Birth Obstruction During Labour
Certain factors associated with your baby may hamper the birth process, and so require intervention or a delivery that is assisted (for example, using forceps) or managed (such as a caesarean section).
In some cases, these can be predicted beforehand, and either a caesarean section or a closely monitored labour (called a trial of labour) would be advised. In other cases, problems can arise without warning during labour. This is because it is difficult to predict which women will, and which will not, run into problems during labour.
Remember that most women deliver their babies normally without problems, but everyone still has a chance of difficulties arising during labour, especially during a first labour. Women who have had a successful vaginal delivery previously are much less likely to run into labour problems than those who have not had a normal delivery in the past.
While in labour your doctor or midwife will assess the rate of opening (dilatation) of your cervix. This is done by means of a vaginal or internal examination. The normal rate of cervical dilatation is approximately 1cm/hour, although it can vary among women and is usually quicker in those who have had a vaginal delivery previously. If your cervix doesn’t open, this can usually be explained in one of three ways:
- the baby is too big or the head of the baby isn’t well applied to the cervix
- the uterus isn’t contracting enough to push the baby down
- the passage for the baby is not sufficient to allow the baby to descend into the vagina for birth; this can obviously be related to the size of the baby
- the management of this process is dependent on what your doctor or midwife believes is the problem, presuming, of course, that the baby appears to be coping with the labour
If your baby is too large to pass through the pelvis or vaginal opening easily and safely, then a caesarean section may need to be considered. The baby may be large if you are diabetic, but most large babies are born to normal mothers. Large babies are those over 4 or 4.5kg. If the baby is very large, a caesarean may be recommended before labour begins.
However, what is more important for the labour process is the relative size of your baby to your pelvis, taking into account points 2 and 3 above. So, short petite women with large babies may deliver without any difficulties, while tall women with relatively small babies may still run into problems during labour. This is called cephalopelvic disproportion.
The only real way of testing this is to see how the labour proceeds. The midwife or doctor will do this by checking how far the neck of the womb is dilating on internal examination, and how far down in the pelvis your baby’s head is moving. If you are in your first labour and everything else is normal but the progress is slow or the contractions weak, your doctor may prescribe a oxytocin drip to strengthen the contractions during pregnancy. This manages the situation in point 1 above. This should allow the baby to pass through the birth canal; if there is still no further progress two to four hours later, a caesarean may be advised as the only safe way to deliver your baby.
An assisted delivery (forceps or vacuum) may also be required in situations where the head has already moved down into the pelvis but cannot descend any further. It would only be performed when the cervix is fully dilated.
Maternal causes of birth obstruction
Various conditions associated with the mother can also lead to obstruction during childbirth, which, again, will require intervention by way of induction or by assisted or managed delivery.
Such causes of obstruction include:
- pelvic defects or disproportion. Cases where the size of your baby’s head and your pelvis do not correspond (for example, if your pelvis is too small to accommodate your baby’s head) are known as pelvic or cephalopelvic disproportion. This may be due to a previous fracture of the pelvic bones, or due to illness in childhood impairing growth of the pelvic bones. In rare cases, there are some genetic causes of small pelvic bones. Most women who develop cephalopelvic disproportion in labour, however, have a normal pelvis and a normal baby; it is just that there is a relative discrepancy in the size of their pelvic bones for that particular baby. This may affect the descent of your baby and can lead to fetal distress. In such situations, you may have to have your baby delivered by caesarean section since normal delivery may be dangerous or even impossible. In addition, a vacuum or, occasionally, forceps may be used to deliver a baby that has moved down far enough in the birth canal for this to be safe, but where further descent is prevented. Furthermore, if your baby’s head actually becomes jammed in the middle of the pelvis, then a vacuum or forceps may be used by an expert to rotate the head to facilitate delivery using a procedure known as mid-cavity delivery. Alternatively, a caesarean will be performed.
- the presence of pelvic tumours or a cyst in the ovaries
- problems with the uterus, cervix or vagina
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