Smoking in Pregnancy and ADHD - Kate Langley

Question 1

(background):

Describe some symptoms of ADHD

Answer 1

• Excessive inattention, hyperactivity and impulsivity
• Impairment of functioning e.g. academic, peer and family impairments
• Symptoms and impairment across multiple settings (home & school)
• Leads to problems in later life (relationship/social difficulties, academic underachievement, job issues, car accidents)

UK prevalence 4.3% of school aged population

Question 2

(background):

What causes ADHD?

Answer 2

Large genetic component – heritability estimates of 76%

Environmental factors also important:
Low birth weight
Lead exposure
Maternal stress
Family factors
Exposure to toxins during pregnancy

Smoking during pregnancy

Question 3

(background):

Children whose mothers smoke during pregnancy are _____ as likely to have ADHD.

Answer 3

Children whose mothers smoking in pregnancy are twice as likely to have ADHD (OR=2.39, 95% CI: 1.61, 3.52p<0.0001;Langley et al., 2005)

Question 4

(background):

What is one of the issues with previous human research to support the ADHD and smoking during pregnancy?

What new design could be conducted to overcome this?

Answer 4

They prove correlation not causation.

There are differences between mothers who smoke and those who don’t and these might explain the observed associations.

Not all of these confounding factors can be measured/statistically controlled for.

NEW DESIGN
Comparing maternal and paternal risk.

If smoking during pregnancy causally leads to ADHD through intrauterine effects only mother smoking should have an effect

Fathers aren’t pregnant and so can’t influence the child through their womb

But, fathers do share genetic factors with their child (and other confounding effects)

By comparing risks of ADHD when mothers and fathers smoke, we can test if the effect is causal – mothers should have a greater risk

Question 5

(background):

Are there other differences between mothers who smoke and mothers who don’t?

Answer 5

Yes:

• Younger
• Have more depression and antisocial behaviour
• Are more likely to use other drugs
• Come from lower socio-economic backgrounds
• Have more pregnancy complications
• Continue to smoke/have other difficulties after the child is born

Question 6

(Langley’s Research):

What was the study’s experimental hypothesis?

Answer 6

(Langley et al., 2010):

Experimental hypothesis -

There is a causal (intrauterine) effect of smoking during pregnancy on offspring ADHD.

(based on prior knowledge and expectation)

Question 7

(Langley’s Research):

Describe the procedure of this study.

Answer 7

(Langley et al., 2010):

PROCEDURE
ALSPAC = large longitudinal study, data including smoking during pregnancy and ADHD at age 7 years

27% women and 40% men smoked during the pregnancy (nb: only looking at biological fathers)

Because epidemiological (population) sample, few have ADHD diagnosis, preferable to look at ADHD symptoms, especially when dividing the sample further (by smoking)

Statistically tested whether those in the smoking group had higher ADHD symptoms than those in the non-smoking group

Using regression analysis:

• Looks at association between your independent variable (smoking in pregnancy) and dependent variable (ADHD symptoms)
• Allows to statistically control for known confounders

Separate analyses for mothers and fathers

Compared whether there was a difference between mothers and fathers smoking

Hypothesis (causal effects) suggested a significant association where mothers smoked BUT NOT fathers

(look at relevant google doc, might help)

Question 8

(Langley’s Research):

What were the results of this research?

Answer 8

(Langley et al., 2010):

Smoking in both parents was associated with ADHD.

(suggests non intrauterine effects)

Does not support hypothesis

Question 9

(Langley’s Research):

Since this study’s results did not support the hypothesis, what were the researchers arguments as to why this might have occurred?

Answer 9

(Langley et al., 2010):

• Non-smoking mothers exposed to passive smoking from smoking fathers so this still directly impacts the child through placenta. Therefore, still possible causal intrauterine effect.

However, mothers exposure to passive smoking was NOT associated with ADHD.

Question 10

(Langley’s Research):

Since one study is not enough to answer this hypothesis,

what are some additional designs to carry out?

Answer 10

(Langley et al., 2010):

Comparing the rates of ADHD when a mother smokes during pregnancy for one child, but not the other
Sibling’s risk for ADHD the same whether smoking was in their pregnancy or not

Looking at children born following IVF – some offspring are genetically unrelated to mother who undergoes the pregnancy (egg donation, surrogacy, embryo donation), others related (homologous IVF, sperm donation)

By comparing associations across differently related mother-child pairs, can test the causal hypothesis
Smoking during pregnancy only associated with ADHD in the related mother-child pairs

Question 11

(Langley’s Research):

Why is this research so important?

Answer 11

(Langley et al., 2010):

Essentially:
- Proved that associations doesn’t equal causation.

(look at relevant google doc, end slides, to answer this more thoroughly)