This is done by means of an external examination followed by an internal examination of the pregnant woman. The external obstetric examination has already been described in detail in the section “Subsequent Check-Ups – Regular Check-Ups During Pregnancy“.
Presentation and position are commonly used terms within the field of obstetrics. These need to be accurately defined. ‘Presentation’ is first and foremost used to indicate the position of the foetus in the uterus. A distinction is made between longitudinal presentations and transverse presentations. In the case of a longitudinal presentation, the longitudinal axis of the foetus is parallel to the longitudinal axis of the uterus. Two longitudinal presentations are possible:
- Vertex presentation – The head is the presenting part.
- The breech presentation – The buttocks are the presenting part.
In the rarely occurring transverse presentation, the longitudinal axis of the foetus is more or less transverse to the longitudinal axis of the uterus. This presentation is fairly common in the early stages of pregnancy as there is quite a lot of space in the uterus. Towards the end of the pregnancy, the longitudinal presentation is much more stable and this position can be maintained.
A vertex presentation is in general, more stable than a breech presentation because the smooth rounded scalp fits well in the pelvic brim. The buttocks fit less well in the pelvis, and in a full breech presentation the foetus can push with its feet against the brim of the pelvis. In the rare case that a transverse presentation still occurs in a woman who is full-term, a vaginal birth is impossible without correction.
The term presentation is used in the second place to indicate the position of the head of the foetus with respect to the torso of the foetus (degree of flexion).
In this, a distinction is made between flexed and extended (deflexed) presentations. In the flexed presentation, the head of the foetus is bent forwards at the cervical vertebral column towards the chest of the foetus. There are two flexion presentations:
- The occiput presentation.
- The sinciput presentation.
The head may be (almost) maximally flexed with the chin on the chest. In this case, the occiput of the child is located in or near the pelvic axis of the mother and this is referred to as an occiput presentation.
The head may also be less flexed, so that not the occiput but the sinciput is in or near the pelvic axis. This is referred to as a sinciput presentation.
These presentations can be established during the obstetric manual examination.
The occiput (O) presentation is in general the most favourable presentation for a smooth birth and is the most prevalent. In this presentation, the skull passes with its smallest circumference through the pelvic outlet. The sinciput presentation is a slightly less favourable position but in general it still allows a natural birth.
In the case of extended (deflexed) presentations, the head of the foetus is bent backwards in relation to the torso of the foetus. There are two extended presentations:
– The brow or fronto (F) presentation.
– The facial or mento (M) presentation (hyperextended).
In the first case, the brow of the foetus lies along the pelvic axis. In the second case, the face lies along the pelvic axis. Both presentations are rare. In the case of a brow presentation of a full-term child, a vaginal birth is not normally possible. In the case of a facial presentation, a vaginal birth may be possible if the chin rotates forwards on its axis (towards the symphysis pubis).
In obstetrics, the term ‘position’ describes the position of the presenting part (head or buttocks) in relation to the mother’s pelvis. The position is indicated using a ‘reference point’ to indicate where the foremost part is located in the maternal pelvis. This reference point can, in principle, be located at different points in the pelvis [Figure 21].
Figure 21
Left and right refer to the left and right sides of the mother.
For the occiput and sinciput presentations, the reference point is the small fontanel, for brow and facial presentations the chin is the reference point, [Figures 22a-k] and for the breech presentation the sacrum is used.
For a transverse presentation, the back (foremost) is used as the reference point and as a second orientation point the head is used.
Figure 22a: Vertex Presentation Occiput Anterior (OA)
Figure 22b: Vertex Presentation Left Occiput Anterior (LOA)
Figure 22c: Vertex Presentation Left Occiput Transverse (LOT)
Figure 22d: Vertex Presentation Left Occiput Posterior (LOP)
Figure 22e: Vertex Presentation Occiput Posterior (OP)
Figure 22f: Vertex Presentation Right Occiput Posterior (ROP)
Figure 22g: Vertex Presentation Right Occiput Transverse (ROT)
Figure 22h: Vertex Presentation Right Occiput Anterior (ROA)
Figure 22i: Brow Presentation Left Occiput Transverse (LOT)
Figure 22j: Facial Presentation Left Mentum Anterior (LMA)
Figure 22k: Brow Presentation Right Mentum Transverse (RMT)
Rotation During Delivery – Demonstrated Using A Pelvic Skeleton
Rotation During Delivery – Demonstrated On A Model
Inspection of the vulva
Note the following:
- Spotting/show (blood and mucus).
- Amniotic fluid (vernix flakes).