Research from the University of Cardiff found that the negative reactions to smoking and drinking from health professionals “irritated and alienated” pregnant women.
Over a fifth of women in Wales are recorded as smokers at the time of their first pregnancy assessment, according to recent figures.
The women involved in the study also reported having "awkward" relationships with their midwives and received health advice in a "judgemental tone”, which made them less likely to seek advice and support.
Some told the researchers they had been judged negatively by anti-smoking partners.
Many of the participants in the study, both smokers and non-smokers, said they found smoking in private to be acceptable in pregnancy. However, this contrasted with their views of smoking in public.
Some added that they would make an immediate negative judgement of pregnant women who smoked in public.
Condemnation of pregnant women who smoked in public was not restricted, however, to those smoking cigarettes; one e-cigarette user reported judgement from strangers.
The study involved researchers interviewing 10 low income pregnant women from deprived areas of south Wales after they had completed visual activities (eg. timelines, collaging or thought bubbles).
Dr Aimee Grant, from Cardiff University's Centre for Trials Research, said: "Moral judgements are commonly directed towards mothers through reference to health behaviour in pregnancy, and working-class mothers are particularly subject to this criticism, ignoring the challenges of living on a low income.
"Our study shows that these looks and comments - including by members of the public - irritate and alienate pregnant women, making them less likely to seek help. No one wants to be judged and shamed."
The NHS strongly advises women not to smoke during pregnancy, outlining that the 4,000 chemicals in a cigarette harms an unborn baby and restricts their essential oxygen supply.
The Chief Medical Officers for the UK recommends that for women who are pregnant or planning to become pregnant, the safest approach is not to drink alcohol to keep risks to your baby to a minimum.
“Drinking in pregnancy can lead to long-term harm to the baby, with the more you drink, the greater the risk,” reads the NHS website.
The Royal College of Obstetricians and Gynaecologists (RCOG) outlines that there is no proven safe amount of alcohol that women can drink during pregnancy.