Adult daughters of mothers who smoked in pregnancy more likely short, obese
18 March 2019
A new international Liggins Institute-led study highlights another reason for women to avoid tobacco during pregnancy: it heightens the chances of their daughters growing up short, as well as their chances of developing obesity in adulthood.
The study – which only looked at daughters - found that women whose mothers smoked during early pregnancy were 47 percent more likely to be affected by obesity as adults, and 51 percent more likely to be short compared to women whose mothers were non-smokers.
Previous research that linked Swedish birth register data on mothers with army conscript register data on their young adult sons found similarly heightened risks for obesity and short stature in the sons.
Lead investigator Dr José Derraik, a senior research fellow from the University of Auckland-based Liggins Institute and A Better Start National Science Challenge, says it appears that harmful chemicals in cigarettes change the way babies’ genes are expressed.
“In simple terms, they may turn on or off genes involved in controlling growth.”
In 2015, one in seven (14 percent) New Zealand mothers across all age groups and one in three teenage mothers said they smoked in early pregnancy. It is likely that the true number was higher.
When a woman smokes during pregnancy, chemicals from the cigarettes travel through her bloodstream across the placenta and then to the baby, permanently changing the way the baby's body uses and stores energy.
The new study, published this week in Scientific Reports, is the latest in a series by researchers from the Institute and from Uppsala University in Sweden. The team has been analysing a rich body of data on Swedish women and their children from national registers to better understand the long-term effects of early life events and conditions that occur before, during, and after pregnancy.
The researchers analysed measurements from 22,421 Swedish women born in 1973-1988 taken at an average age of 26 years. Forty-two percent of the women’s mothers had reported at their first antenatal visit (around 10-12 weeks into their pregnancy) that they smoked.
The risk of obesity was higher in daughters of mothers who were heavier smokers, compared to those who smoked fewer than 10 cigarettes a day.
Dr Derraik: “When a woman smokes during pregnancy, chemicals from the cigarettes travel through her bloodstream across the placenta and then to the baby, permanently changing the way the baby's body uses and stores energy. Some of these chemicals can interfere with growth, which probably explains why babies born to mothers who smoked during pregnancy are often smaller.”
A 2016 meta-analysis which pulled together data from many studies identified nearly 3000 genes whose activity appeared to be affected in babies whose mothers smoked during pregnancy.
Dr Derraik says research in the US showed that smoking during pregnancy seems to make babies better at forming fat cells. “This would be useful in helping a small baby grow faster, but it would also explain, at least in part, why they have a greater risk of obesity later in life.”
The study’s other authors were Liggins Institute researchers Dr Sarah Maessen and Professor Wayne Cutfield, and in Sweden, Associate Professor Fredrik Ahlsson and Dr Maria Lundgren at Uppsala University.
Says Dr Maessen, “Other studies have shown that people who are shorter than the average person in their community are less likely to be successful in school and work, tend to be treated differently in society compared to those who are taller, and are more likely to have problems with mental health."
Professor Cutfield, who is also Director of A Better Start National Science Challenge, stresses that stopping smoking before pregnancy is one of the most important social interventions that could improve the health and wellbeing of children.
"Beyond obesity and short stature, women quitting smoking before pregnancy would reduce the risk of pregnancy complications, birth defects and miscarriage, as well as low birth weight and asthma in their children. And of course, there would be huge health benefits for the women themselves.”
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