Is it Time to End the Use of Base Deficit for Fetal Well-being Assessment?

( Am J Obstet Gynecol . 2024;231(3):315–320. doi: 10.1016/j.ajog.2024.01.031) The traditional reliance on the base deficit (BD) in umbilical artery blood as an indicator of fetal health and forecast of neonatal brain injury is being scrutinized closely due to weak evidence to support use and poor predictive performance. Although it has been a standard in clinical practice for over 50 years, BD's dependability is undermined by inherent problems in its relevance to fetal physiology and controversial types and calculations. Existing BD equations rely on adult acid-base metrics (pH 7.40 and partial CO 2 pressure of 40 mm Hg) and do not consider the distinct in utero conditions where fetal pH and CO 2 concentrations vary considerably. This oversight results in errors when identifying neonatal metabolic acidosis and may mislead doctors in handling fetal distress or anticipating negative neonatal results.