Does smoking delay pregnancy? Data analysis by a tweaked geometric distribution answers

Ramalingam Shanmugam


Background: Smoking is generally known to be carcinogenic and health hazardous. What is not clear is whether the smoking impacts on the woman’s reproductive process. There have been medical debates on whether a woman in the child bearing age may delay her pregnancy due to smoking. A definitive conclusion on this issue has not been reached perhaps due to a lack of appropriate data evidence. The missing link to answer the question might be exercising a suitable model to extract the pertinent data information on the number of missed menstrual cycles by smoking women versus non-smoking women. This article develops and demonstrates a statistical methodology to answer the question.

Methods: To construct such a needed methodology, a new statistical distribution is introduced as an underlying model for the data on the number of missed menstrual cycles by women who smoke. This new distribution is named Tweaked Geometric Distribution (TGD). Several useful properties of the TGD are derived and explained using a historical data in the literature.

Results: In the data of 100 smokers and 486 non-smokers, on the average, smoking women missed 3.22 menstrual cycles and non-smoking women missed only 1.96 menstrual cycles before becoming pregnant. The smoking women exhibited more variation than the non-smoking women and it suggests that the non-smoking women are more homogeneous while the smoking women are more heterogeneous. Furthermore, the impairment level to pregnancy due to smoking among the 486 women is estimated to be 5% in a possible scale of zero to one. The 5% impairment level appears like a small amount, but its impact can be felt once it is cast in terms of fecundity. What is fecundity? The terminology fecundity refers the chance for a woman to become pregnant. The fecundity is 0.24 for smoking woman while it is 0.34 for non-smoking woman. The fecundity of a non-smoking woman is more than twice the fecundity of a smoking woman.

Conclusion: The smoking is really disadvantageous to any one in general and particularly to a woman who wants to become pregnant.


p-value, Statistical power, Prevalence, Hypothesis test, Nuisance parameter

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Gilman SL, Xun Z. Smoke: A global history of smoking, edited by Gilman SL, Xun Z. Reaktion Books Ltd., London, 2004.

Weinberg CR, Gladen BC. The beta geometric distribution applied to comparative fecundability studies. Biometrics 1986; 42: 547-560.

Stuart A, K. Ord. Kendall’s Advanced Theory of Statistics. 1st Edn., Griffin Publication, London, U. K., 1994.

Last JM. A Dictionary of Epidemiology. Oxford University Press, Oxford, U. K., 2001.

Wald A. Tests of statistical hypotheses concerning several parameters when the number of observations is large. Transactions of the American Mathematical Society 1943; 54: 426-482.

Schott JR. Matrix Analysis for Statistics, John Wiley Press, Hoboken, N. J., 2005.