Spontaneous natural labour can sometimes become difficult. There are three possibly inter related reasons for this: the powers, the passages and the passenger. The driving power of the contractions may be poor. There may be an element of misfit of the baby to the birth canal: a large baby and a small woman. The baby may have adopted an unfavourable position of its head in the womb. The latter reasons may cause poor contractions although poor contractions can occur de novo.

Difficulties in labour manifest with the neck of the womb dilating slowly or not at all. This is observed by the midwife and the doctor. An assessment is then made of the contractions and the size of the baby by abdominal examination while an assessment of the position of the baby’s head and the size of the pelvis is made by vaginal examination.

In most cases the use of oxytocin is required. Oxytocin is a human hormone produced by the pituitary gland in the brain which promotes contractions of the womb. Synthetic oxytocin (Syntocinon) is diluted in sugar saline and infused through a drip in the arm in the same way as during induction of labour. This should increase the strength and frequency of contractions as well as the pain! Pain relief is important at this stage and an epidural anaesthetic is appropriate.

The contractions are observed over the next two hours. A further assessment is then made to see if the dilatation of the cervix has improved. If there is a mechanical problem or the back of the baby’s head is posterior then this process may be very slow. The doctor decides for how long to continue with this treatment depending on the evolving results.

• Poor dilatation of the cervix,
• poor descent of the presenting part,
• persistent occipito-posterior position,
• the moulding of the baby’s head to a sausage shape and
• swelling on the top of the baby’s head (caput) are all adverse signs.

During this treatment with Syntocinon it is important that the fetal heart is monitored continuously to ensure that relative lack of oxygen is not being reduced due to strong contractions. If adverse signs develop then an emergency caesarean section becomes necessary. If the cause has been mechanical then the diagnosis is cephalo-pelvic disproportion.

So-called fetal distress may occur in labour. Even with a head first presentation the journey of birth is a dangerous one for the baby. The contractions temporarily reduce blood flow to the placenta. Well grown healthy babies can tolerate this. Lack of oxygen due to blood flow deficit can be seen in the pattern of the baby’s heart on the fetal monitor print out: the CTG.

The problem is that other factors cause changes in the heart rate pattern and these are not well understood. It is notable that the use of Syntocinon in abnormal or induced labour causes these changes and such an infusion should be suspended until the reason for the changes has been elucidated. It is obviously important that the cause is elucidated because lack of oxygen cannot improve during labour because of the very nature of the cumulating contraction stress.

Other elements need to be considered such as the colour of the amniotic fluid. Babies open their bowel in the womb and pass the contents (meconium) into the amniotic fluid. At term about 20% of babies show meconium staining of the amniotic fluid. In the majority of cases this is a natural event with no sinister significance. However when it is thick (green) and undiluted it is suggestive of lack of oxygen. The passage of discoloured amniotic fluid at any time is a cause for concern. The heart rate pattern should always be checked and carefully observed when this happens. Syntocinon should not be given unless the fetal heart pattern is clearly normal.

Abnormal fetal heart patterns are caused by fetal head compression, umbilical cord compression, change of maternal position: all of these are not indicative of fetal distress. They should be recognised and corrected if necessary.

Distinguishing harmless from harmful causes of an abnormal CTG can be difficult without constant education and training. Some believe that the taking of a blood sample from the fetal scalp by placing a instrument in the vagina is helpful. The aim is to determine the acidity (pH) of the fetal blood which is an indicator of oxygen supply. A pH of 7.25 or greater is acceptable, 7.20-7.25 should be repeated in 30 minutes and less than 7.20 is an indication for urgent delivery.

Many babies are delivered by emergency caesarean section for so-called fetal distress and are in very good condition. Regrettably some babies are not delivered in spite of evidence of fetal distress and are born in poor condition later to suffer cerebral palsy.

The condition of the baby at birth is judged by its Apgar score. This is assessed by considering:

• The heart rate,
• tone,
• colour,
• movement and
• breathing at 1 and 5 minutes.

Most babies score 9 or 10 out of 10. A more precise assessment of the oxygen status is made by taking a blood sample for the baby’s umbilical cord blood vessel. A level of greater than 7.25 is good. Otherwise a range from a very poor pH of 6.8 is seen. The lactate or base deficit level are also relevant to assess the difference between a metabolic and respiratory acidosis