There are many factors that can affect fetal wellbeing during labour and delivery. The fetus is dependent on good functioning of the placenta and good supply of nutrients and oxygen from the maternal blood circulation. Whenever there is inadequacy in maternal supply or placental function, the fetus will be at risk of asphyxia, which is going to be manifested by the fetal heart beat deviating from the normal range. Other factors that will affect fetal wellbeing, which may be indicated by abnormal fetal heart rate, are shown in the Box below.

Reasons for fetal heart rate deviating from the normal range

Placental blood flow to the fetus is compromised, which commonly occurs when there is:

Hypertensive disorder of pregnancy
Maternal anaemia
Decreased maternal blood volume (hypovolemia) due to blood loss, or body fluid loss through vomiting and diarrhoea
Maternal hypoxia (shortage of oxygen) due to maternal heart or lung disease, or living in a very high altitude
A placenta which is 'aged'
Amniotic fluid becomes scanty, which prevents the fetus from moving easily; the umbilical cord may become compressed against the uterine wall by the baby's body
Umbilical cord is compressed because of prolapsed (coming down the birth canal ahead of the fetus), or is entangled around the baby's neck
Placenta prematurely separates from the uterine wall (placental abruption).

With that background in mind, counting the fetal heart beat every 30 minutes and recording it on the partograph, may help you to detect the first sign of any deviation for the normal range. Once you detect any fetal heart rate abnormality, you shouldn't wait for another 30 minutes; count it as frequently as possible and arrange referral quickly if persists for more than 10 minutes.