In the first study of its kind in this country, medical experts found the risk of births before 37 weeks was more common among obese first-time mums.
The report highlighted the danger of early delivery among mothers with a high body mass index which increases the likelihood of health risks for babies.
“Maternal obesity is an independent risk factor for pre-term delivery in singleton pregnancies,” the report noted.
The four-year study of over 38,000 deliveries at the Coombe Hospital in Dublin between 2009 and 2013 found obesity increased the likelihood of both unplanned and planned premature births.
The rate of unplanned premature births was nearly three times as likely among obese first-time mothers compared to the overall rate.
The rate of premature births was also twice as high in underweight mothers undergoing first-time pregnancies.
Professor Michael Turner from the UCD Centre for Human Reproduction at Coombe Women and Infants University Hospital said the study has made a link for the first time between obesity and premature delivery in Ireland.
“The message — which is new — is obese women are more likely to have preterm deliveries which are associated with an increased risk,” he said. “One in six women are obese. Obesity is modifiable and modifiable before you become pregnant so it’s another reason why women should avoid becoming obese before pregnancy and between pregnancies.”
The study found severe obesity increased the risk of both spontaneous early delivery and elective early delivery by almost one and a half times in pregnancies.
“Elective is where the obstetrician makes a decision to deliver the woman preterm and that for conditions such as pre-eclampsia or gestational diabetes or a problem with the growth of the baby”, said Professor Turner.
“Diabetes and pre-eclampsia are commoner in women who are obese.”
The findings are a cause for concern as the study reported the rate of obesity in first trimester of pregnancy between 19% and 25% at the first prenatal visit.
Preterm delivery, defined as being prior to 37 weeks, is the main cause of deaths and illness in babies in the first weeks of life, worldwide.
“It is associated with high rates of interventions and specialised obstetrical and neonatal care, and long-term disability of the offspring, which in turn leads to increased emotional costs for families and financial costs for families and society”, the report said.
Preterm deliveries are common in multiple pregnancies, with 55% of multiple births being delivered before 37 weeks’ gestation, compared with the rate of 6%- 10% in singleton pregnancies.
Of the 39,528 deliveries in the Coombe from the start of 2009 to the end of 2013, 94% were to term with 5.9% classed as preterm or premature.
The report also found that when compared with women who delivered at term, women with premature births were more likely to be non-European, over the age of 35 years, unemployed, first-time mothers, had fertility treatments, or irregular attendance to prenatal care.
Women from this group were also more likely to smoke, use illicit drugs and be exposed to domestic violence during pregnancy.