Wednesday August 14 2013
It's estimated that a quarter of all UK adults are obese
New research looking at the health outcomes for children of overweight or obese women has prompted a flurry of media headlines, with BBC News outlining that, "Children born to obese and overweight mothers are more likely to die early".
The research examined a large group of 28,540 Scottish women who gave birth between 1950 and 1976. All the women had their body mass index (BMI) measured during pregnancy. The 37,709 children were linked through national registers to identify their hospital discharge and mortality records in adult life.
The researchers found that children born to overweight and obese mothers were more likely to die from any cause during follow-up, and were specifically more likely to die before the age of 55. They were also at an increased risk of hospital admission for a cardiovascular disease event, such as a heart attack or stroke.
The relationship between maternal weight during pregnancy and their child's health outcomes is likely to be complex and involve many factors.
There are obvious environmental factors to consider, for instance. Children brought up in a household where unhealthy eating patterns are the norm are more likely to adopt these patterns themselves.
There may also be many hereditary factors influencing the child's tendency to be overweight or obese, as well as their risk of disease.
Whatever the reasons for the association, this study reinforces the importance of women trying to achieve a healthy weight when planning to have a baby, as this may reduce the risk of complications in pregnancy.
Read more about obesity, pregnancy and safe ways to lose weight before you conceive.
Where did the story come from?
The study was carried out by researchers from the University of Edinburgh and the University of Aberdeen and was funded by grants from the Scottish Chief Scientist Office and Chest, Heart and Stroke Scotland, with additional support from Tommy's and the British Heart Foundation.
It was published in the peer-reviewed British Medical Journal on an open access basis, so it is free to read or download.
The study was reported on accurately by the media, with stories including some additional useful advice from independent experts.
What kind of research was this?
Obesity is a global health problem, with many women of reproductive age who are overweight or obese.
The researchers say that previous studies have observed that babies who had adverse exposures while in the womb (suggested by a low birthweight) are more likely to have diseases in later life, in particular cardiovascular disease.
The current cohort study aimed to see whether maternal obesity during pregnancy is linked to their children having an increased risk of death from cardiovascular disease in adult life. To do this, they used hospital admissions and mortality data for a large number of Scottish people whose mothers' BMIs were recorded during pregnancy.
This is a good study design to look at whether a possible exposure (maternal obesity during pregnancy) is associated with an outcome (offspring cardiovascular disease). However, it cannot prove direct cause and effect. This is because the study is unlikely to be able to fully account for the many other hereditary, environmental and lifestyle factors that may be associated with both the mother's risk of obesity and the child's risk of cardiovascular disease. These confounders mean it is likely that there are multiple factors involved in the association seen in this study.
What did the research involve?
The research used the Aberdeen Maternity and Neonatal Databank (AMND), which has collected information about pregnancy events for women living in Aberdeen since 1950. Aberdeen is said to have a fairly stable population and the AMND has been regularly checked for completeness against NHS records.
All women who delivered a live single baby at full-term between 1950 and 1976 who also had their weight recorded at their first antenatal visit were identified. Women were grouped according to their BMI:
- underweight (BMI less than 18.5)
- normal weight (BMI 18.5 to 24.9)
- overweight (BMI 25 to 29.9)
- obese (BMI great than 30)
Other data collected about the pregnancy included:
- maternal age
- number of previous pregnancies
- husband/partner's social class
- gestation (number of weeks of pregnancy) at time of delivery
- sex of baby
- date of birth of baby
The babies' birth records were linked to NHS Scotland, the Scottish General Register of Deaths and the Scottish Morbidity Record systems of the Information and Services Division.
Cardiovascular events in the offspring during their adult life (such as angina, heart attack or stroke) were identified using hospital discharge codes according to the international classification of diseases (ICD).
The researchers looked at the relationship between the mother's BMI and risk of death, adjusting for the above variables measured during the pregnancy.
What were the basic results?
The research included 28,540 women who had their BMI measured during pregnancy and their 37,709 children.
Almost a quarter of the women (21%) were overweight during pregnancy and 4% were obese. Obese women tended to be older, of a lower social class, and had had more children.
Among the children there were 6,551 deaths from any cause (17% of the children). The leading cause of death was cardiovascular disease, followed by cancer.
After adjustment for the measured confounders, offspring born to overweight or obese mothers were 35% more likely to have died from any cause during follow-up than children born to normal-weight mothers (hazard ratio [HR]1.35, 95% confidence interval [CI]1.17 to 1.55).
When looking at the age of the offspring when they died, children born to overweight or obese mothers were significantly more likely to die at an earlier age (before the age of 55). Above the age of 55, there was no difference in risk of death than children born to normal-weight mothers.
Overall, 7.6% of the children were admitted to hospital with some form of cardiovascular disease event. Children born to overweight mothers were 15% more likely to have been admitted to hospital for any cardiovascular disease event (HR 1.15, 95% CI 1.04 to 1.26). Children born to obese mothers were 29% more likely (HR 1.29, 95% CI 1.06 to 1.57).
When looking at individual disease events, the pattern was less clear and significant associations were inconsistent. This may be because of the small number of disease events that could be linked with maternal BMI when the researchers divided the overall cardiovascular diseases into specific events.
How did the researchers interpret the results?
The researchers conclude that maternal obesity during pregnancy is associated with an increased risk of their children's earlier death.
They suggest that, "as one in five women in the United Kingdom is obese at antenatal booking, strategies to optimise weight before pregnancy are urgently required".
This valuable research has examined a large cohort of 28,540 Scottish women who had their BMI measured during pregnancy and gave birth to a single baby between 1950 and 1976. Its strengths include the use of a reliable maternity database linking more than 80% of the offspring to national registers. This allowed the researchers to identify hospital discharges and mortality records for the children.
The study suggests a link between mothers who are overweight or obese during pregnancy and an increased risk of their children's death overall – specifically prior to age 55 – as well as an increased risk of their children being admitted to hospital for a cardiovascular disease event.
The results perhaps seem unsurprising, but this study cannot prove that it is specifically maternal weight during pregnancy that directly influences the child's risk of death.
Although the researchers attempted to adjust for confounders that they had measured during pregnancy, this is not a full set of influencing factors.
There are many factors that are likely to influence both the mother's likelihood of being overweight or obese and her child's risk of having cardiovascular disease or dying at a young age, as well as the child's probability of being overweight or obese (although offspring BMI was not measured).
These factors include genetic make-up and a predisposition to specific body type or developing certain diseases. The parents are also likely to share certain lifestyle factors with their children, such as diet and exercise, at least in the earlier years.
Overall, however, this research does suggest that, whatever the underlying reasons, mothers who are overweight or obese during pregnancy are not only at risk of adverse health outcomes themselves, but their children may also be at risk of weight problems and poorer disease outcomes as they age.
For more advice, see the Planning for a baby feature, which is part of the NHS Choices Pregnancy and baby guide.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.