Which is it to be? Elective section, ''trial of scar', or section early in labour?

If a mother has had one Caesarean section the alternatives for her next pregnancy are: (1) An elective section, before she goes into labour. (2) Section in early labour. (3) An attempt at vaginal delivery (a ''trial of scar'). How can you choose between these three?

A lower segment Caesarean section is sometimes done for such conditions as fetal distress, placenta praevia, or the prolapse of the cord or an arm, which are unlikely to happen again in a later pregnancy. When a mother like this becomes pregnant again, there is every reason to expect that her labour will be normal, except for the scar that she now has in her uterus. This will almost always give some warning before it ruptures, so you can safely let her have further attempts at delivering her babies vaginally. This is called a ''trial of scar'. She can have as many trials as she likes, provided the previous one was successful, but she must have had only one previous Caesarean section. If she has had two sections or more, always section her. Contributors differ greatly in their use of a trial of scar. One only does them in exceptional circumstances.

''TWO CAESARS OR MORE, ALWAYS A CAESAR'' When you do a trial of scar, admit her to hospital and observe her closely. Should her scar show signs of rupturing, section her immediately. These warning signs only last an hour or two, before her uterus ruptures, so you must admit her and observe her with the greatest care.

If CPD was the reason for her Caesarean section, it reduces the chances of a successful trial of scar in this pregnancy, but does not exclude it, because: (1) The pelvis continues to grow up to the age of 25. (2) Uterine action is often poor in the under-16s. An accurate measurement of her true conjugate done at the time of her previous section, as in Fig. 18-16, helps. A trial of scar is unwise if it is [lt]9 cm. It is contraindicated in a breech presentation if the true conjugate is [lt]10 cm. A trial of scar is absolutely contraindicated if her previous Caesarean section was classical.

ONE ''CLASSICAL', ALWAYS A CAESAR Good care during a trial of scar means that her pulse must be taken reliably, and you must be able to section her immediately. If, for example, her uterus shows signs of rupturing at 3 a.m., section must be possible before 4 a.m., not at 10 am the following morning. If the organization and discipline of your hospital are not such that it can provide care of this quality, elective section will give her a better chance of saving her baby, her uterus, and perhaps her life. If it takes several hours to find a driver, to fetch you, and to prepare the theatre, a trial of scar will be dangerous. Ideally, a uterus should never rupture during a trial of scar. If more than the very occasional one ruptures, patients should be referred to wait to go into labour at a larger hospital.

Even when conditions are not ideal, a trial of scar may be justified, because the immediate and future risks of a further section can be considerable. If mothers know that they cannot have a trial of scar in hospital, they may try to have trials themselves at home. A mother will usually understand if you say ''We will give you a try, and if you have any difficulty, we will do another Caesarean section''.

Ask the clinics to refer all mothers who have had a previous Caesarean section, and who are sure of their dates, at 34 weeks, so that you can assess them as described below. If a trial of scar is not indicated, plan an elective section at 38 weeks, or in early labour, if a mother is not sure of her dates.

The best indication that a uterine scar is going to rupture is a rise in her pulse rate. Take this half-hourly. If it rises above 100, or she has pain between contractions, her scar is probably rupturing, so section her. Other signs are described below.

Elective Caesarean sections are one of the alternatives to a trial of scar, but they are not the complete answer: (1) They may not be popular, so find out what your mothers think about them. If they are unpopular, avoid them, but at the antenatal clinic make the decision to section a mother in early labour. (2) Her dates may be uncertain, but even if they are certain, they need to be confirmed by a corresponding fundal height in mid pregnancy, before 20 weeks. (3) She is easily sectioned too early, so that her baby is at risk from prematurity.

HARBANS KAUR (38, gravida 4 para 3) was admitted at 9 a.m. on a Saturday, for a trial of scar, having had one previous Caesarean section with her first pregnancy. She was 7 cm dilated and had good contractions. At noon she was fully dilated and her baby's head was 3/5 above the brim. During the next half-hour it remained there. The doctor on duty was called for another emergency Caesarean section, so the intern was advised to attempt vacuum extraction. He failed, but in doing so, he included her cervix under the cup, and tore it. At 3 p.m. she developed pain, shock, and abdominal tenderness, and the fetal heartbeat disappeared. She was rushed to the theatre. Her uterus had ruptured, and the tear had extended into her bladder. The superintendent was called. He found that her ureter had been caught in a hastily applied suture. The following day she was found to be leaking urine vaginally. LESSONS. These are many, they include: (1) In multips the second stage should not last longer than 20 minutes. (2) A vacuum extractor was applied when the head was 3/5 above the brim. It should be only 1/5 up or less (except for a trial of vacuum or symphysiotomy). (3) When you apply the cup of a vacuum extractor, you should make sure that you don't include her cervix. (4) When a trial of scar is done, it must be possible to do an immediate Caesarean section if the trial fails. WARNING SIGNS MAY ONLY LAST AN HOUR OR TWO BEFORE RUPTURE

TRIAL OF SCAR INDICATIONS. (1) A patient who has had one lower segment Caesarean section, and the reason for it is absent in this pregnancy. For example, it might have been done for a malposition or malpresentation, maternal or fetal distress, or CPD due to hydrocephalus, etc. (2) The scar from a myomectomy (provided her uterine cavity was not opened during the operation), hysterotomy, or uterine perforation during a ''D and C'.

CONDITIONS. (1) She must have had not more than one previous Caesarean section. (2) When labour starts, she must either be in hospital, or not more than one hour away from it, with certain access to suitable transport. (3) Caesarean section must be available any time of the day or night, within one hour of the decision to section her. (4) Her pregnancy must have been normal. (5) Her baby must be a vertex presentation in the occipito[nd]anterior position (some obstetricians will do a trial of scar for a breech). (6) There must be no fetal or maternal distress.

CONTRAINDICATIONS. (1) Two or more previous lower segment Caesarean sections. (2) One previous classical Caesarean section. (3) Any degree of CPD, or suspected CPD in this pregnancy, as suggested by a true conjugate of [lt]9 cm or a diagonal conjugate of [lt]11.5 cm. Although this is the ideal figure, it is unrealistic in some countries; in New Guinea, for example, a figure of 10.5 cm is used for the diagonal conjugate. ]](4) An occipito-posterior presentation. (5) Any other form of malpresentation, or obstetric complication. (6) Sepsis following a previous section is a relative contraindication only. (7) Any need for an oxytocin drip.

A request for tubal ligation favours the decision to do an elective Caesarean section. On its own, it is not a sufficient contraindication to vaginal delivery, because a vaginal delivery followed by tubal ligation will be safer. If a patient arrives in labour, use the same criteria as if she arrived during pregnancy.

ASSESSMENT. See all mothers with a previous section in the antenatal clinic at 36 weeks, and decide whether to do a trial of scar or not. Take a careful history. Assess her pelvis clinically and assess the size of her baby by measuring the height of her fundus; if it is [mt]40 cm, don't do a trial of scar. If you have not previously measured her true conjugate, X- ray pelvimetry is useful but not essential.

METHOD. Ask her to avoid heavy work during the last month of pregnancy, or to come in for rest. If she can be sure to reach hospital within an hour of labour starting, let her wait at home until labour starts. Otherwise, admit her at 36 weeks for rest and observation. Allow her fluids only by mouth during labour.

Don't induce labour. Unless your blood bank can be relied upon to have blood available within an hour, have it cross- matched, and ready to give if necessary. Record her pulse and the fetal heart rate carefully.

You may sometimes be able to feel the scar in her lower segment, when you examine her vaginally. This will be easier if you are using epidural anaesthesia. If it bulges or feels weak, section her immediately. The tenderness of a scar is difficult to assess in labour, and is not, on its own, an indication for section. Assist her with outlet forceps, or vacuum extraction, if necessary.

Abandon the trial if: (1) She crosses the alert line on the cervicograph! (2) Her pulse rises to 100. (3) She has pain between contractions. (4) Her pain is generalized. (5) She has unexplained vaginal bleeding. (6) Her uterine contractions cease. (7) She has rectal or vaginal tenesmus.

Stay with her during labour so that you can examine her lower uterine segment vaginally immediately after delivery of the placenta, so as to be sure that it has not ruptured. One contributor considers this impractical, and only recommends it if she has had a PPH; others do it routinely. Examining it is uncomfortable, but does not need anaesthesia. If you find a rupture, repair it at laparotomy (9.2, 18.17).

If she has a postpartum haemorrhage, the scar in her uterus has probably broken open; confirm this by doing a vaginal examination, and repair it abdominally if you find it.