In the very unfortunate case of poor neonatal outcomes such as seizures or bleeding in the brain, parents and providers want answers. One test we have to help understand timing of possible hypoxia (or when a baby doesn't get oxygen) is a test called cord blood analysis. A blood sample is taken from the umbilical cord immediately following delivery, put on ice, and sent for analysis. The diagnosis of "metabolic acidosis" is given when the blood meets two criteria: pH<7 and "base deficit" > or =12.
Thus far, most of our understanding of cord blood gases comes from small observational studies. In their newly published article in the Green Journal, researchers at the University of Texas in Dallas reviewed the cord blood results of over 300,000 deliveries from 1988 to 2013. They only looked at deliveries of singletons (no twins) between 35 and 42 weeks gestation with no congenital malformations. Cord blood gases were available for 95% of the deliveries at the hospital. Of all the deliveries, 0.39% had a metabolic acidosis. The researchers' primary focus was on seizures because they are a marker for possible alteration of brain function. Of all the infants who suffered from seizures, 19% had a metabolic acidosis. Therefore, about 80% of seizures were not related to a metabolic acidosis, which means that the majority of neonatal seizures may not be linked to specific birth trauma. Conversely, of all infants with metabolic acidosis, 94% did not develop seizures.
Most interestingly, metabolic acidosis was linked to almost all the negative neonatal outcomes studied, including low APGAR scores, difficulty breathing, low blood sugar, severe infection, seizures, bleeding in the brain, and death. These relationships remained significant even after researchers controlled for possible confounding factors. Similarly, obstetric complications were also significantly linked to metabolic acidosis. These included diabetes, high blood pressure, prolonged second stage of labor (a long time pushing), intrapartum infection (chorioamnionitis), forceps delivery, c-section for fetal distress, umbilical cord prolapse (umbilical cord coming out before the baby), and placental abruption (the placenta separating too early). Only c-section for fetal distress and placental abruption were associated with neonates having both seizures and metabolic acidosis. This large study therefore supports the belief that cord blood gases indicative of metabolic acidosis are linked to poor neonatal outcomes and obstetric complications. More research is needed to better delineate which infants are at risk for these outcomes before birth and how to prevent them.