POSTGRAD. MED. J. (I963), 39, 469

COMPLICATIONS OF THE FIRST STAGE OFLABOUR TREATED BY VACUUM EXTRACTION

M. A. AUSTIN, M.B., M.R.C.O.G.Senior Registrar, Obstetric Department, Lewisham Hospital, London, S.E. 3

THE vacuum extractor or ventouse has beenwidely used on the Continent as an alternative toforceps delivery for about 15 years, but in theBritish Isles the first modern report of its exten-sive use was by Chalmers and Fothergill (I960).An unsuccessful attempt to effect delivery bysuction, using a cupping glass, was recorded asearly as 1706. Simpson, in I849, wrote a treatise'On a suction-tractor, or new mechanical power,as a substitute for the forceps in tedious labours'.Since that time there have been various arbitrarydesigns of suction apparatus, using rubber ormetal cups. The mathematical calculations andexperiment essential to the designing of a tech-nically efficient suction apparatus were carriedout by Malstrom (1954, 1957). The instrumentnow used in England is based on his design.

Since October 1960 the ventouse has beenused in this hospital for complications of the firststage of labour, so obviating a Caesarean sectionin many cases. It has not been adopted for allforceps deliveries as Kielland's forceps are felt tobe of more practical use to the housemen in theirlater careers as general practitioners.

In the past 21 years the ventouse has-beenapplied, prior to full dilatation, on only 32 occa-sions in over 4,000 deliveries, an incidence of0.7% (Table i). The indications, results, anddangers will be discussed.

ApparatusThe vacuum extractor consists of a metal traction

cup which is connected to a traction handle by means ofa metal disc within the cup and its attached chain. Thechain is maintained in position by a pin inside thetraction handle. Suction tubing joins the cup to thetraction handle and thence to the vacuum bottle, where avacuum gauge records the pressure in kg./cm.2. The handpump, which creates the vacuum, is connected to thebottle by further rubber tubing and metal connectortubing containing a screw-release valve. There arethree sizes of traction cup, VE 30, 40 and 50, all witha standard depth of 20 mm. The two larger cups have arotation knob which is directed towards or over theocciput during application.

Leaking around the vacuum bottle bung can be trouble-some but after the production ofa suitable vacuum a gate-clip can be screwed firmly onto the tubing. Another cause

TABLE I

SUMMARY OF DELIVERIES

I Stillbirths andNumber of Neonatal Deaths

Cases (uncorrected)Deliveries .. 4,377 201 (4.6%)Caesarean sections .. 259 17 (6.5%)Forceps deliveries .. 398 I7 (4.3%)Ventouse deliveries

(includes forceps) 35 o

of difficulty in maintaining a vacuum is leaking due to aworn washer beneath the pin in the traction handle.The apparatus is easily dismantled for sterilizing byboiling. The vacuum bottle, protected by a plasticcovered metal frame, can be placed on or hung from atrolley.

PrinciplesProduction of a vacuum sucks adjacent scalp

tissue into the cup, creating an 'adhesive force'.The rim of the cup has a smaller circumferencethan the cavity of the cup so that the skin isdrawn in at a suitable reference angle, thus pre-venting detachment. The effect of suction andtraction is distributed to the cup edge. Providingthe suction force is greater than the traction thecup will remain attached. A traction force be-tween 9 to 22 kg. can cause detachment. Tractionmust be applied at right angles to the centre ofthe site of attachment, for maintenance of anoblique pull reduces the 'adhesive force'.Malstrom (I957) considered that the increase

in intracranial pressure during suction is negligible,as the scalp tissue drawn into the cup can moveindependently of the cranium and galea. This,however, is disputed by de Boer (1960) who foundthat application of the ventouse, without traction,to the scalp of a fresh stillbirth raised the spinalpressure from o to 25 cm. He attributed thisresult to the lack of rigidity of the baby's cranium.Using external tocometry, Malstr6m demon-

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strated that intermittent traction exerted by thevacuum extractor synchronous with uterine con-tractions prior to full dilatation of the cervix,stimulates uterine contractions at the internal oslevel. There is a close correspondence betweenthe strength of traction and uterine response.ApplicationA preliminary pudendal block with o.5% or i%

lignocaine was used in all cases except one.General anaesthesia was used to replace an armprior to application of the instrument.The size of cup used depends on the degree of

cervical dilatation. Sometimes a small introitusprevents insertion of the large cup and an earlyepisiotomy is not advisable, since the deliveryinterval may exceed an hour. The medium cuphas been most frequently used. The cup isinserted obliquely into the vagina and applied asclose to the vertex as possible. The head tendsto displace upwards in multigravidae, particularlywhen above the level of the spines, but supra-pubic pressure helps to control this.The vacuum is slowly induced, as advised by

Malstr6m (I957), an initial vacuum of 0.2kg./cm.2 being increased by o.I or o.2 kg./cm.2every two minutes, to a level of o.6 kg./cm.2, sothat detachment of the cup is less likely. Duringthis process it is important to check that thecervix has not been drawn under the cup. Thecervix may be freed easily by sweeping a fingerbetween it and the head. The artificial caputthus raised is more conveniently termed 'chignon'.The o.6 kg./cm.2 suction force is sufficient for thelight traction necessary to stimulate uterine con-tractions until full dilatation. Initially, continuouslight traction is more effective in cases of inertia.In primigravidas, a vacuum of o.8 kg./cm.2 isnecessary to allow strong traction.

Indications and ResultsThe indications for interference in the first

stage of labour are shown in Table 2. As inother series (Snoeck, 1960; Lillie, 1960; Fother-gill and Chalmers, 1961; and Willcocks, 1962),the commonest indications are delay and fcetaldistress. Chalmers (1960) advocates use of theventouse after failed conservative management ofprolonged labour.

Patients with delay in labour formed thelargest group delivered with the ventouse andinclude a large proportion of cases of prolongedlabour (by arbitrary definition over 36 hours-Standard Maternity Hospital Report Committee).The ventouse was only applied with the cervixless than half-dilated in one of the nine primi-gravidae, full dilatation being reached in aboutan hour but as no descent occurred on traction,

TABLE 2

INDICATIONS FOR APPLICATION OF VENTOUSE

Number of CasesIndication

Primiparae Multiparxe Total

Delay in first stageor uterine inertia 9 5 14

Fcetal distress . 3 4 7

Occipito - posteriorposition .. .. 5 6

Intrapartum hamor-rhage .. .. o 2 2

Malpresentation .. . I 2

Maternal distress .. i o I

Kielland's forceps were applied. Rotation of thehead could not be completed and there followeda difficult delivery with the head in an obliqueanterior position. The baby cried well but waslater slightly cerebral. Only one of the primiparaewas delivered with the ventouse, traction beingused for 55 minutes and the second stage lasting35 minutes. The baby was normal. The remainingseven primiparae were all delivered by forcepsfor varying reasons, viz. detachment of the cup,non-rotation or descent of the head within 15minutes of full dilatation, and thick perineum.On five occasions in multigravidae, the ventouse

was used for delay when the cervix was 2 to 4fingers (3 to 6 cm.) dilated. Wrigley's forceps werenecessary once, as the baby was still not delivered25 minutes after full dilatation. This groupincluded the child with cerebral damage, theremainder being healthy. There was slightabrasion and scalp bruising in two instances, thetraction times being 20 and 75 minutes.The group of occipito-posterior positions

mostly had an additional reason for expeditingdelivery, such as maternal distress or pre-eclamptictoxaemia. The malposition had been noted earlyin labour and the cervix was over half dilated(8 cm.). Only one of these primiparae was success-fully delivered with the ventouse, the remainderrequiring Kielland's rotation and forceps extrac-tions, two being classed as difficult. It isimportant in this group to assess the pelvis assome cephalopelvic disproportion is often present.The time taken to deliver cases of foetal distress

varied from 12 to 70 minutes. Four of the babieswere in good condition at birth and three were alittle limp, but only required mild resuscitation.Two primigravidae had early foetal distress but asfull dilatation was slowly acheived, forceps werethen applied. One multigravida having only had

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TABLE 3CERVICAL DILATATION RELATED TO TRACTION TIME

Primipare MultiparseDilatation Traction Traction Total

No. time over No. time over30 mins. 30 mins.

2-4 fingersdilated (up 3 2 7 5 10to 6 cm.)i-i dilated(8 cm. and 10 5 6 2 I6over)Rim ofcervix .. 6 2 o o 6

a Caesarean section previously, had forcepsapplied electively and the lower segment scarwas examined and found to be intact. Snoeck(I960) suggests that grave foetal distress is adisputable indication for vacuum extraction.However, in multigravidae in the first stage oflabour it is possible to deliver the baby morerapidly by vacuum extraction than by preparingfor and performing a Caesarean section.The ventouse is certainly of value in the

management of intrapartum haemorrhage. Thebleeding with each contraction in a twin pregnancywas effectively controlled by traction and livinginfants delivered. A Syntocinon drip was usedto induce labour in a patient with Rhesus anti-bodies at 36 weeks as the cervix was 'unripe'.This was later followed by a I2-ounce blood lossand an irregular fcetal heart rate. A severelyaffected infant was delivered with the ventouse,two exchange transfusions being needed.The malpresentation encountered in both

instances was an arm prolapsed alongside thehead. A general anaeesthetic was used duringreplacement of a recurrent arm prolapse in aprimigravida and, although it took an hour tocomplete delivery, the infant needed only mildresuscitation. The other case followed surgicalinduction of labour at 36 weeks for Rhesusantibodies, the induction delivery interval beingprolonged.

Other indications for interference have beenrecorded. Snoeck (I960) and Fothergill andChalmers (I96I) mention uterine scars frommyomectomy or Caesarean section. The sameauthors and Alment (I960) have used the ventousefor antepartum hsemorrhage of the accidentaltype and for placenta praevia.Foetal ComplicationsThe time taken to effect delivery or to decide

to apply forceps is related to the degree of cervical

TABLE 4F(ETAL COMPLICATIONS RELATED TO TRACTION TIME

Complication Traction TimeUp to 30 mins. Over 30 mins.

Scalp trauma: abrasionor bruise .

Infection orulceration . ..

CephalhiematomaCerebral irritation ..

Perinatal mortality ..

5 2

o

o

0

3

o

3

o

dilatation. When the cervix was three-quartersor less dilated in primigravidae, over 30 minutes'traction was required in half the cases. Thisagain applies to multigravidae, when the cervix isless than 4 fingers (6 cm.) dilated (Table 3). Thefoetal complications must be assessed in relationto these two factors.

In this series (Table 4), feetal complicationsoccured on i occasions. The three infants withcerebral irritation had associated scalp traumaand traction lasted over 30 minutes. The scalpabrasions were of a minor nature in seven cases andall were healed prior to discharge from hospital.Abrasions seemed to occur when the cup wasdetached during traction. There was circularscabbing of the scalp at the cup site in three cases,preceded by a scalp haematoma and bruising intwo babies and blistering noted at birth in one.The former had bald areas in this region at follow-up. Beneath the scabs of the latter infectiondeveloped and an abcess formed in the rightoccipital region, about I- inches away from thetraumatised area. The abscess required incisionbut there was no apparent balding at six weeks.One cephalhaematoma occured, giving an

incidence of 3%. This is a much lower incidencethan that recorded by Huntingford (I96I).The important complication associated with

the technique is cerebral irritation (Table 5). Intwo infants of primiparae, this was of a mildnature, increased tone being noted which requiredcot-nursing for 48 hours. Both deliveries werecompleted by forceps. Over an hour's tractionwas needed to achieve full dilatation in oneinstance, this being followed by easy rotation butdifficult extraction with Kielland's forceps.Detachment of the cup occurred in the other case,on commencing firm traction after full dilatation,so Kielland rotation and forceps delivery wasnecessary. Holtorff (I96I), in a follow-up studyof foetal mortality and morbidity following deliverywith forceps and vacuum extraction, finds thatsome disappointments will occur: cerebral

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472 POSTGRADUATE MEDICAL JOURNAL August I963

TABLE 5DETAILS OF CASES WITH CEREBRAL IRRITATION

Length of Duration of Birth Condition Follow-upParity Indication Labour Traction Weight Scalp at Birth Progress

o Static at i dilata- 29 hours Approxi- Abrasion. Small White Increased Bald patch.tion mately 40 7.12 slough asphyxia tone. Cot Normal de-

minutes nursed 24 hrs. velopment.

o Prolonged labour Bruised caput. High pitched Bald patch.occipito-posterior 44 hours 70 minutes 8.4 Scabbing. Good cry. Increased Normal de-position. Under tone velopment.6 cm. dilated.

2 Delay, cervix thick Minimal Blue Twitching of Normal at 5under 6 cm. dilated I 9 hours 40 minutes 7.14 abrasion asphyxia. right side. months.Mild aortic steno-l Slow to Sedation. Backwards atsis. cry. Satisfactory I9 months

l at 6 days. ? Right hemi-I paresis.

irritation is particularly liable when both vacuumextractor and forceps are used on the same child.

Serious cerebral irritation occured once. Thehead was above the spines and well flexed in aposterior position. A good application wasobtained with the small cup at 5 to 6 cm. dilatation.Little further dilatation occurred during the firsthalf hour of traction and the patient was ratherrestless, complaining of pain and cramp in theright leg. Delivery occurred after 40 minutes oftraction. Although the infant's breathing wasregular at birth, the cry was poor and, the followingday, signs of cerebral irritation were presentand right-sided twitching pecessitated sedation.Progress seemed normal at five months, but atI9 months he was not walking or talking and aright hemiparesis is probable.

Maternal ComplicationsThe vacuum extractor is considered very safe

for the mother and free from soft tissue damage(Chalmers and Fothergill, I960; Smedley, I960).It will be noted that vaginal laceration occuredtwice in this series (Table 6), on both occasionscausing postpartum hlimorrhage. The lacerationswere attributable to the subsequent Kiellandrotation and forceps deliveries. The twin deliverycomplicated by intrapartum hamorrhage also hada small postpartum hamorrhage. The forciblecervical dilatation did not cause cervical tears andDuhrssen's incisions were never considered.The only other relative maternal complication

was a peroneal nerve palsy, which has not beenrecorded previously. The lithotomy position wasmaintained for about I hours, with the legs out-side the poles, and traction continued inter-mittently for 40 minutes. During this time, thepatient complained of severe pain in the right leg.Since her previous children had similar birth

TABLE 6

MATERNAL COMPLICATIONSPostpartum haemorrhage 3 (2 from lacerations)Vaginal laceration 2Manual removal of placenta IPeroneal nerve palsy ..IPuerperal pyrexia I (urinary tract infection)Puerperal psychosis I

TABLE 7

INDICATIONS FOR APPLICATION OF FORCEPS

Occipito-posteriorIndications and Transverse Anterior

Position Position

Failed ventouse rotation 3 o

Minor disproportion,posterior position .. 4 o

rcetal distress .. I

Detachment ventouse .I I

Failed traction withventouse .. 0 3

Rigid perineum .. o

Elective I O

II_ 6

weights and no local pressure on the nerveoccurred, the lesion must have been due topressure on the lumbosacral cords by the descend-ing faetal head. Cole (I946) believes the pelvismust have certain characteristics for this to occur:these are a flat sacral promontory, shallow sacralalae, and a short posterior portion of the iliacbones.

Forceps were applied after full dilatation in17 cases, probably an unnecessarily high figure

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Number of Cases

II

16

7

I9

Percentage20.4%29.8%I3.o%35.1%1.7%

(Table 7). The failures were mostly with posteriorpositions, although this is one of the main indica-tions listed by Willcocks (1962) for the use of theventouse in the second stage of labour. Astraction was prolonged before reaching fulldilatation in several instances, it was felt that theduration of the second stage should be limited.Of course, there were also failures from cupdetachment and forceps were therefore applied.The value of vacuum extraction is also apparent

in dealing with prolonged labour, itself a rareoccurrence (Table 8). Spontaneous deliveries occur,following adequate sedation and hydration, in aconsiderable proportion of cases, 35% in thisseries and 24% in a series reported by Jeffcoate(196I). Caesarean section was performed 11times; in seven, vacuum extraction had beenconsidered but was rejected as some disproportionwas evident. In another seven cases vaginaldelivery was thought possible and was effected,labour lasting from 39 to 53 hours and dilatationvarying from over 3 fingers to a rim all round.

DiscussionThe value of the vacuum extractor as an

alternative to Caesarean section and the resultsobtained both from forceps and from vacuumextraction will be discussed from the foetal andmaternal aspects.Most obstetricians, reporting on the ventouse,

agree that one great advantage of this instrumentis that it may safely be used to expedite delivery,prior to full dilatation of the cervix. Some considerthat the degree of cervical dilatation is unimportant(Lillie, I960), others that the cervix should beabout 5 cm. dilated prior to application of theinstrument (Bruniquel and Israel, 1958; Snoeck,I960), and Chalmers (I960) considers that thevacuum extractor is best used when the cervix isthree-quarters dilated although he has used it atlesser dilatations. The ventouse effected fulldilatation, if not delivery, in all our cases, thedilatation being from 3 cm. upwards. Howeverthe object is not only vaginal delivery but birth of

TABLE 8PROLONGED LABOUR (OVER 36 HOURS)

Number of Cases 54. Percentage of all deliveries 1.2%Method of Delivery

Csesarean section ..

Forceps delivery ..

Vacuum extraction ..

Spontaneous delivery

Breech extraction .

an unharmed infant. Therefore, use of theventouse is only justified if the results obtainedare as good as or better than Caesarean sectionfrom all aspects.Alarming fietal results following vacuum

extraction for delay in the first stage of labour werereported by Huntingford (I96I). Two neonataldeaths occurred in 1 deliveries. One resultedfrom intracranial haemorrhage, apparently relatedto the application of the ventouse. The secondneonatal death demonstrated another hazardof this method, viz. unsuspected disproportionnecessitating Caesarean section. The baby diedof atelectasis from meconium aspiration. Fourother infants showed cerebral irritation, thetraction time varying from 25 to 75 minutes.Huntingford, therefore, advised 'cautiousappraisal' of the use of the vacuum extractor fordelay in the first stage.

Evidence from the series reported in this papersuggests that the incidence of significant scalptrauma and cerebral damage is related to theduration of traction. This was 40 minutes or overin all cases affected. It would therefore seemwise to limit traction to 30 minutes as suggestedby Willcocks (I962) and Lauridsen, Pless, andUhrenholdt (I962). As the traction time is alsorelated to the degree of cervical dilatation (Table 3)the ventouse should seldom be applied beforeone-half dilatation in multigravidae and not tillover one-half dilatation in primigravidae.The majority of minor abrasions heal without

infection, prior to discharge from hospital.Lauridsen and others (I962), following up infantsafter vacuum extraction, found slight pigmentationof the scalp in three, and an area of alopecia inone of 15 cases of minor abrasions. The dangerfrom potential infection mentioned by Hunting-ford (1961) is lessened in this hospital by thepractice of giving antibiotics to all infants born48 hours or more after rupture of the membranes,a routine affecting a number of the cases treatedby vacuum extraction.

Neonatal deaths from intracranial haemorrhage,associated with vacuum extraction, have beenrecorded by many authors (Hochuli and St6ckli,1960; Snoeck, 1960; Holtorff, I96I; Huntingford,1961; and Willcocks, I962). The stage of labourin which the ventouse was applied was not alwaysrecorded and, in some, intra-uterine anoxia waspartly responsible.

Cerebral irritation was noted by Fiirstenbergand S6derhjelm (I960), Huntingford (I96I), andWillcocks (I962). Holtorff (I96I) found that it isparticularly liable to occur if forceps are appliedafter the ventouse, which agrees with ourexperience. The one case of definite cerebraldamage reported in the present series had no

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TABLE 9CEREBRAL TRAUMA ASSOCIATED WITH VACUUM

EXTRACTION

Neo- Deaths from CerebralAuthors Cases natal intracranial irritation

deaths haemorrhageFiirstenberg andS6derhjelm(1960) . . 67 I 4

Hochuli and NotSt6ckli (I960) 265 i 3 2 recorded

Holtorff (1961) 119 2 I Notrecorded

Huntingford(1961) .. 2 I 4

Fothergill andChalmers(I96I) .. 200 2 2 0

Willcocks (I962) 00oo 3 3Lauridsen andothers (I962).. 69 o o o

Present series .. 32 0 o 3

counterpart in a follow-up study by Lauridsen andothers (I962), or in the padiatricians' follow-upof Willcocks' series (I962).The real dangers to the foetus, then, are possible

intracranial hemorrhage or cerebral damage,which, in recorded series (Table 9) have a verylow incidence. Although de Boer (I960) hasshown that the ventouse will raise the intracranialpressure, evidently a harmful effect is seldomproduced.There is a well-defined group of primigravidae

who become post-mature with an occipito-posterior position and who often commencelabour with rupture of the membranes. Thecontractions that follow are ineffectual or progressbecomes arrested and maternal or fcetal distressdevelops. Prior to the introduction of the ventouse,Caesarean section was necessary, with its attendantrisks to the fcetus of central depression fromgeneral anaesthesia and pulmonary complications.Now, with judicious use of the ventouse, it ispossible to deliver these patients with inertia orprolonged labour vaginally and often prior to thedevelopment of foetal distress, providing thatthere is no clinical evidence of disproportion.

Multiparae in established labour, with feetaldistress, can be delivered rapidly with the ventouse,again without resorting to general anaesthesia.

Considerable difficulty may be experienced insecuring premature delivery in cases of Rhesusincompatibility. The ventouse has been used toadvantage on two occasions when surgical induc-

tion and Syntocinon infusion have failed toestablish progressive labour.The overall safety of the vacuum extractor for

delivery is confirmed by Bergman and Malstrom(I96I). Analysing the 1958 records of 29 SwedishHospitals, they found that in 44,767 vertexdeliveries the foetal mortality was 4.1% for 793forceps deliveries compared with only I.5% forvacuum extraction. The greater safety of applica-tion of the vacuum extractor in mid or highpelvis was also demonstrated. In addition, fatalintracranial injury occurred in only 0.7% ofdeliveries with the instrument compared with1.5% for forceps. From our figures (Table i),it is seen that the uncorrected foetal mortalityassociated with Caesarean section and forcepsextraction are considerable, 6.5% and 4.2%respectively, but that there was no mortalityafter use of the ventouse.There are only two reported maternal deaths

associated with vacuum extraction and neitherdeath was related to the mode of delivery.Caesarean section, however, has a maternalmortality of at least 0.33% (Report on ConfidentialEnquiries into Maternal deaths, I960), death beingmainly due to haemorrhage and shock, pulmonaryembolism, sepsis and ileus, or anaesthesia. Vacuumextraction, which causes no damage to the softtissues, makes no further demands on the maternalreserves, which are already depleated in cases ofprolonged labour and maternal distress. This isnot true of Caesarean section, to which the dangersfrom anaesthesia and blood loss are added andconvalescence may be impaired by infection orpulmonary complications.The use of local anaesthesia for vacuum extrac-

tion allows voluntary effort of the mother to assistdelivery when full dilatation is reached, particu-larly in multiparae. The second stage is completedin ten minutes in the majority of cases. However,the lithotomy position is not comfortable for thelong periods of time necessary in some cases.One patient, who was in the position for justunder two hours, subsequently said her worstmemory was of the long labour prior to inter-ference. If, in future, the vacuum extractor isonly used when the anticipated time to achievedelivery is less than 40 minutes, this disadvantagewill be eliminated. The rare complication of aperoneal nerve palsy must have been related totraction applied with the head in the obliqueposterior position. This palsy may even followspontaneous delivery (Chassar Moir, 1956).

Huntingford's (I961) suggestion that the forciblecervical dilatation may be followed by cervicalincompetence is of interest. So far no case hasbeen encountered here.

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August I963 AUSTIN: Complications of the First Stage of Labour 475

Conclusionsi. The vacuum extraction is an effective

method of treating complications of the firststage of labour.

2. The risks to mother and child are less thaneither Cesarean section or forceps delivery.

I would like to acknowledge the encouragement andadvice given by Mr. A. L. Gunn and Mrs. J. Karnicki.

REFERENCESALMENT, E. A. J. (I960): The Vacuum Extractor (Ventouse)-An Alternative to the Obstetric Forceps, Proc. Roy

Soc. Med., 53, 759.BERGMAN, P., and MALSTROM, T. (I96I): Vacuum Extraktor eller Forceps, Nord. Med., 65, 644.BRUNIQUEL, G. and ISRAEL, A. (1958): Contributions e, etud. de la Ventouse Obstetricale son Champ d'Application,

ses Avantages, Gynec. et Obstet., 57, 222.CHALMERS, J. A. (I960): The Vacuum Extractor (Ventouse)-An Alternative to the Obstetric Forceps, Proc. Roy.

Soc. Med., 53, 753.and FOTHERGILL, R. J. (I960): Use of a Vacuum Extractor (Ventouse) in Obstetrics, Brit. med. J., i, 1684.

CHASSAR MOIR, J. (1956): 'Munro Kerr's Operative Obstetrics'. London: Bailliere, Tindall and Cox.COLE, J. T. (1946): Maternal Obstetric Paralysis, Amer. J. Obstet. Gynec., 52, 372.DE BOER, C. H. (I960): The Vacuum Extractor (Ventouse)-An Alternative to the Obstetric Forceps, Proc. Roy. Soc.

Med., 53, 758.FOTHERGILL, R. J., and CHALMERS, J. A. (I96I): The Place of the Ventouse (Vacuum Extractor) in Domiciliary Practice,

Practitioner, I86, 559.FORSTENBERG, N., and S6DURHJELM, L. (I960): Vacuum Extraktionens Verkau pa Barnen, Nord. Med., 64, 843.HOCHULI, E., and STOCKLI, A. (1960): Erfahrungen mit dem Vakuumestraktor nach Malstroem bei 265 Fiillen, Geburtsh.

u. Frauenheilk, 20, 346.HOLTORFF, J. (I96I): Die Kindliche Mortalitiit und Morbiditat bei Zangen- und Vakuumextrationen, Zbl. Gyndk.,

83, 26 I.HUNTINGFORD, P. J. (I96I): The Vacuum Extractor in the Treatment of Delay in the First Stage of Labour, Lancet, ii,

1054.JEFFCOATE, T. N. A. (I96I): Prolonged Labour, Lancet, ii, 6i.LAURIDSEN, L., PLESS, J., and UHRENHOLDT, A. (I962): Vacuum-extraction, a Follow-up Study, J. Obstet. Gynec.

Brit. Cwlth., 69, I0I9.LILLIE, E. W. (I960): The Vacuum Extractor (Ventouse)-An Alternative to the Obstetric Forceps, Proc. Rov. Soc.

Med., 53, 758.MALSTR6M, T. (1954): The Vacuum Extractor. An Obstetrical Instrument, Act2 obstet. gynec. scand., 33, suppl. 4.MALSTROM, T. (1957): The Vacuum Extractor. An Obstetrical Instrument, Ibid., 36, suppl. 3.'Report on Confidential Enquiries into Maternal Deaths in England and Wales, 1955-I957' (I960). London: H.M.

Stationery Office.SIMPSON, J. Y. (I849): On a Suction-Tractor, or New Mechanical Power, as a Substitute for the Forceps in Tedious

Labours, Proc. Edinb. Medico-Chir. Soc., 556.SMEDLEY, G. T. (I960): The Vacuum Extractor (Ventouse)-An Alternative to the Obstetric Forceps, Proc. Roy. Soc.

Med., 53, 757.SNOECK, J. (I960): Ibid., 53, 749.'Standard Form Recommended by the Royal College of Obstetricians and Gynecologists for the Production of Maternity

Hospital Medical Reports' (1957): J. Obstet. Gyncec. Brit. Emp., 64, 752.WILLCOCKS, J. (I962): The Vacuum Extractor-An Evaluation, 57. Obstet. Gyncc. Brit. Cwlth., 69, 267.

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