Re: Re: Quitting Smoking Early in Pregnancy and Adverse Birth Outcomes: Questions Unanswered
I appreciate the authors' response to my letter. However, they did
not provide adequate information on the following major concerns:
1. Were the risk of adverse birth outcomes in children born to
mothers who continued smoking less than 10 cigarettes/day statistically
significantly different from children born to mothers (a) who continued to
smoke more than 10 cigarettes/day and (b) those who stopped smoking by 15
weeks? The adverse birth outcomes from smoking could be a time-dependent
effect, as the authors concluded but it could also be a function of
duration and dosage of the offending factor, smoking in this case, such
that risk associated with smoking less than 10 cigarettes/day over the
entire pregnancy is not different than stopping smoking by 12 weeks, or
not smoking at all. Because most non-smoking mothers do not start smoking
during pregnancy, whether timing of exposure is associated with adverse
birth outcomes cannot be fully examined. However, the authors have the
data to examine the dose and duration of exposure effects and compare the
risk estimates with mothers who did not smoke and those who stopped
smoking early in pregnancy.
2. Having the three smoking groups so different in physical (BMI) and
psychosocial factors, mere adjustment of these factors without assessing
and reporting their impacts on the outcomes of interest (as confounders
and effect modifiers) is likely to influence the results and could
potentially lead the readers to biased conclusions.
I will very much appreciate if the authors revisit their data to
answer these key research questions in a following letter. Having the data
that could answer critical scientific questions and not addressing those
to the fullest extent is definitely unjustifiable.
Competing interests:
None declared
Competing interests:
03 April 2009
Muhammad T Salam
Research Associate
Preventive Medicine, Univ of Southern California, 1540 Alcazar St, CHP-236, Los Angeles, CA 90033
Rapid Response:
Re: Re: Quitting Smoking Early in Pregnancy and Adverse Birth Outcomes: Questions Unanswered
I appreciate the authors' response to my letter. However, they did not provide adequate information on the following major concerns:
1. Were the risk of adverse birth outcomes in children born to mothers who continued smoking less than 10 cigarettes/day statistically significantly different from children born to mothers (a) who continued to smoke more than 10 cigarettes/day and (b) those who stopped smoking by 15 weeks? The adverse birth outcomes from smoking could be a time-dependent effect, as the authors concluded but it could also be a function of duration and dosage of the offending factor, smoking in this case, such that risk associated with smoking less than 10 cigarettes/day over the entire pregnancy is not different than stopping smoking by 12 weeks, or not smoking at all. Because most non-smoking mothers do not start smoking during pregnancy, whether timing of exposure is associated with adverse birth outcomes cannot be fully examined. However, the authors have the data to examine the dose and duration of exposure effects and compare the risk estimates with mothers who did not smoke and those who stopped smoking early in pregnancy.
2. Having the three smoking groups so different in physical (BMI) and psychosocial factors, mere adjustment of these factors without assessing and reporting their impacts on the outcomes of interest (as confounders and effect modifiers) is likely to influence the results and could potentially lead the readers to biased conclusions.
I will very much appreciate if the authors revisit their data to answer these key research questions in a following letter. Having the data that could answer critical scientific questions and not addressing those to the fullest extent is definitely unjustifiable.
Competing interests: None declared
Competing interests: