fetal assessment during labour

Fetal assessment in labour
A healthy term fetus is usually able to withstand the rigours of a normal labour. However, with each contraction, placental blood fl ow and oxygen transfer are temporarily interrupted and a fetus that is already compromised before labour will become increasingly so. Insuffi cient oxygen delivery to the fetus causes a switch to anaerobic metabolism and results in the generation of lactic acid and hydrogen ions. In excess, these saturate the buffering systems of the fetus and cause a metabolic acidosis which, in the extreme, can cause neuronal damage and permanent neurological injury, even intrapartum fetal death. Hypoxia and acidosis cause a characteristic change in the fetal heart rate pattern, which can be detected by ausculatation and the cardiotocograph (CTG). Meconium is often passed by a healthy fetus at or after term as a result of maturation of gastrointestinal physiology; in this
scenario, it is usually thin and a very dark green or brown colour. However, it may also be expelled from a fetus exposed to marked intrauterine hypoxia or acidosis; in this scenario, it is often thicker and much brighter green in colour.
Fetal assessment in labour takes four forms:
1. observation of the colour of the liquor – fresh meconium staining and heavy bleeding are markers of potential fetal compromise
2. intermittent auscultation of the fetal heart using a Pinard stethoscope or a hand-held Doppler ultrasound,
3. continuous external fetal monitoring (EFM) using CTG,
4. fetal scalp blood sampling (FBS).