Thursday May 7 2009
Many women have nausea and vomiting during pregnancy
Research suggests that “women who suffer morning sickness during pregnancy may be more likely to have a child with a high IQ”, The Daily Telegraph reported. It said that doctors believe babies’ development could be aided by the same hormones that make expectant mothers suffer nausea and vomiting. A study of mothers and children, the newspaper reported, found that children of mothers who experienced morning sickness were more likely to do better in intelligence tests.
The study this story is based on examined the effect of morning sickness on a child’s long-term neurodevelopment (the development of things like intelligence, behaviour, memory and attention) and what effect a drug for treating vomiting in pregnancy had on this.
One of its conclusions was that the severity of sickness is a significant predictor of higher IQ scores in children. Despite these claims, however, this would need to be proven in further research. In addition, the researchers’ theory that hormones might be involved would need to be tested in a study that actually measures these hormones.
Where did the story come from?
Dr Irena Nulman and colleagues from the Hospital for Sick Children in Toronto, Canada carried out this research. The study was supported by Duchesnay, a pharmaceutical company that markets Diclectin, the drug tested in this study, and vitamin tablets for use in pregnancy.
The study was published in the peer-reviewed medical journal The Journal of Pediatrics.
What kind of scientific study was this?
The aim of this cohort study was to determine the effects of mother’s nausea and vomiting during pregnancy (NVP) on the child’s long-term neurological development. The study also looked at the effect of the drug Diclectin on the child’s neurodevelopment. The researchers explain that in Canada the only approved drug for use in pregnancy to treat vomiting is Diclectin. This drug contains 10mg each of doxylamine (not available in the UK) and vitamin B6. Separately, these components are used worldwide to control NVP.
The participants were recruited from the Toronto Motherisk NVP telephone hotline. This is an information and counselling service for women and healthcare professionals that offers advice on NVP and treatment safety. Expectant mothers who called up were asked about the medication they took, their alcohol and tobacco intake and any other illnesses or complications of pregnancy they had experienced. They were also asked about the severity and duration of nausea and vomiting leading up to week 20 of their pregnancy. Weekly follow-up by phone documented the treatment (number of Diclectin tablets) and clinical presentation of NVP. The researchers also asked the mothers’ doctors for additional information. Women were interviewed six to nine months after childbirth about the delivery of their child and their child’s developmental milestones.
The callers identified by the database were grouped into three groups of mother–child pairs. One group had NVP treated with Diclectin. A second had NVP but did not take Diclectin. A third had no NVP and were calling for advice on something else.
Women with twins, those who drank alcohol and those who had other illnesses were excluded. Children were excluded if they had other causes of neurodevelopmental delay such as head injury. All mother–child pairs were matched for the mother’s age at conception, pregnancy duration and child age at testing.
Three to seven years later the women were contacted to discuss participation in the study and to schedule an appointment for assessment at the hospital. The children were assessed with a comprehensive battery of standardised, age-appropriate psychological tests, including measures of intelligence, selective neurocognitive abilities and behaviour, such as the Wechsler Preschool and Primary Scale of Intelligence–Revised test, picture and number memory tests and a Conner’s Parent Rating Scale for behaviour and attention.
Maternal IQ and socioeconomic status (SES) were also assessed during this visit, as these could be potential confounders to the child outcome measures.
What were the results of the study?
The researchers say that children of women with NVP had significantly higher nonverbal intelligence scores, but similar verbal intelligence scores to children whose mothers did not have NVP. Among the children exposed to NVP, 21% scored 130 or more on the IQ scale. This is significantly more than the population average of 100 and compares to 7% of children not exposed to NVP who attained this score.
All children scored in the normal range for IQ, with the group that was exposed to NVP scoring higher than the non-exposed group on performance IQ, tests of verbal fluency, auditory processing and numerical memory. Using statistical modelling the researchers found that the severity of NVP and maternal IQ predicted better results.
What interpretations did the researchers draw from these results?
The researchers say that NVP improves children's developmental outcomes and that the drug Diclectin does not appear to affect foetal brain development adversely and can be used to control NVP when clinically indicated.
What does the NHS Knowledge Service make of this study?
There are several points to note about this study, including:
- Although children’s IQ was measured after the women were recruited to the study, this was a retrospective component to the study and has a potential for recall bias. The women were asked to recall some aspects of their pregnancy over the phone and their recall may not have been completely accurate.
- The researchers used different versions of the assessment instruments, partly because the study spanned a period of several years, during which newer versions of two of the tests became available. This means that comparing the children's test results might lead to errors, such as significant differences when the children were not different.
- The age range of the children when tested was wide (three to seven) so that it may not have been possible to take into account fully the effect of age on IQ.
- The researchers found eight significant differences out of 90 possible comparisons and, despite statistical corrections, it is possible some of these differences may have occurred by chance.
This study has shown that exposure to the drug Diclectin did not adversely affect children’s cognitive abilities, which could be reassuring for parents. However, the claim that nausea and vomiting in pregnancy might enhance IQ is not proven by this study. The researchers’ theory that hormones might be involved would need to be tested by a study that actually measures these hormones.