Thursday July 28 2011
Social and economic factors were actually behind the link
“IVF children have bigger vocabulary than unplanned babies,” The Daily Telegraph has reported.
The news is based on a large study investigating how pregnancy planning, time taken to conceive and the use of infertility treatment (including IVF) influenced cognitive ability of children at ages three and five. Researchers found that unplanned children had lower cognitive ability scores than those who were planned, with, for example, differences in verbal ability at age five equating to a developmental delay of more than five months. However, once researchers considered the effect of factors such as socioeconomic status (parental wealth) this difference almost entirely disappeared, suggesting that pregnancy planning had virtually no direct influence.
The finding that pregnancy planning had little influence was not well documented in news coverage, and the greater implication of this study is that it highlights the strong influence that social and economic factors can have on the cognitive ability of children.
Where did the story come from?
The study was carried out by a collaboration of researchers from the University of Oxford, University of Essex and University College London. It was funded by a grant from the Medical Research Council.
The study was published in the peer-reviewed British Medical Journal.
The authors say that previous research shows children born after a prolonged time to conception and assisted reproduction are at greater risk of poor health, and some researchers have also reported lower cognitive scores in such children. They report that unplanned pregnancies also have poorer health outcomes in early childhood, but that there is little information on whether a child’s development is associated with pregnancy planning and intention to become pregnant.
The Daily Telegraph’s coverage was balanced overall. However, its headline emphasising differences between children conceived through IVF compared to those born after unplanned pregnancies was misleading. The study itself stated that these factors did not appear to influence cognitive development, as social and economic factors were likely to be behind the association.
What kind of research was this?
This study used data from the Millennium Cohort Study in the United Kingdom. The Millennium Cohort Study is a nationally representative prospective cohort study of 18,552 families across the UK. This study used a random sample of all enrolled infants born in 2000 to 2002 that were resident in the UK at nine months of age.
This study investigated how pregnancy planning, time taken to achieve planned conception and infertility treatment influenced cognitive development at ages three and five.
What did the research involve?
Parental interviews captured information on health and socioeconomic status as well as information about pregnancy planning and infertility treatment. Children’s cognitive abilities were tested at three and five years.
Mothers were asked if they had planned to conceive and how they felt when they discovered they were pregnant. Those for whom the pregnancy was planned were asked how long they took to conceive and if they received treatment to aid their conception. Women were then grouped into the following six categories:
- Unplanned (unexpected, unhappy about pregnancy)
- Mistimed (unexpected, happy about pregnancy)
- Planned (planned, time to conception <12months)
- Subfertile (planned,time to conception ≥12months)
- Induced ovulation (planned, used drugs to induce ovulation)
- Assisted reproductive technologies (planned, used technologies such as in vitro fertilisation (IVF) or intracytoplasmic sperm injection).
The researchers used a measure called British Ability Scales (BAS II) to assess three elements of cognitive ability in the children. At age three children completed a naming vocabulary component, which assessed verbal ability. This was repeated at age five, together with measures of non-verbal and spatial abilities. The results of the BAS II are adjusted for age and so indicated how a child’s cognitive abilities have developed relative to their peers.
In total 18,114 children were resident in the UK and eligible for the study. Of these, 11,790 (65%) completed cognitive tests and provided data on socioeconomic status at age three years. A similar number of children completed the verbal, non-verbal and spatial tests at age five.
The analysis was restricted to singletons (only children). The researchers first looked at the simple (unadjusted) relationship between pregnancy planning and children’s cognitive ability. They then assessed this relationship to take into account a range of other influencing factors, including age, smoking habits in pregnancy, socioeconomic status, family income and alcohol consumption. This gave the researchers an “adjusted” relationship, taking into account all these external influences. This type of analysis is appropriate.
What were the basic results?
In total, 41% of children were born after an unexpected pregnancy – 15% of mothers who felt unhappy or ambivalent about the pregnancy (“unplanned pregnancy”) and 26% of mothers who were happy (“mistimed pregnancy”). Some 53%, of mothers reported a planned pregnancy conceived in less than 12 months. One per cent were born after assisted reproduction.
Pregnancy planning and cognitive ability score
In all unadjusted analysis, the unplanned children had lower cognitive ability scores than those who were planned. The difference between verbal ability score at age five, for instance, was equivalent to a developmental delay of more than five months.
However, after adjusting for other factors these differences almost entirely disappeared, equivalent to no developmental delay in cognitive ability. The authors say that socioeconomic status was the most important factor in the differences observed between the two groups and not pregnancy planning.
Subfertility, fertility treatment and cognitive ability score
The relationship between subfertility and fertility treatment and cognitive ability was less clear, as each group’s results differed across the three elements of cognitive ability assessed.
In unadjusted analysis, children who were born after assisted reproduction had better verbal ability scores than the planned children at ages three and five. These differences were equivalent to an average of three to four months difference in development between the groups. These differences were reduced after adjusting for other influencing factors.
Children born after fertility treatment had lower non-verbal ability scores than other children, equivalent to a developmental delay of two months on average. Spatial ability scores were also lower in children born after assisted reproduction equivalent to a delay of one and a half months. These results, however, were not statistically significant.
How did the researchers interpret the results?
The authors conclude that “pregnancy planning, subfertility or assisted reproduction do not adversely affect children’s cognitive development at ages three or five”. They state that the differences in the unadjusted analysis are almost entirely explained by differences in socioeconomic circumstances between the groups.
This was a large cohort study of singleton children that looked at how pregnancy planning, time to conception and infertility treatment influenced cognitive development at ages three and five.
This study provides good evidence that pregnancy planning, subfertility or assisted reproduction do not adversely affect children’s cognitive development at ages three and five, and that the cognitive differences found appeared to be due to social and economic factors rather than parental planning, unplanned pregnancy or the use of fertility treatment.
This conclusion is not surprising. Parents with improved socioeconomic circumstances are more likely to be able to choose or plan when pregnancies occur due to their greater economic means, which are also likely to be associated with factors such as being more highly educated parents or being able to offer more parental involvement. These types of social and demographic factors are likely to have a large effect on cognitive ability during early childhood.
A few points to note:
- This study only looked at singletons (only children) so the findings may not be directly relevant to families of larger size.
- Cohort studies can suffer from bias if lots of information is missing on participants, particularly if they drop out as the study progresses. This study had only a small amount of missing data and so the conclusions of the study are unlikely to be affected.
Overall, this study highlights the strong influence of social and economic inequalities on cognitive ability in children rather than suggesting these are directly affected by the nature of a child’s conception.