Obstructed labour

The exact point at which the ''delay' discussed in the previous section becomes the ''obstruction' discussed in this one is arguable. Obstruction is ''the failure of the presenting part to descend in spite of uterine contractions' (M 23.1). What really distinguishes delay from obstruction is the secondary signs and complications that follow: severe moulding and caput, foetal distress, a stretched lower segment, bloody urine, fistulae and rupture of the uterus, etc. Whereas delay in labour is usually inevitable and readily treatable, and is comparatively harmless, obstructed labour is none of these things. It should never happen where care is adequate.

Obstruction may be due to: (1) An abnormality in a mother's pelvis (a contracted pelvis). (2) An abnormality in her baby (hydrocephaly, etc.). (3) An abnormality in the relationship between them. This can either be: (a) an abnormal lie or presentation (a breech, a brow, or a face, or a shoulder presentation, or a prolapsed arm in a transverse lie), or (b) an unfortunate coincidence of their relative sizes (CPD, cephalopelvic disproportion, he may be too big for her, or she may be too small for him). (4) Rarer causes, such as stenosis of the vagina, locked twins, or a pelvic tumour, particularly fibroids or an ovarian cyst. CPD is the most important cause (two-thirds of cases), and an impacted transverse lie is the next. This is much less readily anticipated antenatally, especially when it complicates the delivery of a second twin. Much of the purpose of antenatal care is to screen mothers who are at risk from obstructed labour. The purpose of the partogram is to detect it early.

In practice, when the presenting part stops moving through the birth canal, you may not be able to tell if this is because: (1) the uterine contractions are weak (uterine inertia), or (2) because the baby and the pelvis are such that one will not go through the other (CPD). Often, there is a combination of inertia and CPD.

Preventing obstruction depends on: (1) Good nutrition starting in childhood, so that mothers reach their genetically determined height, and their pelves their genetically determined size. (2) Universal antenatal care, so that obstructed labour can be anticipated from a mother's history, and any risk factors for it identified. (2) The monitoring of labour by skilled staff, so that she can be referred at the first sign of danger, before she obstructs. The detailed preventive measures are: (a) Screening for risk factors, especially short stature (M 5.3). (b) A pelvic assessment at 36 weeks (M 6.6). (c) The routine use of the partogram. When adequate antenatal care is impossible, and where health centre and hospital beds are limited, the establishment of a ''mother's waiting area' or a ''mother's village' is a useful alternative.

Obstructed labour is a major failure of obstetric care. Unfortunately, it still happens, even in some hospitals. How often you will see it will depend on the prevalence of CPD in your area, and the quality of your antenatal and obstetric care. Alas, the poorest communities with the worst health services are usually those with the most CPD.

In a labour that is going to obstruct, the first stage is often prolonged, but it can be normal or even short. A mother's membranes rupture, and her liquor escapes. Her uterus contracts and retracts, and forces her baby into its lower segment, which gradually becomes overstretched. Obstruction prevents his escape, so her lower segment moulds closely round him and thins. The contractions of her uterus become hypertonic, and relaxation between them poor. The placenta is poorly perfused, there is fetal distress, and he dies.

l Obstructed labour has two main dangers: (1) Her vagina, bladder, and rectum are trapped between his head and her pelvis, so that they become necrotic, slough, and develop fistulae. (2) Her uterus ruptures. Primips usually develop fistulae, and multips usually rupture their uteri, but both can do either, and rupture and fistulae can occur in the same patient.

A primip begins to have trouble when her cervix fails to dilate normally. An oxytocin drip (M 22.2) may speed it up if her CPD is minimal, but cannot do so if it is gross. The result is that her labour usually obstructs before she is fully dilated, although she will usually reach full dilatation eventually. If her obstruction is not rapidly relieved: (1) It produces asphyxia in her baby, due to prolonged uterine contractions reducing the placental blood flow. (2) It may injure his head, so that he is born with a birth injury. (3) It causes a pressure necrosis, and sloughing of her anterior vaginal wall. As this slough separates, she develops a fistula between her bladder and her vagina (18.18), which may involve the proximal half of her urethra and/or the neck of her bladder, up to its ureteric orifices. Later, as the ring of necrosis in her vagina heals and contracts, it stenoses. Or, she may develop a fistula between her rectum and her vagina (18.19). If she does not die herslf, she delivers an injured, severely moulded dead baby.

She is also at risk from septic shock (53.4), peritonitis, peritoneal abscesses, atonic postpartum haemorrhage (19.11a), and foot drop from the pressure of his head on her sciatic nerves. Even if her fistula can be repaired, and there is at best only about an 80% chance of this, she may be infertile, and her vagina may be so stenosed that sex is difficult. If it is repaired, and she becomes pregnant again, she must be sectioned to prevent the repair breaking down. If it is not repaired (in which case she is less likely to become pregnant), stenosis of her vagina is likely to prevent vaginal delivery. Here is one such primip.

MPHO MOKETE (14 years, para 0, gravida 1) became pregnant after her first period. She hid her pregnancy from her parents, and so received no antenatal care. She arrived tired, exhausted, anxious, and febrile, with a fast pulse. Her contractions were strong and painful, with little relaxation between them. The head of her baby, who showed signs of fetal distress, was high, and overlapped the brim of her pelvis. Her liquor had drained, so that her uterus was moulded around him.

Her vulva and cervix were oedematous, and although his head could be felt just inside her cervix, this was not because it had descended, but because his head was severely elongated. Abdominal examination showed that most of it was still above her pelvic brim. Her vagina was dry and ''hot', and her cervix not fully dilated.

Her bladder was distended. Catheterizing her was difficult, and his head had to be dislodged by putting two fingers into her vagina, and pushing it up. Her bladder was drawn up so high that the catheter had to be passed a long way before any urine flowed; when it did so, it was blood-stained. Her baby was alive, and his head was 4/5 above the brim, so she was not suitable for symphysiotomy or vacuum delivery. She was therefore resuscitated with intravenous fluids, given antibiotics, and delivered by Caesarean section. He survived, but her wound became infected, and she developed a pelvic abscess, which was drained. She was in hospital a month, and was lucky not to develop a fistula. LESSONS (1) The decision to section her was correct, but it should have been done extraperitoneally (18.13). (2) She is only 14, so her pelvis will continue to grow. (3) She is at risk of a ruptured uterus in future, so she must deliver in hospital. A multip may show the same failure to dilate as a primip, or her cervix may dilate normally to begin with, and then slow during the active phase, only to dilate finally if she is left untreated. Meanwhile, the presenting part fails to descend. Here is one such multip.

MAPULESA (35, para 8 gravida 10) arrived just before her uterus ruptured. She too was anxious, distressed, and febrile. Her cervix however was fully dilated. Her lower segment had continued to retract and thin, so that the junction between her upper and lower segments had risen in her uterus as far as her umbilicus. She had a ''three-tumour abdomen'[md]an oedematous distended bladder, a distended, tender lower segment, and a tonically contracted upper segment. A ring (Bandl's ring) could be felt through her abdominal wall between her upper and lower segments (G, Fig. 18-3). Her round ligaments stood out on either side of her ballooned lower segment, like the guy ropes of a tent. Vaginal examination revealed a brow presentation. She was resuscitated with intravenous fluids, and sectioned. At operation her uterus was found to have ruptured into her abdominal cavity. Her baby was alive, but was asphyxiated, and died in an hour. Her uterus was repaired, her tubes were tied, and she recovered uneventfully. LESSONS (1) Even a patient who has had many normal deliveries may get an obstructed labour from a malpresentation or malposition. (2) A partogram would have given earlier warning of her impending obstruction. The critical event in a patient like this is rupture of her uterus. This usually starts in her thin lower segment, and extends downwards on one side into her vagina, as well as upwards towards her fundus. Several things can then happen: (1) The presenting part may remain jammed in her pelvis. (2) Her baby may be expelled through the rupture into her peritoneal cavity. (3) She may bleed from the rupture into her vagina. (4) Occasionally, her bladder also ruptures, especially if it has stuck to the scar of a previous lower-segment Caesarean section.

Before rupture the signs that it is imminent are: (1) The failure of labour to progress. Lack of progress should therefore alert you to the possibility that rupture might be imminent. (2) Bandl's ring. (3) A distended bladder which is difficult to catheterize. (4) Frequent strong uterine contractions, with little or no pause between them. If a patient is brought in on the verge of rupture, you may perhaps see it occurring, before you can treat her.

After rupture, a mother may have little or no pain. If you ask her, she will tell you that contractions were strong, but then suddenly stopped, and were replaced by a lesser continuous pain, or no pain. She may be in severe hypovolaemic shock, with cold, sweaty skin, and a weak or absent radial pulse. She may be quite obviously collapsed, or alert and even talkative. You can feel no uterine contractions, but you can usually feel her baby through her abdominal wall lying free in her abdomen.

For the management of a ruptured uterus, see Section 18.17.

To summarize: (1) A primip's uterus seldom ruptures, but she often develops fistulae. (2) A grand multip's uterus often ruptures, but she seldom develops fistulae. (3) Failure to dilate is a useful warning signal in a primip, and in most multips. In a multip the first sign of obstruction may be failure of the presenting part to descend at full dilatation, in spite of strong and frequent contractions, and increased moulding of her baby's head. A multip who has not delivered after 20 minutes in the second stage is in great danger.

Fig. 18-3 OBSTRUCTED LABOUR. A, B, and C, during a normal labour the hemispherical lower segment is converted into a cylinder: it thins but does not elongate. During the second stage the uterus shortens itself by contraction of the upper segment. During an obstructed labour the uterus cannot empty, so the thinned lower segment elongates (D, and E). F, sometimes a palpable ring (Bandl's ring) forms between the upper and lower segments. G, you may sometimes see or feel three distinct abdominal swellings: (1) the bladder, (2) the lower segment, (3) the upper segment. Bandl's ring separates the lower and the upper segments. After Lawson JB and Stewart DB, ''Obstetrics and Gynaecology in the Tropics', Fig 11.2. Edward Arnold (1967), with kind permission.