Aetiology and Complication of Abnormal Lie

Dun like killer examiner :

2nd question: Do the same complications of unstable lie apply as well in transverse and oblique lie? e.g rupture of uterus and compund presentation

30 Sep 2011 5.30 PM

Answer

In approaching this question, we need some area of clarification for the usage of the term.. Basically, we refer all this problem as abnormal lie. Lie is defined as relationship between longitudinal axis of fetus to the longitudinal axis of maternal uterus.

Presentation is defined as part of fetal that presenting at the superior strait of the maternal pelvis. Simply put, it means, what part of fetus that appear at maternal pelvis.

Meanwhile, unstable lie is defined as the lie of fetus persistently changed at term because it is a physiological act of the baby to change it’s lie and presentation before 36 weeks. After 36 week, the normal lie is longitudinal.

Patient with unstable lie may have transverse or oblique lie during labour. Be it at term or during delivery. It may also turn back to longitudinal lie.

The most common cause for abnormal presentation is uterine laxity seen in patient with multiparity or anything that cause distension of uterus (previous multiple pregnancy, fibroid etc). Other causes includes, multiple gestation, polyhydramnios, prematurity/ wrong dating, placenta previa, fetal anomaly, uterine anomaly, pelvic mass and contracture of the uterus.

You also need to know the physiology of the growing fetus and the anatomy of the uterus. In early pregnancy, all baby have unstable lie. As the uterus getting bigger and bigger, the pear shape of the uterus make the upper space being occupy the larger part of the baby (buttock) and the lower space being occupy by the head.

However, in lax uterus, the baby may settle down it position in transverse position and it become more comfortable with that position. As the uterus and baby grow, it just fit in that position.

Polyhydramnios, prematurity multiple gestation will have this problem simply because there are a lot / bigger space in wombs that they easily turning around. (relative liquor volume in relation to fetal size)

Meanwhile, any injury/ abnormality of the uterus make the baby unable to turn into longitudinal lie and remain in their position.

Using the same principle, you may explain why baby with neural tube defect have unstable lie which basically due to the polyhydramnios.

After you understand the physiology of the baby lie and uterus anatomy, then you can explain easily the complication of the abnormal lie with regards to their aetiology.

Why did uterine rupture occur? Basically it is due to the obstructed labour in over distended uterus.

Abnormal presentation be it compound, cord, face, brow can also due to the complication of unstable lie. Because, as i mentioned earlier, presentation simply means relation of fetal part with maternal pelvis. So anything can happen but there will be certain condition that will have abnormal presentation as complication. For example, cord prolapse more common in footling breech, compound presentation more commonly occur in transverse lie and many more.