During labour a doctor or midwife keeps a check on the progress of mother and baby. Basic forms of monitoring their condition include recording the mother’s pulse rate and blood pressure, the baby’s position and pulse rate (using a foetal stethoscope), and the length and intensity of uterine contractions as felt through the mother’s abdominal wall.
In recent years more sophisticated forms of monitoring have been developed. One is the use of high-frequency sound waves (similar to the ultrasonic scan of) to detect and amplify the sound of the
baby’s heartbeat. This type of monitoring is often called Doppler ultrasound or phono-cardiography and requires a device attached to the mother’s abdomen, hence the alternative name of external foetal monitoring (EFM). By linking the monitor to an electronic recorder a continuous trace of the foetal heart rate can be obtained during the first and second stages of labour.
The EFM device is often combined with a pressure gauge which measures the intensity of uterine contractions. When pulse rate and pressure are recorded in parallel, the response of the baby’s heart to the pressure of contractions can be seen. Normally the heart rate is about 140 beats per minute and tends to slow slightly during a strong contraction, particularly during the second stage. However, if recordings show the average rate is slow (110 or less) or high (160 or more), or if the rate slows considerably after a contraction, it is likely that the baby is in some degree of distress. It may, for example, be suffering from a reduced blood supply to vital organs such as the brain, with a risk of permanent damage. When such warning signs are seen, the midwife and doctor can discuss with the mother whether the baby should be delivered as a matter of urgency.
A more reliable form of monitoring that gives the same type of information as EFM is internal foetal monitoring or IFM. A small electrode is attached to the baby’s scalp at a convenient time such as during a vaginal examination or when rupturing the amniotic membrane. The electrode works in a similar way to the electrodes used for an ECG (electrocardiograph) machine and produces, by means of a recorder, an ECG trace of the baby’s heartrate.
IFM is usually combined with an external pressure gauge as in EFM. Its advantages over EFM are that the electrode is out of the mother’s way and is less likely to be dislodged, whereas EFM devices are often uncomfortable and tend to move about during contractions.
If foetal monitoring shows that the baby is distressed, this may be further investigated by taking a tiny sample of blood from the baby’s scalp, collecting it in a small tube and analyzing it for oxygen content and the degree of acidity. This is particularly necessary if the foetal heartbeat is persistently abnormal or irregular. Low blood oxygen levels and a high level of acids indicate the need for urgent action to maintain the baby’s health.
Foetal monitoring is usually employed when the risk of developing problems is higher than normal. This may be the case in, poor foetal growth or in premature labour.
In some maternity centres the approach has been to monitor all labours, because in theory problems can arise in anyone. This trend has reversed in recent years but there is still controversy as to who should receive foetal monitoring and why.