Uterine Activity in Moderate-Severe Neonatal Encephalopathy: A Case Control Study

The advent of therapeutic hypothermia has improved outcomes for babies born with hypoxic-ischemic encephalopathy. However, the risk of death, seizures, cerebral palsy or intellectual impairment remains significant, especially among the most severely affected infants. Prevention remains a promising strategy to reduce the incidence of complications arising from hypoxic-ischaemic neonatal encephalopathy.

Excessive uterine activity may be one of several aetiological factors that contribute to depressed neurological function in the newborn. During labour, uterine contractions can compress the fetal cranium at pressures high enough to impair cerebral perfusion. Contraction rates greater than 7 in 15 minutes are associated with an increased risk of neonatal encephalopathy.

The American Congress of Obstetricians and Gynecologists defines uterine tachysystole as more than 5 contractions in 10 minutes, averaged over a 30-minute window. By this definition, excessive uterine activity is common and, at best, a non-specific predictor of depressed neurological function in the newborn. There is a need for predictors of neonatal encephalopathy that are more specific and clinically applicable.

Contraction and relaxation duration are two measures that closely reflect the proposed role of excessive uterine activity in the pathogenesis of neonatal encephalopathy. Prolonged contractions with short relaxation periods result in progressive reductions in fetal cerebral oxygenation. Shorter uterine contraction periods are associated with an increased risk of low umbilical cord pH values.

Our primary aim is to measure parameters of uterine activity, for example relaxation and contraction duration, and determine their relationship with the risk of neonatal encephalopathy. We will also investigate how measures of uterine activity interact with other measures of labour and fetal well-being, including cervical dilation rates and fetal heart rate patterns. In babies with neonatal encephalopathy, we will investigate the relationship of uterine activity with electrophysiological, radiological and developmental outcomes.

We will perform a retrospective case-control study of babies born in the Rotunda hospital from 2005 until the present. Cases and controls must be over 35 weeks gestational age and have at least 15 minutes of Cardiotocograph (CTG) recording from labour available for analysis. Cases will be babies with moderate or severe neonatal encephalopathy of apparent hypoxic-ischemic aetiology. Controls will be the first healthy babies born before and after the cases to satisfy the study criteria. Controls will be matched for parity.

The assessor of the CTG recordings will be blind to the disease status of the infants. For each recording, every uterine contraction and rest interval will be measured. Summary variables created from these measures will be used to compare the case and control groups. The primary variable will be mean rest interval duration.

For further detail please see the study protocol.

Cases

The inclusion criteria will be:

• Moderate or severe neonatal encephalopathy
• Gestational age of 35+0 weeks or greater
• Singleton pregnancy
• Inborn

The exclusion criteria will be:

• Non-hypoxic-ischaemic aetiology or postnatal hypoxic-ischaemia
• Major congenital abnormalities
• Less than 15 minutes of digital CTG recording from labour available Controls

The inclusion criteria will be:

• Gestational age of 35+0 weeks or greater
• Singleton pregnancy
• Inborn

The exclusion criteria will be:

• APGAR score of less than 5 at 1 minute or less than 7 at 5 or 10 minutes
• Admission to the neonatal unit
• Major congenital abnormalities
• Less than 15 minutes of digital CTG recording from labour available