Perineal scanning

The use of intrapartum ultrasound to diagnose malpositions and cephalic malpresentations

Fetal malpositions and cephalic malpresentations are well-recognized causes of failure to progress in labor. They frequently require operative delivery, and are associated with an increased probability of fetal and maternal complications. Traditional obstetrics emphasizes the role of digital examinations, but recent studies demonstrated that this approach is inaccurate and intrapartum ultrasound is far more precise. The objective of this review is to summarize the current body of literature and provide recommendations to identify malpositions and cephalic malpresentations with ultrasound. We propose a systematic approach consisting of a combination of transabdominal and transperineal scans and describe the findings that allow an accurate diagnosis of normal and abnormal position, flexion, and synclitism of the fetal head. The management of malpositions and cephalic malpresentation is currently a matter of debate, and individualized depending on the general clinical picture and expertise of the provider. Intrapartum sonography allows a precise diagnosis and therefore offers the best opportunity to design prospective studies with the aim of establishing evidence-based treatment. The article is accompanied by a video that demonstrates the sonographic technique and findings.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

A blueprint for the prevention of preterm birth: vaginal progesterone in women with a short cervix

Preterm birth is the leading cause of perinatal morbidity and mortality worldwide, and is the most important challenge to modern obstetrics. A major obstacle has been that preterm birth is treated (implicitly or explicitly) as a single condition. Two thirds of preterm births occur after the spontaneous onset of labor, and the remaining one third after "indicated" preterm birth; however, the causes of spontaneous preterm labor and "indicated" preterm birth are different. Spontaneous preterm birth is a syndrome caused by multiple etiologies, one of which is a decline in progesterone action, which induces cervical ripening. A sonographic short cervix (identified in the midtrimester) is a powerful predictor of spontaneous preterm delivery. Randomized clinical trials and individual patient meta-analyses have shown that vaginal progesterone reduces the rate of preterm delivery at <33 weeks of gestation by 44%, along with the rate of admission to the neonatal intensive care unit, respiratory distress syndrome, requirement for mechanical ventilation, and composite neonatal morbidity/mortality score. There is no evidence that 17-α-hydroxyprogesterone caproate can reduce the rate of preterm delivery in women with a short cervix, and therefore, the compound of choice is natural progesterone (not the synthetic progestin). Routine assessment of the risk of preterm birth with cervical ultrasound coupled with vaginal progesterone for women with a short cervix is cost-effective, and the implementation of such a policy is urgently needed. Vaginal progesterone is as effective as cervical cerclage in reducing the rate of preterm delivery in women with a singleton gestation, history of preterm birth, and a short cervix (<25 mm).

Transabdominal evaluation of uterine cervical length during pregnancy fails to identify a substantial number of women with a short cervix

OBJECTIVE

To assess the diagnostic performance of transabdominal sonographic measurement of cervical length in identifying patients with a short cervix.

METHODS

Cervical length was measured in 220 pregnant women using transabdominal and transvaginal ultrasound (US). Reproducibility and agreement between and within both methods were assessed. The diagnostic accuracy of transabdominal US for identifying cases with a cervical length <25 mm was evaluated.

RESULTS

Twenty-one out of 220 cases (9.5%) had a cervical length <25 mm by transvaginal US. Only 43% (n = 9) of patients with a short cervix were correctly identified by transabdominal US. In patients with a cervical length of <25 mm by transvaginal US, transabdominal measurement of the cervix overestimated this parameter by an average of 8 mm (95% LOAs, -26.4 to 10.5 mm). Among women without a short cervix, transabdominal US underestimated cervical length on average (LOA) by 1.1 mm (95% LOAs, -11.0 to 13.2 mm). Transvaginal US was also more reproducible (intraclass correlation coefficient: (ICC) (0.96; 95% CI, 0.94 to 0.97) based on comparisons between 2D images and immediately acquired 3D volume datasets relative to transabdominal US (ICC: 0.71; 95% CI, 0.57 to 0.84). Transvaginal US detected 13 cases with funneling and six cases with sludge whereas only three cases of funneling and one of sludge were detected by transabdominal US.

CONCLUSION

Transabdominal measurement overestimated cervical LOA by 8 mm among women with a short cervix and resulted in the underdiagnosis of 57% of cases.

Ultrasound measurement of fetal adrenal gland enlargement: an accurate predictor of preterm birth

OBJECTIVE

The objective of the study was to test whether ultrasound-measured fetal adrenal gland volume (AGV) and fetal zone enlargement (FZE) predicts preterm birth (PTB) better than cervical length (CL).

STUDY DESIGN

Three-dimensional and 2-dimensional ultrasound were used prospectively to measure fetal AGV, FZE, and CL in women with preterm labor symptoms. We corrected AGV for fetal weight (cAGV). The ratio between whole gland depth (D) and central fetal zone depth (d) (d/D) was used to measure FZE. Ability of cAGV, d/D, and CL to predict PTB 7 days or less was compared.

RESULTS

Twenty-seven of 74 women (36.5%) presenting between 21 and 34 weeks had PTB of 7 days or less. FZE greater than 49.5% was the single best predictor for PTB (sensitivity/specificity 100%/89%) compared with cAGV (81%/87%) and CL (56%/60%; P < .05). Prediction was independent of obstetrics history and tocolytic use.

CONCLUSION

The 2-dimensional measurement of the adrenal gland FZE is highly effective performing superior to CL in identifying women at risk for PTB within 7 days.

Methods of sonographic cervical length measurement in pregnancy: A review of the literature

In this review we give an overview of the methods and pitfalls in cervical length measurements. We compared the different techniques and investigated factors that influence visualization of the cervix. The data in this overview may be used to establish guidelines in clinical practice.

The classification of placenta praevia – time for a change?

The techniques employed in the diagnosis of placenta praevia have altered radically since Guillemeau first described the condition in 1685, stating that ‘The surgeon must consider if it is the child or if it is the after-birth who presents first’. However, his description went unnoted, for Giffart in narrating a case of haemorrhage wrote in 1730: ‘I cannot receive as absolutely true the opinion of those authors, who say that the placenta is always attached to the fundus uteri, for in this case, as in many others, I have every reason to believe that it adhered on the internal orifice, or very near to it; and that, in dilating, the latter occasioned the separation of the after-birth, and as a consequence the haemorrhage.’

Transvaginal versus transperineal ultrasonography: a blinded comparison in the assessment of cervical length at midgestation

OBJECTIVE

The study's objective was to determine the correlation and agreement between transperineal ultrasonography and transvaginal ultrasonography in the assessment of cervical length in gravid patients.

STUDY DESIGN

After a pilot, unblinded series of transperineal and transvaginal cervical length measurements in 200 gravid patients, 206 study patients between 14 and 34 weeks' gestation with intact membranes and cervical dilatation of < or = 2 cm underwent transperineal and transvaginal cervical length assessment under a blinded, 2-sonographer protocol. The Pearson correlation coefficient, Lin concordance coefficient, and Bland-Altman plot were used. Acceptable concordance was defined as > 0.82, with an acceptable correlation of > 0.9 and an acceptable difference between the means of < 3 mm. The power of the study to detect this degree of concordance was estimated to be 95% at this sample size.

RESULTS

Paired ultrasonographic measurements were obtained for all 206 study patients. Transperineal mean cervical length was 35 +/- 8.6 mm. Transvaginal mean cervical length was 35.9 +/- 8.8 mm. The Pearson correlation coefficient was 0.959, and the Lin concordance coefficient was 0.955, with a 95% confidence lower bound of 0.949. Close agreement between transperineal and transvaginal measurements was observed across the full range of cervical lengths (1-5 cm). The estimated difference between the paired means was 1 mm. The 95% tolerance interval for any given paired observation (Transperineal length - Transvaginal length) was -5.7 to +4 mm.

CONCLUSIONS

Cervical length measured by transperineal ultrasonography demonstrates close correlation and agreement with transvaginal measurements. With sonographer experience and optimal technique, approximately 95% of transperineal cervical length observations can be expected to be within 5 mm of a given paired transvaginal measurement. Transperineal ultrasonography may be a preferred method of cervical length assessment for situations in which vaginal placement of instruments should be minimized.

Cervical ultrasonography compared with manual examination as a predictor of preterm delivery

OBJECTIVE

Our purpose was to compare the accuracy of ultrasonographic and manual cervical examinations for the prediction of preterm delivery.

STUDY DESIGN

One hundred two singleton pregnancies at high risk for preterm delivery were followed up prospectively from 14 to 30 weeks with both serial cervical ultrasonography measurements and manual examinations of the length of the cervix. The primary outcome studied was preterm (< 35 weeks) delivery.

RESULTS

Excluding six induced preterm deliveries, 96 pregnancies were analyzed. The mean cervical length measured by ultrasonography was 20.6 mm in pregnancies delivered preterm (n = 17) and 31.3 mm in pregnancies delivered at term (n = 79) (p = 0.003); the mean cervical lengths measured by manual examination were 16.1 mm and 18.6 mm in the same preterm and term pregnancies, respectively (not significant). The sixteenth- and twentieth-week ultrasonographic cervical lengths predicted preterm delivery most accurately (p < 0.0005). The 25th percentiles of ultrasonographic (25 mm) and manual (16 mm) cervical lengths showed relative risks for preterm delivery of 4.8 (95% confidence interval 2.1 to 11.1, p = 0.0004) and 2.0 (95% confidence interval 0.5 to 4.7, p = 0.1), respectively; sensitivity, specificity, and positive and negative predictive values were 59%, 85%, 45%, 91%, and 41%, 77%, 28%, and 86%, respectively.

CONCLUSION

Cervical length measured by ultrasonography is a better predictor of preterm delivery than is cervical length measured by manual examination. Cervical ultrasonography in patients at high risk for preterm birth seems to be most predictive of preterm delivery when it is performed between 14 and 22 weeks' gestation.

Transperineal versus transvaginal color Doppler imaging of the uterine circulation

Transperineal sonography has been described as being useful in assessing patients in special clinical situations such as posterior placenta previa, preterm labor, stress incontinence, and vaginal atresia. We explored the feasibility of this approach in assessing the uterine circulation in 54 subjects, of whom 36 were postmenopausal. We found that visualization of the uterine artery by the transperineal approach was satisfactory in most patients. The uterine arterial Doppler indices obtained from this approach were compared with those obtained by the transvaginal route. Highly significant correlations were found (correlation coefficient tau for pulsatility index = 0.74, p < 0.0001). No significant differences in results between the two approaches were detected using the Wilcoxon Matched-Pairs Signed-Rank test. We conclude that transperineal Doppler studies of the uterine circulation are possible and may be useful in certain patient groups.

Transvaginal ultrasonographic evaluation of the cervix before labor: presence of cervical wedging is associated with shorter duration of induced labor

OBJECTIVE

Our purpose was to test the hypothesis that transvaginal ultrasonographically determined characteristics of the cervix are associated with duration of induced labor.

STUDY DESIGN

Fifty-three patients scheduled for induction of labor underwent transvaginal ultrasonography and digital cervical examinations before labor induction. Cox proportional-hazards multiple regression analysis was performed to determine the variables that made a significant contribution to the prediction of latent-phase and total labor duration. In the analysis the possible confounding effects of exogenous prostaglandin, previous vaginal delivery, and previous termination of pregnancy were controlled.

RESULTS

Latent-phase and total labor duration were significantly associated with the presence of cervical wedging noted on transvaginal ultrasonography and administration of prostaglandin but not with the result of digital examination of cervical effacement or dilatation. Latent-phase duration was also associated with cervical length measured by transvaginal ultrasonography. The presence of wedging was significantly associated with shorter latent (15.9 +/- 1.7 vs 34.1 +/- 3.8 hours, p = 0.0001) and total (22.0 +/- 1.8 vs 38.3 +/- 3.6 hours, p = 0.0001) labor length.

CONCLUSION

The presence of wedging and decreased cervical length observed by transvaginal ultrasonography is associated with a shorter duration of induced labor and may be useful in the evaluation of induction candidates.

Assessment of cervical dilatation during labor: a review

Various techniques for assessment of cervical dilatation during labor or 'cervimetry' have been described, including digital, (electro)mechanical, electromagnetic and ultrasound cervimetry. In this paper the validity and usefulness of instrumental cervimetry is assessed on the basis of the available literature. Cervimetry using ultrasound transducers allows continuous and reliable recording of cervical dilatation during labor with little discomfort to the patient. In comparison with other instrumental techniques for measurement of cervical dilation ultrasound cervimetry seems to be the most promising method available.

Vaginal ultrasound for diagnosis of placenta previa

Transvaginal sonography was compared with transabdominal sonography in 35 women with suspected placenta previa. The transvaginal sonographic technique did not result in vaginal bleeding in any of the patients. The internal os and its relationship to the location of the placenta were visualized by transvaginal sonography in all patients, but only in 24 patients (69%) by transabdominal sonography. Transvaginal sonography ruled out placenta previa in 13 cases thought to be placenta previa by abdominal sonography. The transvaginal diagnosis in these 13 patients was confirmed at delivery. Thirty-four of the 35 women have been delivered. The diagnosis at delivery confirmed the transvaginal sonographic diagnosis in 29/34 cases and the transabdominal diagnosis in 16/34. Transvaginal sonography did not predict the delivery diagnosis in five patients who were erroneously believed to have placenta previa by both sonographic techniques.