RENO, NEV. — Newborn infants with neurologic injury resulting in death are twice as likely to have had a nighttime delivery as healthy infants, according to a study presented by Adam C. Urato, M.D., at the annual meeting of the Society for Maternal-Fetal Medicine.
The causes of this association are unclear, but may include prolonged labor, differences in staffing at night, and errors by medical personnel due to fatigue, said Dr. Urato of Tufts University, Boston.
The study made use of a Florida state database of perinatal neurologic injuries, created as a result of a law providing for no-fault compensation of families whose children suffer a birth-related neurologic injury.
Of the 447 cases of neurologic injury recorded from 1989 to 2002, there were 80 that resulted in the death of an infant. The database is limited to live-born children with brain or spinal cord injury whose birth weight was greater than 2,500 g. The neurologic problems were caused by oxygen deprivation or mechanical injury occurring in a hospital during labor, birth, delivery, or post delivery.
The 80 deaths were compared with a control group of 999 randomly selected births in Florida from 1996, the midpoint of the time span covered in the neurologic injury database, according to Dr. Urato.
Among the control group, 28% were born during the hours of 11 p.m. to 8 a.m. But 45% of the births with neurologic injury resulting in death occurred during those nighttime hours. Even after correcting the odds ratio for repeat cesarean deliveries, the deaths were 1.95 times more likely to occur at night, a statistically significant increase in risk.
Index cases were significantly less likely than controls to have been born via a normal spontaneous vaginal delivery (12.3% vs. 70.7%), and significantly more likely to have been born via cesarean section (71.7% vs. 21.4%), vacuum delivery (12.3% vs. 6.4%), or forceps delivery (3.7% vs. 1.5%).
Prolonged labor is one possible explanation for the excess of nighttime neurologic injuries resulting in death. Spontaneous labor often leads to an afternoon delivery, but most inductions start during the day. Labors that continue into the night may represent a group at higher risk. But a review of the 80 deaths showed that most did not follow prolonged labor.
Nighttime differences in staffing might be another explanation. All hospital departments, including anesthesia, nursing, pediatrics, and obstetrics, have lower staffing levels at night. But of the 80 deaths, a staffing issue was noted in only a single chart. In that case, the obstetrician was forced to wait for an operating room to perform a cesarean. Other staffing delays might not have been mentioned in the charts, Dr. Urato said.
The third explanation involves fatigue by medical personnel. At some point from 11 p.m. to 8 a.m. most people are at their circadian nadir, with an increased sleep propensity. Many studies of workers have documented an increased risk of accidents and errors at night. No mention of fatigue was made in any of the charts, however.
“Perhaps more than any other field of medicine, obstetrics is associated with nighttime work,” he said. “The image of the obstetrician awakened in the middle of the night to deliver a baby is embedded in our collective consciousness. This finding of increased risk in our field of obstetrics should not surprise us given the preponderance of evidence for other fields that demonstrate that night is indeed a time of increased risk.”