Study finds older mums have healthier children

"Children born to older women have a better start in life," the Daily Mail has reported.

The news is based on the results of a large study of children born in England that looked at child health and wellbeing and the age of the mother. The research looked at children up to the age of five and assessed unintentional injuries and hospital admissions, immunisations, body mass index, language development and social and emotional development. The study found that increasing maternal age was associated with improved child health and development up to five years of age. This association was independent of how educated the mother was, family income or whether the parents were married – all factors that may have been expected to underlie the association.

Increasing maternal age is linked to increased risk of pregnancy and birth-related complications. However, this study has found that increasing maternal age may be linked to improved child health and development after the birth. Further studies are required:

to see if these differences are maintained as children grow older
to see whether there are other factors that could be responsible for the differences seen
to establish why improved outcomes are seen in children of older mothers

It is important not to view the results of this research as evidence that older mothers are "better" at bringing up their children healthily. It merely finds an association between a mother’s age and some measures of health in their children.

Where did the story come from?

The study was carried out by researchers from University College London, University of London and the University of California. It was funded by the Wellcome Trust. The study was published in the peer-reviewed British Medical Journal (BMJ).

The research was reported by the Daily Mail. While the overall tone of the coverage is largely accurate, there are several factual errors. For example, the number of children in the study is incorrectly reported.

The Mail also states that the researchers report that “older mothers tend to be more educated, have higher incomes and be married – all factors associated with greater child well-being”. While the researchers do state this, and it is true that these factors can be expected to underlie the association, the researchers also state that they adjusted for these factors in their analyses. In addition, the researchers included children who were part of the National Evaluation of Sure Start study, who were from the most disadvantaged areas (those in the lowest 20%).

What kind of research was this?

This was a cohort study that aimed to investigate whether maternal age is linked to child health and development. It used data from two large British cohorts to see if there were associations between the age of the mother and several indicators of child health and wellbeing, while adjusting for personal and background characteristics.

A cohort study is the ideal study design to address this question. However, it cannot prove that maternal age is directly responsible for any associations seen. This is because, although the researchers have attempted to adjust for many factors that could be responsible for any association seen (called confounders), there could be others that the research has not been able to take into account.

What did the research involve?

The researchers used data from two large British cohorts:

the Millennium Cohort Study, which recruited children born between September 2000 and the end of 2001 living in 398 wards
the National Evaluation of Sure Start study, which recruited children born during the 29 months from January 2002 living in disadvantaged areas

The total sample included 31,257 infants aged nine months (18,552 from the Millennium Cohort Study and 12,705 from the National Evaluation of Sure Start). These children were followed up until they were five years old, with an additional assessment at three years of age. The number of children participating in the study was 24,781 at three years of age and 22,504 at five years of age. The age range of mothers was between 13 and 57 years.

The researchers collected information on indicators of child health and wellbeing, including:

social difficulties experienced by the child – assessed by parents using a standard questionnaire at three and five years (judged by ‘standard deviations’ from the mean score)
unintentional injuries requiring medical treatment in the past year – reported by parents at nine months, three and five years
admission to hospital within the past year – reported by parents at nine months, three and five years
whether the child had all their recommended immunisations – reported by parents at nine months and three years
weight and height – measured by the researchers at three and five years
language development – assessed by the researchers at three and five years (judged by ‘standard deviations’ from the mean score)

The researchers then looked to see if there was an association between these indicators and the age of the mothers. They took into account several factors that may play a role in any association seen, including:

the child’s gender and age
the birth weight of the child
whether the child was breastfed for at least six weeks
the number of times the mother had given birth and the number of siblings a child had
ethnic group
whether the child was raised in a workless household
family income
the mother’s educational attainment
the mother’s social class
the age of the father
whether the father was present or absent

When the association between the age of the mother and body mass index (BMI) of the child was examined, the BMI of the mother was also taken into account.

What were the basic results?

The researchers found that a child’s BMI was not associated with mother’s age if the mother’s BMI was taken into account. However, a series of child health and development factors were related to the mother’s age. These were:

The risk of unintentional injuries to the child declined with increasing maternal age

at nine months of age the risk of unintentional injury to the child decreased with increasing maternal age, from 9.5% for children of mothers aged 20, to 6.1% for mothers aged 40
at three years of age, the relationship between the age of the mother and risk was more complicated, but reached a minimum when mothers were aged 40.5 years old – at this point the risk was 28.6% compared with 36.6% for mothers aged 20 years old
when children were aged five years old, the risk of unintentional injury to the child decreased with increasing maternal age, from 29.1% for children of mothers aged 20, to 24.9% for mothers aged 40

The risk of the child being admitted to hospital decreased with maternal age

when the children were nine months old, the risk was 16.0% when mothers were aged 20 and 10.7% when the mothers were aged 40
when the children were three years old, the risk was 27.1% when mothers were aged 20 and 21.6% when the mothers were aged 40
when the children were five years old, although the risk decreased with increasing maternal age, the differences were not significant

The proportion of children fully immunised depended on maternal age

when the children were nine months old, 94.6% of children of mothers aged 20 were fully immunised, compared with 98.1% of children with mothers aged 40
when the children were aged three, the highest proportion of fully immunised children was seen in mothers aged 27.3 years old, with lower rates seen in younger and older mothers

The researchers suggest that the lower rate of uptake in older mothers may have been due to the MMR scare.

Language development was better in children of older mothers

at three years of age, the score for language development was 0.22 standard deviations lower in children of mothers aged 20 than in children of mothers aged 40
when the children were aged five years old, the difference was 0.21 standard deviations

Children of older mothers had fewer social and emotional difficulties

at three years of age, the score for social and emotional difficulties was 0.28 standard deviations lower in children of mothers aged 20 than in children of mothers aged 40
when the children were aged five years old, the difference was 0.16 standard deviations

How did the researchers interpret the results?

The researchers conclude that: “In contrast with the obstetric risks known to be associated with older motherhood these results indicate that increasing maternal age was associated with children having fewer hospital admissions and unintentional injuries, a greater likelihood of better protection from ill health through completed immunisations by age 9 months, better language development and fewer social and emotional difficulties. The findings are noteworthy given the continued increase in mean age of childbearing”.

Conclusion

This study looked at the relationship between child health and wellbeing and the age of mothers in a large cohort of children born in England. It found that increasing maternal age was associated with improved child health and development up to five years of age. Health and development was assessed by monitoring a range of childhood health factors such as immunisations, hospital admissions and language development.

However, the study cannot show that maternal age was responsible for the associations seen. Although the researchers accounted for a number of factors that could have been responsible for the association, including education, income and whether the parents were married, the researchers could not exclude the possibility that there are other factors that are responsible.

Increasing maternal age is linked to an increased risk of pregnancy and birth-related complications, such as pre-term labour and congenital malformations. However, this study has found that increasing maternal age may be linked to improved child health and development beyond the foetal stage. Further studies are required to see if these differences are maintained as children grow older, whether there are other factors that could be responsible for the differences seen, and to establish why improved outcomes are seen in children of older mothers.