Fetal distress is a term in common usage. It may, therefore, surprise many that, even experts in the field don’t agree on the exact meaning of the term.

In essence, fetal distress refers to a state where insufficient oxygen is reaching the fetus. If oxygen deficiency is severe and prolonged, permanent damage to the baby could result. It is, therefore, the norm, to err on the side of caution.

Causes of fetal distress before labor

There are several potential causes.

Fetal distress is commonly a feature of established labor but could occur before labor onset. This is uncommon.

Placental abruption which is a condition where the placenta. (afterbirth) detaches from its base partially or wholly, is one of the more common causes of pre-labor fetal distress.   

Vigorous fetal activity sometimes leads to a cord accident, which may be in the form of a knot or entanglement of the cord around a limb. This could lead to partial occlusion of the vessels in the cord, leading to distress.

Vasa previa is usually undiagnosed before labor and will cause sudden bleeding and acute fetal distress in labor.

Sometimes the cause of fetal distress remains unestablished even after the baby is born. 

Causes of fetal distress during labor

Any activity that reduces the blood supply to the fetus will cause fetal distress.

If the cord is compressed, either as a result of being around a fetal limb, neck, trunk or simply by being compressed by the fetal head against the pelvic side-wall, features of fetal distress will follow. 

Correction to this can occur spontaneously as a result of fetal movement or the cord sliding away from the pressure point, hence relieving the compression. Sometimes this does not occur and a rescue procedure needs to be carried out.

Hyper-stimulation of the womb and fetal distress

Over-stimulation of the uterus can occur spontaneously or following the infusion of oxytocin. If the uterus contracts strongly, with the contractions being prolonged and coming close together, this will reduce the amount of blood (and therefore oxygen) that is getting to the placenta and ultimately to the baby.

If over-stimulation is sustained over several minutes, fetal distress will ensue.

Overcoming uterine hyper-stimulation

Hyper-stimulation of the womb is overcome quite easily simply by stopping the oxytocin infusion, if this was the cause.

If the hyper-stimulation occurs spontaneously, an intravenous injection of a tocolytic drug can be given and this will very quickly calm the over-stimulation. These drugs (tocolytics) are also available in an inhalational (aerosol) form but this method is associated with a slight delay in action. 

Tocolytic drugs work by relaxing the muscles of the womb to negate the effect of sustained strong contractions.