Objective
To examine perinatal morbidity and rate of hypoxic-ischemic encephalopathy in infants exposed to intrapartum sentinel events.
Study Design
Retrospective cohort study from 2000-2005. Perinatal mortality, perinatal morbidity and rate of hypoxic-ischemic encephalopathy were compared in 3 groups of infants exposed to different risk factors for perinatal asphyxia (sentinel events, nonreassuring fetal status, elective cesarean section).
Results
Five hundred eighty-six infants were studied. Perinatal mortality was 6% in the sentinel event group and 0.3% in the nonreassuring fetal status group (relative risk, 2.4; 95% confidence interval, 1.95–2.94). Perinatal morbidity was 2-6 times more frequent in infants exposed to sentinel events; the incidence of hypoxic-ischemic encephalopathy was 10%, compared with 2.5% in the nonreassuring fetal status group (relative risk, 1.93; 95% confidence interval, 1.49–2.52). No infant in the elective cesarean section group died, had perinatal morbidity, or developed encephalopathy.
Conclusion
Intrapartum sentinel events are associated with a high incidence of perinatal morbidity and hypoxic-ischemic encephalopathy.
Clinical signs of fetal compromise (abnormal heart rate pattern, meconium stained liquor), are poor predictors of neonatal outcome. The substitution of the term fetal distress for the more imprecise term nonreassuring fetal status (NRFS) acknowledges the low predictive value of these obstetric signs, and in particular, the limitations of the intrapartum fetal monitoring in the prediction of hypoxic-ischemic brain injury.
The opposite scenario occurs when a sentinel event (SE) takes place immediately before or during labor. SEs are acute events that can cause hypoxic and/or ischemic brain damage in a previously healthy fetus. Despite this assumption, and although patterns of brain injury and short- and long-term outcomes in infants with neonatal hypoxic-ischemic encephalopathy (HIE) after SE have been recently reported, there is very little information about the general and neurologic morbidity associated with SE in the term infant.
The aims of this study were to examine the prevalence of perinatal morbidity and neonatal HIE associated with SE in the term or near-term infant; and to compare it with the morbidity associated with a NRFS. We hypothesized that infants exposed to intrapartum SE would have greater perinatal morbidity and a higher rate of HIE than infants born after a NRFS.
Materials and Methods
Study design
This is a retrospective double cohort study, designed to compare perinatal morbidity and rates of HIE between 3 groups of infants exposed to different risk factors for intrapartum asphyxia: infants exposed to intrapartum SE, infants delivered by emergency operative delivery (cesarean section or instrumental vaginal delivery) because of an abnormal fetal heart rate (FHR) pattern, and infants delivered by elective prelabor cesarean section (CS).
We considered for the first group the following SE: uterine rupture (UR), placental abruption (PA), cord prolapse (CP), and amniotic fluid embolism (AFE). None of the mothers in the second group had an operative delivery for other reasons than the persistent abnormal FHR pattern and in no infant in that group a suspected or confirmed SE coexisted with the abnormal FHR pattern.
Operative definitions
UR was defined as any disruption of the uterine wall associated with maternal symptoms and requiring emergency laparotomy. Complete ruptures were those involving the entire uterine wall and resulting in a direct connection between the peritoneal space and the uterine cavity. Asymptomatic uterine scar dehiscences were not included.
PA was defined as complete or partial placental separation before delivery. Abruption was classified as mild if <50% of the placental was detached, and as severe if >50% of the placental was separated.
CP was defined as the descent of the umbilical cord through the cervix into the vagina and was diagnosed by palpation of the cord below or beside the presenting fetal part after the rupture of the membranes.
AFE was defined as a clinical syndrome characterized by the sudden onset during labor of maternal dyspnea, hypoxia, hypotension, and altered mental status, followed by cardiovascular collapse, multiple organ failure, and disseminated intravascular coagulation.
NRFS was defined as a persistent abnormal FHR pattern after a period of normal tracing. The following FHR patterns were considered abnormal: bradycardia or prolonged deceleration, persistent variable decelerations, persistent late decelerations, and reduced heart rate variability. Abnormal FHR patterns already present at the time of admission to the hospital were not included.
Population and data
The study was conducted in La Paz University Hospital, Madrid, Spain. La Paz is a tertiary referral center providing care for low- and high-risk pregnant women. The hospital attends approximately 9500 births a year. Obstetricians, obstetric anesthesiologists, and neonatologists (resident and attending) provide 24/7 inhouse coverage. The number of home births in Spain is negligible.
We identified, between January 2000 and December 2005, all births with an intrapartum SE and those with a persistent abnormal FHR pattern leading to an emergency operative delivery. These 2 groups formed the main cohorts. Cases were identified from the Hospital Discharge Database.
We also selected, among the 427 women who underwent a planned repeat CS in the same period, 100 cases by simple random sample to serve as external controls.
Exclusion criteria for all 3 groups were as follows: gestational age < 35 weeks, antepartum deaths, and major congenital malformations.
The following maternal, obstetric, and perinatal data were analyzed: maternal diseases, obstetric history, complications during pregnancy, FHR pattern, fetal presentation and mode of delivery, sex, birthweight, Apgar scores, cord blood gas parameters, and delivery room care management. Birthweight percentile was calculated using the Spanish growth reference tables. HIE was diagnosed when the infant met the following 2 criteria: (1) neonatal depression (cord arterial pH ≤7.00, or Apgar scores of ≤3 at 1 minute and/or ≤5 at 5 minutes; or need for advanced resuscitation), and (2) neonatal encephalopathy (difficulty with initiating and maintaining respiration, an altered alertness and excitability, and an abnormal tone pattern, with or without seizures). In infants who died, postmortem reports were reviewed.
The study was approved by the institutional review board.
Statistical analyses
Comparisons between groups were performed using the analysis of variance (ANOVA) or Kruskal-Wallis test for continuous variables, and χ 2 or Fisher exact test for categorical variables. Post hoc tests (Bonferroni and Dunnett) were performed. Relative risks (RRs) and confidence intervals (CIs) for the main perinatal outcomes were determined by means of logistic regression analysis. Statistical analyses were performed using SPSS 11.0 (SPSS; Chicago, IL). P values of < .05 were considered statistically significant.
Results
From January 2000 through December 2005, there were 57,835 deliveries at our center. We identified 307 SEs. Prevalence of SE is shown in Table 1 . PA was the most prevalent event, followed by CP. We excluded 115 cases: 90 occurred in pregnancies <35 weeks, 3 infants had major congenital anomalies and 2 died before admission to hospital, in 17 there was lack of data, and 3 events occurred after the delivery of the infant.
| Variable | Placental abruption | Cord prolapse | Uterine rupture | Amniotic fluid embolism | All SE |
|---|---|---|---|---|---|
| Total no. of cases | 161 | 113 | 29 | 4 | 307 |
| Total no. of deliveries in the study period (2000–2005) | 57,835 | ||||
| Prevalence | 0.28% | 0.19% | 0.05% | 0.007% | 0.53% |
| 1/359 births | 1/511 births | 1/1994 births | 1/14,459 births | 1/188 births | |
| Cases excluded | |||||
| <35 wks’ gestation | 58 | 27 | 5 | 0 | 90 |
| Antepartum death | 0 | 2 | 0 | 0 | 2 |
| Congenital anomalies | 2 | 1 | 0 | 0 | 3 |
| SE after birth | 0 | 0 | 2 | 1 | 3 |
| Lack of data | 11 | 6 | 0 | 0 | 17 |
| Cases included | 90 | 77 | 22 | 3 | 192 |
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