Fetal exposure to alcohol during the first trimester affects the development of the facial features. The areas most affected are the eyes and midface. The three facial features are:
- Small palpebral fissures: short horizontal length of the eye opening, defined as the distance from the endocanthion to the exocathanion
- Smooth philtrum: diminished or absent ridges between the upper lip and nose
- Thin upper lip: with small volume
Most people with FASD do not have the three sentinel facial features.
More detailed information on assessing sentinel facial features can be found in Section C and Appendix C and Appendix D of the Australian Guide to the diagnosis of FASD.