How to Manage Cervical Incompetence byApplication of a Cervical Cerclage Suture in thePregnant Mare

Stefania Bucca, DVM

Placement of a cerclage suture over the caudal os of the cervix can effectively restore cervical closurein pregnant mares at risk of anatomical or functional incompetence, unresponsive to progestagensupplementation. Author’s address: Qatar Racing and Equestrian Club, Muaither Rayyan, POBox 7559, Doha, Qatar; e-mail: stefbucca@gmail.com. © 2013 AAEP.

1. Introduction

Cervical incompetence in the mare is widely recog-nized as a major cause of pregnancy failure. Fail-ure to attain adequate closure during pregnancyis a key predisposing factor to ascending placen-titis. In humans, cervical insufficiency is of majorconcern1 and can result in preterm birth and late-term abortions, similar to observations in mares.Emerging clinical2,3 and laboratory-based evidence4

suggests that focusing on the uterine cervix mayprovide significant elements of diagnostic value toidentify patients at risk for preterm delivery, offer-ing guidelines to implement preventive interven-tion.5 A variety of techniques have been used inhuman medicine to address cervical incompetence,including medical therapy with progesterone, cer-vical cerclage, and the placement of a cervical pes-sary,6–8 some of which may be applicable in themare. A recent study in human medicine comparedvaginal progesterone versus cerclage, with the use ofplacebo/no cerclage as the control treatment.9 Theauthors concluded that progesterone and cervicalcerclage are equally effective for the prevention of

preterm birth and adverse perinatal outcomes inpatients with a short cervix and history of pretermbirth.

A common treatment strategy used on mares thathave previously lost a foal because of placentitis orthat have anatomical abnormalities in the caudalreproductive tract making them at risk of ascendingplacentitis is to administer an antimicrobial, a non-steroidal anti-inflammatory drug and altrenogestdaily until delivery of the foal.10 The shortcomingof this treatment is that mares may still have apreterm delivery/fetal loss with histopathologicalevidence of ascending placentitis despite treatment.This report describes a technique for cervical cer-clage applied to a population of mares with knowncervical incompetence.

2. Materials and Methods

Six cervical cerclage procedures were carried outon four mares. Two mares underwent the cerclageprocedure during two successive pregnancies.Three of the four mares were aged Thoroughbredsand the fourth was a 9-year-old Arabian mare.Cervical incompetence was detected through serial

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NOTES

ultrasound examinations.11 The gestational ageat the time of diagnosis varied between mares butranged from 5 to 8 months of gestation.

Case 1, a 17-year-old Thoroughbred mare, pre-sented a 2-year history of abortion and a histo-pathological diagnosis of ascending placentitisdespite weekly administrations of altrenogest andantimicrobials, each month of gestation. Case 1was presented at 220 days of gestation for investi-gation of her history of pregnancy loss. Prematurecervical ripening was evident on ultrasound exami-nation, and a cerclage suture was placed at 234 daysof gestation, after 2 weeks of increased altrenogestadministration (of 0.088 mg/kg twice daily) with noimprovement in ultrasound cervical parameters.

Case 2, the same mare as in case 1, the year afterher first cervical cerclage treatment, was monitoredfor ultrasound evidence of cervical ripening from day120 of gestation. Signs of cervical ripening weredetected 205 days after ovulation, with cervical pa-rameters progressing from grade 3 to grade 411 de-spite altrenogest administration. Cervical cerclagewas then carried out.

Case 3, a 19-year-old Thoroughbred mare, hada 3-year history of pregnancy loss and histopatho-logical evidence of ascending placentitis despitealtrenogest/antimicrobial treatment administration.Signs of cervical ripening were detected at day 170of gestation, and a cervical cerclage suture wasplaced 21 days later.

Case 4, same mare as in case 3, the year after herfirst cervical cerclage treatment, showed evidenceof cervical ripening at day 154 of gestation andwas treated with cervical cerclage after 3 weeks ofaltrenogest administration, with no improvement incervical parameters.

Case 5 was initially presented for intermittentvaginal bleeding at approximately 7 months of ges-tation. The source of bleeding was readily identi-fied in some vestibular varicosities and promptlycorrected, but ultrasonography of the caudal repro-ductive tract showed evidence of premature cer-vical ripening. Case 5 had already been placed onaltrenogest and antimicrobial treatment by the re-ferring veterinarian because of the mare’s historyof abortion caused by ascending placentitis the pre-vious year. After cervical assessment with evi-dence of premature cervical relaxation, treatmentwith altrenogest continued at an increased dose of0.088 mg/kg twice daily for 3 weeks. A cervical

cerclage suture was placed at day 240 of gestationbecause of the persisting state of cervical relaxationand the significant increase in the combined thick-ness of the utero-placental unit (CTUP) at the cer-vical pole (11 mm).

Case 6, a 9-year-old Arabian mare at her secondgestation, was referred for mild signs of early mam-mary development at 7 months of gestation. Themare had a history of stillbirth and dystocia theprevious year. She had been bred naturally verylate that year and was not checked for pregnancyafterward.

No abnormalities were detected on clinical exam-ination of the mare, but, on rectal palpation, thecervix was short and fibrotic. Ultrasonography ofthe caudal reproductive tract per rectum revealed ashort (�6 cm) cervical canal with disrupted centrallinear striation and a heterogeneous echo patternof the muscular layer. An area of increased CTUP(12.4 mm), markedly hypoechoic, was identified atthe cervical pole, extending rostrally to the caudalbody of the uterus for 6 to 8 cm. Transabdominalfeto-placental evaluation was unremarkable. As-cending placentitis associated with cervical incom-petence was suspected and was probably related tocervical damage received during dystocia correctionthe previous year. A cervical cerclage suture wasplaced 13 days after initial diagnosis.

Table 1 summarizes historical and gestational pa-rameters relevant to the procedure.

Technique

The application of a purse-string suture over thevaginal os of the cervix was carried out on the se-dated mare that was restrained in stocks. Themare’s rectum was evacuated and the tail wrappedand tied to one side. The perineum was surgicallyscrubbed and dried. Sedation was administeredbefore the procedure (detomidine HCLa 0.02 mg/kgin association with butorphanol tartrateb 0.04 mg/kg). The mare’s cervix was visualized with theuse of a modified Finochietto retractor (Fig. 1).The cervix was then grasped with long-handledKnowles forceps (Fig. 2). A purse-string suturewas placed with the use of long-handled instru-ments and a single-stranded No. 2 nylon suture(Fig. 3). Three partial-thickness bites (avoidingpenetration of the cervical lumen), approximately1.5 to 2 cm long, were applied to the circumferenceof the external cervical os, starting dorsally at the

Table 1. Historical and Gestational Parameters of Six Cervical Cerclage Procedures

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

Age, years 17 18 19 21 14 9History of pregnancy loss 2 years N/A 3 years N/A 1 year NoneGestation at initial diagnosis, days 220 205 170 154 218 213Gestation at cerclage suture, days 234 226 191 183 240 226Gestation at parturition, days 339 344 362 371 348 328

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2 o’clock position to end at the 11 o’clock position(Fig. 4). The length of the bites varied according tothe state of relaxation of the cervical os and there-fore its size. The knot was electively tied in anupper position (11 to 1 o’clock positions) to facilitateremoval at the appropriate time.

Antimicrobials, non-steroidal anti-inflammatorydrugs, and altrenogest were administered peri-operatively and continued for about 5 days afterintervention. After cerclage placement, treatedmares were kept under close observation for signsof impending parturition, while cervical parametersand cerclage suture were monitored by transrectalultrasonography. The cerclage suture was removedat the mare’s due date or in the presence of earlymammary development. Suture removal was per-formed in the standing sedated mare, restrained

in stocks, with the use of long-handled scissors andFinochietto retractors (Figs. 5, 6, and 7).

3. Results

After cervical cerclage, all mares delivered livefoals. Foals survived to at least 1 year of age.Serial evaluation of the caudal reproductive tractdid not reveal abnormalities (placental changes, cer-vical shortening) after cerclage sutures were placed.Post-foaling inspection and examination at foal heatwere also unremarkable for potential complicationsof the cerclage procedure.

4. Discussion

Cervical incompetence in the mare is commonly as-sociated with difficulty conceiving or carrying a foalto term and is widely recognized as a major cause of

Fig. 1. The cervix is visualized through the use of modifiedFinochietto retractors.

Fig. 2. The cervix is grasped with the use of long-handledKnowles forceps.

Fig. 3. Placement of a purse-string suture over the vaginal os ofthe cervix, with the use of long-handled instruments and single-stranded No. 2 nylon suture.

Fig. 4. Schematic drawing of the placement of a cervical cerclagesuture.

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pregnancy failure. Yellon et al12 have appropri-ately referred to the cervix as the “gatekeeper forpregnancy.” The cervix functions as the final andmost cranial barrier to ascending aggressors be-cause it separates the uterine lumen from vaginalcontent. Failure of the cervix to form a functionalbarrier will expose the uterine environment to phys-ical, chemical, or biological challenges from the cau-dal reproductive tract and predispose the mare tochronic endometritis and ascending placentitis.Cervical incompetence recognizes anatomical andfunctional origins. In humans,13 it has been re-ported that remodeling of the cervix occurs slowlyover a length of time and that the progressivechanges in the cervix precede the uterine contrac-tions by several weeks in normal pregnancy.14

Similar conclusions may be drawn from the resultsof a recent study on the ultrasonographic features ofthe equine pregnant cervix.11 The study indicatesthat in the mare, evidence of cervical remodelingleading to ripening may be observed during the last2 months of gestation, with gradual changes in sizeand echotexture. Cervical ripening entails changesin cellular structure and molecular biology of thecervical cells,14 and this gradual process will alterthe mechanical attributes of the cervix, with a cer-

tain degree of variability among individuals. Pre-mature remodeling/ripening of the cervix andshortening of the cervical canal may be suggestive ofpreterm birth, on the basis of loss of mechanicalsupport and because the bacterial flora of the caudalgenital tract is moved closer to the fetal membranesoverlaying the internal os. Cervical ripening causesutero-placental instability at its interface, with re-sulting areas of detachment, hemorrhage, and in-flammatory change, radiating from the cervical pole.Avillous detached areas may prolapse into the innercervical os, under the mechanical forces of fetalextremities and fetal fluid pressing on it. Largedetached areas may create a marked “funneling”effect, in which the free allantochorion may pro-lapse through the length of the cervical canal andbecome exposed to microorganisms ascending fromthe vagina, through the relaxed cervix. Prematurecervical ripening may be a transient phenomenonand may spontaneously resolve; it may be observedin pregnant mares recovering from systemic dis-ease and/or post-surgery. Gestation will progressundisturbed to term, providing that the local inflam-matory process subsides and microorganism coloni-zation of the allantochorion at the cervical pole isprevented.

Fig. 5. Cerclage suture removal. The suture is grasped withthe use of a long-handled needle holder.

Fig. 6. Cerclage suture removal. The suture is cut with the useof long-handled scissors.

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Changes of the utero-placental unit at the cervicalpole may be detected by transrectal ultrasonographyas a consequence of premature cervical ripening inthe mare, suggestive of ascending placentitis. Thepresence of sonographically identifiable collectionsof material referred to as “amniotic sludge,” accumu-lated above the internal os, represents a correspon-dent change associated with adverse pregnancyoutcome in women who have premature cervical rip-ening.15 There is general agreement that somecases of premature cervical ripening are related toinfection.14 In humans, infection may account forup to one-third of preterm births, and the inflamma-tory response elicited by infectious agents has alsobecome the accepted mechanism for preterm birth.In contrast, other instances associated with prema-ture cervical ripening are attributed to less definedcauses such as genetic background of the mother orfetus, environmental factors, intercurrent illness,or health conditions,14 and this may very well holdtrue in the pregnant mare.

Progesterone is considered a key hormone forpregnancy maintenance, and a decline in progester-one action is implicated in the onset of parturition.If such decline occurs in the midtrimester in women,cervical shortening may occur, and this would pre-

dispose to preterm delivery. It is recognized thatprogesterone has a demonstrable effect on the rateof cervical shortening and preterm delivery whenadministered to women admitted for preterm laborbetween 25 and 33 �6 weeks of gestation.16 A sim-ilar effect may be observed in mares with ultrasono-graphic evidence of premature cervical ripeningduring altrenogest supplementation, with signifi-cant improvement in cervical grading (author’s ob-servation) and gradual palpable increases in cervicaltone and length. In the author’s experience, failureto respond to altrenogest supplementation is themajor indication for cervical cerclage in cervical in-competence cases, particularly when incrementsin CTUP are observed at the cervical pole. Maresthat have chronic medical conditions, endocrineimbalances, and toxic disorders have been observedto show ultrasound evidence of premature cervicalrelaxation, even under progestagen supplementa-tion (personal communication). Under these cir-cumstances, a cervical cerclage procedure is likely toprevent the development of ascending placentitis.

In the case series presented in this report, cases 1and 3 showed the inadequacy of progestagen treat-ment alone in promoting adequate cervical compe-tence, as histopathology of fetal membranes indicatedascending placentitis as the cause of pregnancy fail-ure for the previous two gestations in case 1 and forthe 3 preceding years for case 3. Placement of acervical cerclage suture prevents exposure of thecervical lumen and ultimately of the allantochorionto aggressors from the caudal reproductive tract.It also provides a means of stabilizing and strength-ening the cervix from the mechanical forces appliedby fetal parts and fetal fluid volumes shifting backand forth during episodes of activity. Penetrationof the cervical luminal mucosa during placement ofthe cerclage suture should be avoided because itmay create an intralumenal inflammatory focus andthe opportunity for bacterial colonization from thecaudal reproductive tract. Particularly during epi-sodes of cervical funneling, the allantochorion mayadvance toward the vaginal os of the cervix, withample opportunity for bacterial contamination.

5. Conclusions

Focus on the uterine cervix may identify mares atrisk for ascending placentitis/preterm delivery andmay yield approaches to prevent it. Ultrasono-graphic monitoring of cervical parameters can beeasily applied under field conditions and should beimplemented in mares with a repeated history ofpreterm delivery and evidence of ascending placen-titis, starting as early as 4 months of gestation.Placement of a cervical cerclage suture is warrantedwhen progestagen supplementation fails to achieveadequate cervical closure and significant changesof the utero-placental unit take place at the cer-vical pole. Although no complications have beenreported in association with cervical cerclage, closesupervision of treated mares for signs of impending

Fig. 7. Cerclage suture removal. The suture is gently pulledout.

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parturition is of critical importance to prevent cer-vical damage in the case of untimely delivery withthe suture still in place.

References and Footnotes1. Shortle B, Jewelewicz R. Cervical incompetence. Fertil

Steril 1989;52:181–188.2. Andersen HF, Nugent CE, Wanty SD, et al. Prediction of

risk for preterm delivery by ultrasonographic measurementof cervical length. Am J Obstet Gynecol 1990;163:859–867.

3. Romero R. Prevention of spontaneous preterm birth:the role of sonographic cervical length in identifying patientswho may benefit from progesterone treatment. UltrasoundObstet Gynecol 2007;30:675–686.

4. Kuon RJ, Shi SQ, Maul H, et al. Pharmacologic actions ofprogestins to inhibit cervical ripening and prevent deliverydepend on their properties, the route of administration, andthe vehicle. Am J Obstet Gynecol 2010;202:455, e1–e9.

5. Vidaeff AC, Ramin SM. Management strategies for the pre-vention of preterm birth, part II: update on cervical cer-clage. ACOG Comm Opin 2009;21:485–490.

6. Dharan VB, Ludmir J. Alternative treatment for a shortcervix: the cervical pessary. Semin Perinatol 2009;33:338–342.

7. Hassan SS, Romero R, Vidyadhari D, et al. Vaginal proges-terone reduces the rate of preterm birth in women with asonographic short cervix: a multicenter, randomized,double-blind, placebo-controlled trial. Ultrasound ObstetGynecol 2011;38:18–31.

8. Romero R, Nicolaides K, Condeagudelo A, et al. Vaginalprogesterone in women with an asymptomatic sonographicshort cervix in the midtrimester decreases preterm deliveryand neonatal morbidity: a systematic review and meta-

analysis of individual patient data. Am J Obstet Gynecol2012;206124.e1–124.19.

9. Condeagudelo A, Romero R, Nicolaides K, et al. Vaginalprogesterone versus cervical cerclage for the prevention ofpreterm birth in women with a sonographic short cervix,singleton gestation, and previous preterm birth: a system-atic review and indirect comparison meta-analysis. Am JObstet Gynecol 2013;208:42.e1–42.e18.

10. LeBlanc MM. Ascending placentitis in the mare: an up-date. Reprod Domest Anim 2010;45(Suppl 2):28–34.

11. Bucca S, Fogarty U. Ultrasonographic cervical parametersthroughout gestation in the mare, in Proceedings. Am AssocEquine Pract 2011;57:235–241.

12. Yellon SM, Burns AE, See JL, et al. Progesterone with-drawal promotes remodeling processes in the nonpregnantmouse cervix. Biol Reprod 2009;81:1–6.

13. Word RA, Li XH, Hnat M, et al. Dynamics of cervical re-modeling during pregnancy and parturition: mechanismsand current concepts. Semin Reprod Med 2007;25:69–79.

14. Larsen B, Hwang J. Progesterone interactions with the cer-vix: translational implications for term and preterm birth.Infect Dis Obstet Gynecol 2011.

15. Gauthier S, Tetu A, Himaya E, et al. The origin of Fusobac-terium nucleatum involved in intra-amniotic infection andpreterm birth. J Matern Fetal Neonat Med 2011;24:1329–1332.

16. Facchinetti F, Paganelli S, Comitini G, et al. Cervicallength changes during preterm cervical ripening: effects of17�-hydroxyprogesterone caproate. Am J Obstet Gynecol2007;196:453.e1–453.e4.

aDormosedan� Orion Corporation, Espoo, Finland.bTorbugesic�, Fort Dodge Animal Health, Fort Dodge, IA

50501.

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