The Non Stress Test - Important Health Check in Pregnancy or Misguided Use of Technology?
This post has been brewing for a while so I finally had some time to crack on with it. It’s an important one as the NST (non-stress test) is recommended to so many expectant moms during pregnancy – especially in the US. Yet there are very few unbiased articles on this topic and plenty of one sided articles in the mainstream pregnancy websites. A quick google of ‘NST in pregnancy’ will show you what I mean). I hope this will be a helpful resource for you to as a discussion starter with your careprovider.
The million dollar question is whether this test is improving outcomes for moms and babies or not – and the answer might surprise you.
What Is The Pregnancy Non Stress Test (NST)?
The non stress test measures your baby’s heart rate over about 20-30 minutes in the last few weeks of your pregnancy. It’s called "non stress" because during the test your baby should be bobbing around happy as can be and not in any way stressed (labor surges are supposed to slightly stress your baby to prepare him for life outside of the uterus so stress isn’t always a bad thing). Your careprovider is looking for what’s called ‘reactivity’. NST is based on the premise that your baby’s heart rate will ‘react’ and go up temporarily when he moves. Just like when you move off the couch - your heart rate goes up a little. Sometimes your NST appointment will happen right as your baby is going into a sleep cycle so of course his heart rate is not going to accelerate and your test might take longer.
What Happens During The NST?
It’s usually done in hospital (sometimes your careproviders office). You’ll be asked to lie down or sit reclined. A stretchy belt with a sensor that picks up your baby’s heart rate is placed around your bump and the machine records the activity. If you’re close to full term some careproviders may include another belt and sensor that picks up any surges you may be having. (It can be very exciting to see that the uterus may already be doing some pain free warm ups that you might not have been aware of - not unusual for our GentleBirth and hypnobirthing moms).
What Do The Results Mean?
Your careprovider is expecting two or more accelerations (speeding up) of your baby’s heart rate in a 20-minute period. This is considered ‘reactive’ and suggests (it does not predict) that right now your baby seems healthy). If your baby doesn’t have these accelerations in his heart rate it could just mean that baby is asleep and the test will continue longer and you may be offered some juice to drink or have your position changed. It may also mean that your baby may be having problems and isn’t getting enough oxygen.
With that in mind - the test itself isn’t stressful on your baby but it can be very stressful on parents and may lead to a very different labor (or cesarean) to the one they envisioned depending on who is interpreting the results given the high false alarm rate.
Indications for NST (Who Needs It)?
This is where the waters get a little murky. Depending on where you’re living it’s not really clear which moms should have this test. It would seem logical that moms who are having a complicated pregnancy would benefit from this test in the hope of avoiding the tragedy of having a stillborn baby but the risk is low and in fact 30% to 50% of perinatal deaths happen with no warning in seemingly healthy well babies. Added to that disagreements between careproviders on what is ‘normal’ or ‘abnormal’ we need to widen the lens a little and see what’s happening outside of the US (especially given the US has such poor outcomes and spends more than any other developed country on maternity services).
How Accurate is the Test
The false-positive (think of it as false alarm) rate of a nonreactive non stress test can be as high as 55% . That means the test incorrectly diagnosed complications for up to 55% of the babies monitored). What does that mean for you? More testing? A unplanned induction or cesarean?
In my experience I’ve seen moms laid almost flat on the bed (not recommended) and a deceleration is observed…which then puts everyone on high alert and mom ends up potentially being sent to L&D to have more monitoring and after several hours of worry later they’re sent home or asked if they would like to induce ‘while they’re there’.
What About Gestational Diabetes?
There is a growing trend in the increase of recommendations for this test in women with very well managed gestational diabetes and/or women who are over 36 years of age and some very healthy women too depending on their careprovider.
So if you have Gestational Diabetes that’s managed with diet and exercise here’s how your care would differ depending on where you live.
UK – NST not recommended
Australia – NST not recommended
Canada – NS not recommended (In most cases a normal NST is predictive of good perinatal outcome for one week (providing the maternal-fetal condition remains stable), except in women with insulin dependent diabetes or with a postdates pregnancy, in which case NSTs are recommended at least twice weekly.
USA - NST recommended (remember - US care falls short in the developed world compared to many other countries).
So international guidelines don’t recommend it for well managed GD – unless there is a suspicion that your baby isn’t growing at the appropriate rate for your pregnancy.
Things You Can Do:
Talk to your careprovider about the accuracy, benefits and potential tradeoffs of having this test and talk to your partner about what might happen if the test suggests your baby is unwell.
If you choose to have the NST be sure you are sitting in an upright position.
Have a sugary drink just before the test – which may increase your baby’s activity.
Keep in mind that your baby may be having a sleep cycle during this time (they spend a LOT of time sleeping in the final trimester although it may not feel like it at 2am).
Use one of your favorite Mp3s from the app to relax you - these tests can be stressful.
Consider asking staff to turn the volume down on the machine so if you or your baby move during the test the silence in the room doesn’t panic you.
Opt out of the NST.
Lots of food for thought - did you have the NST? What was your experience?
Additional Reading
NICE Guidelines (UK)
Monitoring fetal growth and wellbeing
1.3.31Offer pregnant women with diabetes ultrasound monitoring of fetal growth and amniotic fluid volume every 4 weeks from 28 to 36 weeks. [2008]
1.3.32Routine monitoring of fetal wellbeing (using methods such as fetal umbilical artery Doppler recording, fetal heart rate recording and biophysical profile testing) before 38 weeks is not recommended in pregnant women with diabetes, unless there is a risk of fetal growth restriction. [2008, amended 2015]
1.3.33Provide an individualised approach to monitoring fetal growth and wellbeing for women with diabetes and a risk of fetal growth restriction (macrovascular disease and/or nephropathy). [2008, amended 2015]
Cochrane Review
Antenatal CTG is a commonly used form of fetal assessment in pregnancy and uses the fetal heart rate as an indicator of fetal well‐being (Boyle 2004). It may be used in isolation, sometimes referred to as the ‘non‐stress test' or with the stimulation of uterine activity to see how the fetal heart responds, sometimes known as the ‘contraction stress test’ (Owen 2001).
It is important that the caregiver understands the potential advantages and disadvantages of the application of the test before the test is offered to the woman, including information about the further testing that it may lead to. As with any other test that is used in pregnancy, the test should only be undertaken with the informed consent of the woman after adequate and appropriate counselling as to the implications, benefits, limitations and consequences of such investigation (RANZCOG 2006b).
led to the belief that performance of a CTG would allow early identification of fetal heart rate changes associated with hypoxia and allow subsequent early intervention with improved outcomes. However, later studies have demonstrated a lack of specificity and high false positive rates when using the CTG to detect fetal compromise (Sadovsky 1981; Trimbos 1978b).
Potential Adverse Effects of Antenatal CTG/EFM
It is important to consider the potential adverse effects of this form of fetal assessment. These may include the consequences of false negative results, inappropriate interpretation and subsequent false reassurance of fetal well‐being for the mother and the health practitioner. Also, in the case of a false positive result, the consequences are unnecessary procedures or interventions for mother or fetus or newborn and increased use of healthcare resources.
Authors' conclusions
We found no good evidence to support the use of traditional cardiotocography (CTG), or computerised CTG, in pregnancy for improving fetal outcomes. The data are not of high quality and lacked power to detect possible important differences in either benefit or harm. We recognise that many aspects of maternity care may have changed since the trials reviewed here were carried out, so new studies are needed to assess the effects of traditional and computerised antenatal CTG before they are used in clinical practice. In order to be relevant to current practice, future trials and reviews may need to assess not only antenatal CTG in isolation, but also combinations of different fetal assessment tests.
Research on the effectiveness of traditional CTG should focus on women with specific conditions that pose risks to fetal health. For example, the use of CTG for fetal assessment in women with a post‐term pregnancy, assessment of fetal health in pregnancies with hypertension requiring 'day stay' assessment, or CTG in women with decreased fetal movements or at increased risk of stillbirth. In addition, studies in both high‐income and low‐income countries are required, and the use of CTG in combination with other tests of fetal well‐being should also be assessed.
The use of computerised CTG should be evaluated with some urgency as there is currently little high‐quality evidence to support its use, but preliminary findings appear encouraging. Clinical trials should not only assess infant and maternal health outcomes, but women's views and satisfaction with care. The use of the minimum data set for identifying outcomes proved useful here (Devane 2007), and the outcomes listed in this review should be used in future trials. Assessing women's views will require good qualitative research methods.
Does prenatal monitoring save lives?
