WHY do we listen to babies in labour?
During a contraction, blood flow to the baby is reduced and it’s essentially like the baby is “holding its breath” at the peak of every contraction. A healthy, well-oxygenated baby can withstand hours of this, but if there are certain complications (i.e placental abnormalities, umbilical cord issues) the baby may not be able to tolerate these normal dips in oxygen.
The baby’s heart rate in labour is an indicator of well-being.
HOW do we listen to babies in labour?
There are two ways to listen to a baby in labour:
- Intermittent Auscultation (IA), and
- Continuous Electronic Fetal Monitoring (cEFM or simply EFM)
Intermittent Auscultation (IA), also called “hands-on listening”, means listening to the fetal heart rate using a fetoscope or hand-held Doptone (doppler) for a total of 60 seconds, usually every 15-30 minutes in active labour and every 5 minutes while pushing.
Continuous Electronic Fetal Monitoring (cEFM or EFM) is when the fetal heart rate and contractions are monitored continuously throughout labour using an ultrasound device and contraction-measuring device placed on the mom’s abdomen, where both the fetal heart rate and contraction pattern are printed out on paper or retained digitally.
***Disclaimer: there is a lot of training that goes into the listening and interpretation of the fetal heart in labour, so this is a VERY shallow explanation of what we can hear and is not meant to be treated as a textbook explanation. I’ve drawn some VERY rudimentary diagrams to explain the following terms which are only used when discussing cEFM:***
A normal heart rate for a term fetus is about 110-160 beats per minute, and we expect to see variability: the heart beat goes up and down from second to second and we want the variability over one minute to rest between 5-25 beats per minute. Good variability shows that the sympathetic and parasympathetic parts of the brain are working well together, and a flat line is a VERY bad sign.
An acceleration is where the heart beat rises at least 15 beats above baseline for at least 15 seconds for a term baby, and this shows good brain oxygenation and an active baby. If we listen to the baby for over an hour and don’t see a couple of these accelerations of the heart rate, we would know the baby is in trouble and more testing would be ordered with a plan for possible delivery.
Bradycardia is when the baby’s heart rate remains below 110, and tachycardia when the baseline remains above 160.
The fetal heart can have decelerations too (drops in the heart rate), and they can be from benign to necessitating an immediate delivery.
An early deceleration mirrors the contraction and is very normal, especially at the end of labour when there’s pressure on the fetal head, face and abdomen, leading to nerve stimulation which drops the heart rate during the contraction. These types of decelerations require no action on the part of the care provider.
A variable deceleration is a quick drop of the heart rate and then return to baseline, usually caused by cord compression and can be normal when not seen too frequently, but can quickly turn abnormal with prolonged or extensive cord compression.
A late deceleration begins after the contraction has started and ends after the contraction has ended, and is a sign of placental blood flow issues. These decels are more ominous than other decels and are not as common; we don’t like to see these.
History of continuous Electronic Fetal Monitoring
cEFM was introduced in the 1970’s without evidence from clinical trials, touted as the solution to cerebral palsy (CP) by the industry’s marketing. CP is is caused by oxygen deprivation to the brain, which kills brain tissue and can lead to massive disability. Rates of CP, however, have remained stable since cEFM was introduced, as most studies show that the majority (70%) of CP cases occur before the onset of labour.
False positive rates for predicting Cerebral Palsy based on cEFM strips are as high as 99.8%!!!
Yup you read that right! That means that more than 99% of the time when an EFM strip shows signs of distress and your provider thinks your baby is at risk of brain damage due to low oxygen, it’s unlikely to be the case. This is why most babies born via Caesarean due to abnormal fetal heart rate come out kicking and screaming!
A 2017 Cochrane Review (which is a review of ALL the literature on fetal monitoring) found that when you compiled all the data on cEFM versus IA, there were no differences in Apgar scores or cord blood gases (tests that show us how baby was doing inside), rates of asphyxia, admission to the NICU or perinatal death. There was, however, a 50% higher risk of neonatal seizure in the IA group, but overall rates of seizures in babies are so low (0.15% in EFM group and 0.3% in IA group). Unfortunately, we don’t have any research that shows whether these early seizures affect the long-term health of the baby.
On the other hand, women in the cEFM group were 63% more likely to have a CS and 15% more likely to have vacuum or forceps, and this risk of CS is higher in hospitals that have higher overall CS rates.
This means that the use of continuous Electronic Fetal Monitoring is unlikely to prevent brain damage in your baby but will increase your risk of Caesarean.
What about an admission strip before I'm admitted?
Although the recommendation is to listen to a baby with intermittent auscultation upon admission to hospital, many centres still do an admission strip, which is where they’ll listen with cEFM for a certain amount of time after you arrive in labour, regardless of risk factors.
Research shows that if a woman is given an admission strip, she’s more likely to be on cEFM during her labour; there are no benefits for using EFM on admission for low-risk women.
What do Canadian guidelines say about all this?
The Society of Obstetricians and Gynaecologists of Canada’s 2020 Fetal Health Surveillance Guideline states that there is no evidence to justify the use of cEFM in routine practice, and that IA should be used for low-risk women.
What if I’m not low-risk?
Unfortunately, we don’t actually have evidence comparing women with specific risk factors using IA or EFM in labour; all the guidelines recommending cEFM for complications such as twins, breech, high BMI, prior CS, being overdue, preterm labour, PROM, and oxytocin in labour are expert opinions. There is no evidence that demonstrates that the use of cEFM would benefit these births.
So if EFM isn't reducing rates of brain damage in babies, why is it being used so frequently?
- Liability: if there’s no print out or digital copy of the fetal heart rate in labour, the OB/hospital can’t show the judge and jury in a malpractice suit that it’s not their fault the baby died or has brain damage. Not having this “proof” increases the risk the hospital will lose any lawsuit, or have to settle. The ironic thing is that the introduction of EFM has greatly increased the rates of malpractice suits. This is a great example where the care given is in the hospital’s best interest, not the family’s.
- Lack of resources: providers can watch the strip from their desk as they multi-task and chart.
- Time: it takes time to walk into the room, find the fetal heart and listen for 1 minute, repeating this every 15-30 minutes as required.
- Marketing: Let’s not forget consumerism in all this! There’s a huge push from the makers of the monitors to use them! Research shows that the fetal monitor market is expected to reach $3.6 billion USD by 2022.
Take home lesson:
Assume your care provider should use Intermittent Auscultation on your baby in labour, and if continuous Electronic Fetal Monitoring is recommended or initiated, have a conversation about the indications, decide what YOU want, and go from there!
If you and your care provider both feel that EFM is appropriate for use, consider the use of a wireless EFM monitor so that you are still able to move around and go in the water, which will go a long ways toward reducing your risk of CS!
Alfirevic Z, Devane D, Gyte GML, Cuthbert A. “Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour”. Cochrane Database of Systematic Reviews 2017, Issue 2. Art. No.: CD006066. Accessed online 18 March 2021.
Dekker, R. “The Evidence on: Fetal Monitoring”. Originally published 17 July 2012 and updated 21 May 2018. Evidence Based Birth. Accessed online 18 March 2021.