Dr Sh­erne Kalloo

The term cer­vi­cal in­suf­fi­cien­cy, for­mer­ly called “cer­vi­cal in­com­pe­tence,” de­scribes a sit­u­a­tion in which the cervix—the low­er part of the uterus—short­ens and opens pre­ma­ture­ly dur­ing preg­nan­cy, of­ten with­out con­trac­tions or sig­nif­i­cant pain. This can re­sult in a sec­ond-trimester mis­car­riage or very ear­ly preterm birth.

It is im­por­tant to dis­tin­guish this from the much more com­mon caus­es of mis­car­riages of ear­ly preg­nan­cy. Most first-trimester mis­car­riages are re­lat­ed to chro­mo­so­mal ab­nor­mal­i­ties in the de­vel­op­ing em­bryo. Re­peat­ed preg­nan­cy loss­es in the sec­ond trimester, par­tic­u­lar­ly when they oc­cur with pain­less cer­vi­cal di­la­tion, should raise sus­pi­cion of cer­vi­cal in­suf­fi­cien­cy.

What caus­es it?

There is rarely one sin­gle cause. Risk may be in­creased by pre­vi­ous cer­vi­cal surgery or pro­ce­dures, in­clud­ing some treat­ments for ab­nor­mal cer­vi­cal cells, pre­vi­ous cer­vi­cal trau­ma, con­gen­i­tal dif­fer­ences in the uterus or cervix, or a pre­vi­ous sec­ond-trimester loss or spon­ta­neous preterm birth. How­ev­er, many women with cer­vi­cal in­suf­fi­cien­cy have no ob­vi­ous risk fac­tor.

The old­er be­lief that the cervix is sim­ply a per­ma­nent­ly “weak” struc­ture has al­so been re­fined. Cur­rent ev­i­dence views cer­vi­cal func­tion as a con­tin­u­um in­volv­ing cer­vi­cal short­en­ing, tis­sue changes and oth­er process­es that can lead to pre­ma­ture di­la­tion.

How is it di­ag­nosed?

A woman’s pre­vi­ous preg­nan­cy his­to­ry is ex­treme­ly im­por­tant. Dur­ing preg­nan­cy, trans­vagi­nal ul­tra­sound can ac­cu­rate­ly mea­sure cer­vi­cal length and de­tect short­en­ing be­fore the cervix opens. A cer­vi­cal length of 25 mm or less in the mid-trimester is gen­er­al­ly con­sid­ered short in a sin­gle­ton preg­nan­cy with­out a pre­vi­ous spon­ta­neous preterm birth.

Women with a pre­vi­ous sec­ond-trimester loss or spon­ta­neous preterm birth may re­quire in­di­vid­u­alised sur­veil­lance and spe­cial­ist as­sess­ment.

How is it treat­ed?

The best-known treat­ment re­mains a cer­vi­cal cer­clage, com­mon­ly called a cer­vi­cal stitch. Un­der gen­er­al anaes­the­sia, usu­al­ly around 14 weeks’ ges­ta­tion, a su­ture is placed around the cervix via the vagi­na to pro­vide sup­port. De­pend­ing on the woman’s his­to­ry and ul­tra­sound find­ings, it may be placed elec­tive­ly ear­ly in preg­nan­cy or lat­er if cer­vi­cal short­en­ing or di­la­tion de­vel­ops. It is usu­al­ly re­moved near 36–37 weeks if a vagi­nal birth is planned. One im­por­tant risk in in­sert­ing the su­ture is spon­ta­neous rup­ture of mem­branes.

Vagi­nal prog­es­terone al­so has an im­por­tant role in se­lect­ed women with a short cervix. For ex­am­ple, SMFM rec­om­mends vagi­nal prog­es­terone for an asymp­to­matic woman with a sin­gle­ton preg­nan­cy and cer­vi­cal length of 20 mm or less be­fore 24 weeks, with con­sid­er­a­tion at 21–25 mm through shared de­ci­sion-mak­ing.

Cer­clage is not au­to­mat­i­cal­ly re­quired for every woman with a short cervix. In women with­out a pre­vi­ous spon­ta­neous preterm birth, SMFM rec­om­mends against cer­clage for a cer­vi­cal length of 10–25 mm when there is no cer­vi­cal di­la­tion.

For women who have had a pre­vi­ous failed vagi­nal cer­clage fol­lowed by a very ear­ly spon­ta­neous de­liv­ery, par­tic­u­lar­ly be­fore 28 weeks, a trans­ab­dom­i­nal cer­clage may be con­sid­ered. This can be per­formed be­fore preg­nan­cy or dur­ing ear­ly preg­nan­cy, but it gen­er­al­ly means that de­liv­ery must be by Cae­sare­an sec­tion.

What about bed rest?

This is one of the im­por­tant changes from old­er med­ical ad­vice. Rou­tine bed rest or ac­tiv­i­ty re­stric­tion is no longer rec­om­mend­ed sim­ply be­cause a woman has a short cervix or is con­sid­ered at risk of preterm birth. Ev­i­dence has not shown suf­fi­cient ben­e­fit; how­ev­er, the psy­cho­log­i­cal ben­e­fit of bed rest war­rants re­view.

The im­por­tant mes­sage

Cer­vi­cal in­suf­fi­cien­cy can be fright­en­ing, par­tic­u­lar­ly for a woman who has pre­vi­ous­ly lost a preg­nan­cy. But mod­ern ob­stet­rics of­fers sev­er­al ways of iden­ti­fy­ing women at in­creased risk and, when ap­pro­pri­ate, re­duc­ing the chance of an­oth­er late mis­car­riage or very ear­ly birth.

The key is ear­ly dis­cus­sion with an ob­ste­tri­cian, prefer­ably be­fore (pre-con­cep­tion) or ear­ly in the next preg­nan­cy, so that pre­vi­ous preg­nan­cy out­comes, cer­vi­cal his­to­ry and ul­tra­sound find­ings can be con­sid­ered to­geth­er. The ap­pro­pri­ate treat­ment—whether sur­veil­lance, prog­es­terone, cer­clage or, in se­lect­ed cas­es, trans­ab­dom­i­nal cer­clage—de­pends on the in­di­vid­ual woman rather than a sin­gle di­ag­no­sis.

Dr Sherene Kalloo

MDW, MBBS, DGO, DM, FACOG

Spe­cial­ist Ob­ste­tri­cian & Gy­nae­col­o­gist