Being born small doesn’t tend to disadvantage IVF babies’ cognitive development

10 March 2021

Children conceived through medically assisted reproduction who are born small do just as well in cognitive tests during childhood and adolescence as naturally conceived children who are born a normal weight, finds a new study led by UCL researchers.

The new research, published today in the International Journal of Epidemiology, is one of the first studies to examine the links between medically assisted reproduction (MAR) – including techniques such as IVF treatment, artificial insemination and ovulation induction – birth weight and cognitive development.

The study shows that being born small – weighing less than 2,500 grams ­­(5.5 pounds) – does not tend to hamper MAR children’s cognitive development as it does for their naturally conceived counterparts. The authors explain that MAR children are more likely to come from better off families who may be able to compensate for the negative consequences of being born small by providing more financial and educational resources for their children.

Researchers from the Centre for Longitudinal Studies at the UCL Social Research Institute analysed data collected from a nationally representative group of over 19,000 children who have been taking part in the Millennium Cohort Study (MCS) since they were born in 2000-02.

In their analyses, they divided children into four groups: MAR children born small, MAR children who were normal weight, naturally conceived children born small, and naturally conceived children who were normal weight. To examine the role played by medically assisted reproduction and low birth weight on children’s cognitive development, they then compared cognitive test scores across the four groups at ages 3, 5, 7, 11 and 14.

At all ages, MAR children born small performed, on average, similarly or better in cognitive assessments as naturally conceived children who were normal birth weight. At age 5, they gained higher scores, and at ages 3, 7, 11 and 14 there were no differences in performance. In addition, up to age 7, MAR children born small gained higher scores than naturally conceived children who were low birth weight.

MAR children who were born normal weight gained higher cognitive scores at all ages than both naturally conceived children of low birth weight and normal weight. Naturally conceived children born small had the lowest cognitive scores up to age 7.

Once the researchers considered children’s family circumstances – measured by characteristics such as mothers’ educational level, age at birth and marital status – the differences in cognitive ability scores mostly disappeared, suggesting that socioeconomic background is an important factor in explaining the cognitive advantage of children conceived through MAR who were born small.

Although MAR children were much more likely to be born small than naturally conceived children, they were also more likely to have parents who were well off and well educated. The study’s authors explained that having access to greater financial and educational resources, especially in early childhood when parental involvement in learning is key, were likely to counter the negative association between being born low birth weight and children’s cognitive development.

The study found that 22% of the 396 MAR children involved in the study were born small compared to only 7% of naturally conceived children. Almost half of mothers of MAR children (46%) had a university degree, compared to a third of mothers of naturally conceived children (33%). Mothers of MAR children were, on average, more than three years older (33.1 years old) than mothers of naturally conceived children (29.6 years old) when they gave birth, and, in addition, they were more likely to be married or cohabiting (98% vs 86%).

Co-author, Dr Alice Goisis (UCL Centre for Longitudinal Studies) said: “Research has previously shown that children conceived through medically assisted reproduction tend to perform as well as or better in cognitive tests than naturally conceived children. But one important aspect that has been overlooked is whether this is also the case for those born small, who account for over 20% of children conceived through medically assisted reproduction, and who, according to previous research, tend to do worse in cognitive assessments than those born normal weight.”

“In this study, we found that MAR conceived children born small have similar or slightly higher cognitive ability scores compared to naturally conceived children. However, these differences in cognitive ability between MAR and naturally conceived children are explained by parents’ socioeconomic background.

“MAR parents are on average better off and so are perhaps more likely to have the means to offer their children a wider range of stimulating extra-curricular and educational activities alongside school which can benefit children’s development.

“Taken together, these characteristics and behaviours might enable MAR parents to compensate for the possible initial disadvantage of being born small that their children face.”

The study was funded by the Economic and Social Research Council (ESRC).

Media coverage of this research

Daily Telegraph (£) – Premature and small babies can end up being just as clever as other children, study finds

Further information

For more information or to speak to the researchers involved, please contact:

Ryan Bradshaw, UCL Centre for Longitudinal Studies. T: +44 (0)207 612 6516 (diverts to mobile phone) E:

Kath Butler, UCL Centre for Longitudinal Studies. T: +44 (0)20 7911 5389 (diverts to mobile phone) E:

The cognitive development from childhood to adolescence of low birth weight children born after medically assisted reproduction – a UK longitudinal cohort study by Marco Cozzani, Siddartha Aradhya and Alice Goisis is available on the International Journal of Epidemiology journal website.

Study methodology notes

Medically assisted reproduction

Children in the study were categorised as conceived with MAR if the mother underwent one of the following treatments to conceive: in-vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), intrauterine insemination, or ovulation induction. More than half of MAR children (53%) were conceived through ovulation induction, 24% through IVF, 12% through ICSI, and 4% via intrauterine insemination.

Cognitive assessments

Children’s cognitive ability was assessed with the British Ability Scales (BAS II). BAS II is a battery of twelve core sub-tests of cognitive ability and educational achievement. It assesses spoken vocabulary, language ability, language development, expressive language skills, vocabulary knowledge, recognition of printed words, and verbal reasoning ability.

Measures of family socioeconomic background

The researchers considered a number of factors related to family background when investigating the relationship between medically assisted reproduction, birth weight and cognitive development. These included child’s sex, whether they were part of a multiple birth, mother’s educational level, whether the child was first born, mother’s age at the time of birth, mother’s marital status at the time of birth, timing of the first prenatal visit, ethnic origin, and whether the mother smoked during pregnancy.

Because of the cost associated with undergoing MAR treatments (in the UK the majority of treatments take place in the private sector), MAR couples are on average advantaged. The researchers were not able to examine the cognitive development of disadvantaged MAR children who were born small as there are very few disadvantaged MAR children. As a result, there were not enough observations in the Millennium Cohort Study data to reliably analyse the outcomes of this group.

The Millennium Cohort Study (MCS) is following 19,517 young people born across the UK in 2000-02, building a uniquely detailed portrait of the children of the new century. The last survey of parents and children took place in 2018-19 when the study members were age 17. Data from the Age 17 Survey is now available. The MCS is funded by the Economic and Social Research Council and a consortium of government departments, and managed by the UCL Centre for Longitudinal Studies at the UCL Social Research Institute. Visit

The UCL Centre for Longitudinal Studies (CLS) is a resource centre based at the UCL Social Research Institute. CLS is home to four national longitudinal cohort studies, which follow the lives of tens of thousands of people. The Centre is funded by the Economic and Social Research Council (ESRC).

The UCL Social Research Institute (SRI) is one of the leading centres in the UK for multidisciplinary teaching and research in the social sciences. Based at the UCL Institute of Education, and with more than 180 academic, research and professional staff, it works to advance knowledge and to inform policy in areas including gender, families, education, employment, migration, inequalities, health and child/adult wellbeing.

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The Economic and Social Research Council (ESRC). The ESRC, which funds the UCL Centre for Longitudinal Studies, is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government. For more information visit

The ESRC is the UK’s largest funder of research on the social and economic questions facing us today. It supports the development and training of the UK’s future social scientists and also funds major studies that provide the infrastructure for research. ESRC-funded research informs policymakers and practitioners and helps make businesses, voluntary bodies and other organisations more effective.

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