Almost one in eight mothers in Ireland smoked throughout their pregnancy and those who smoked the most were more likely to give birth to smaller babies, according to a new report.

The report on maternal health behaviours is part of the Growing Up In Ireland study - a national study of almost 20,000 children which has been ongoing since 2007. For this specific topic, it used data on over 11,000 infants and their families to investigate the extent of three specific maternal behaviours - smoking in pregnancy, alcohol consumption in pregnancy and breastfeeding.

It found that between 1999 and 2007, the proportion of women who smoked during their pregnancy fell from 28% to 17%, however almost one in eight mothers - 13% - admitted to smoking throughout their pregnancy.

Women who were poor and had a low level of education were more likely to smoke and smokers were much less likely to quit the habit if their partner also smoked.

However, the data also revealed that smoking during pregnancy was strongly related to a woman's mental health. In fact, those who considered themselves to be under ‘a great deal of stress' were almost 40% more likely to smoke.

The report also noted a strong link between the number of cigarettes smoked during pregnancy and birth weight. Smoking more than 11 cigarettes per day decreased a baby's birth weight by an average of a third of a kilo.

The report noted that as few women take up smoking during pregnancy, the key is to prevent young women from taking up the habit in the first place.

Furthermore, as women are less likely to quit if their partner smokes, smoking cessation efforts should be directed at the partners of women who smoke, as well as the women themselves.

The researchers also suggested that as stress is strongly linked to smoking in pregnancy, women should be assessed for stress and anxiety at their first booking appointment as a matter of priority.

When it came to drinking alcohol during pregnancy, the report revealed that women with higher levels of education and higher incomes were more likely to consume alcohol while pregnant.

The researchers noted that because consumption of alcohol in Ireland is high, many unborn children may be exposed to high levels of alcohol before a pregnancy is actually confirmed - in other words, before a woman knows she is pregnant.

They insisted that reducing the amount of alcohol consumed by young women would benefit not only their health, but the health of their future children.

The report also looked at breastfeeding and found that women who gave birth in a maternity hospital which was accredited under the BFHI (Baby Friendly Hospital Initiative), were 10% more likely to attempt breastfeeding.

The BFHI is a global campaign by the World Health Organization and UNICEF, which recognises that implementing best practice in maternity services is crucial to the success of programmes to promote breastfeeding.

Meanwhile, the data found that less breastfeeding and earlier weaning of babies onto solid foods were linked to an unhealthy pattern of weight gain during infancy. Furthermore, almost 50% of children were weaned onto solids before the recommended age of six months, but the reasons for this were unclear.

The report suggested that all maternity hospitals should be BFHI accredited and resources for the promotion of breastfeeding should be increased.

It also said that parents need to be provided with more information on the potential health consequences of early weaning onto solids.

"Poor child and maternal environment during pregnancy and infancy contributes to early ill health and may have life-long consequences. Research internationally shows that Investment in maternity services and community health services saves money both in the short and long run," commented the study's author, Prof Richard Layte of Trinity College Dublin.

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