C-Section and IQ: Does Being Born by Cesarean Affect Intelligence?

Being born by C-section makes little or no difference to IQ: among 579,244 Swedish men, those born by cesarean scored 0.84 points lower on a conscription intelligence test at about age 18, and when brothers born by different delivery methods were compared, the gap disappeared (0.07 points, in the other direction). Population studies in several countries find gaps of about 1 IQ point or less, and family-based comparisons suggest that family background accounts for most of it.

This page covers what the largest studies show, what happens when researchers compare siblings, why the claim exists in two opposite forms (C-section babies are smarter, or C-section babies are less intelligent), and the factors that make delivery mode and IQ hard to separate.

The biggest IQ study on the question comes from Sweden. Viktor Ahlqvist and colleagues linked birth records for 579,244 men born between 1973 and 1987 to the cognitive test battery they took at military conscription, scored on the familiar IQ scale with a mean of 100 and a "standard deviation", a measure of spread, of 15. Men born by cesarean averaged 99.3 and men born vaginally averaged 100.1. After adjustment for other factors, the gap was 0.84 points. Planned (elective) and unplanned cesareans showed similar gaps of about 1 point.

A Danish study by Agnes Ladelund and colleagues followed 1,408,230 children born from 1978 to 2000. Those born by cesarean were slightly less likely to finish secondary school and had slightly lower grade point averages. On the Danish conscription test, a 78-item intelligence test whose scores have a standard deviation of about 10, the adjusted gap was 0.36 points. Converting with the usual rule (divide by the test's standard deviation, then multiply by 15), that is about half an IQ point. The authors described all of these differences as very small.

School grades tell a similar story. In a Swedish study of 1,489,925 adolescents, Eileen Curran and colleagues found that elective cesarean birth was linked to grades 1 to 3 points lower, and emergency cesarean to grades 2 to 5 points lower, on a scale that runs from 0 to 320. In Australia, Cain Polidano and colleagues studied 3,666 children in a national birth cohort and found that cesarean-born children scored up to a tenth of a standard deviation lower on a national numeracy test at ages 8 to 9, about 1.4 points on an IQ-style scale (0.095 multiplied by 15). On a matrix reasoning task, a common nonverbal problem-solving measure, the adjusted gaps were smaller (0.04 to 0.07 standard deviations) and not statistically significant at the conventional level.

Comparing brothers and sisters is the most direct way to test whether the delivery itself matters. Siblings share their parents, their home and much of their genes, so a gap that survives within families is harder to blame on background. In the Swedish conscription data, when brothers born by different delivery methods were compared, the 0.84-point gap shrank to 0.07 points in the opposite direction, with a confidence interval (the range of values compatible with the data) of -0.31 to 0.45. The authors concluded that the association seems to be largely explained by familial factors shared between siblings.

Diagnoses follow the same pattern. A 2019 meta-analysis of 61 studies by Tianyang Zhang and colleagues found that children born by cesarean had higher odds of autism (odds ratio 1.33) and ADHD (1.17), with a much less precise estimate for intellectual disability. A follow-up study by the same group, covering 1,179,341 Swedish children, found that the links with any neurodevelopmental disorder, including intellectual disability, became non-significant when full siblings were compared. Their conclusion was that unmeasured familial confounding most likely explained the association.

The claim runs in both directions depending on where you look. A team led by H. T. Li reported that most mothers in China believed a cesarean on maternal request could improve a child's intelligence, and their cohort study tested this with 4,144 preschool children given a Chinese version of a Wechsler IQ test. Children born by requested cesarean scored 3.9 points higher in a raw comparison, but after adjustment for the mother's education, occupation and own IQ, the advantage shrank to 1.6 points and was no longer statistically significant. A Brazilian cohort in São Luís found something similar in 18- and 19-year-olds tested with the WAIS-III: a 5.8-point raw advantage for cesarean birth fell to 1.9 points, and was not significant, once socioeconomic and birth factors were taken into account.

In the Swedish, Danish and Australian data, by contrast, cesarean-born children scored slightly lower, which feeds the opposite claim. Small studies add noise. A Czech study of 168 five-year-olds, only 51 of them born by cesarean, reported lower scores on two nonverbal tests and concluded that cesarean birth may harm cognitive development, but it was far too small to settle the question.

Researchers have proposed biological reasons why cesarean birth could matter, and these remain hypotheses. Babies born vaginally pick up bacteria resembling their mother's vaginal microbes, while babies born by cesarean first acquire bacteria typical of skin, as Maria Dominguez-Bello and colleagues showed in a small study of 10 newborns. Eileen Curran and colleagues, in a Swedish sibling study of ADHD, summarize the two main proposals: changes in the gut microbes, or in the baby's stress response, might affect psychological development. In that study, the small link between planned cesarean and ADHD disappeared among siblings. Polidano's team found that lower breastfeeding rates and health problems explained less than a third of the small gap they measured. Breastfeeding itself has a complicated relationship with IQ, which we cover in our page on IQ and breastfeeding.

A cesarean is usually performed for a reason, and the reason is often linked to the child's development. Studies that compare all cesarean births with all vaginal births mix many different situations together.

• The reason for the cesarean: Emergency cesareans are often done because of complications in labor, and emergency cesarean birth is tied to slightly worse outcomes than elective cesarean in several of these studies.

• Prematurity and birth weight: In the Australian cohort, cesarean births carried more perinatal risk factors, and preterm birth has its own well-documented link with later scores, covered in our page on IQ and premature birth.

• Maternal age and background: In the Australian cohort, mothers of cesarean-born children were older on average (31.8 versus 30.4 years) and more often had higher education and private insurance. Older maternal age has its own complicated relationship with child IQ, discussed in our page on IQ and maternal age.

• Parents' own IQ: In the Chinese study, adjusting for the mother's IQ, education and occupation removed most of the raw advantage for cesarean birth.

Sibling comparisons handle the stable family factors well, but they cannot rule out everything, because the reason one child was born by cesarean and the other was not may itself matter. Even so, the largest family-based studies point to a direct effect on IQ that is zero or very close to it. Decisions about how to give birth depend on medical factors and should be discussed with an obstetrician or midwife.

On average they score slightly lower in some countries, by about 1 IQ point or less. When brothers born by different delivery methods were compared in Swedish data, the gap was 0.07 points and statistically indistinguishable from zero.

No good evidence supports that claim. In Chinese and Brazilian cohorts, cesarean-born children scored higher in raw comparisons, but the advantage shrank and lost statistical significance once family background was taken into account.

Emergency cesareans are linked to slightly worse school results in some studies, probably because they often follow complications in labor. In the Swedish conscription data, neither type was associated with IQ in sibling comparisons.

Cesarean birth is associated with slightly higher rates of both, but in a Swedish study of over a million children, the links with neurodevelopmental disorders became non-significant when siblings were compared.

The evidence does not show that delivery mode changes IQ in a meaningful way. Birth planning involves medical considerations that an obstetrician or midwife can explain.

Studies of C-section and IQ find small gaps of about 1 point or less in population data, and the direction even flips between countries depending on who has cesareans. When siblings are compared, the gap in Swedish conscription scores falls to 0.07 points, which suggests that family background explains most of the difference. Delivery mode is a medical decision, and it is not a meaningful factor in a child's later intelligence. If you are curious about your own reasoning abilities, you can take the RIOT IQ test.

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2. Ladelund, A. K., Slavensky, J. A., Bruun, F. J., Fogtmann Sejer, E. P., Mortensen, E. L., Ladelund, S., & Kesmodel, U. S. (2023). Association of birth by cesarean section with academic performance and intelligence in youth: A cohort study. Acta Obstetricia et Gynecologica Scandinavica, 102(5), 532-540. [doi.org/10.1111/aogs.14535](. doi.org

3. Curran, E. A., Kenny, L. C., Dalman, C., Kearney, P. M., Cryan, J. F., Dinan, T. G., & Khashan, A. S. (2017). Birth by caesarean section and school performance in Swedish adolescents: A population-based study. BMC Pregnancy and Childbirth, 17(1), 121. [doi.org/10.1186/s12884-017-1304-x](. doi.org

4. Polidano, C., Zhu, A., & Bornstein, J. C. (2017). The relation between cesarean birth and child cognitive development. Scientific Reports, 7(1), 11483. [doi.org/10.1038/s41598-017-10831-y](. doi.org

5. Zhang, T., Sidorchuk, A., Sevilla-Cermeño, L., Vilaplana-Pérez, A., Chang, Z., Larsson, H., Mataix-Cols, D., & Fernández de la Cruz, L. (2019). Association of cesarean delivery with risk of neurodevelopmental and psychiatric disorders in the offspring: A systematic review and meta-analysis. JAMA Network Open, 2(8), e1910236. [doi.org/10.1001/jamanetworkopen.2019.10236](. doi.org

6. Zhang, T., Brander, G., Mantel, Ä., Kuja-Halkola, R., Stephansson, O., Chang, Z., Larsson, H., Mataix-Cols, D., & Fernández de la Cruz, L. (2021). Assessment of cesarean delivery and neurodevelopmental and psychiatric disorders in the children of a population-based Swedish birth cohort. JAMA Network Open, 4(3), e210837. [doi.org/10.1001/jamanetworkopen.2021.0837](. doi.org

7. Li, H. T., Ye, R. W., Pei, L. J., Ren, A. G., Zheng, X. Y., & Liu, J. M. (2011). Cesarean delivery on maternal request and childhood intelligence: A cohort study. Chinese Medical Journal, 124(23), 3982-3987. [pubmed.ncbi.nlm.nih.gov](. pubmed.ncbi.nlm.nih.gov

8. Lima, A. B. S., Martins Neto, C., Ferraro, A. A., Barbieri, M. A., & Simões, V. M. F. (2023). Nascer de cesariana e associação com quociente de inteligência em adolescentes: Contribuição do Consórcio de Coortes RPS (Ribeirão Preto, Pelotas e São Luís), Brasil [Cesarean section and association with intelligence quotient in adolescents]. Cadernos de Saúde Pública, 39(3), e00064422. [doi.org/10.1590/0102-311xpt064422](. doi.org

9. Blazkova, B., Pastorkova, A., Solansky, I., Veleminsky, M., Veleminsky, M., Rossnerova, A., Honkova, K., Rossner, P., & Sram, R. J. (2020). The impact of cesarean and vaginal delivery on results of psychological cognitive test in 5 year old children. Medicina, 56(10), 554. [doi.org/10.3390/medicina56100554](. doi.org

10. Dominguez-Bello, M. G., Costello, E. K., Contreras, M., Magris, M., Hidalgo, G., Fierer, N., & Knight, R. (2010). Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proceedings of the National Academy of Sciences, 107(26), 11971-11975. [doi.org/10.1073/pnas.1002601107](. doi.org

11. Curran, E. A., Khashan, A. S., Dalman, C., Kenny, L. C., Cryan, J. F., Dinan, T. G., & Kearney, P. M. (2016). Obstetric mode of delivery and attention-deficit/hyperactivity disorder: A sibling-matched study. International Journal of Epidemiology, 45(2), 532-542. [doi.org/10.1093/ije/dyw001](. doi.org

Hero image: Surgical Instruments 01, by آرمین, CC0. Via Wikimedia Commons.