Diagnostic methods based on history, ultrasound and physical examination; thresholds and pitfalls of cervical length measurement; The evidence base for the choice between vaginal progesterone and cerclage.
⚕️ Target audience: This clinical review is intended for physicians and healthcare professionals; It is a summary of current literature and guidelines for educational purposes. Clinical decisions should be made based on patient-specific evaluation and applicable institutional protocols.
Cervical insufficiency is defined as painless cervical dilation resulting in expulsion of the fetus (miscarriage or preterm birth) in the second trimester. ACOG's definition is: “the failure of the uterine cervix to sustain pregnancy into the second trimester in the absence of clinical contraction and/or labor (ACOG PB 142, 2014)” (ACOG Practice Bulletin 142, 2014). Although the diagnosis may be suspected in the first pregnancy, it is considered confirmed when it recurs in consecutive pregnancies, according to the classical definition.
The concept itself is controversial, and this debate directly affects clinical decisions. Structural cervical weakness—prior cervical trauma, rarely congenital abnormality—produces a true picture of mechanical failure, to which mechanical support (cerclage) is a logical response. In contrast, decidual inflammation/infection, bleeding at the decidua-placenta interface, or uterine hyperdistention leads to premature cervical shortening through a biochemical chain; This pathway typically produces a single, non-recurrent second trimester loss, and the benefit expected from mechanical support is not the same (UpToDate, cervical insufficiency, October 2025).
Practical conclusion: a short cervix detected on transvaginal ultrasound alone does not diagnose cervical insufficiency — most pregnant women with a short cervix deliver at term even if no intervention is performed. Diagnosis is usually limited to singleton pregnancies, because the pathogenesis of second trimester loss/extreme preterm birth in multiple pregnancy is not related to anatomical weakness of the cervix (UpToDate, cervical insufficiency, October 2025).
Cervical trauma is probably the most common risk factor: labor or birth itself (spontaneous, forceps/vacuum-assisted, caesarean section), mechanical cervical dilatation before gynecological procedure, and treatment of cervical intraepithelial neoplasia. Congenital cervical abnormality is rare; structural uterine anomalies, genetic disorders affecting collagen (e.g. Ehlers-Danlos syndrome), and intrauterine diethylstilbestrol exposure fall under this heading (UpToDate, cervical insufficiency, October 2025). A history of short cervical length in a previous pregnancy is a common anamnesis but is a poor predictor on its own (UpToDate, cervical insufficiency, October 2025).
The classic obstetric history carries three elements: recurrent second trimester pregnancy loss or extremely preterm live birth (most often before 24 weeks) · absence or very mild symptoms · dilation and effacement detected on physical examination cannot be explained by the current level of uterine activity. It is also typical that the time between the discovery of the finding and birth is very short and the loss gradually shifts to earlier weeks in successive pregnancies (UpToDate, cervical insufficiency, October 2025).
Cervical insufficiency is not diagnosed with a single test; There are three different diagnostic pathways and each corresponds to a different cerclage indication. Choosing the correct diagnostic method also determines the level of evidence of the intervention.
| Diagnostic path | Criteria | Corresponding cerclage |
|---|---|---|
| History-based | Classic history with ≥2 consecutive second trimester losses or extremely preterm birth (<28 weeks), no or very mild symptoms. Some authors suggest that diagnosis can be made after a single loss—especially if there is a risk factor for structural weakness. | History-indicated (12-14 weeks) |
| USG based | History of spontaneous preterm birth (especially second trimester loss or <28 weeks) + TV USG cervical length ≤25 mm before 24 weeks in this pregnancy; other diagnoses excluded | USG-indicated |
| Based on physical examination | Dilated (≥1 cm) and effaced cervix on examination at 14-27 weeks; Contraction is absent or too light/irregular to explain dilation. Membranes may prolapse or rupture at diagnosis; This finding is not an indication for automatic cerclage. For new cerclage, membranes must be intact and the following contraindications must be excluded: | Physical examination-indicated (formerly "rescue/emergency cerclage") |
History-based: ACOG PB 142 accepts at least one second-trimester loss due to painless cervical dilation without labor or placental abruption, or prior cerclage for the same reason, as an indication. RCOG Green-top Guideline No. 75 gives its general history-indicated recommendation for at least three prior preterm births and/or second-trimester losses; with fewer events, additional risk factors and serial cervical surveillance are evaluated. UpToDate's classic history definition is ≥2 consecutive losses/extremely preterm births. A diagnostic definition and an institution's cerclage threshold are not identical; there is no single universal number. Planned history-indicated cerclage is usually performed at 12–14 weeks.
Look for dilatation in a very short cervix: Cervical dilatation is a separate finding on examination with a short cervix. SMFM #70 states that when a very short cervix, defined in studies as <11 or <15 mm, is detected, a cervical examination should be considered to identify candidates for cerclage based on physical examination. UpToDate v108 performs speculum and digital examination in the 11–15 mm group. This approach does not mean that dilation evaluation will be skipped in the 10–<11 mm group; The actual examination finding is taken into account before the cerclage decision (SMFM #70, 2024, B7; UpToDate, short cervix, October 20, 2026).
To exclude before making a diagnosis: labor (by tocodynamometry — increasing regularity, frequency and severity over time), bleeding due to placental abruption or previa (by history, examination and ultrasound) and infection. Each of these presentations can produce the same clinical picture through biochemically mediated cervical ripening, regardless of structural cervical weakness (UpToDate, cervical insufficiency, October 2025).
Who has amniocentesis? UpToDate authors routinely perform amniocentesis to look for subclinical infection when the cervix is ≥2 cm dilated—the incidence of intraamniotic infection in these patients is approximately 20-50%. On a case-by-case basis, it is evaluated if there are ultrasound findings compatible with inflammation, such as debris ("sludge" or biofilm) in the amniotic fluid, or if membranes are visible in the external os but dilation is <2 cm (in this case, the incidence probably does not exceed 5-10%). If evidence of infection is found, cerclage is not performed; expectant management with antibiotics is unproven and not recommended (UpToDate, cervical insufficiency, October 2025).
Since cervical shortening starts from the internal os and progresses caudally, a short cervix is detected on ultrasound before physical examination. Measurement becomes reliable around week 14 and is consistently possible at 16-18 weeks, when the cervix can be distinguished from the lower uterine segment. Cervical length is stable between weeks 14-28; The median value is 40 mm before 22 weeks, 35 mm between 22-32 weeks, 30 mm after 32 weeks, and approximately 90% of nulliparous singleton pregnant women have >30 mm between 16-22 weeks (UpToDate, short cervix, October 20, 2026).
Technique — in order: the patient empties her bladder · the probe is gently advanced into the anterior fornix without excessive pressure on the anterior cervical lip · the cervical image is magnified to fill at least half of the screen · the internal os, the echodense triangle at the external os, and the endocervical canal are visualized in the same sagittal plane · the measurement is the closed length between the internal os and external os (if the internal os is open, from the tip of the funnel to the external os) · three measurements differing by less than 10% are obtained and the shortest is recorded as "shortest best". Fundal pressure applied toward the uterine axis for 15 seconds may unmask a "dynamic" cervix; at least five minutes should be allotted for the entire examination. With proper technique, intraobserver and interobserver variability is less than 10% (UpToDate, short cervix, October 20, 2026).
Measurement pitfalls — all make the cervix look LONGER than it is: (1) Excessive probe pressure is the most common error; the anterior cervical lip and lower uterine segment are compressed. To avoid: once a good image is obtained, the probe is withdrawn until the image becomes blurry, then advanced until the image becomes clear. The anterior and posterior cervical lips should be approximately equal in thickness; If the cervix is thin in the front and thick in the back, the pressure is high. (2) Hasty measurement — wait ~5 minutes for temporary compression effect to wear off. (3) Lower uterine segment contraction is the most common misleading finding and is seen in 16-43% of scans immediately after bladder emptying; If it continues despite waiting for 20 minutes, the measurement is not reported and the patient is called back another day. (4) Underdeveloped lower uterine segment (suspect if cervix appears >50 mm) and (5) previous cervical surgery distort the signs. On a curved cervix, do not measure by drawing the canal—the sum of two straight lines is used; curved cervix usually means long cervix anyway (UpToDate, short cervix, October 20, 2026).
Funneling is the protrusion of membranes into the cervical canal and follows the sequence T-Y-V-U with effacement of the cervix ("U" for almost complete effacement, highest risk). However, funnel is not an independent predictor when closed channel length is taken into account; The funnel seen with normal residual length is usually due to lower uterine segment contraction and has little to no clinical significance (UpToDate, short cervix, October 20, 2026). Separation of membranes from decidua and debris/sludge near the internal os suggest subclinical infection and increased risk of spontaneous preterm birth (UpToDate, short cervix, October 20, 2026).
Short cervix before 24 weeks is diagnosed with transvaginal cervical length ≤25 mm (2nd-3rd percentile at these weeks)—regardless of the patient's obstetric history. This threshold was chosen because it is the threshold for intervention studies (vaginal progesterone, cerclage) to initiate treatment; Treatments started at this threshold report a 30-40% reduction in preterm birth (UpToDate, short cervix, October 20, 2026). Worldwide, the trigger threshold varies: some guidelines use <15 mm (0.5th percentile), some use <20 mm (1st percentile) (ACOG PB 234, 2021).
The performance of the threshold should not be exaggerated. The reported sensitivity of prelabor cervical length ≤25 mm for preterm birth ranges from 6% to 76% in the literature; a reasonable estimate is 33% (UpToDate, short cervix, October 20, 2026). There is no threshold below which the patient always delivers early: 25% of pregnant women without a measurable cervical length at 14-28 weeks delivered at ≥32 weeks, and 50% of pregnant women with a cervical length of ≤13 mm at 24 weeks delivered at ≥35 weeks (UpToDate, short cervix, October 20, 2026).
| Institution | Previous spontaneous preterm birth YES | Previous spontaneous preterm birth NO |
|---|---|---|
| ACOG (Practice Bulletin 234, 2021; confirmed 2025) | Cervical length scanning with serial TV USG is indicated | In the fetal anatomy scan at 18+0 – 22+6 weeks, the cervix is viewed transabdominally or transvaginally |
| SMFM (2016 screening notification; Consult Series #70, 2024) | Routine TV USG screening is recommended between 16-24 weeks | The cervix is evaluated at the 18-22 week anatomy scan; TV USG is preferred and required for diagnosis/management |
| ISUOG (2022) | — | TV USG as part of anomaly screening in all singleton pregnancies at 18-24 weeks |
| FIGO (2015) | — | TV USG at 19+0 – 23+6 weeks in all singleton pregnancies |
| UpToDate author | Serial measurement starting at 14-16 weeks (the earlier the previous birth, the earlier the screening begins) | Single TV USG measurement at approximately 20 weeks (18-24) |
In the section where UpToDate v108 explains the SMFM screening approach, it is stated that routine cervical length screening should not be performed in pregnant women with cerclage, PPROM, or placenta praevia (UpToDate, short cervix, October 20, 2026). Screening ends at week 24 because all intervention studies started treatment before week 24; After 30 weeks, the measurement loses its predictive value because the cervix becomes physiologically shorter in pregnant women who will give birth at term (UpToDate, short cervix, October 20, 2026).
Universal screening itself is also controversial: a 2019 meta-analysis of randomized trials found insufficient evidence for or against routine screening due to limitations of the included studies; in contrast, a 2024 meta-analysis of predominantly nonrandomized studies associated universal TV US with a significant reduction in spontaneous preterm birth at <32 weeks (OR 0.84; 95% CI 0.76-0.94) (UpToDate, short cervix, October 20, 2026).
This is the question central to the management of a short cervix, and the answer varies with obstetric history and degree of cervical length.
The first line in this group is vaginal progesterone (200 mg every evening)—consistent with ACOG guidance (ACOG PB 234, 2021). In an updated meta-analysis with individual participant data (four high-quality randomized trials, 966 participants; majority without previous spontaneous preterm birth), vaginal progesterone compared with placebo reduced spontaneous preterm birth at <34 weeks 15% versus 20% (RR 0.72; 95% CI 0.55-0.95), all preterm birth at <34 weeks 17% versus 26% (RR 0.65; 95% CI 0.51–0.83), composite neonatal morbidity and mortality 8% versus 14% (RR 0.58; 95% CI 0.37-0.90), respiratory distress syndrome 4% versus 10% (RR 0.45; 95% CI 0.26-0.80), and neonatal intensive care unit admission 17% versus 24% (RR 0.69; 95% CI 0.53-0.88) (Romero 2025, AJOG).
Cerclage is considered in this group only when the cervix becomes very short. In a meta-analysis with individual patient data combining 507 asymptomatic singleton pregnancies (cervical length ≤25.9 mm) from six randomized studies, cerclage did not significantly reduce delivery before 37 weeks' gestation in the overall group: 33.5% versus 39.8%; RR 0.88 (95% CI 0.59-1.31). In the planned subgroup analysis, in those with cervical length ≤20.9 mm, birth before 37 weeks was significantly reduced (30.9% vs. 41.5%; RR 0.75; 95% CI 0.56-0.99) and the time from randomization to birth was significantly prolonged (p = 0.049) (Berghella 2025, AJOG MFM; PMID 40829743). UpToDate also reports a signal of benefit in the <16 mm subgroup (32.5% vs 44.4%; RR 0.73; 95% CI 0.54-0.99). Based on this the UpToDate approach is this:
| TV USG cervical length | Approach |
|---|---|
| 11 – 25mm | Vaginal progesterone 200 mg/day + repeat measurement every 1-2 weeks until 23+6 weeks (progressive shortening is sought) |
| 11 – <21 mm | UpToDate v108: cerclage may be offered in selected cases. SMFM #70: if there is no dilatation, it is against cerclage in the range of 10–25 mm; This difference should be preserved |
| Very short cervix | SMFM #70: Physical examination may be considered for a very short cervix, defined in studies as <11 or <15 mm. UpToDate v108: Performs speculum and digital examination in the 11–15 mm group. If ≥1 cm dilation is identified, physical examination-indicated cerclage is considered provided membranes are intact and clinical conditions are appropriate. |
| <11mm | UpToDate v108: Cerclage is offered before 24 weeks. SMFM #70: may be considered through shared decision-making only for <10 mm; exactly 10 mm and 10–<11 mm without dilation fall under the recommendation against cerclage. |
Asymptomatic singleton pregnancy without a history of spontaneous preterm birth: Transvaginal measurement and examination before 24 weeks are evaluated together. SMFM #70 (2024) opposes cerclage at 10–25 mm cervix in the absence of dilatation (GRADE 1B); When <10 mm, cerclage may be considered by mutual decision. UpToDate (October 20, 2026, v108) offers cerclage for <11 mm, stating that it can be offered to selected cases in the range of 11–<21 mm. These two approaches are not the same, especially in the full 10 mm and 10–<11 mm range; The measurement is not equalized by rounding. The absence of previous birth history does not exclude cerclage in all circumstances; The development of new dilatation is a separate evaluation method.
Limit of new evidence: Benefit in the 2025 IPD meta-analysis was seen in a subgroup with short cervix; The randomized trial comparing cerclage + progesterone with progesterone alone was terminated early due to slow enrollment and showed no significant difference in the primary preterm birth outcome. UpToDate's October 20, 2026 synthesis discusses these data as options in the selected case. These findings do not mean that SMFM #70's recommendation for the 10–25 mm/non-dilatation group has changed to routine cerclage for all pregnant women. The decision is individualized by source name, actual measurement, history, and examination findings.
In the approach of the author of UpToDate v108, when a short cervix is detected in this group, a USG-based diagnosis of cervical insufficiency is made and vaginal progesterone and cerclage are offered together. NICE NG25 §1.2.1 recommends that, when its specified obstetric-history criteria and the ≤25 mm criterion are met, the choice of vaginal progesterone or cerclage should be made after discussing the risks and benefits. The combination is not a common standard for all institutions (UpToDate, 20 October 2026; NICE NG25 §1.2.1 and research recommendation 5). In a randomized trial meta-analysis, USG-indicated cerclage reduced preterm birth at <24, <28, <32, <35, and <37 weeks compared to no cerclage (e.g., RR 0.70 for <35 weeks; 95% CI 0.55-0.89) (Berghella 2011, Obstet Gynecol).
Screening instead of history-indicated cerclage: In a meta-analysis of randomized trials comparing cervical length screening in pregnant women with a previous preterm birth and placing a cerclage on those who were shortened versus a history-indicated cerclage on all, the two groups were similar: <37 weeks preterm birth 31% versus 32% (RR 0.97; 95% CI 0.73-1.29), <34 weeks 17% versus 23% (RR 0.76; 95% CI 0.48-1.20), perinatal mortality 5% versus 3% (RR 1.77; 95% CI 0.58-5.35). The critical difference is in practice: in the screening arm, only 42% of patients developed a short cervix and received cerclage, whereas in the history arm, 100% underwent surgery. So screening prevents unnecessary surgery by approximately 60% (Berghella and Mackeen 2011, Obstet Gynecol).
The use of vaginal progesterone in the pregnant woman with a previous spontaneous preterm birth and a non-shortening cervix is a real point of divergence: the UpToDate author initiates 200 mg/day at week 16; ACOG recommends not using vaginal progesterone to reduce the risk of recurrent preterm birth (Practice Advisory, 2023); SMFM, on the other hand, recommends a shared decision process. The evidence base explains this dissociation: in a 2022 meta-analysis (10 studies, 2958 participants), vaginal progesterone reduced preterm birth at <37 weeks to 32.0% versus 37.8% (RR 0.64; 95% CI 0.50–0.81), but none of these reductions remained significant when restricted to studies with low risk of bias and adjusting for small study effect (Conde-Agudelo and Romero 2022, AJOG).
Combination therapy. In a meta-analysis of comparative studies in high-risk pregnant women (cervical length <25 mm or previous preterm birth), the combination of vaginal progesterone + cerclage compared to cerclage alone resulted in preterm birth at <37 weeks 11% versus 24% (RR 0.45; 95% CI 0.29-0.71), compared to progesterone alone 36% versus 42% (RR 0.75; 95% CI 0.58-0.96); Reductions in births at <34, <32 and <28 weeks and neonatal mortality compared to cerclage alone have also been reported (Aubin 2023, AJOG MFM). Limitations to interpretation: some of the studies were of low quality and at significant risk of bias, and the risk characteristics of the patient population were mixed. The randomized trial comparing cerclage + progesterone with progesterone alone in pregnant women with no previous preterm birth and a cervical length ≤25 mm was terminated early due to slow enrollment (93 of 206 planned): preterm birth at <35 weeks was less common in the combined arm, but the difference was not significant (16.3% vs 23.4%; RR 0.70; 95% CI 0.30-1.63); in contrast, time from randomization to delivery was extended by 13 days (95% CI 5-20; p=0.01) and birth week was extended by 1.0 weeks (95% CI 0.2-1.7; p=0.035) — this effect was maintained in both the ≤15 mm and 16-25 mm subgroups (Boelig 2025, AJOG MFM ; PMID 39880123).
17-OHPC out of place: Hydroxyprogesterone caproate (Makena) has been withdrawn from the market due to lack of efficacy. Both ACOG and SMFM recommend not prescribing 17-OHPC in this indication, including compound formulations (ACOG Practice Advisory, 2023). Currently, only vaginal progesterone is used to prevent preterm birth.
| Type | Indication | Timing | UpToDate approach (institution differences in text) |
|---|---|---|---|
| History-indicated | History-based diagnosis of cervical insufficiency | 12-14 weeks | Grade 1B (preferred to USG monitoring) |
| USG-indicated | Previous spontaneous preterm birth + cervical length ≤25 mm (<24 weeks) in this pregnancy; Separate institution thresholds are above for very short cervix without history | When shortening is detected | Grade 2B |
| Physical examination-indicated | ≥1 cm dilation at examination before 24 weeks; intact membranes, no infection, active bleeding, or labor. NICE's emergency cerclage window is separately 16+0–27+6 weeks | At diagnosis | Grade 2C (preferred to expectant management) |
Prior spontaneous preterm birth/loss and short cervix: ACOG PB 142 uses a prior spontaneous birth at <34 weeks, cervical length <25 mm, and gestational age <24 weeks in a current singleton pregnancy. RCOG 75 uses a threshold of ≤25 mm at <24 weeks with a history of ≥1 spontaneous second-trimester loss or preterm birth. NICE NG25 §1.2.1 recommends discussing vaginal progesterone or cerclage if cervical length is ≤25 mm at 16+0–24+0 weeks and there is a history of either spontaneous birth at up to 34+0 weeks or pregnancy loss from 16+0 weeks onward. NICE §1.2.4 also defines a separate assessment pathway for ≤25 mm with prior PPROM or cervical trauma. A prior medically indicated preterm birth is not treated the same as a history of spontaneous birth.
Timing limits. Preventive/ultrasound-based cerclage is most often evaluated before 24 weeks. History-based planned implementation is usually in 12–14 weeks. Physical examination-based/emergency cerclage: Requires painless cervical dilation, visible but unruptured membranes, and appropriate clinical conditions. UpToDate mostly evaluates at ≥1 cm dilation before 24 weeks; ACOG PB 142 limits this procedure to the second trimester before viability. NICE NG25 §1.6 states that it can be considered in selected cases at 16+0–27+6 weeks; Evaluation and shared decision with the senior obstetrics and neonatal team is required. If there is evidence of infection, active vaginal bleeding, uterine contraction or PPROM, a new cerclage is not applied. The decision to remove/keep the suture in existing post-cerclage PPROM is a separate question. The benefit of routine cerclage for short cervix alone after 24 weeks has not been demonstrated; The case of urgent dilatation should be evaluated separately (NICE NG25 §1.6; ACOG PB 142; UpToDate).
Absolute contraindications — conditions in which the procedure is not expected to reduce the risk of preterm birth or improve fetal outcome: fetal anomaly incompatible with life · intraamniotic infection/clinical chorioamnionitis · active preterm labor · PPROM · fetal death · active bleeding detachment. Advanced dilatation and prolapsed membranes count as relative contraindications: there is no dilatation threshold at which cerclage will not be attempted, but prognosis worsens when dilatation exceeds 4 cm, and up to 65% of patients develop iatrogenic membrane rupture when membranes prolapse from the external os (UpToDate, transvaginal cerclage, April 2025).
Perioperative medication use varies by indication. In history-indicated cerclage, prophylactic antibiotics and tocolytics are not given (minimal risk of infection, no uterine irritability). For USG-indicated cerclage, UpToDate authors do not provide preoperative prophylaxis but give indomethacin for up to 48 hours to those with contractions after the procedure. In physical examination-indicated cerclage, antibiotics and indomethacin are routinely administered to prolong latency (Grade 2C): The only regimen tested in a randomized study is cefazolin 1 g (2 g for ≥100 kg) IV preoperatively and postoperatively at the 8th and 16th hours + indomethacin 50 mg orally at the same times; This regimen increased the rate of patients maintaining latency beyond 28 days to 92% versus 63% in a randomized study of 53 patients. However, a 2025 meta-analysis did not find perioperative indomethacin or antibiotic use to be associated with a reduction in preterm birth <28 weeks or perinatal mortality (Delatorre 2025, Eur J Obstet Gynecol Reprod Biol).
There are two common transvaginal techniques. McDonald's cerclage is a purse-string suture that does not involve dissection: four to six deep bites are placed on the cervix as high as possible (close to the internal os), avoiding the bladder, rectum, and uterine vessels at 3-9 o'clock; Each bite should extend through at least half of the cervical stroma but not enter the endocervical canal. Shirodkar cerclage requires the bladder to be dissected from the front and the rectum from the back; Thus, the suture can be placed closer to the internal os and does not pass through the cervical stroma. The technical goal is the same in both methods: strengthening the cervix at the level of the internal os — lengthening is a secondary gain; If the internal os cannot be reached, the cerclage should be at least 2 cm cranial from the external os (UpToDate, transvaginal cerclage, April 2025).
Which is superior? In a meta-analysis of mostly retrospective studies, the Shirodkar technique was associated with a small reduction in preterm birth <37 weeks (RR 0.91; 95% CI 0.85-0.98), but this finding lost significance when studies at significant risk of bias were excluded; The only randomized trial comparing the two techniques (34 participants per arm) found no difference. The choice should be left to surgical principles and the experience of the practitioner (UpToDate, transvaginal cerclage, April 2025).
Suture type — C-STICH: In the multicenter randomized trial (2002 pregnancies) comparing monofilament versus braided suture, the frequency of pregnancy loss was similar (8.0% vs 7.6%; adjusted RR 1.05; 95% CI 0.79-1.40). In contrast, monofilament suture was associated with lower rates of clinical chorioamnionitis (2.7% versus 6%; adjusted RR 0.45; 95% CI 0.29-0.71) and maternal sepsis (3.9% versus 6.8%; adjusted RR 0.58; 95% CI 0.40-0.82); There was no significant difference in preterm birth rates (Hodgetts Morton 2022, Lancet).
Transabdominal cerclage supports the cervix at the cervico-isthmic level and is more invasive; It is generally reserved for patients who cannot undergo a transvaginal procedure or who have not been able to deliver a healthy newborn despite at least one previous prophylactic transvaginal cerclage. In the study that randomized 111 patients with previous failed vaginal cerclage to transabdominal, high vaginal, and low vaginal cerclage, transabdominal cerclage provided the lowest risk of fetal loss with <32, <34, and <37 weeks preterm birth; High vaginal cerclage was not superior to low vaginal cerclage (UpToDate, transvaginal cerclage, April 2025).
If prolapsed membranes are present, they should be gently reduced back into the uterine cavity before cerclage: steep Trendelenburg position → uterine relaxant (nitroglycerin) → bladder filling in 250 mL increments → gently drawing and rocking the cervix with ring forceps/stay sutures → gentle reduction with a smooth, flat-surfaced instrument. If these measures are insufficient, ultrasound-guided transabdominal amnioreduction (typically 150-250 mL) allows the sac to retract. A single cerclage is generally sufficient; a routine reinforcing second suture has not improved outcomes, and a repeat cerclage is not recommended for early (before 24 weeks) suture migration (Grade 2C — UpToDate, transvaginal cerclage, April 2025).
The frequency of complications increases with increasing gestational age and cervical dilatation; There is no difference between McDonald and Shirodkar. In a meta-analysis covering more than 4500 singleton pregnancies, perioperative complications were clearly differentiated by indication:
| Complication | History-indicated | USG-indicated | Physical examination-indicated |
|---|---|---|---|
| PPROM | 0.0% (0,0-1,7) | 0.3% (0,0-0,8) | 2.5% (0,91-4,5) |
| Bleeding | 0.9% (0,0-7,9) | 1.4% (0,0-4,1) | 2.3% (0,0-7,6) |
The median frequency of intraamniotic infection has been reported as 2% after history-indicated cerclage and 25% after non-history indications. Suture migration occurs in 3-13% of cases (most often in late gestation, with little clinical significance); cervical dystocia and cervical trauma at birth are less than 5% (UpToDate, transvaginal cerclage, April 2025).
Time of removal: Cerclage is removed electively at 36+0 – 37+0 weeks in anticipation of labor. In preterm labor before 36 weeks, immediately at the beginning of regular contractions if the pregnancy is ≥34 weeks; It is taken at <34 weeks when unresponsiveness to tocolysis is detected. After planned removal, only approximately 10% of patients enter spontaneous labor within 48 hours (UpToDate, transvaginal cerclage, April 2025). The McDonald cerclage is routinely removed and can often be discontinued in the office without analgesia; Shirodkar cerclage requires more frequent returns to the operating room because the knot is embedded or infiltrated by tape granulation tissue and can be left in place if a cesarean section is planned and pregnancy is considered in the future (UpToDate, transvaginal cerclage, April 2025).
Should the cerclage be removed in PPROM? The debate continues. In a six-study meta-analysis (377 participants), removal of the cerclage reduced the odds of prolonging pregnancy beyond 48 hours (OR 0.15; 95% CI 0.07-0.31) and longer than 7 days (OR 0.30; 95% CI 0.11-0.83) and shortened latency (mean difference −2.84 days) compared to leaving it in place, but also reduced the risk of chorioamnionitis (OR 0.57; 95% CI 0.34-0.96). The UpToDate author removes the cerclage in the presence of chorioamnionitis, ≥32 weeks of pregnancy, or vaginal bleeding; Before 32 weeks, if there is no infection/bleeding/preterm labor, it is left in place. SMFM, on the other hand, states that both removal and leaving in place are reasonable in the PPROM, and that the decision should be made jointly by discussing the risks.
In terms of overall effectiveness, cerclage in singleton pregnancies at high risk of pregnancy loss based on history and/or short cervix and/or physical examination reduced preterm birth <34 weeks in the Cochrane review by 18% versus 24% (RR 0.77; 95% CI 0.66-0.89; nine studies, 2415 pregnancies; high-quality evidence) and likely reduced perinatal loss (7.5% versus 9.2%; RR 0.82; 95% CI 0.65-1.04; moderate quality evidence). For physical examination-indicated cerclage, the evidence is almost entirely observational: in the meta-analysis compared with expectant management, overall survival was 73% versus 36% (RR 1.6; 95% CI 1.2-2.1) and mean gestational age increased from 25.4 to 30.5 weeks; The only randomized study included only 23 patients (Althuisius 2003, AJOG).
Two separate questions should not be confused here. Placing a routine cerclage simply because it is a twin pregnancy is not supported by evidence; UpToDate recommends avoiding it (Grade 2C) and reminds that the diagnosis of cervical insufficiency is usually limited to singleton pregnancies anyway (UpToDate, cervical insufficiency, October 2025). Only cervical shortening in a twin and cervical dilatation should be evaluated separately during examination. SMFM #70 (2024) opposes the routine use of progesterone, pessary, or cerclage outside of clinical research for the treatment of cervical shortening in twin pregnancy (GRADE 1B). Routine cerclage is not recommended in the non-dilated CL 15–25 mm group; Thresholds in a singleton pregnancy are not automatically transferred to the twin. The retrospective data for very short cervix discussed by the SMFM and the small randomized study for ≥1 cm dilation are not interchangeable; dilatation is a separate pathway (SMFM #70, B8 and B10) that requires expert evaluation with intact membranes and infection/action exclusion.
The following meta-analysis findings are observational associations; It does not eliminate the SMFM recommendation against routine use and cannot be used as a treatment decision for a single twin pregnancy. In a systematic review and meta-analysis covering 18 studies and 1465 twin pregnancies, cerclage in twin pregnancies with a short cervix on ultrasound or dilation on examination was associated with reduced preterm birth, with RR 0.73 (95% CI 0.59–0.91) at <34 weeks, RR 0.69 (0.57–0.84) at <32 weeks, and RR 0.54 (0.43–0.67) at <28 weeks; extended gestational age by 2.32 weeks (95% CI 0.99-3.66); It reduced perinatal loss by RR 0.38 (0.25-0.60) and composite adverse outcome by RR 0.69 (0.53-0.90). Across subgroups, the benefit was maintained in both those with cervical length <15 mm (RR 0.74; 0.58-0.95) and those with cervical dilatation (RR 0.68; 0.57-0.80) (D'Antonio 2023, PLoS Med).
Why this evidence is considered "different": The above association is all contributed by observational studies and the quality of evidence is low in the GRADE assessment. The authors clearly write that the findings need to be confirmed in adequately powered randomized studies. On the side of emergency (physical examination-indicated) cerclage, a meta-analysis covering 96 studies and 3239 pregnancies reported that survival was similar in singleton and twin pregnancies (overall survival 74%), concluding that emergency cerclage should be considered in both groups — although the superiority over expectant management was less evident in twins than in singleton pregnancies (Hulshoff 2023, AJOG MFM).
The theoretical basis of the cervical pessary is that it changes the axis of the cervical canal, removes the weight of the uterine content from the cervix, and creates a barrier to ascending infection by obstructing the internal os. However, randomized trial meta-analyses could not show that pessary significantly reduces spontaneous preterm birth or improves perinatal outcome in asymptomatic high-risk pregnant women with short cervix. In the well-designed TOPS study (544 pregnancies, Arabin pessary vs usual care at 16-23 weeks; cervical length <20 mm, progesterone in both arms) the rate of preterm birth or fetal death at <37 weeks was the same (45.5% vs 45.6%; RR 1.00; 95% CI 0.83-1.20); furthermore, fetal or neonatal/infant death occurred more frequently in the pessary arm (13.3% vs 6.8%; RR 1.94; 95% CI 1.13-3.32)—it is unclear whether the excess was due to the pessary or a confounder (Hoffman 2023, JAMA ). In a 635-patient randomized trial comparing pessary with vaginal progesterone, there was also no reduction in adverse perinatal outcome (6% vs. 6%) or preterm birth <34 weeks (9% vs. 9%) in the pessary arm (van Dijk 2024, BMJ).
Bed rest is also not recommended: it does not prolong pregnancy, increases the risk of venous thromboembolism and deconditioning, and may increase the risk of preterm birth — activity restriction has been associated with an increased risk of preterm birth in pregnant women with short cervical length. Patients in all three diagnostic categories are recommended to continue their usual daily activities without restrictions other than those given to healthy pregnant women.
The outcome of the index pregnancy determines the path to be followed in the next pregnancy. The criterion for success is usually taken as birth at ≥34 weeks.
| Index cerclage in pregnancy | Result successful (≥34 weeks) | Result failed (<34 weeks) |
|---|---|---|
| History-indicated | History-indicated cerclage is usually repeated (if the indication is not evidence-based, serial cervical length screening may also be offered as a safe option) | Interpregnancy transabdominal cervico-isthmic cerclage recommended |
| USG-indicated | Serial TV USG cervical length scan; If it becomes shorter, repeat USG-indicated cerclage. Approximately 50% of these patients require repeat cerclage in a subsequent pregnancy | History-indicated cerclage at 12-14 weeks (these patients always develop a short cervix in subsequent pregnancies); If that also fails, transabdominal/laparoscopic cerclage |
| Physical examination-indicated | TV USG scan starting from 12-16 weeks; If shortened, USG-indicated cerclage | History-indicated cerclage in subsequent pregnancies |
An important caveat: a good outcome after USG-indicated cerclage neither establishes nor excludes the diagnosis of cervical insufficiency. A significant portion of pregnancies with early cervical effacement result well in both the index and subsequent pregnancies, even without surgical intervention (UpToDate, cervical insufficiency, October 2025). This is especially true for patients who do not go into labor within two weeks after their cerclage is removed at 36–37 weeks.
Last updated: . Guide numbers and publication years have been verified against current catalogues.