Number and gestational age of prior preterm births does not modify the predictive value of a short cervix

SMFM Consult Series #70: Management of short cervix in individuals without a history of spontaneous preterm birth

Most deliveries before 34 weeks of gestation occur in individuals with no previous history of preterm birth. Midtrimester cervical length assessment using transvaginal ultrasound is one of the best clinical predictors of spontaneous preterm birth. This Consult provides guides for the diagnosis and management of a short cervix in an individual without a history of preterm birth. The following are Society for Maternal-Fetal Medicine recommendations: (1) we recommend that all cervical length measurements used to guide therapeutic recommendations be performed using a transvaginal approach and in accordance with standardized procedures as described by organizations, such as the Perinatal Quality Foundation or the Fetal Medicine Foundation (GRADE 1C); (2) we recommend using a midtrimester cervical length of ≤25 mm to diagnose a short cervix in individuals with a singleton gestation and no previous history of spontaneous preterm birth (GRADE 1C); (3) we recommend that asymptomatic individuals with a singleton gestation and a transvaginal cervical length of ≤20 mm diagnosed before 24 weeks of gestation be prescribed vaginal progesterone to reduce the risk of preterm birth (GRADE 1A); (4) we recommend that treatment with vaginal progesterone be considered at a cervical length of 21 to 25 mm based on shared decision-making (GRADE 1B); (5) we recommend that 17-alpha hydroxyprogesterone caproate, including compounded formulations, not be prescribed for the treatment of a short cervix (GRADE 1B); (6) in individuals without a history of preterm birth who have a sonographic short cervix (10-25 mm), we recommend against cerclage placement in the absence of cervical dilation (GRADE 1B); (7) we recommend that cervical pessary not be placed for the prevention of preterm birth in individuals with a singleton gestation and a short cervix (GRADE 1B); and (8) we recommend against routine use of progesterone, pessary, or cerclage for the treatment of cervical shortening in twin gestations outside the context of a clinical trial (GRADE 1B).

Associations of temporal changes in cervical length and lower uterine segment length with spontaneous preterm delivery risk: a prospective study of 727 Japanese women

PURPOSE

A prospective assessment of the risk of spontaneous preterm delivery (sPTD) by evaluating temporal changes in cervical measurements.

METHODS

We analyzed clinical variables, focusing on cervical length (CL) and lower uterine segment (LUS) length (LUSL) as measured by transvaginal ultrasonography in 727 pregnant Japanese women.

RESULTS

In women undergoing term deliveries, CL increased from gestational week (GW) 8-25. In contrast, the combination of CL and LUSL (ComL for "combined length") gradually decreased and sole LUSL became almost 0 mm by GW 25. Univariate logistic regression analysis suggested that a history of PTD was a risk factor for sPTD. CL, LUSL, and ComL were not significant predictors of sPTD.

CONCLUSION

To assess the risk of sPTD in the second trimester, it is not necessary to distinguish the cervix from the LUS.

Predictors of preterm birth

Cervical length (CL) measured by transvaginal ultrasound examination (TVUE) best identifies the risk for preterm birth (PTB). It identifies women at risk who can benefit from corticosteroids or in utero transfer. Early screening improves effectiveness of tocolysis. It reduces iatrogenicity and cost. In preterm premature rupture of membranes (PPROM), CL is devoid of infectious risk and predicts duration of the latency phase but not the risk of perinatal sepsis. Asymptomatic women at risk should be screened at a 2-week interval starting from 16 to 18 weeks, up to 24 weeks. CLs <10th centile are at risk of PTB, especially with decrease in CL after 16 weeks. Repeat ultrasound improves predictive values. Stable CL calls for term delivery. Funneling does not improve predictivity of CL. In twin pregnancies, CL reduces unnecessary interventions. In symptomatic women, fetal fibronectin performs less than CL. Its combination with inconclusive CL has not emerged productive through randomized controlled trials (RCTs), and studies with homogeneous management for preterm labor (PTL) suggest that up to 15% of unjustified hospitalizations and treatment could be avoided.

Second trimester cervical length and risk of preterm birth in women with twin gestations treated with 17-α hydroxyprogesterone caproate

OBJECTIVE

To compare rates of preterm birth before 35 weeks based on cervical length measurement at 16-20 weeks in women with twin gestations who received 17-α hydroxyprogesterone caproate (17OHPC) or placebo.

METHODS

This is a secondary analysis of a randomised, double-blind, placebo-controlled trial of twin gestations exposed to 17OHPC or placebo. Baseline transvaginal ultrasound evaluation of cervical length was performed prior to treatment assignment at 16-20 weeks. Cervical length measurements were categorised according to the 10th, 25th, 50th and 75th percentiles in the women studied. The effect of 17OHPC administration in women with a short (25th percentile) and long (75th percentile) cervix was evaluated.

RESULTS

Of 661 twin gestations studied, 221 (33.4%) women enrolled at 11 centers underwent cervical length measurement. The 10th, 25th, 50th, 75th percentiles for cervical length at 16-20 weeks were 32, 36, 40 and 44 mm, respectively. The risk of preterm birth <35 weeks was increased in women with a cervical length <25th percentile (55.8 vs. 36.9%, p=0.02). However, a cervical length >75th percentile at this gestational age interval was not protective for preterm birth (36.5 vs. 42.9%, p=0.42). Administration of 17OHPC did not reduce preterm birth before 35 weeks among those with either a short or a long cervix (64.3 vs. 45.8%, p=0.18 and 38.1 vs. 35.5%, p=0.85, respectively).

CONCLUSION

Women with twin gestations and a cervical length below the 25th percentile at 16-20 weeks had higher rates of preterm birth. In this subgroup of women, 17 OHPC did not prevent preterm birth before 35 weeks gestation. A cervical length above the 75th percentile at 16-20 weeks did not significantly reduce the risk of preterm birth in this high risk population.

Gestational age at previous preterm birth does not affect cerclage efficacy

OBJECTIVE

The purpose of this study was to evaluate the effect of earliest previous spontaneous preterm birth (SPTB) gestational age on cervical length, pregnancy duration, and ultrasound-indicated cerclage efficacy in a subsequent gestation.

STUDY DESIGN

Planned secondary analysis of the National Institute of Child Health and Human Development-trial of cerclage for cervical length of <25 mm. Women with at least 1 previous SPTB between 17-33 weeks 6 days of gestation underwent serial vaginal ultrasound screening between 16 and 23 weeks 6 days of gestation; cervical length at qualifying randomization evaluation was used.

RESULTS

We observed a significant correlation (P = .0008) between previous SPTB gestational age and qualifying cervical length. In a linear regression model that was controlled for cervical length and cerclage, neither previous SPTB gestational age nor the interaction between cerclage and previous birth gestational age was significant predictor of subsequent birth gestational age.

CONCLUSION

Although there is an association between previous SPTB gestational age and cervical length in women with a mid-trimester cervical length of <25 mm, there does not appear to be a disproportionate benefit of cerclage in women with earlier previous SPTB.

Management strategies for the prevention of preterm birth: Part II - Update on cervical cerclage

PURPOSE OF REVIEW

Cerclage was devised more than 50 years ago based on the hypothesis that for some women, weakness or malfunction of the cervix has a causative role in the pathway to preterm birth (PTB). There have been many theories around the concept of cervical insufficiency but not much in the way of convincing evidence. The purpose of this review was to follow the recent developments in risk identification and prognostication of PTB in connection with appropriately targeted prophylactic interventions.

RECENT FINDINGS

Sonographic cervical length measurement has emerged as an effective prognosticator for PTB in all populations studied so far, independently of obstetric history, consequently deriving a wider applicability than other predictors of PTB. However, the mechanisms leading to cervical shortening are poorly understood, and it cannot be assumed that all cases with a short cervix would benefit from cerclage. Specific conditions may actually reduce the efficacy and advisability of cerclage. For this reason, attempts have been made recently to further characterize the short cervix, leading to the conclusion that only women with a short cervix in the absence of infection/inflammation may be candidates for cerclage. Furthermore, two recent randomized trials of cerclage in women with short cervix on a second trimester ultrasound suggested a benefit with cerclage in PTB rate reduction only in those cases with a cervical length of less than 15 mm.

SUMMARY

The existent literature has treated PTB prevention focusing exclusively on either progesterone use or cerclage, leaving the practitioners without any guidance on when to proceed with medical or surgical prophylaxis. Understanding that high-risk populations are not homogeneous and no single-approach modality is likely to be generally applicable, we have combined the available evidence on both progesterone and cerclage to provide guidance on how to identify subgroups of women at significantly increased risk for PTB and how to preferentially consider progesterone versus cerclage.

Risk of recurrent preterm birth and placental pathology

OBJECTIVE

To estimate whether placental pathological lesions from an index preterm birth are associated with an increased risk of recurrent preterm birth and to estimate whether certain pathologic lesions recur in a woman's next delivery.

METHODS

We performed a retrospective cohort study of all women who delivered at less than 37 weeks and had their next delivery at our institution during a 5-year period. Women were included in the cohort if placental pathology was available from their preterm birth. Placental pathology from their subsequent birth was also collected. Placental pathology was classified into presence or absence of two classes of lesions-inflammatory and thrombotic. Variables considered as possible confounders included race, gestational age of preterm birth, interpregnancy interval, tobacco use, payor status, years of education, and maternal medical problems.

RESULTS

Inflammatory lesions (n=173) were associated with recurrent preterm birth overall as well as recurrent spontaneous preterm birth (P<.001). Thrombotic lesions (n=158) were not associated with recurrent preterm birth or any subtypes of preterm birth. The association between inflammatory lesions and recurrent spontaneous preterm birth remained significant when controlling for gestational age of preterm birth, race, and tobacco use, with an adjusted odds ratio of 2.4 (95% confidence interval 1.2-4.7). Inflammatory placental lesions (n=194) were associated with inflammatory lesions in the subsequent delivery P=.001).

CONCLUSION

Recurrent preterm birth is more likely among women with inflammatory lesions on placental pathology from a prior preterm birth. Additionally, these women are more likely to have placental inflammatory lesions with their next delivery.

LEVEL OF EVIDENCE

II.

Transvaginal sonographic measurement of cervical length to predict preterm birth in asymptomatic women at increased risk: a systematic review

OBJECTIVES

To estimate the ability of cervical length measured by transvaginal ultrasonography in asymptomatic high-risk women to predict spontaneous preterm birth.

METHODS

MEDLINE, PubMed, EMBASE and the Cochrane Library were searched for articles published in any language between January 1980 and July 2006, using the keywords 'transvaginal ultrasonography' or ('cervix' and ('ultrasound' or 'ultrasonography' or 'sonography')); and ('preterm' or 'premature') and ('delivery' or 'labour/labor' or 'birth'), identifying cohort studies evaluating transvaginal ultrasonographic cervical length measurement in predicting preterm birth in asymptomatic women who were considered at increased risk (because of a history of spontaneous preterm birth, uterine anomalies or excisional cervical procedures), with intact membranes and singleton gestations. The primary analysis included all studies meeting the inclusion criteria. Secondary analyses were also performed specifically for (1) women with a history of spontaneous preterm birth; (2) those who had undergone an excisional cervical procedure; and (3) those with uterine anomalies.

RESULTS

Fourteen of 322 articles identified (involving 2258 women) met the criteria for systematic review. Cervical length measured by transvaginal ultrasonography predicted spontaneous preterm birth. The shorter the cervical length cut-off the higher the positive likelihood ratio (LR). The most common cervical length cut-off was < 25 mm. Using this cut-off to predict spontaneous preterm birth at < 35 weeks, transvaginal ultrasonography at < 20 weeks' gestation revealed LR+ = 4.31 (95% CI, 3.08-6.01); at 20-24 weeks, LR+ = 2.78 (95% CI, 2.22-3.49); and at > 24 weeks, LR+ = 4.01 (95% CI, 2.53-6.34). In women with a history of spontaneous preterm birth (six studies involving 663 women) cervical length at < 20 weeks revealed LR+ = 11.30 (95% CI, 3.59-35.57) and at 20-24 weeks LR+ = 2.86 (95% CI, 2.12-3.87), but there were limited data on the use of cervical length of more than 24 weeks in this group (one study involving 42 women). In women who had had excisional cervical procedures, two studies presented data on cervical length (one at < 24 weeks and one at > 24 weeks), finding cervical length at < 24 weeks to be predictive of spontaneous preterm birth at < 35 weeks (LR+ = 2.91, 95% CI, 1.69-5.01). One study (of 64 women) evaluated cervical length in women with uterine anomalies, finding it predictive of spontaneous preterm birth at < 35 weeks (LR+ = 8.14, 95% CI, 3.12-21.25).

CONCLUSION

Cervical length measured by transvaginal ultrasonography in asymptomatic high-risk women predicts spontaneous preterm birth at < 35 weeks. Further research may be warranted to evaluate the use of transvaginal ultrasonography after 24 weeks' gestation in women with a history of spontaneous preterm birth, and in women with uterine anomalies.

Progesterone vaginal gel for the reduction of recurrent preterm birth: primary results from a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Preterm birth is the leading cause of perinatal morbidity and mortality worldwide. Treatment of preterm labor with tocolysis has not been successful in improving infant outcome. The administration of progesterone and related compounds has been proposed as a strategy to prevent preterm birth. The objective of this trial was to determine whether prophylactic administration of vaginal progesterone reduces the risk of preterm birth in women with a history of spontaneous preterm birth.

METHODS

This randomized, double-blind, placebo- controlled, multinational trial enrolled and randomized 659 pregnant women with a history of spontaneous preterm birth. Between 18 + 0 and 22 + 6 weeks of gestation, patients were assigned randomly to once-daily treatment with either progesterone vaginal gel or placebo until either delivery, 37 weeks' gestation or development of preterm rupture of membranes. The primary outcome was preterm birth at </= 32 weeks of gestation. The trial was analyzed using an intent-to-treat strategy.

RESULTS

Baseline characteristics were similar in the two treatment groups. Progesterone did not decrease the frequency of preterm birth at </= 32 weeks. There was no difference between the groups with respect to the mean gestational age at delivery, infant morbidity or mortality or other maternal or neonatal outcome measures. Adverse events during the course of treatment were similar for the two groups.

CONCLUSION

Prophylactic treatment with vaginal progesterone did not reduce the frequency of recurrent preterm birth (</= 32 weeks) in women with a history of spontaneous preterm birth. The effect of progesterone administration in patients at high risk for preterm delivery as determined by methods other than history alone (e.g. sonographic cervical length) requires further investigation.

Prediction and Prevention of Recurrent Spontaneous Preterm Birth

Rates of preterm birth have continued to rise despite intensive research efforts over the last several decades. A woman who has a spontaneous preterm birth is at high risk for a subsequent preterm birth. Studies have identified clinical, sonographic, and biochemical markers that help to identify the women at highest risk. Determining cervical length and measuring cervicovaginal fibronectin have been proposed as useful tools for evaluating women at risk of preterm birth and may identify those who might benefit from a timely course of antenatal corticosteroids, but effective interventions to prevent preterm birth remain elusive. In the prevention of recurrent spontaneous preterm birth, recent trials have confirmed the use of progesterone beginning in the second trimester as an effective intervention. Optimal management of women with a history of spontaneous preterm birth includes a thorough review of the obstetric, medical, and social history, with attention to potentially reversible causes of preterm birth (eg, smoking cessation, acute infections, strenuous activities), accurate ultrasound dating, consideration of progesterone therapy beginning at 16-20 weeks of gestation, and close surveillance during the pregnancy for evolving findings. Results from the ongoing trials of cerclage as an interventional therapy and omega-3 fatty acid supplementation as a preventive therapy will provide additional knowledge for the optimal management of these high-risk women.

Recurrent preterm birth

Recurrent preterm birth is frequently defined as two or more deliveries before 37 completed weeks of gestation. The recurrence rate varies as a function of the antecedent for preterm birth: spontaneous versus indicated. Spontaneous preterm birth is the result of either preterm labor with intact membranes or preterm prelabor rupture of the membranes. This article reviews the body of literature describing the risk of recurrence of spontaneous and indicated preterm birth. Also discussed are the factors which modify the risk for recurrent spontaneous preterm birth (a short sonographic cervical length and a positive cervicovaginal fetal fibronectin test). Patients with a history of an indicated preterm birth are at risk not only for recurrence of this subtype, but also for spontaneous preterm birth. Individuals of black origin have a higher rate of recurrent preterm birth.

Recurrence risk for preterm delivery

OBJECTIVE

To estimate recurrence risk of preterm delivery in third births.

STUDY DESIGN

We conducted a population-based cohort study of Missouri mothers who delivered 3 consecutive singleton live births during 1989-1997. The recurrence risk was computed for 4 cohorts based on prior preterm delivery status and adjusted using Mantel-Haenszel stratified analysis.

RESULTS

The study population included 19,025 third births. The recurrence risk ranged from 42% (for women with 2 prior preterm deliveries), through 21% (term/preterm) and 13% (preterm/term), to 5% (term/term). The recurrence risk was highest (57%) for women with 2 prior very preterm deliveries (21-31 weeks) and lowest (33%) for those with 2 prior moderate preterm deliveries (32-36 weeks). The recurrence risk was less pronounced for women with 1 prior very or moderate preterm delivery.

CONCLUSION

These data show a strong association between prior preterm delivery and recurrence risk, which is affected by the frequency, order, and severity of prior preterm births.

Inpatient management for a shortened cervix: who is really at risk?

OBJECTIVE

The objective of the study was to identify risk factors associated with spontaneous preterm delivery (SPD) within 2 weeks of admission in patients with a shortened cervix.

STUDY DESIGN

We reviewed records of patients hospitalized in 2003-2004 with a cervix of 25 mm or less at less than 32 weeks' gestation. The primary outcome was SPD 2 weeks or less of admission.

RESULTS

Sixty-six patients met inclusion criteria. Twelve delivered at 2 weeks or less of admission. There were no differences in maternal and gestational age at admission, history of SPD, and rate of multifetal pregnancy. Those with cervical length (CL) of 5 mm or less were more likely to deliver within 2 weeks than those with CLs 6-25 mm (50% vs 12.5%; P = .01). Logistic regression identified CL less than 5 mm as the only independent predictor of delivery within 2 weeks of admission (P = .01).

CONCLUSION

CL of less than 5 mm in patients at less than 32 weeks' gestation is associated with a high rate of SPD within 2 weeks of diagnosis.

The short and funneling cervix: when to use cerclage?

PURPOSE OF REVIEW

The diagnosis of cervical incompetence remains extremely difficult because there is no diagnostic test available prior to, during or after pregnancy. This review will summarize the latest publications on the use of transvaginal ultrasonography to identify women at high risk of preterm delivery and the use of cervical cerclage in these women.

RECENT FINDINGS

Cervical length is not only inversely related to the risk of preterm delivery but also inversely related to the risk of intrauterine infection in women with preterm labor. Furthermore, previous history of preterm delivery is related to the risk of preterm delivery. Cerclage trials on women with short cervical length present conflicting results both in low and high-risk populations. Assessment of risk factors and obstetric history remain important in the diagnosis of cervical incompetence. Women at high risk of preterm delivery due to cervical incompetence should be followed-up with transvaginal measurements of cervical length. Only a minority of these women will develop a short cervical length and will consequently be at high risk of preterm delivery.

SUMMARY

A combination of assessment of risk factors, obstetric history and follow-up of cervical length enables us to identify women who benefit from a cervical cerclage.

Rates of recurrent preterm birth by obstetrical history and cervical length

OBJECTIVE

This study was undertaken to determine rates of recurrent preterm birth according to number of prior preterm births, 1 versus 2 or more and cervical length by endovaginal ultrasound at 22(0) to 24(6) weeks, less than 25 mm versus more than 25 mm.

STUDY DESIGN

We retrospectively analyzed data from charts of women with prior spontaneous preterm birth seen in a Prematurity Prevention Clinic from 1998 through 2004. Women with a history of 1 or more spontaneous preterm births (18(0)-36(6) weeks) were included. Women with multiple gestations, uterine anomalies, and prior cervical surgery were excluded. Transvaginal sonography was used to evaluate each woman's cervical length at 22(0) to 24(6) weeks. Cerclage, bed rest, tocolysis, and steroids were used when clinically appropriate. Primary outcome was gestational age at delivery less than 32 and less than 35 weeks. Data were analyzed according to number of prior preterm births (1 vs > or = 2) and sonographic cervical length at 22(0) to 24(6) weeks (<25 mm vs > or = 25 mm).

RESULTS

A total of 188 eligible women were evaluated. Median gestational age of earliest preterm birth was 26.3 weeks. Of the total 188, 118 (62.8%) women had 1 prior and 70 (37.2%) had 2 or more preterm births. Thirty-eight (20.2%) of the women had a cervical length less than 25 mm and 150 (79.8%) had a cervical length 25 mm or greater. A higher percentage of women with a cervical length less than 25 mm and 2 or more preterm births delivered less than 32 weeks compared with women with 1 prior preterm birth, although this did not reach statistical significance (21.5% vs 12.5%, P = .47). Rates of delivery less than 35 weeks in women with a cervical length less than 25 mm were similar in those with a history of 1 and 2 or more preterm births. Women who had 2 or more prior preterm births were analyzed separately to identify if a cervical length greater than 30 mm or greater than 35 mm could be reassuring for decreasing the risk of recurrent preterm birth.

CONCLUSION

Rates of preterm birth less than 32 and less than 35 weeks were similar in women whose cervical length was less than 25 mm at 22(0) to 24(6) weeks, regardless of number of prior preterm births. Women with 2 prior preterm births and a cervix greater than 35 mm were at low risk for subsequent preterm birth less than 35 weeks.