Birth by caesarean section and school performance in Swedish adolescents- a population-based study
© The Author(s). 2017
Received: 9 January 2017
Accepted: 7 April 2017
Published: 17 April 2017
Our objective was to assess the impact of obstetric mode of delivery, and in particular birth by Caesarean section (CS), on school performance in adolescents using a large, population-based cohort.
We extracted data from the Swedish Medical Birth Register and National School Register. We included all live singleton births in Sweden from 1982–1995 (n = 1,489,925). School grades were reported on a scale from 0 to 320, scores less than 160 (i.e. “pass”) were considered to be “poor school performance.” Mode of delivery was categorised as: unassisted vaginal delivery (VD), assisted VD, elective CS and emergency CS. We measured the association between mode of delivery and “poor school performance” using logistic regression. We then used quantile regression to assess the association between mode of delivery and school performance across the distribution of scores. We adjusted for maternal age, parity, small and large for gestational age, gestational age, maternal country of birth, maternal depression, non-affective disorder or bipolar disorder, parental income at time of birth, and parental social welfare at time of birth. We also conducted sensitivity analyses to investigate the association further.
With logistic regression analysis, the adjusted odds ratio (aOR) of assisted VD and poor school performance, compared to unassisted VD, was 1.06 (95% CI: 1.03–1.08). For elective CS it was 1.06 (95% CI:1.03-1.09) and for emergency CS it was 1.12 (95% CI: 1.09–1.15). With quantile regression, assisted VD showed little difference in scores, when compared to unassisted VD, at any point across the distribution. Elective CS was associated with a 1–3 point decrease in scores, and emergency CS was associated with a 2–5 point decrease in scores.
A slight association was found between birth by CS and school performance. However, the effect was quite small and given the complex nature of the relationship, should be interpreted with caution.
KeywordsCaesarean section: School performance Cohort study Quantile regression
Rates of Caesarean section (CS) are rising globally. A recent study including data from thirty one European countries, reported the median rate of CS in those countries to be 25%,  though this trend is by no means limited to Europe or other high-income countries. Another recent study reported that in 2010–2011, among the 21 countries included, the rate of CS in countries with a high Human Development Index (HDI) was 40.0%, in countries with moderate HDI it was 32.4% and in countries with low HDI it was 20.3% . Given such a large and growing rate of CS, it is becoming of increasing interest to understand potential long-term effects of birth by CS,  as even a small increase in risk could potentially have a large impact globally.
It has been hypothesised that birth by CS leads to changes in psychological development, due to “early term” birth [4, 5] or alterations in microbiota or stress response . In animal models, birth by CS and changes in microbiota have been associated with changes in behaviour, stress response, and anxiety . Notably, these theories apply more to pre-labour or “elective” CS. Previous evidence suggests the association between CS and neurodevelopmental disorders in human populations may be primarily driven by confounding . However, it is also possible that birth by CS may lead to sub-clinical changes in behavioural development, for example increased anxiety, that are not included in official diagnoses. One way to potentially assess the overall impact on psychological well-being is through school performance. School performance has been associated with several psychological outcomes including behavioural problems,  attention problems,  substance abuse,  and insomnia . In addition, school performance as a teenager has been linked to psychological well-being as an adult, including depression and self-harm [12, 13]. Therefore, if CS has an impact on behavioural development, it may lead to changes in overall school performance.
Elective CS has been associated with delays in personal social skills and gross motor function at age 9 months,  and early term birth has been associated with increased special education requirements . However, to our knowledge, no one has examined the potential association between obstetric mode of delivery, more specifically birth by CS, and school performance. To that end, the objective of the current study was to investigate the possible impact of birth by CS on school performance in a large, population-based Swedish cohort.
We included data from 4 Swedish Registers: Medical Birth Register, National School Register, Multi-Generation Register, and National Patient Register. Each resident of Sweden is given a personal identification number (PIN) which is the same in each of these registers, and can be used to link data across registers. The Medical Birth Register was established in 1973 and includes data on over 98% of all births in Sweden . For our cohort, we included all live singleton births in the Swedish Medical Birth Register that occurred between 1982 and 1995. As both mode of delivery and school performance are likely to be highly correlated in multiple births, these were excluded. Variables detailing the timing of onset of labour and CS are available from 1982, thus marking the beginning of our cohort births. Ethical approval was obtained from the regional ethical research committee of Stockholm at Karolinska Institutet. Informed consent was waived by the ethics committee.
Exposure-obstetric mode of delivery
Obstetric mode of delivery, extracted from the Medical Birth Register, consisted of “unassisted vaginal delivery VD,” “assisted VD,” “elective CS” and “emergency CS”. Unassisted VD was defined as VD without the use of forceps or vacuum extraction, and assisted VD was VD with the use of forceps or vacuum extraction. Unassisted and assisted VD included both spontaneous and induced VD. Elective CS was defined as CS which started before onset of labour (as indicated on medical charts by water departure, bleeding or regular and sustained pain) and emergency CS was defined as CS which started after onset of labour.
Data on school performance were extracted from the National School Register, which are available beginning in 1988. In Sweden, upon finishing the compulsory years of school (age 16), grades in 16 subjects are recorded. Starting in 1998, these grades were categorised into 4 levels for each subject: not pass (score of 0), pass (score of 10), pass with distinction (score of 15), and pass with great distinction (score of 20). This allowed for a maximum total score of 320 (i.e. a score of 20 in each of the 16 subjects). Prior to 1998 there was a different grading system, but as the oldest children in our cohort turned 16 in 1998 only the current method was included. Children that “drop out” of school before compulsory grading still technically graduate but are recorded as having received a total of 0 for their final grade, and are not able to continue on to high school. These children were included in our population and were recorded as having a total score of 0. Scores were assessed in both categorical and continuous (from 0 to 320 in jumps of 5) form [16, 17].
Based on previous literature and the use of a directed acyclic graph (DAG)  (Additional file 1: Figure S1), the following a priori co-variates were included in the analysis: maternal age at time of birth (<25 years, 25–34 years, 35–44 years, 45+ years),  birth order (first born),  small for gestational age (SGA),  large for gestational age (LGA) (defined as birth weight less or greater than 2 standard deviations from the mean for gestational age, respectively), gestational age (<37 weeks, 37, 38, 39, or 40 weeks, >40 weeks),  maternal country of birth (Swedish, other Nordic, other),  maternal depression, non-affective disorder, or bipolar disorder (never diagnosed, diagnosed before birth, diagnosed after birth), parental income at time of birth (in quintiles), and parental social welfare at time of birth (yes/no, note: available from 1983),  and parental highest education (pre-high school, high school, post-high school) [16, 19, 20].
Though not identified as confounders in the DAG, further co-variates that were identified based on previous literature were also assessed, including: year of birth,  year of school completion, smoking at time of first antenatal visit (none, 1–9 cigarettes/day, 10+ cigarettes/day), [16, 20] infant gender, [16, 19] Apgar score at 5 min (“low” [0–3], “intermediate” [4–6], “high” [7–10]), [16, 21] paternal country of birth (Swedish, other Nordic, other),  paternal depression, non-affective disorder, and bipolar disorder (never diagnosed, diagnosed before birth, diagnosed after birth), parental co-habitation at time of birth [19, 20].
Distribution of descriptive variables by mode of delivery
First born child
Smoking at time of first antenatal visit
Born Prior to 1990
Parental social welfare status
Born Prior to 1983
Apgar Score (5 min)
Diagnosed before birth
Diagnosed after birth
Maternal Non-affective Disorder
Diagnosed before birth
Diagnosed after birth
Maternal Bipolar Disorder
Diagnosed before birth
Diagnosed after birth
Diagnosed before birth
Diagnosed after birth
Paternal Non-affective Disorder
Diagnosed before birth
Diagnosed after birth
Paternal Bipolar Disorder
Diagnosed before birth
Diagnosed after birth
Co-habitating with child's father
Maternal Country of Birth
Paternal Country of Birth
Natural science poor performance
Civics poor performance
Sports poor performance
Arts poor performance
Swedish poor performance
For the logistic regression, we considered “poor school performance” to be a total score of less than160, [16, 17, 22] meaning the individual did not have an average of at least 10 (i.e. “pass”) for the 16 subjects. In Sweden, scores are assigned by teachers rather than a standardised test, and thus standards for a particular grade could vary school-to-school. To account for this, we used mixed effects modelling with a random intercept for school ID.
The data on school performance have been previously reported to be highly skewed [16, 20]. We used quantile regression to analyse school performance in its continuous form. Quantile regression is similar to an ordinary least squares (OLS) model, except the model regresses on the quantile of interest (such as the median), instead of the mean. Quantile regression also does not require an assumption of normality or equal variance, and allows for assessment across the distribution (i.e. at every quantile). In this way we were able to determine if there was an effect of mode of delivery across the distribution of scores (for example, a possible effect only on the high or low scores), rather than an effect only on passing scores as seen with logistic regression. We plotted quantile regression coefficients for every fifth quantile from the 5th to the 95th using the kernel-based method for estimating standard errors . We also looked at coefficient estimates for specifically the 5th, 25th, 50th, 75th, and 95th quantiles. In adjusted analysis we included the same co-variates as the fully adjusted logistic regression model.
We conducted several sub-group analyses. In the logistic regression, we restricted to births from 1990 onwards (the year data on parental education became available), and assessed the association with and without adjustment for parental education. We assessed the association only among male babies. We also excluded children born through a secondary CS (children born by CS whose mothers’ had previously given birth through CS), and children with a low Apgar score at 5 min. Though the vast majority of the population finishes compulsory years of school at age 16 (95%), there are some students who finish younger or older. To that end, we also restricted the population to those who were 16 at the time they finished compulsory school to determine what effect age may have had on school performance. To account for potential clustering of academic performance within families, we restricted the population to one-child families and first born children. We then repeated overall analysis with a random intercept for maternal ID instead of school ID. For both logistic and quantile regression we conducted sensitivity analyses by excluding children who received a “0” as a grade (i.e. children who did not complete the compulsory years of schooling).
Additionally, we conducted logistic regression to assess the association between birth by CS and school performance in five subject categories:  natural sciences (biology, chemistry and physics), social sciences (geography, religion, history and society knowledge), arts (art and handicraft), sports, and Swedish. An average below “pass” (10 points per subject) was considered poor performance in each category. Similar to overall school performance analysis, sub-group analyses were conducted where children who were recorded as a “0” in any subject were excluded from that category.
The logistic regression analysis was conducted in SAS v9.3 (Cary, N.C) using PROC GLIMMIX  and quantile regression analysis was conducted in R v3.2.2 using the QUANTREG package . Missing data were addressed using the missing indicator method, with a category for each variable used to indicate “missing” status .
Association between mode of delivery and poor school performance
Unadjusted OR (95% CI)
Adjusted OR (95% CI)
When school performance was divided into subjects, the association was similar to the overall association between birth by CS and poor school performance (Additional file 5: Table S4).
In unadjusted analysis, the 5th, 25th, 50th, 75th and 95th percentiles for unassisted VD were 70, 175, 210, 250 and 300, respectively. Assisted VD was 20 points higher for the 5th percentile, and 5 points higher for the 50th and 75th percentiles. Elective CS was the same as unassisted VD at all five percentiles. Emergency CS was 5 points lower than unassisted VD at the 25th and 50th percentiles. In adjusted analysis, the 5th, 25th, 50th, 75th, and 95th percentiles for unassisted VD were 17.2, 132.8, 180, 215, and 274.7, respectively. Assisted VD was largely equal to unassisted VD. Elective CS showed a slight decrease (ranging from −1.4 to −2.78) in scores across the distribution, with the exception of the 75th percentile where it was equal. Similarly, emergency CS also showed a slight decrease in scores (ranging from −2 to −5) with the exception of the 75th percentile, which showed no change. Excluding scores of 0 did not change results (Data not shown, available on request).
We assessed the impact of obstetric mode of delivery, and in particular birth by CS, on school performance at age 16 using a large, population-based cohort. Two separate analyses were conducted, logistic and quantile regression, assessing school performance in both dichotomous and continuous form. There was a slight association between birth by CS and a reduction in school performance in both analyses. In logistic regression, elective CS was significantly associated with increased likelihood of poor school performance. However, children born by CS were only 6% more likely to receive a poor grade when compared to children born through unassisted VD. The association between emergency CS and poor school performance was somewhat stronger but still small (OR = 1.12, [95% CI:1.09–1.15]). With quantile regression analysis, there again appeared to be a slight association between birth by CS and school performance, primarily in adjusted results. Children born by elective or emergency CS had a 1–5 point decrease in score across the distribution, translating to a 0.31–1.56% decrease.
There are several possible explanations for an observed association between birth by CS and a small reduction in school performance. A range of characteristics influence school performance including not only behaviour  and personality,  but also cognitive ability,  and external factors such as ethnic diversity in the district . It is possible that rather than having an effect across this wide range of factors and behaviours, birth by CS is having an effect on only one aspect, such as anxiety. Another potential explanation is that this result is being driven by confounding, such as confounding by indication or residual confounding. Confounding by indication occurs when an outcome is causally associated with an indication for the exposure of interest . For example, foetal distress and maternal anxiety may be indications for emergency or elective CS,  and may also have an impact on school performance [29, 30], leading to a non-causal association between CS and poor school performance. Additionally, the association could be driven by residual confounding . The relationship between pre and perinatal risk factors and psychological development is complex, and it can be difficult to rule out the effect of difficult to measure confounders, such as social adversity . Regardless of what is driving the association, the decrease in score is very slight. A previous study on this population reported comparable effect sizes for the association between current asthma, rhinitis, eczema and school performance (change in mean score ranging from −3.1 to 4.1) and similarly concluded that though there were statistically significant associations they were likely not clinically meaningful or causally associated . For comparison, the same study reported that severe nasal symptoms is associated with a 12.1 point decrease in mean grade,  and another study reported consumption of fish at least once a week is associated with a 14.5–19.9 point increase in mean grade .
Strengths and limitations
The strengths of the present study include the use of population-based registries, limiting selection, information bias and measurement error, as we were able to include the entire population and received data from official records. Also, due to the extensive nature of these registries, we were able to assess the effect of a wide variety of co-variates and potential confounders including not only obstetric information, but also demographic and socio-economic factors. Additionally, due to the grading system in Sweden and the use of quantile regression, we were able to assess the impact of mode of delivery across a range of school grades, rather than merely assessing the likelihood of a “passing” grade.
The present study also has several limitations. First, we had no data on breast feeding, which has been linked to both mode of delivery  and school performance . However, Sweden has a very high rate of breast feeding and close to 100% of Swedish-born children have ever been breast fed . Additionally, as breast feeding may be affected by mode of delivery it is more likely to be a mediator rather than a confounder in this situation. Second, a range of factors affect school performance, and we cannot rule out a potential effect on more specific outcomes, such as anxiety, disruptive behaviour, or cognition. Previous results would indicate that mode of delivery does not have an impact on childhood neurodevelopment,  but results on behavioural difficulties are conflicting [14, 37]. Finally, it is worth noting that birth by CS in Sweden may not be representative. Access to medical care in Sweden is egalitarian, and the associations between social class and CS seen in other countries are not as prevalent . Additionally, Sweden has a very low rate of birth by CS compared to other European countries,  and it is probable that we had a low incidence of non-medically indicated CS. Though we did not have access to information on indications for CS, we were able to separate pre- and post-labour CS, which had no impact on results.
The present study used two analysis methods, adjusted for a wide variety of potential confounders, and conducted several sensitivity analyses to further investigate a potential association. With these robust analysis methods, we have concluded there is a slight association between birth by CS and poor school performance. Given the complex nature of the relationship between perinatal risk factors, such as birth by CS, and development, this small association should be interpreted with caution.
Adjusted odds ratio
Directed acyclic graph
Human development index
Large for gestational age
Personal identification number
Small for gestational age
We thank Mr. Henrik Dal and Dr. Beata Jablonska, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden, for providing data management support and advice.
This work was supported by The Irish Centre for Fetal and Neonatal Translational Research (INFANT) (Science Foundation Ireland (SFI) funded centre, Grant number 12|RC|2272). The Alimentary Pharmabiotic Centre (APC) is a research centre also funded by SFI (grant number SFI/12/RC/2273). GC, TGD and JFC are supported by the Health Research Board (HRB) through Health Research Awards (grants no HRA_POR/2011/23; TGD, JFC and GC, and HRA_POR/2012/32; JFC, TGD). GC is supported by a NARSAD Young Investigator Grant from the Brain and Behavior Research Foundation (Grant Number 20771). TD and JFC are also funded by the European Community's Seventh Framework Programme (MyNewGut, FFP7-KBBE/2013–2018, grant agreement no 613979). The APC has conducted studies in collaboration with several companies including GSK, Pfizer, Wyeth and Mead Johnson. Funding bodies had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.
Availablility of data and materials
The data that support the findings of this study are available from Karolinska Institutet but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available.
EAC contributed to study design, analysis and interpretation, and drafted the initial manuscript. LCK contributed to study design and interpretation, and critical revision of the manuscript. CD contributed to study design and interpretation, and critical revision of the manuscript. PMK contributed to study design and interpretation, and critical revision of the manuscript. JFC contributed to interpretation of the results and critical revision of the manuscript. TGD contributed to interpretation of the results and critical revision of the manuscript. ASK contributed to study conception, design and interpretation, and critical revision of the manuscript. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
The authors declare that they have no competing interests.
Consent for publication
Consent for publication was not required, as data were anonymised and informed consent was waived by the ethics committee.
Ethics approval and consent to participate
Ethical approval was obtained from the regional ethical research committee of Stockholm at Karolinska Institutet. Informed consent was waived by the ethics committee.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Macfarlane AJ, Blondel B, Mohangoo AD, Cuttini M, Nijhuis J, Novak Z, et al. Wide differences in mode of delivery within Europe: risk stratified analyses of aggregated routine data from the Euro-Peristat study. BJOG. 2016;123(4):559–68.View ArticlePubMedGoogle Scholar
- Vogel JP, Betrán AP, Vindevoghel N, Souza JP, Torloni MR, Zhang J, et al. Use of the Robson classification to assess caesarean section trends in 21 countries: a secondary analysis of two WHO multicountry surveys. Lancet Glob Health. 2015;3(5):e260–e70.View ArticlePubMedGoogle Scholar
- Blustein J, Liu J. Time to consider the risks of caesarean delivery for long term child health. BMJ. 2015;350:h2410.View ArticlePubMedPubMed CentralGoogle Scholar
- MacKay DF, Smith GC, Dobbie R, Pell JP. Gestational age at delivery and special educational need: retrospective cohort study of 407,503 schoolchildren. PLoS Med. 2010;7(6):e1000289.View ArticlePubMedPubMed CentralGoogle Scholar
- Quigley MA, Poulsen G, Boyle E, Wolke D, Field D, Alfirevic Z, et al. Early term and late preterm birth are associated with poorer school performance at age 5 years: a cohort study. Arch Dis Child Fetal Neonatal Ed. 2012;97(3):F167–73.View ArticlePubMedGoogle Scholar
- Cho CE, Norman M. Cesarean section and development of the immune system in the offspring. Am J Obstet Gynecol. 2013;208(4):249–54.View ArticlePubMedGoogle Scholar
- Cryan JF, Dinan TG. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nat Rev Neruosci. 2012;13(10):701–12.View ArticleGoogle Scholar
- Curran E, Dalman C, Kearney P, Kenny LC, Cryan JF, Dinan T, et al. The association between obstetric mode of delivery and autism spectrum disorder: A population-based sibling design study. JAMA Psychiatry. 2015;72(9):935–42.View ArticlePubMedGoogle Scholar
- Poropat AE. A meta-analysis of adult-rated child personality and academic performance in primary education. Brit J Educ Psychol. 2014;84(2):239–52.View ArticlePubMedGoogle Scholar
- McLeod JD, Uemura R, Rohrman S. Adolescent mental health, behavior problems, and academic achievement. J Health Soc Behav. 2012;53(4):482–97.View ArticlePubMedPubMed CentralGoogle Scholar
- Kronholm E, Puusniekka R, Jokela J, Villberg J, Urrila AS, Paunio T, et al. Trends in self-reported sleep problems, tiredness and related school performance among Finnish adolescents from 1984 to 2011. J Sleep Res. 2015;24(1):3–10.View ArticlePubMedGoogle Scholar
- Jablonska B, Lindberg L, Lindblad F, Rasmussen F, Ostberg V, Hjern A. School performance and hospital admissions due to self-inflicted injury: a Swedish national cohort study. Int J Epidemiol. 2009;38(5):1334–41.View ArticlePubMedGoogle Scholar
- McCarty CA, Mason WA, Kosterman R, Hawkins JD, Lengua LJ, McCauley E. Adolescent school failure predicts later depression among girls. J Adolesc Health. 2008;43(2):180–7.View ArticlePubMedPubMed CentralGoogle Scholar
- Khalaf SY, O'Neill SM, O’Keeffe LM, Henriksen TB, Kenny LC, Cryan JF, et al. The impact of obstetric mode of delivery on childhood behavior. Soc Psychiatry Psyciatr Epidmiol. 2015;50(10):1557–67.View ArticleGoogle Scholar
- The Swedish Centre for Epidemiology. The Swedish medical birth register- a summary of content and quality. 2003 [cited 2016 May 18] Available from: https://www.socialstyrelsen.se/Lists/Artikelkatalog/Attachments/10655/2003-112-3_20031123.pdf.
- Lambe M, Hultman C, Torrång A, MacCabe J, Cnattingius S. Maternal smoking during pregnancy and school performance at age 15. Epidemiology. 2006;17(5):524–30.View ArticlePubMedGoogle Scholar
- Gardner RM, Lee BK, Magnusson C, Rai D, Frisell T, Karlsson H, et al. Maternal body mass index during early pregnancy, gestational weight gain, and risk of autism spectrum disorders: Results from a Swedish total population and discordant sibling study. Int J Epidemiol. 2015;44(3):870–83.View ArticlePubMedPubMed CentralGoogle Scholar
- Textor J, Hardt J, Knuppel S. DAGitty: a graphical tool for analyzing causal diagrams. Epidemiology. 2011;22(2):745.View ArticlePubMedGoogle Scholar
- Szulkin R, Jonsson JO. Ethnic segregation and educational outcomes in Swedish comprehensive schools. Stockholm: The Stockholm University Linnaeus Center for Integration Studies (SULCIS); 2007.Google Scholar
- D'Onofrio BM, Singh AL, Iliadou A, Lambe M, Hultman CM, Neiderhiser JM, et al. A quasi experimental study of maternal smoking during pregnancy and offspring academic achievement. Child Dev. 2010;81(1):80–100.View ArticlePubMedPubMed CentralGoogle Scholar
- Stuart A, Otterblad Olausson P, Källen K. Apgar scores at 5 minutes after birth in relation to school performance at 16 years of Age. Obstet Gynecol. 2011;118(2, Part 1):201–8.View ArticlePubMedGoogle Scholar
- D’Onofrio BM, Rickert ME, Frans E, Kuja-Halkola R, Almqvist C, Sjolander A, et al. Paternal age at childbearing and offspring psychiatric and academic morbidity. JAMA Psychiatry. 2014;71(4):432–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Koenker R. Quantile regression in R: a vignette. 2015 [cited; Available from: https://cran.r-project.org/web/packages/quantreg/vignettes/rq.pdf
- Li J, Alterman T, Deddins JA. Analysis of large hierarchical data with multilevel logistic modeling using PROC GLIMMIX. [cited 2016 May 18] Available from: http://www2.sas.com/proceedings/sugi31/151-31.pdf.
- Rosander P, Bäckström M, Stenberg G. Personality traits and general intelligence as predictors of academic performance: A structural equation modelling approach. Learn Individ Differ. 2011;21(5):590–6.View ArticleGoogle Scholar
- Bosco JL, Silliman RA, Thwin SS, Geiger AM, Buist DS, Prout MN, et al. A most stubborn bias: no adjustment method fully resolves confounding by indication in observational studies. J Clin Epidemiol. 2010;63(1):64–74.View ArticlePubMedGoogle Scholar
- Stjernholm YV, Petersson K, Eneroth E. Changed indications for cesarean sections. Acta Obstet Gynecol Scand. 2010;89(1):49–53.View ArticlePubMedGoogle Scholar
- Galler JR, Ramsey FC, Harrison RH, Taylor J, Cumberbatch G, Forde V. Postpartum maternal moods and infant size predict performance on a national high school entrance examination. J Child Psychol Psyciatr. 2004;45(6):1064–75.View ArticleGoogle Scholar
- van Handel M, Swaab H, de Vries LS, Jongmans MJ. Long-term cognitive and behavioral consequences of neonatal encephalopathy following perinatal asphyxia: a review. Eur J Pediatr. 2007;166(7):645–54.View ArticlePubMedPubMed CentralGoogle Scholar
- Thapar A, Rutter M. Do prenatal risk factors cause psychiatric disorder? Be wary of causal claims. Br J Psychiatry. 2009;195(2):100–1.View ArticlePubMedGoogle Scholar
- Sundberg R, Toren K, Hoglund D, Aberg N, Brisman J. Nasal symptoms are associated with school performance in adolescents. J Adolesc Health. 2007;40(6):581–3.View ArticlePubMedGoogle Scholar
- Kim JL, Winkvist A, Aberg MA, Aberg N, Sundberg R, Toren K, et al. Fish consumption and school grades in Swedish adolescents: a study of the large general population. Acta Paediatr. 2010;99(1):72–7.PubMedGoogle Scholar
- Prior E, Santhakumaran S, Gale C, Philipps LH, Modi N, Hyde MJ. Breastfeeding after cesarean delivery: a systematic review and meta-analysis of world literature. Am J Clin Nutr. 2012;95(5):1113–35.View ArticlePubMedGoogle Scholar
- Heikkila K, Kelly Y, Renfrew MJ, Sacker A, Quigley MA. Breastfeeding and educational achievement at age 5. Matern Child Nutr. 2014;10(1):92–101.View ArticlePubMedGoogle Scholar
- OECD Family Database. CO1.5: Breastfeeding rates. 2009. [cited 2016 May 18] Available from: http://www.oecd.org/els/family/43136964.pdf.
- Curran EA, Cryan JF, Kenny LC, Dinan TG, Kearney PM, Khashan AS. Obstetrical mode of delivery and childhood behavior and psychological development in a British Cohort. J Autis Dev Disord. 2015;46(2):603–14.View ArticleGoogle Scholar
- Thomas J, Hildingsson I. Sweden. In: Kennedy P, Kodate N, editors. Maternity Services and Policy in an International Context: Risk, Citizenship and Welfare Regimes: Routledge; 2009.