Monitoring the baby’s heart in labour · 552 real births
The baby’s heart on the monitor: what doctors saw on the trace, and how the babies were born
The top line is the baby’s heart, the bottom one the mother’s contractions: the last hour before full dilatation, from a real birth at University Hospital Brno, in the Czech Republic. Read the trace, choose what you would do, then see how the baby was born and what doctors said about the same trace. Most of these babies had a normal pH at birth (375 of 552), and doctors often read the same paper differently.
The doctors who read the same half hour
The cord blood at birth
Anonymised records, used for learning. This page does not give medical advice.
Your calls so far
Your results appear here after the first birth.
When most doctors saw a pathological trace, what pH did the babies have?
Each dot is one of the 506 babies born vaginally. The higher the row, the more of the doctors who read its trace called it pathological; the further left a dot, the lower the pH in the cord. Right of the 7.20 line the pH is normal; left of the 7.05 line is acidaemia. For traces read by fewer than nine doctors, the count is scaled to nine.
traces you have read
At full dilatation, most doctors called 55 traces pathological. 29 of those babies (53%) had a normal pH, 19 a slightly low one and 7 acidaemia. Of the 25 babies born with acidaemia, 18 had traces that most doctors had not called pathological.
The alarm is not blind, though. Among babies whose traces were called pathological, acidaemia was three times as common (13%) as among the rest (4.0%). And in the second stage of labour, close to birth, the doctors flagged more of the babies with acidaemia. Of the 352 traces whose last window could be rated, most doctors called 52 pathological; 38% of those belonged to babies with a normal pH, and 13 of the 21 babies with acidaemia were flagged.
| Traces most doctors called pathological | 55 |
|---|---|
| … babies with normal pH (≥ 7.20) | 29 |
| … slightly low pH (7.05–7.19) | 19 |
| … acidaemia (pH < 7.05) | 7 |
| Babies with acidaemia, of 506 | 25 |
| … whose traces most did not flag | 18 |
| Traces on which every doctor who rated them gave the same answer | 31 |
How to read a CTG trace
A cardiotocograph has two sensors on the mother’s abdomen: an ultrasound one follows the baby’s heart, the other records the womb’s contractions. Guidelines read four things, usually over the last 10–30 minutes 7.
The baseline
The average heart rate in calm stretches, leaving out accelerations and decelerations, over at least 10 minutes. Between 110 and 160 beats a minute is normal; below 100 or above 160 is a warning sign 7.
Variability
How much the line wobbles around the baseline from second to second. A band of 5–25 beats is a reassuring sign. Under 5 beats for more than 50 minutes is a warning sign 7.
Decelerations
Drops of more than 15 beats below the baseline lasting 15 seconds or more. How they line up with contractions matters: those that start late and reach their lowest point more than 20 seconds after the contraction’s peak are more worrying; variable ones, very common, usually come from pressure on the cord. Repetitive means with more than half the contractions 7.
Contractions
The bottom line. Fewer than 5 contractions in 10 minutes is normal; 5 or more shorten the rest between them 7.
The classification joins the four: a trace is normal when all are reassuring, suspicious when one raises a question, and pathological when one is worrying or two raise questions 7. The Brno doctors classified the traces by the FIGO criteria used in Czech hospitals, built on the same four features 4.
Why a worrying trace often belongs to a baby with a normal pH
Doctors do not read alike.
Nine Czech obstetricians, with a median of 15 years’ experience, read the same traces without knowing what happened 5. At full dilatation, all the doctors who rated the same window gave the same answer for only 31 of 506 traces.
A very low pH is rare.
Even in this collection, where a low pH is deliberately more common than in life (7.2% of babies have a pH below 7.05) 1, most babies have a normal pH. When an outcome is rare, many worrying traces will belong to babies who do not have it. In an ordinary maternity unit, where acidaemia is rarer, the share of worrying traces from babies with a normal pH is probably higher still.
Sometimes an alarm was followed by action.
Of the 506 vaginal births, 44 were helped by vacuum or forceps, and the records do not say which 1. A baby delivered quickly after a worrying trace may have a normal pH precisely because someone acted. The database’s authors note that a timely caesarean can prevent the very fall in pH that the trace foretold 1.
pH is a sign, not a diagnosis.
The pH in the cord artery describes the baby’s blood at birth; a low pH can go with a lack of oxygen near the end, but on its own it cannot say what happened or how the child will be. The page calls a pH below 7.05 acidaemia, and a pH below 7.05 together with a base deficit of at least 12 mmol/L metabolic acidosis (18 of 552 babies here). The Apgar score shows how the baby breathed and responded just after birth. The fields on how the babies fared afterwards are not filled in the public database.
Continuous monitoring or listening now and then: what the trials show
A Cochrane review gathered 13 randomised trials with more than 37,000 women; 12 compared continuous monitoring with intermittent listening to the baby’s heart (with a Pinard stethoscope or a handheld Doppler 7) 6. Compared with intermittent listening, with the continuous monitor, seizures in newborns halved. Perinatal death and cerebral palsy did not clearly differ. Caesareans were 1.63 times as common, and vacuum or forceps births 1.15 times. The authors rate the evidence for most outcomes as low quality.
That is why the UK’s NICE guideline recommends intermittent listening for women with no identified risk, moving to a continuous monitor if a reason appears 7.
Caesareans in Romania
In 2019, the last year with data from almost every country, hospitals in Romania performed 43.9 caesareans per 100 live births, the third-highest of the 25 European Union countries that reported; the median was 25.7, and the Czech Republic, where the traces come from, had 23.3 8 9. The report counts operations in hospitals and births are counted separately, so the values are approximate.
Public data do not say why each caesarean was done, so they cannot show how much of the gap is down to the monitor. A companion page on Romania’s midwives follows who attends births and how the share of caesareans has grown since 1993.
How the page is made, and what it cannot say
The traces. The CTU-UHB database holds 552 CTG recordings from labour, made between 2010 and 2012 at University Hospital Brno, in the Czech Republic, and chosen by its authors from 9,164 1 2 3. Each has the baby’s heart rate and the contractions, four times a second, up to 90 minutes before birth, with pushing lasting at most 30 minutes. The page shows them twice a second; gaps are moments with no signal. The data were anonymised at the hospital and time is given relative to birth 1.
The outcomes. For each baby the cord-artery pH, base deficit and Apgar score are published. The page uses thresholds from the studies reviewed by the database’s authors: a pH of 7.20 or above is normal, below 7.05 is acidaemia, and with a base deficit of at least 12 mmol/L it is metabolic acidosis 1.
The doctors. The classifications come from annotations published by the authors: obstetricians from six Czech university clinics classified each trace as normal, suspicious or pathological in 30-minute windows, then predicted whether there would be hypoxia 4 5. Nine doctors answered for 522 traces, six to eight for the rest. Some traces were rated twice by the same doctor; the page uses the first rating. “Most” means more than half of those who classified that window.
The selection. The collection does not represent an ordinary maternity unit: its authors kept more births with a low pH than occur in reality. The 46 caesareans were added on purpose, some with a low pH and the rest as a comparison group, so they appear as individual births but not in the figures about proportions. The page’s first 6 births are chosen to show each kind of outcome; the chart of all the babies shows the proportions in the collection.
What it is not. It is a replay for learning. A doctor on duty sees the woman, not just the paper, and can run further tests, so “expedite the birth” here is not a clinical decision. Nothing on the page says that any particular intervention was or was not needed.
Sources
- Chudáček V, Spilka J, Burša M, Janků P, Hruban L, Huptych M, Lhotská L. Open access intrapartum CTG database. BMC Pregnancy and Childbirth 2014;14:16. doi.org/10.1186/1471-2393-14-16
- CTU-UHB Intrapartum Cardiotocography Database, version 1.0.0, PhysioNet, 2014. Open Data Commons Attribution License 1.0. doi.org/10.13026/C22013
- Goldberger AL, Amaral LAN, Glass L, et al. PhysioBank, PhysioToolkit, and PhysioNet. Circulation 2000;101:e215–e220. doi.org/10.1161/01.CIR.101.23.e215
- Hruban L, Spilka J, Chudáček V, Janků P, et al. Agreement on intrapartum cardiotocogram recordings between expert obstetricians. Journal of Evaluation in Clinical Practice 2015;21:694–702. Expert annotations, free for non-commercial use. doi.org/10.1111/jep.12368
- Spilka J. Expert annotations for the CTU-UHB database (file ExpertAnnCTU-UHB-CTG_20150203.csv). people.ciirc.cvut.cz/~spilkjir/data.html
- 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, CD006066.pub3. doi.org/10.1002/14651858.CD006066.pub3
- NICE. Fetal monitoring in labour (NG229), 2022, with later updates. www.nice.org.uk/guidance/ng229/chapter/Recommendations
- Eurostat. Surgical operations and procedures performed in hospitals (hlth_co_proc2), caesarean section (ICD-9-CM 74.0–74.2, 74.4, 74.99), all patients. ec.europa.eu/eurostat/databrowser/view/hlth_co_proc2/default/table
- Eurostat. Population change, demographic balance (demo_gind), live births. ec.europa.eu/eurostat/databrowser/view/demo_gind/default/table