The effects of smoking on the unborn have been noted as far back as 1935 in the literature; a study by Sontag and Wallace
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found that smoking one cigarette a day during the last month of pregnancy produced either an increase or decrease of fetal heart rate, both are hazardous. They also found that smoking can effect the whole circulatory system of the fetus. In 1957 Simpson
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found that as a result of heavy smoking, expectant mothers who carried to term delivered twice as many low-birth-weight babies as nonsmoking mothers. The heavy smokers had twice as many low-birth-weight babies as moderate smokers. The sample in this study was 7,449 pregnant mothers.
In a follow-up study Frazier
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was able to replicate Simpson’s findings. However, Frazier included in his conclusion possible reasons for these negative outcomes. He felt, first, that due to the heavy maternal smoking habits there is a decrease in appetite (you already are aware of the results of poor nutrition from the previous section). Second, smoking may constrict the placental blood vessels and thus decrease the oxygen supply to the fetus. Third, it is possible that a woman smokes heavily during pregnancy for the same reasons (such as tension and anxiety) that also cause low-birth-weight babies.