In most births the position of the foetus is longitudinal this means that the long axis of the foetus's body runs parallel to the long axis of the mother's body.
Due to the increased incidence of perinatal injuries affecting both mother and baby and the increase in fetal and neonatal mortality, the choice of delivery route for non-cephalic fetal positions is an important clinical issue.
Depending on the part of the fetus's body that is anterior, the fetal position is divided into:
- pelvic position
- complete - anteriority of the buttocks and two feet
- incomplete - prominence of the buttocks and one foot
- buttock position
- buttock prominence, feet cast on fetal belly
- prone position
- complete - prominence of two feet
- incomplete - prominence of one foot
- kneeposition
- complete - forefoot of both knees
- incomplete - forefoot of one knee
In most cases, the position of the fetus is unknown. Factors favouring longitudinal pelvic position of the fetus are:
- preterm birth
- multiple pregnancies
- malformations of the foetus (hydrocephalus, anencephaly)
- abnormalities of the uterus (uterine myomas, cervical tumours)
- abnormal amniotic fluid volume
- abnormalities of the mother's pelvis (narrow pelvis, abnormal structure)
Due to the specific mechanism of birth in the longitudinal pelvic position, there are five main groups of risks to the fetus associated with the double pelvic position. These include hypoxia, intracranial haemorrhage, premature rupture of the fetal bladder and prolapse of the umbilical cord.
Thetransverse and oblique position of the foetus is defined as a position in which the long axis of the foetus's body runs at right or acute angles to the long axis of the mother's body.
Predisposing factors for transverse and oblique fetal position are:
- excessive fetal mobility
- flaccidity of the uterus
- amenorrhoea
- intrauterine fetal demise
- second foetus in a twin pregnancy
- preterm birth.
Transverse vaginal birth is not possible because it poses a risk to the mother as well as the foetus. The main risks to the foetus associated with birth in the transverse position are hypoxia, prolapse of the umbilical cord and mechanical trauma to the foetus.
In a normal physiological birth in the longitudinal cephalic position, the fetus's chin is already in contact with the chest at the beginning of labour and in this position, the fetus moves up to the pelvic floor. Any degree of head erection is called a prone position. Due to the increased fetal size in breech positions, there is a prolonged second period of labour, a higher incidence of hypoxia and mechanical damage to the fetus and damage to the woman's genital tract.