Being Born Small Doesn’t Tend to Disadvantage IVF Babies’ Cognitive Development

Summary: Lower birth weight in medically assisted reproduction babies does not appear to hamper cognitive development to the same degree that it does in naturally conceived children with lower weight at birth.

Source: UCL

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 2.5 kilograms (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 Institute of Education 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%). 

This shows a smiling baby
The study shows that being born small – weighing less than 2.5 kilograms (5.5 pounds) – does not tend to hamper MAR children’s cognitive development as it does for their naturally conceived counterparts. Image is in the public domain

Co-author, Dr Alice Goisis 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.”

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

About this cognitive development research news

Source: UCL
Contact: Rowan Walker – UCL
Image: The image is in the public domain

Original Research: Open access.
The cognitive development from childhood to adolescence of low birthweight children born after medically assisted reproduction—a UK longitudinal cohort study” by Marco Cozzani, Siddartha Aradhya, Alice Goisis. Journal of Epidemiology


The cognitive development from childhood to adolescence of low birthweight children born after medically assisted reproduction—a UK longitudinal cohort study


Previous research has documented that children conceived through medically assisted reproduction (MAR) are at increased risk of poor birth outcomes, such as low birthweight (LBW), which are risk factors for stunted longer-term cognitive development. However, parents who undergo MAR to conceive have, on average, advantaged socioeconomic backgrounds which could compensate for the negative effects of being born LBW. Previous studies have not analysed whether the negative effects of LBW are attenuated among MAR conceived children.


We draw on the UK Millennium Cohort Study (sweeps 1–6) which contains a sub-sample of (N = 396) MAR-conceived children. The dependent variable measures cognitive ability at around ages 3, 5, 7, 11 and 14. We examine the cognitive development of four groups of children: MAR-conceived low birthweight (MAR LBW); MAR-conceived non-low birthweight (MAR NLBW); naturally conceived low birthweight (NC LBW); naturally conceived non-low birthweight (NC NLBW). We estimate the two following linear regression models for each sweep: (i) a baseline model to examine the unadjusted association between cognitive development and low birthweight by mode of conception; and (ii) a model adjusted by socio-demographic family characteristics.


In baseline models, MAR LBW children [age 3: β  =  0.021, 95% confidence interval (CI): -0.198, 0.241; age 5: β  =  0.21, 95% CI: 0.009, 0.418; age 7: β  =  0.163, 95% CI: -0.148, 0.474; age 11: β  =  0.003, 95% CI: -0.318, 0.325; age 14: β  =  0.156, 95% CI: -0.205, 0.517], on average perform similarly in cognitive ability relative to NC NLBW at all ages, and display higher cognitive scores than NC LBW children until age 7. When we account for family characteristics, differences are largely attenuated and become close to zero at age 14.


Despite the higher incidence of LBW among MAR compared with NC children, they do not seem to experience any disadvantage in their cognitive development compared with naturally conceived children. This finding is likely explained by the fact that, on average, MAR children are born to socioeconomically advantaged parents.

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