Just as your heartbeat changes from time to time, it’s normal for your baby’s heart rate to also fluctuate. A baby’s heart beats much faster than an adult’s – on average between 120 and 160 beats per minute (healthy men have a pulse of about 60, for women it’s 80). Smoking, alcohol and recreational drugs during pregnancy decrease the oxygen supply to the baby and this quickens the baby’s heartbeat. Taking an extra-hot shower can have the same effect. Lying on your back for too long in the bath can also interfere with blood circulating to the placenta and may slow your baby’s heart. These last two examples are short-lived and not dangerous for your baby – but they should be avoided because they could stress your baby.
If you’re worried about your baby’s movements in the second half of your pregnancy, and if there are signs of problems such as high blood pressure, diabetes, the amount of amniotic fluid (too much or too little) or if you lost a previous pregnancy, your doctor/midwife may take the precaution of sending you for a non-stress test.
This is a painless, non-invasive test to check your baby’s heartbeat in relation to his movements. It may be done in the consulting room or at the hospital. If the baby’s heartbeat stays within the safety perimeters, no further tests will be needed. But if the baby’s heartbeat does not score well, more tests will be done. If the condition is life-threatening for the baby, it may be necessary to deliver the baby prematurely. Fortunately this is very rare.
A non-stress test means that the baby’s heartbeat is monitored according to his movements in the absence of contractions. This test may take from 20 to 60 minutes depending on whether the baby is awake or not. You should lie on your side and you will be given a button to push every time your baby moves to record these movements on the graph.
An electronic foetal monitor is strapped over your tummy at the point where the baby’s heartbeat is strongest. This unit produces high-frequency sound waves that bounce off the baby’s heart, producing echoes. These echoes are recorded onto graph paper. They’re also digitally displayed and the sound of the baby’s heartbeat is amplified.
What your baby will be expected to do
- Your baby will have one or more “breathing” movement of the lungs, each lasting 30 seconds.
- Your baby will move his body, arms and legs at least three times in 30 minutes.
- Your baby will stretch and open and close his hands at least once during the non-stress test.
- Your baby’s heartbeat will quicken with movement, increasing the rate by 15 beats per minute for about 15 seconds at least every 20 minutes during the test.
If your baby is sleeping during the test, you can try to wake him by having something to eat or drink or changing your position.
If the doctor is not happy with the baby’s score, particularly if there are other medical problems such as anaemia in the baby (this can be caused by the couple’s blood-group incompatibility), the presence of an infection, if the baby is small for dates or there is a problem with oxygen and nutrition supply to the placenta, a contraction stress-test will be necessary or the doctor may order a biophysical profile or ultrasound. This more advanced test, with the help of a scan, will monitor the baby’s movements as well as muscle tone, breathing movements, the health of the placenta and the amount of amniotic fluid.
If the tests are all normal and you and baby are healthy, there is no need for further tests. If you have a medical problem or there is concern that your baby is at risk, the non-stress test maybe repeated once a week or more often if you are a diabetic. In more severe cases, you may be admitted to hospital and retested after 24 hours. If the score has deteriorated during this time, your baby may need to be delivered early. If the pregnancy is 36 weeks or more and the baby is in danger of not getting enough oxygen and the cervix is soft, labour maybe induced.
One of the challenges of modern living, particularly for pregnant women, is stress. Stress increases and prolongs adrenaline levels that can affect other systems of the body, namely nerves, the heart, the endocrine system and immunity. Having to go for a non-stress test can be stressful in itself. It can cause you and your partner to worry about eventualities that may never happen.
If you’re going to antenatal classes, discuss your concerns with your midwife. It’s good to remember that while modern tests help your doctor to take extra precautions, your baby also has reliable back-up systems and mother nature has sustained the life of babies for aeons!