 cigarettes or fewer per day may be advised to use behavioural support instead of NRT 3.
Low-dose intermittent nicotine replacement therapy is considered a safe treatment modality for women who smoke during pregnancy 4.

Studies have investigated the safety and efficacy of NRT for smoking cessation during pregnancy, including:

The risks and benefits of nicotine to aid smoking cessation in pregnancy, with recommendations for efficacy trials and a national registry for NRT use during pregnancy 5.
The safety and efficacy of smoking cessation treatments for pregnant women, with limited research available on current treatments other than NRT 4.

Office-based protocols can be effective in increasing quit rates among pregnant women who smoke, including:

Systematically identifying pregnant women who smoke and offering treatment or referral 6.
Using the 5A's office-based intervention, which includes ask, advise, assess, assist, and arrange, under the guidance of trained practitioners 6.
Providing pregnancy-specific educational materials and referrals to smokers' quit lines as part of a short counseling session 6.