The Effect of Maternal Smoking on Carboxyhemoglobin Levels and Acid-Base Balance of the Fetus

Abstract

The weU-documented birthweight reduction in the infants of mothers who smoke throughout pregnancy [1] has prompted a number of studies to determine the actual mechanism involved. Rheological effects have been postulated [2], and nicotine has been shown to be dose-related to fetal breathing movements in utero [3]. A majority of the studies, however, has concentrated on carbon monoxide as the causative agent, reviewed recently by Yaffe [4].

It i s now over a decade since infants of smoking mothers were shown to be more acidotic and to have higher pC0z levels than those of nonsmoking mothers [5]. Maternal and fetal carboxyhemoglobin (COHb) levels at birth have been related to the extent of maternal smoking during pregnancy [6], a study which also showed fetal COHb levels to be almost double those in the mother. No study, however, has yet correlated combined pH, pOz, pC02, and COHb levels with the extent of maternal smoking during pregnancy, and this i s the purpose of this paper.