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Re: Is gestational week at birth an important marker of the impact of ambient air pollution?

Dear Editor,

We read with great interest the article by Mannes et al., which related the adverse effects of ambient air pollution on birth weight.[1] That article well described the effects of pollutant exposure on the risk of low birth weight using a marker of small for gestational age (SGA). However, that study presents some shortcomings.

First, gestational week at birth is obstetrically and socially a more important marker for infancy and childhood than birth weight.[2] In recent studies such as Mannesf, the gestational week at birth or both the gestational week at birth and birth weight are used rather than birth weight.[3] We are convinced that the gestational week should be incorporated into their methods as an appropriate marker. Secondly, almost all infants in multiple gestations are SGA even if the pregnancy course is uneventful.[2] Accordingly, Mannes et al. were compelled to exclude multiple gestations from the study materials. Finally, the blood-placental barrier prevents various materials from passing through to the fetus in a similar manner to that of the blood-brain barrier. Accordingly, it is inferred that those materials do not easily reach the fetus even if they can reach to the mother. Mannes et al.fs study would have been better researched and more useful if the above problems had been addressed in their discussion section.

References

1) Mannes T, Jalaludin B, Morgan G et al. Impact of ambient air pollution on birth weight in Sydney, Australia. Occup Environ Med 2005;62:524-30.

2) Cunningham FG, Leveno KJ, Bloom SL et al. Williams Obstetrics (22nd edn) TX, McGraw-Hill 2005