Mental Health Lay Summaries

2014

An adverse prenatal environment has lasting effects on the mental health of children and adolescents

Keywords: mental health, behaviour, trajectories, pregnancy

What is already known about this subject:

  • One in five children and adolescents experience mental health problems. Childhood and adolescent mental health problems often persist into later life.
  • Many factors influencing the prenatal (before birth) environment are known to affect a child’s risk of mental health problems. These include maternal behaviours (smoking, drinking alcohol, stress); pregnancy complications (high blood pressure, preeclampsia, preterm birth, low birth weight); and socioeconomic and psychological factors (household income, family dysfunction).
  • While it is known that these factors have a measurable effect on mental health, it is still not clear how they affect mental health over the long-term and how they may interact.

What this Raine study adds:

  • Mental health data collected at 2, 5, 8, 10 and 14 years of age from Raine participants, together with maternal and pregnancy data describing socioeconomic factors, stress, maternal behaviours and obstetric complications revealed that children who experienced adverse prenatal environments experienced higher levels of problem behaviours in childhood.
  • An adverse prenatal environment was also related to worse mental health over time.
  • Demographic factors were more important in predicting child behaviour than obstetric complications. The most important factors were maternal education, family income and family exposure to stress.
  • Prevention and early intervention are important in reducing the impact of mental health problems on individuals and society as a whole.

Tearne, J. E., et al. (2014). “The association between prenatal environment and children’s mental health trajectories from 2 to 14 years.” Eur Child Adolesc Psychiatry. [publink]

A quick and effective tool for assessing family function

Keywords: questionnaires, family functioning, psychometrics

What is already known about this subject:

  • Time is one of the greatest challenges faced by large population-based studies; fitting in all of the tests required into a reasonable time-frame and not placing too large a burden on the participants.
  • Finding valid ways to shorten the time required for testing without compromising data quality can be a challenge.
  • Family functioning is often an important component of population-based testing; however the full version of the test (the McMaster Model of Family Functioning) contains 60 items.
  • A shortened 12-item version of the McMaster assessment has been shown to be reliable in population-based studies for characterising overall family functioning, but it is not known if a shorter 6-item version could reliably be used in its place.

What this Raine study adds:

  • Family functioning data from the Raine Study and the Western Australian Child Health Survey revealed that the 12-item and 6-item scales produced almost identical results and identified almost exactly the same families with good and poor levels of functioning.
  • The 6-item scale is quick and effective, and is a valid and useful measure to gain an overall perspective on family functioning in population-based studies.

Boterhoven de Haan, K. L., et al. (2014). “Reliability and validity of a short version of the General Functioning Subscale of the McMaster Family Assessment Device.” Family Process. [publink]

Low levels of testosterone exposure during fetal development affect language processing in the male brain

Keywords: brain laterality, fetal testosterone, language

What is already known about this subject:

  • ‘Brain lateralisation’ occurs when the brain processes certain types of information on either the left or right side. In most people, language processing occurs on the left side of the brain, and spatial processing on the right, although it is not clear how or why this is so.
  • It is thought that testosterone exposure before birth may influence the lateralisation of language and/or spatial processing by influencing brain development.
  • Exposure to high levels of testosterone during fetal development has been linked to language problems in boys and worse spatial ability in girls, but it is not known if this is due to the effects of testosterone on lateralisation during brain development.

What this Raine study adds:

  • Testosterone levels in umbilical cord blood and data from brain scans in early adulthood in male Raine participants showed that low levels of testosterone in cord blood were associated with different patterns of language lateralisation.
  • Lateralisation of visuospatial memory was not related to testosterone levels.
  • A child’s environment before birth may influence their language development by affecting brain lateralisation.

Hollier, L. P., Maybery, M. T., Keelan, J. A, Hickey, M., & Whitehouse, A. J. O. (2014). Perinatal testosterone exposure and cerebral lateralisation in adult males: Evidence for the callosal hypothesis. Biological Psychology, 103C, 48-53. doi:10.1016/j.biopsycho.2014.08.009. [publink]

Adolescent bullying is linked to mental health problems and alcohol misuse

Keywords: adolescent, aggression, psychology, depression, peer group, substance abuse

What is already known about this subject:

  • Aggressive behaviour between children has important implications for the children involved, whether they are the victims of the aggression or the perpetrators of it.
  • Peer aggression (‘bullying’) is most common between the ages of 9 and 14, and those involved are more likely to experience mental health problems later in life, including depression, anxiety and drug and alcohol abuse.
  • Some children are more vulnerable to bullying or more likely to bully others. It is important to determine whether exposure to peer aggression can directly affect later mental health in any child, or if this only occurs in vulnerable children.

What this Raine study adds:

  • According to questionnaire data, forty percent of Raine participants at 14 years of age had been exposed to peer aggression, whether they had been bullied (10%), had bullied others (21%), or had been bullied and had bullied others (9%).
  • Peer aggression at 14 years of age was directly associated with mental health problems and harmful alcohol use at 17 years of age, and this was not a continuation of pre-existing mental health problems.
  • Adolescents who had been bullied were more likely to have depression and emotional problems, those who had bullied others were more likely to have depression and to abuse alcohol, and those had bullied and been bullied were more likely to have behavioural problems at 17 years of age.
  • Targeting peer aggression in children is an important step in protecting adolescent mental health.

Moore, Sophie E, Rosana E Norman, Peter D Sly, Andrew J O Whitehouse, Stephen R Zubrick, and James Scott. 2014. “Adolescent Peer Aggression and Its Association with Mental Health and Substance Use in an Australian Cohort.” Journal of Adolescence 37 (1) (January): 11-21. doi:10.1016/j.adolescence.2013.10.006. [publink]

Infant health contributes to specific language impairment during childhood

Keywords: specific language impairment, prenatal, obstetric, development, risk factors

What is already known about this subject:

  • Specific language impairment is one of the most common childhood learning disabilities, and is diagnosed when language does not develop normally in children with no hearing loss or other developmental delays.
  • Complications before, during or shortly after birth are risk factors for a number of developmental disorders, but none have been shown to be risk factors for specific language impairment.
  • It is not yet clear whether other, as yet unidentified risk factors contribute to specific language impairment, or whether the effects of previously studied risk factors are small and have not yet been detected.

What this Raine study adds:

  • Data from antenatal and birth records and assessment of language development in Raine participants revealed that children with specific language impairment were more likely to have experienced poor health during their first weeks of life.
  • Complications before or around the time of birth were not related to specific language impairment.
  • While further research is needed to fully understand the factors contributing to specific language impairment, public health approaches targeted at optimising infant health may reduce its impact.

Whitehouse, A. J. O., Shelton, W. M. R., Ing, C., & Newnham, J. P. (2014). Prenatal, perinatal, and neonatal risk factors for specific language impairment: a prospective pregnancy cohort study. Journal of Speech, Language, and Hearing Research : JSLHR, 57(4), 1418-27. doi:10.1044/2014_JSLHR-L-13-0186. [publink]

Detection of the effects of anaesthesia on cognitive function in children depends on the tests used

Keywords: anaesthesia, child behaviour disorders, developmental disabilities, age factors, outcome measures

What is already known about this subject:

  • Exposure to anaesthesia during childhood can have long-lasting effects on cognitive function, although not all studies show this.
  • A variety of measures have been used to test the association between anaesthesia and cognitive function, making the results difficult to compare.
  • No study has specifically compared the ability of different types of measurements to assess a single group of children exposed to anaesthesia.

What this Raine study adds:

  • Raine participants who had been exposed to anaesthesia before 3 years of age were assessed at 10 years of age using three different measures of cognitive function. Anaesthesia exposure was associated with worse cognitive function using two of the three measures.
  • These results may help to explain some of the variation in published studies, and highlight the importance of test selection when measuring cognitive function.

Ing, C. H., DiMaggio, C. J., Malacova, E., Whitehouse, A. J., Hegarty, M. K., Feng, T., … Sun, L. S. (2014). Comparative analysis of outcome measures used in examining neurodevelopmental effects of early childhood anesthesia exposure. Anesthesiology, 120(6), 1319-32. doi:10.1097/ALN.0000000000000248. [publink]

2013

Maternal weight influences childhood mental health

Keywords: depression, mood disorders, obesity, overweight, pregnancy, maternal factors

What is already known about this subject:

  • Mothers who are overweight or obese during pregnancy are at higher risk of complications, and their children are at higher risk of obesity, diabetes and metabolic syndrome in later life.
  • New evidence suggests that a person’s mental health may be at least partly related to factors occurring before they are born.
  • It is thought that a mother’s weight prior to pregnancy may influence the mental health of her child, but this has not been well studied.

What this Raine study adds:

  • Data from mental health assessments in Raine participants at 5, 8, 10, 14 and 17 years of age and maternal pre-pregnancy weight revealed that children born to mothers who were overweight or obese prior to pregnancy were more likely to experience mental health problems such as depression during childhood and adolescence.
  • Programs designed to target obesity in women of childbearing age could potentially also improve community mental health. More research is needed to fully understand the links between maternal weight and mental health in children.

Robinson, M, S R Zubrick, C E Pennell, R J Van Lieshout, P Jacoby, L J Beilin, T A Mori, F J Stanley, J P Newnham, and W H Oddy. 2013. “Pre-Pregnancy Maternal Overweight and Obesity Increase the Risk for Affective Disorders in Offspring.” Journal of Developmental Origins of Health and Disease 4 (1) (February): 42-8. doi:10.1017/S2040174412000578.  [publink]

Maternal stress during pregnancy affects children’s academic achievement

Keywords: literacy, numeracy, education, mothers, psychology, pregnancy, child, stressful life events

What is already known about this subject:

  • Skills developed in primary school, particularly reading, writing and maths, are essential for successful participation in society. Low educational achievement can have far reaching consequences, from self-esteem issues and social, behavioural and emotional problems to unemployment and poverty.
  • Stress experienced by a pregnant woman can affect her child’s temperament, behaviour and cognitive development; although it is not yet clear if academic achievement is also affected.

What this Raine study adds:

  • Assessment of stressful life events in mothers and literacy and numeracy test scores at 10 years of age in children participating in the Raine study showed that maternal stress affected academic achievement in children, but affected boys and girls differently.
  • Girls whose mothers had experienced stressful life events during pregnancy had lower reading scores, particularly if the mother had experienced the death of a friend or family member.
  • Maternal stress improved reading scores and writing scores in boys.
  • Maternal stress should be an important consideration in the provision of support for mothers and children.

Li, J., Robinson, M., Malacova, E., Jacoby, P., Foster, J., & van Eekelen, A. (2013). Maternal life stress events in pregnancy link to children’s school achievement at age 10 years. The Journal of Pediatrics, 162(3), 483-9. doi:10.1016/j.jpeds.2012.09.007. [publink]

Boys whose fathers work long hours are more likely to have behavioural problems

Keywords: maternal employment, mental health, middle childhood, parental involvement, paternal employment, work hours, child behaviour

What is already known about this subject:

  • Parents play an important role in their child’s emotional and behavioural development during the primary school years.
  • Past research has focused on the relationship between a mother’s working hours and her child’s behaviour; however little is known about the role of a father’s work hours.
  • It is also unclear if parental work hours affect boys and girls differently.

What this Raine study adds:

  • Data describing typical parental work hours and child behaviour in Raine participants at 5, 8 and 10 years of age revealed that boys whose fathers worked very long hours (55 hours or more per week) had more behavioural problems.
  • The relationship between fathers’ work hours and child behaviour was not due to reduced parental time during the week, ineffective parenting or poor family functioning.

The impact of fathers’ working hours on their families, particularly their sons, is worth investigating further in order to fully understand how these effects occur.

Johnson, S., Li, J., Kendall, G., Strazdins, L., & Jacoby, P. (2013). Mothers’ and Fathers’ Work Hours, Child Gender, and Behavior in Middle Childhood. Journal of Marriage and Family, 75(1), 56-74. doi:10.1111/j.1741-3737.2012.01030.x. [publink]

Vitamin D levels are related to depression in young men

Keywords: vitamin D, mental health, depression, young adult

What is already known about this subject:

  • Low vitamin D levels have been implicated in depression, but while some studies have shown a link, others have not.
  • Most studies have examined the relationship between vitamin D and depression in older adults, so there is very little data describing how vitamin D levels relate to depression in young adults.
  • It is also unclear if vitamin D levels contribute to anxiety and stress.

What this Raine study adds:

  • Anxiety, depression and stress data and vitamin D levels in blood samples from Raine participants at 20 years of age revealed that vitamin D levels were associated with depression, but not anxiety or stress, in young men.
  • No relationship was found between vitamin D levels and depression, anxiety or stress in young women.
  • It may be useful to investigate the effectiveness of vitamin D supplementation in the treatment of depression.

Black, L. J., Jacoby, P., Allen, K. L., Trapp, G. S., Hart, P. H., Byrne, S. M., … Oddy, W. H. (2013). Low vitamin D levels are associated with symptoms of depression in young adult males. The Australian and New Zealand Journal of Psychiatry. doi:10.1177/0004867413512383. [publink]

Testosterone exposure before birth has some influence on childhood behaviour problems

Keywords: child behaviour, fetal blood, prenatal exposure, testosterone

What is already known about this subject:

  • Exposure to testosterone before birth affects brain development, and helps to differentiate between typically ‘male’ and ‘female’ patterns of behaviour.
  • Behavioural difficulties often differ between boys and girls; emotional problems are more common in girls and behavioural problems are more common in boys.
  • It is thought that varying levels of testosterone exposure during fetal development may contribute to childhood behaviour problems, but this has not been properly tested in a population-based cohort.

What this Raine study adds:

  • Testosterone levels in umbilical cord blood at birth and behavioural assessments in Raine participants at 2, 5, 8, 10 years of age revealed that fetal testosterone levels do not predict an increased overall risk for behaviour problems in childhood in boys or girls.
  • Higher levels of testosterone were associated with improved attention in boys from 5-10 years of age, and more withdrawal behaviour problems in girls at 5 years of age.
  • Testosterone exposure before birth is associated with some behaviour problems in children, but this relationship is not clear-cut and needs further investigation.

Robinson, Monique, Andrew J O Whitehouse, Peter Jacoby, Eugen Mattes, Michael G Sawyer, Jeffrey A Keelan, and Martha Hickey. 2013. “Umbilical Cord Blood Testosterone and Childhood Internalizing and Externalizing Behavior: A Prospective Study.” PloS One 8 (4) (January):
e59991. doi:10.1371/journal.pone.0059991.  [publink]

Children born at 37 weeks gestation are at higher risk of behavioural problems

Keywords: child behaviour, pregnancy, gestational age, premature birth, risk factors

What is already known about this subject:

  • Children born prematurely are at greater risk of physical, behavioural and cognitive problems.
  • Babies born at 37 weeks’ gestation are generally considered to be ‘full term’, and elective deliveries are often performed at this time.
  • There is concern that being born at 37 weeks may still be early enough to increase a child’s risk of behavioural problems, but this has not yet been appropriately studied.

What this Raine study adds:

  • Assessments of child behaviour in Raine participants at 2, 5, 8, 10, 14 and 17 years of age and comprehensive obstetric data from their mothers’ pregnancies revealed that infants born at 37 weeks’ gestation are at increased risk for behavioural problems throughout childhood and adolescence compared with those born later in gestation.
  • The clinical practice of considering 37 weeks gestation to be ‘full term’ may be inappropriate and may have unintended consequences for long-term child and adolescent mental health.

 

Robinson, Monique, Andrew J O Whitehouse, Stephen R Zubrick, Craig E Pennell, Peter Jacoby, Neil J McLean, Wendy H Oddy, Geoffrey Hammond, Fiona J Stanley, and John P Newnham. 2013. “Delivery at 37 Weeks’ Gestation Is Associated with a Higher Risk for Child Behavioural Problems.” The Australian & New Zealand Journal of Obstetrics & Gynaecology 53 (2) (April): 143-51. doi:10.1111/ajo.12012.  [publink]

Maternal weight is linked to emotional and behavioural health in children

Keywords: child and adolescent behaviour, obesity, overweight, mental disorders, pregnancy, prenatal exposure

What is already known about this subject:

  • Maternal overweight and obesity are common complications of pregnancy, affecting up to 40% of women. This poses health risks for both mother and child, with babies born to obese women having higher rates of neural tube defects and increased risk of asthma and obesity later in life.
  • Studies have shown that mothers who are overweight or obese are more likely to have children with emotional and behavioural problems. It is not yet clear if this is due to direct effects on development in utero, or due to other related factors (eg. parental mental health, smoking, alcohol use, socioeconomic status).

What this Raine study adds:

  • Assessments of maternal weight before and during pregnancy, together with parental ratings of emotional and behavioural problems in their children at 5, 8, 10, 14 and 17 years of age revealed that mothers who were overweight or obese prior to pregnancy were more likely to have children with behavioural and emotional problems throughout childhood and adolescence. These associations were not explained by socioeconomic or other factors, suggesting that they were due to developmental changes occurring before birth.
  • Strategies aimed at maintaining a healthy weight before and during pregnancy may be a useful way to improve mental health in young people.

Van Lieshout, Ryan J, Monique Robinson, and Michael H Boyle. 2013. “Maternal Pre-Pregnancy Body Mass Index and Internalizing and Externalizing Problems in Offspring.” Canadian Journal of Psychiatry. Revue Canadienne de Psychiatrie 58 (3) (March): 151-9. [publink]

High blood pressure during pregnancy affects infant temperament

Keywords: child development, pregnancy, hypertension, psychology, temperament

What is already known about this subject:

  • A child’s temperament influences their likelihood of developing mental health problems later in life.
  • High blood pressure-related diseases during pregnancy have been linked to behavioural and mental health problems in children; however this has never been studied in infants.
  • Factors present in a child’s environment during fetal development (before birth) can influence their temperament. It is not known if exposure to a fetal environment complicated by high blood pressure can influence a child’s temperament.

What this Raine study adds:

  • Assessments of temperament in Raine participants at 1 year of age and blood pressure data from their mothers during pregnancy showed that mothers with gestational hypertension or preeclampsia were more likely to have infants with a difficult temperament in the first year of life.
  • Extra support for mothers who had high blood pressure-related diseases during pregnancy and who have infants with difficult temperaments may help to reduce the likelihood of behavioural or emotional problems in these children later in life.

Robinson, Monique, Wendy H Oddy, Andrew J O Whitehouse, Craig E Pennell, Garth E Kendall, Neil J McLean, Peter Jacoby, Stephen R Zubrick, Fiona J Stanley, and John P Newnham. 2013. “Hypertensive
Diseases of Pregnancy Predict Parent-Reported Difficult Temperament in Infancy.” Journal of Developmental and Behavioral Pediatrics : JDBP 34 (3) (April): 174-80. doi:10.1097/DBP.0b013e31827d5761.  [publink]

Genes contribute to difficulties in social communication

Keywords: autism, genetics, social communication

What is already known about this subject:

  • People with autism have difficulties with communication and social interaction, and these difficulties are strongly genetically inherited. Milder problems with communication and social interaction also exist in people without autism.
  • Social communication abilities vary between individuals, and the genes that determine these abilities in the general population may be the same genes that are responsible for social communication and interaction difficulties in people with autism. Genetic studies in the general population may help to identify genes that are important in autism.

What this Raine study adds:

  • DNA from blood samples and data describing parent-reported social communication problems at 10-11 years of age in nearly 7,000 children from the Raine study and a UK-based population cohort found evidence of a genetic contribution to differences in social communication between individuals.
  • Genetic inheritance contributed approximately one-fifth of the variation in social communication difficulties in this group.
  • Understanding the genetic basis of social communication problems may help to identify genes that are important in autism.

St Pourcain, Beate, Andrew J O Whitehouse, Wei Q Ang, Nicole M Warrington, Joseph T Glessner, Kai Wang, Nicholas J Timpson, et al. 2013. “Common Variation Contributes to the Genetic Architecture of Social Communication Traits.” Molecular Autism 4 (1) (January): 34. doi:10.1186/2040-2392-4-34. [publink]

2012

B-vitamins may protect against mental health problems in adolescents

Keywords: vitamins, adolescent, behaviour, mental health, nutrition

What is already known about this subject:

  • One in five Australians children and adolescents will suffer from a mental health problem.
  • A healthy diet is important for maintaining both physical and mental health, and may be particularly important for the developing brain.
  • It is known that B-vitamins are essential for the production of neurotransmitters (chemical messengers within the brain), but it is not yet known if dietary consumption of B-vitamins is directly related to mental health.

What this Raine study adds:

  • Dietary intake and mental health and behaviour data at 17 years of age in Raine participants revealed that higher intake of B-vitamins was protective against adolescent behavioural problems.
  • Low vitamin B6 and folate intake was associated with more internalising disorders.
  • Reduced intakes of five B-vitamins were associated with higher externalising disorders.
  • B-vitamins may contribute to prevention of mental health problems in adolescence.

Herbison CE, Hickling S, Allen KL, O’Sullivan TA, Robinson M, Bremner AP, Huang RC, Beilin LJ, Mori TA, Oddy WH. Low intake of B-vitamins is associated with poor adolescent mental health and behaviour. Prev Med. 2012;55(6):634-8. [publink]

Children with behaviour problems are more likely to be smokers at 17 years of age

Keywords: adolescent smoking, childhood, behavioural disorders, emotional disorders, mental health

What is already known about this subject:

  • While anti-smoking campaigns have been successful in reducing smoking, smoking rates remain high in people with mental illness.
  • It is thought that smoking and mental illness may share common predisposing factors, and that this may explain why they so commonly occur together. These shared predisposing factors may begin to contribute from as early as childhood.
  • Mental health problems often arise during childhood, but it is unclear whether children who experience mental health issues are more likely to smoke later in life.

What this Raine study adds:

  • Smoking data at 17 years of age and mental health assessments at 5, 8 and 14 years of age in Raine participants showed that children with behavioural problems were more likely to smoke at 17 years of age. Childhood emotional problems were not found to be related to smoking behaviour.
  • Children whose mothers smoked during pregnancy were more than twice as likely to be smokers at 17 years of age.
  • The associations linking smoking and mental health are at work from early in development.

Zubrick, S. R., Lawrence, D., Mitrou, F., Christensen, D., & Taylor, C. L. (2012). Early mental health morbidity and later smoking at age 17 years. Psychological Medicine, 42, 1103-1115. doi:10.1017/S0033291711002182. [publink]

Identifying stress-sensitive genes that work together to cause depression

Keywords: neurobiology, stress regulation,behaviour, emotion, depression, genetic inheritance

What is already known about this subject:

  • The genes a person inherits play a large part in determining their risk of depression. While some genes linked to depression have been identified, the overall pattern of genes responsible is not well understood.
  • Most genetic studies of depression focus on the contribution of a single gene, and as a result can only describe a small proportion of the risk.
  • Looking at the stress response system (which is important in anxiety and depression) as a whole may help to identify groups of genes that work together to increase the risk of depression.

What this Raine study adds:

  • Raine study data examining the risks of depression associated with different childhood temperaments demonstrated the usefulness of a system-wide approach in the search for groups of genes that contribute to depression if not functioning normally.
  • Understanding the biology of the stress response system is an important starting point for identifying genes that are potentially relevant to depression. Targeting genes that are involved in relevant neurobiological pathways is likely to lead to the identification of groups of genes that interact to cause depression.
  • Better methods are needed to help understand the inheritance of diseases caused by multiple genes.

Van Eekelen, J. A. M., Ellis, J. A., Pennell, C. E., Craig, J., Saffery, R., Mattes, E., & Olsson, C. A. (2012). Stress-sensitive neurosignalling in depression: an integrated network biology approach to candidate gene selection for genetic association analysis. Mental Illness, 4. doi:10.4081/mi.2012.e21. [publink]

2010

Child behaviour is not measurably affected by light drinking during pregnancy

Keywords: alcohol, behaviour, child, development, prenatal exposures

What is already known about this subject:

  • High levels of alcohol consumption during pregnancy can severely affect the developing child.
  • It is less clear, however, what the effects of low levels of alcohol consumption during pregnancy are.
  • There is weak evidence to suggest that low levels of alcohol consumption during pregnancy can have negative effects on child behaviour, but this has not yet been properly tested.

What this Raine study adds:

  • Alcohol consumption data in pregnant women participating in the Raine study at 18 and 34 weeks of pregnancy, together with childhood behavioural assessments at 2, 5, 8, 10 and 14 years of age showed no adverse effects of light to moderate alcohol consumption.
  • Low levels of alcohol consumption during pregnancy does not appear to be a risk factor for child behaviour problems.
  • Given that many women consume alcohol during early pregnancy simply because they aren’t yet aware that they are pregnant, it is important to be able to offer women of childbearing age appropriate and evidence-based advice on alcohol use.

Robinson M, Oddy W, McLean N, Jacoby P, Pennell C, De Klerk N, Zubrick S, Stanley F, Newnham J. Low-moderate prenatal alcohol exposure and risk to child behavioural development: a prospective cohort study. BJOG: An International Journal of Obstetrics & Gynaecology. 2010;117(9):1139-52. [publink]