Tobacco smoke contains thousands of compounds, including nicotine and carbon monoxide. It is unknown what adverse effects each of these compounds may have on fetal growth, making it difficult to develop measures of tobacco exposure. A number of different biomarkers have been considered.

Thiocyanate is a metabolite of hydrogen cyanide found in cigarette smoke. However, it is impossible to distinguish between elevated thiocyanate levels resulting from the consumption of certain foods and elevated levels resulting from smoking cigarettes.

Exhaled carbon monoxide is easy and inexpensive to measure, but carbon monoxide has a short half-life. This limits its use in light or sporadic smokers.