Despite a risk to their unborn child, thousands of mothers-to-be admit they have not given up cigarettes when they meet their midwife for a "booking-in appointment".
The figures, released by the NHS Information Services Division, cover the first meeting with a midwife, which usually occurs between eight and 12 weeks into the pregnancy.
Smoking is known to increase the risk of miscarriage, premature labour, cot death and stillbirth. It also increases the chance of babies getting infections and developing other health conditions, such as asthma. Children of smokers are also more likely to smoke themselves when they are older.
The Scotland-wide average for pregnant women still smoking is one-fifth (19.3%). However, in NHS Ayrshire and Arran, the figure jumped to 25.9%.
Other health boards which recorded a high number of smoking mothers include Dumfries and Galloway at 24.7%, Fife (23.4%), Borders (22.6%) and Tayside (22.3%).
At the other end of the scale was Western Isles, where 14.4% of expectant mothers – around one in seven – was a smoker at their booking-in appointment.
Younger mothers are most likely still to be smoking – 40.2% of those aged under 20 and 32% in the 20 to 24 age group.
The figures also show that at the time they first see a health visitor at home, 17.4% of pregnant women are smokers.
Gillian Smith, director of Royal College of Midwives in Scotland, said pregnant women smoking was a "major issue" for the NHS.
She said: "Smoking in pregnancy increases the chance of having a miscarriage and can cause problems with growth as there will not be the same amount of oxygen getting to the baby. There is also a problem with secondary smoke around youngsters after they are born. This can increase instances of asthma and glue ear.
"Pregnancy can be stressful and it is not the easiest time for a mother to give up. Most women will want to do their best for their child, but if you are an addict then it can be incredibly difficult. What women need is support, and not to be judged."
Health boards across Scotland have tried several initiatives to lure mothers away from tobacco – including payments to those who have stayed off cigarettes, with a carbon monoxide test used to detect smoking levels.
Sheila Duffy, chief executive of Action on Smoking and Health Scotland, added: "Smoking while pregnant harms both the mother and the child.
"Quitting at any point during pregnancy helps, but the earlier the better. Quitting smoking is difficult for some, but there is no better time to do it and support from local health services, as well as family and friends, can help give a new baby the best start in life."
It was revealed this week almost half of mothers who quit smoking while pregnant resume the habit.
The study, by Nicotine and Tobacco Research, showed 47% of new mothers began smoking again within six weeks of giving birth.
Mothers living with another smoker were six times more likely to take up smoking again.