Pregnancy monitoring: reaching the final stretch

If you're pregnant and the moment of birth is approaching, you've probably already been given your foetal monitoring appointment. It's a routine procedure that may raise questions, which is why our team of midwives has prepared this post for you: “Monitoring at the end of pregnancy”.

What is foetal monitoring in pregnancy?

The non-stress foetal monitoring, colloquially known as pregnancy monitoring, is a very common cardiotocographic method that assesses the baby before birth. It is a non-invasive method and can be carried out in any setting with an electronic foetal monitor. What's more, there is no direct risk of associated maternal or foetal injury, which is why it is performed routinely at the end of pregnancy.

What is the aim of foetal monitoring at the end of pregnancy?

The main aim of antepartum foetal surveillance (monitoring carried out before birth) with non-stress cardiotocographic recording (monitoring), or the stress test (known as the Posse test), is to identify babies with chronic loss of foetal wellbeing, in order to plan strategies or interventions aimed at preventing an adverse event. It is about identifying babies at risk of hypoxic injury (compromised blood flow through the placenta) and intervening, where possible, to prevent adverse outcomes. Bear in mind that the evidence currently available is limited, as there are no conclusive randomised studies on the matter. What's more, the strategies available to us cannot predict acute events. And the secondary aim, and the most common one, is to identify babies who are normally oxygenated, so that the pregnancy can continue safely and unnecessary interventions can be avoided. In addition, other factors are taken into account, such as gestational age, the progress of the pregnancy, maternal conditions (including any medication taken) and the baby's condition (for example, growth restriction, anaemia, arrhythmias, etc.) Start designing your bottle

What is pregnancy monitoring used for

The non-stress foetal monitoring, known as pregnancy monitoring, is used to check the foetal heart rate before birth. There are studies showing a lower incidence of foetal death in pregnancies that undergo this practice, although there is still no conclusive evidence from randomised trials confirming that the use of non-stress monitoring or the Posse test leads to a reduction in foetal death or neurological injury. Even so, monitoring in pregnancy is a standard obstetric practice in developed countries such as Spain, and it is carried out for every pregnant woman.

How is foetal monitoring carried out?

To carry out foetal monitoring, an electronic foetal monitor is used, which continuously records your baby's heart rate on a chart rather like an electrocardiogram. And how is that achieved? These monitors have small devices that are placed on the mother's abdomen during monitoring. One probe acts as a Doppler ultrasound, generating an ultrasound beam onto your baby's heart to determine your baby's heart rate. And the second probe has a pressure sensor that records the uterine contractions, along with their intensity and frequency.

Pregnancy monitoring from which week

The indication for starting antepartum monitoring with non-stress foetal monitoring will be determined by the clinical situation and epidemiological risk factors of the mother and/or the baby, as assessed by the obstetrician. This variation is because high-risk patients can have a mortality rate up to 10 times higher than pregnant women without risk factors. A distinction is therefore made between pregnant women without risk factors and pregnant women with risk factors.

Low-risk pregnancies

If you have a low-risk pregnancy, your midwife will give you a monitoring appointment from week 40 of pregnancy, and if you would like expectant management between week 41-42 of pregnancy, meaning you don't want to be induced, you will have a monitoring session every 48-72 hours plus an ultrasound scan, to also assess the amniotic fluid and the middle cerebral artery (MCA) Doppler.

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Pregnant women with risk factors

If, on the other hand, you have risk factors, monitoring to check antenatal wellbeing will begin according to the risk factor and the corresponding protocol. To give you an idea, if there is no specific protocol for your risk factor, non-stress foetal monitoring will begin between week 28 and 29 of pregnancy.

What's more, if you are over 40 years old, have a BMI (body mass index) ≥ 30 kg/m2 or a diagnosis of intrahepatic cholestasis, the recommendation will be to end the pregnancy from 40 weeks of pregnancy. But if, even in your case, you would rather not be induced, monitoring of your baby's wellbeing will be added every 48 to 72 hours plus an ultrasound scan to determine the amniotic fluid and the MCA Doppler.

Risk factors during pregnancy:

Below is a list of the risk factors so that you can see where your pregnancy fits:

Underlying maternal conditions:

• Maternal diabetes
• other endocrine disorders: thyroid disorder
• Chronic hypertension
• Maternal heart disease
• Maternal kidney disease
• Antiphospholipid syndrome
• Thrombophilias
• Other concomitant medical conditions
• Maternal infections (HIV, etc.)

Epidemiological risk factors

• Maternal age (< 18 years and > 38 years)
• Obesity (BMI > 30)
• Harmful habits (smoking, alcohol consumption)

Obstetric complications

• Poor obstetric history
• Unmonitored pregnancy
• History of abdominal trauma
• Prolonged pregnancy
• Intrauterine growth restriction
• Hypertensive disorder of pregnancy
• Reduced foetal movements
• Premature rupture of membranes
• Twin pregnancy
• Rh isoimmunisation
• Intrahepatic cholestasis
• Abnormal amniotic fluid
• Foetal malformation, chromosomal abnormality, foetal infection
• Placental abnormalities
• Threatened premature birth

How many times will I have monitoring before birth?

There is no high-quality evidence determining an optimal frequency for carrying out monitoring in pregnancy. So the frequency of non-stress foetal monitoring can vary between one test a week, two tests a week or three tests a week. This frequency will be decided by your gynaecologist, and will continue for as long as the indication to carry it out remains.

How long does monitoring take?

The minimum duration of foetal monitoring during pregnancy has not been established, so there is no recommendation for an optimal duration for carrying out this monitoring.

Some sources recommend carrying out monitoring for at least 20 minutes, even if two qualified accelerations have been observed before that time.

The evidence tells us that during non-stress foetal monitoring, on average, the criteria needed for a positive assessment are met by 12 minutes. At 20 minutes, 75% of recordings already meet these criteria. At 40 minutes, 90%. And only 2.5% do not meet the minimum requirements at 60 minutes.

I went to A&E while pregnant and they did a monitoring session

Yes, and that's because if you are more than 24 weeks pregnant and you attend for an obstetric reason, or one where the wellbeing of your baby could be compromised (a feeling of uterine activity, reduced perception of foetal movements, high blood pressure, fever…), you will have a non-stress foetal monitoring session.

If, on the other hand, even though you are more than 24 weeks pregnant, you attend for a non-obstetric reason (such as vulvovaginitis, toothache…), your baby's wellbeing can be assessed with a foetal movement ultrasound scan, an assessment of the amniotic fluid or, if the obstetrician prefers it, by carrying out a non-stress foetal monitoring session as well.

And if you are over 40 weeks with no risk factors, or 38 weeks pregnant with risk factors, a monitoring session will be carried out as set out in the protocol.

Pregnancy monitoring results

The non-stress foetal monitoring will be reactive from week 32 of pregnancy if there are two or more accelerations in the heart rate that reach a peak of at least 15 beats per minute above the baseline heart rate and last at least 15 seconds from the start until the return to the baseline within a period of 20 minutes.

If the non-stress foetal monitoring is positive, it indicates with a reliable level of evidence that the oxygenation of your baby is normal, regardless of how long the observation time needed to demonstrate this reactivity lasted.

If the monitoring is carried out before 32 weeks of pregnancy, we must bear in mind that it will be reactive when there are two accelerations that rise at least 10 beats per minute above the reference value and last at least 10 seconds.

What if I don't have any accelerations on my monitor?

It's nothing to worry about: up to 60% of non-reactive monitoring sessions are usually false positives, which are normally defined as a non-reactive monitor. If that is the case, all that is needed is an additional assessment, such as:

• Repeat the monitoring after 30 minutes
• Carry out vibroacoustic stimulation to trigger accelerations
• Carry out a Posse test

What if decelerations appear on my monitor?

The evidence tells us that the significance of decelerations in a non-stress foetal monitor for the foetal heart rate is not clear. Most foetal heart rate decelerations during monitoring are variable decelerations, which reflect temporary episodes of umbilical cord compression.

What's more, there are multiple observational studies that have described an increase in the frequency of decelerations in the intrapartum foetal heart rate and in surgical birth when this combination occurs, except when they are brief; however, the outcomes are usually good.

If there are variable decelerations, late or prolonged ones, an additional assessment is required, which could include extended monitoring of your baby's heart rate and of uterine activity, as well as an ultrasound assessment of growth and foetal anatomy, and the amniotic fluid volume.

Finally, the decision on how to manage the situation lies with the obstetrician, who should be guided by the results of the additional assessment and other details specific to the clinical situation.

Vibroacoustic stimulation, to stimulate the baby

There are techniques used to obtain a reactive monitor, such as vibroacoustic stimulation. This stimulation uses a vibroacoustic source, usually an artificial larynx, which is placed on the mother's abdomen or just above it, to stimulate the baby's movement. This vibroacoustic stimulation can reduce the number of non-reactive foetal monitoring sessions and also shorten the duration of the test without reducing the predictive value of the non-stress foetal monitoring.

It is not governed by a protocol, but it can be carried out as early as five minutes after the start of monitoring. And the stimulus will be applied for one to five seconds and can be repeated.

There is also no optimal location or established number of stimulus applications. The recommendations of clinical guidelines suggest placing the device on the mother's abdomen and applying a stimulus for one or two seconds. If there is no foetal response, the stimulus can be repeated up to three times with progressively longer durations of up to three seconds.

In addition, as a point of interest, it is worth knowing that a study found that exposing the baby in the womb to recorded music was associated with an increase in foetal movements, with a greater number of accelerations and greater variability. Music is therefore a possible non-invasive and inexpensive tool for shortening the time to reactivity.

Light stimulation

There is also another technique that appears to stimulate babies and can be as effective as vibroacoustic stimulation: light stimulation. Light stimulation of the foetus consists of carrying out transabdominal light stimulation with a halogen light for 10 seconds. Although more safety and efficacy data are needed before this method can be recommended instead of vibroacoustic stimulation.

Since when has non-stress foetal monitoring been carried out?

The use of monitoring or the Posse test became widespread at the beginning of the 80s, after the publication of a study that showed optimal results with regard to this test and neonatal mortality rates.

Later, in 2015, there was a Cochrane review that attempted to determine whether the use of non-stress foetal monitoring could improve maternal or perinatal outcomes by identifying high-risk pregnancies that required rapid induction of labour or an emergency caesarean section.

It is true that no significant differences were observed between the groups in terms of maternal outcomes, such as the frequency of induction of labour or birth by caesarean section, or in terms of infant outcomes, including perinatal mortality, admission to the neonatal intensive care unit and neonatal seizures.

Conclusion: monitoring at the end of pregnancy

Your moment is approaching, the one when you will possibly meet the love of your life. At Happymami, we wish you all the best, and we would certainly recommend that you trust the healthcare professionals who are going to look after you. We are very lucky to have midwives, gynaecologists and obstetricians who are envied all over the world, and who want the best outcome for you and your baby. And as you already know, we will always be here for whatever you need.

Bibliography

1. David A Miller MD. Evidence-Based Clinical Decision Support System| UpToDate | Wolters Kluwer . Nonstress test and contraction stress test; 10 May 2022 . Available at: https://www.uptodate.com/contents/nonstress-test-and-contraction-stress-test?search=monitor%20embarazada&source=search_result&selectedTitle=16~150&usage_type=default&display_rank=6
2. Html, H. O.-F.-A. (n.d.). Bienestar Fetal Anteparto. Retrieved on 8 December 2022, from https://medicinafetalbarcelona.org/protocolos/es/obstetricia/bienestar-fetal-anteparto.html