Background
No new method of assisting vaginal birth has been introduced into clinical practice since the development of the vacuum extractor in the 1950s. The Odon Device is a new device that employs a circumferential air cuff over the fetal head to assist birth. In this study, the Odon Device has been used to assist vaginal birth for standard clinical indications.
Objective
This study aimed to investigate the clinical impact, safety, and acceptability of the Odon Device to women, their babies, and clinicians and to assess the feasibility of recruiting women to an interventional intrapartum research study.
Study Design
This is a nonrandomized, single-arm interventional feasibility study of the Odon Device for operative vaginal birth undertaken in a single maternity unit: Southmead Hospital, Bristol, United Kingdom. The Odon Device was used to assist birth in 40 women who required the birth to be assisted for suspected fetal compromise and/or prolonged second stage of labor. The primary clinical outcome was the proportion of births successfully assisted with the Odon Device, and the primary feasibility outcome was the proportion of eligible women who were approached and who agreed to participate. Neonatal outcome data were reviewed at day 28, and maternal outcomes were investigated up to day 90.
Results
Between October 2018 and January 2019, 298 of 384 approached, eligible women (77.6%) consented to participate. Of these women, 40 received the intervention—the use of the Odon Device. Birth was assisted in all cephalic (occiput anterior, occiput transverse, and occiput posterior) fetal positions, at all stations at or below the ischial spine and with or without regional analgesia. The Odon Device was effective in 19 of 40 cases (48%). Of the 40 births, 21 (52.5%) required additional assistance: 18 of 40 births (45%) were completed using nonrotational forceps, 1 of 40 births (3%) required rotational forceps, and 2 of 40 births (5%) required an emergency cesarean delivery. There was no serious maternal or neonatal adverse event related to the use of the device, and there was no serious adverse device effect. There were 4 devices (10%) that were ineffective because of a manufacturing fault. Furthermore, 39 of 40 women (98%) reported a high birth perception score. All practitioners were able to use the device as intended, although some steps in using the device were reported to be easier to perform (setup and deflation of air chamber) than others (application of the device and withdrawal of the applicator).
Conclusion
Recruitment to an interventional study of a new device for operative vaginal birth was feasible; 78% of eligible women were willing to participate, often expressing an aspiration for an alternative to forceps and vacuum. The success rate of the Odon Device was lower than reported success rates of vacuum and forceps; however, in this study, the device had been used to assist birth for standard clinical indications. There was no significant maternal or neonatal safety concern associated with the use of the device, although the number of births studied was small. Further feasibility study to establish iterative changes to the device, technique, and clinical indications is necessary.
Why was this study conducted?
No new method of operative vaginal birth has been introduced since the development of the vacuum extractor in the 1950s. The Odon Device is a new type of instrument that uses a circumferential air cuff over the fetal head and offers an alternative to vacuum and forceps.
Key findings
There was no serious maternal or neonatal adverse event related to the use of the Odon Device. In the first 40 clinically indicated cases ever to be conducted, the Odon Device was successful in 19 (48%), and there was a high maternal birth perception score.
What does this add to what is known?
The Odon Device currently has a lower success rate than current devices, but this should improve with technique refinements. High recruitment rates to studies of novel devices to assist birth are feasible.
Introduction
The optimal duration of the second stage of labor is contentious, but complications in the second stage of labor remain a major cause of preventable maternal and neonatal morbidities and mortalities globally. Skilled operative vaginal birth improves the outcomes for women and their babies when birth is assisted in the second stage of labor for suspected fetal compromise and/or delay , compared with cesarean delivery. Despite this fact, the rate of cesarean delivery is increasing, whereas the rate of operative vaginal birth is low or nonexistent in many health services (reported rates as low as 0.5% of births). The reasons for low operative vaginal birth rates include inexperienced healthcare workers, lack of equipment, and operator and patient dislike of currently available methods. A new device to assist vaginal birth provides an opportunity to improve outcomes and reinvigorate this essential life-saving skill. However, in contrast to the huge advances in medical care over the past 70 years, no new method for assisting vaginal birth has been introduced into clinical practice since the development of the vacuum extractor in the 1950s. The advantages of the Odon Device compared with the advantages of standard methods for assisting birth (ie, forceps and vacuum) are currently unknown as the device has not yet been used in clinically indicated cases. Potential advantages could include improved neonatal outcomes (eg, reduction in subaponeurotic and retinal hemorrhages, skull fracture, and facial nerve palsy), increased maternal acceptability, reduction in failed rate of operative vaginal birth, decreased risk of adverse maternal outcomes (eg, postpartum hemorrhage and vaginal tears), and ease of use (ie, the same application technique of the device for all cephalic positions).
The Odon Device is a new device that can be used for operative vaginal birth ( Figure 1 ) consisting of a plastic applicator and polyethylene sleeve. The applicator has 4 flexible spatulas that position the sleeve over the fetal head. A progress indicator allows the operator to confirm the correct depth of insertion. The sleeve contains a circumferential air chamber that is inflated around the fetal head, providing the grip for the operator to apply traction ( Video ). The instructions for the use of the Odon Device are shown in Supplemental Figure 1 . A phase 1 study of 4 earlier versions of the Odon Device in 49 healthy volunteers (women who were about to have a spontaneous vaginal birth) demonstrated that the device could be applied to the fetal head during the second stage of labor with no serious safety concern. Animal studies were subsequently performed for safety, and an extensive program of simulation studies confirmed that the device could be reliably sited and used in occiput anterior, occiput transverse, and occiput posterior fetal positions.
The ASSIST Study used the Odon Device to assist birth for routine clinical indications: suspected fetal compromise and/or failure to progress in the second stage of labor. The study aimed to investigate the feasibility of recruitment and to investigate the efficacy, safety, and acceptability of the Odon Device to women and their babies, midwives, obstetricians, and neonatologists.
Materials and Methods
Study design
This is a nonrandomized, single-arm feasibility study of the Odon Device for 40 women who required an operative vaginal birth for a recognized clinical indication. Qualitative work that explored the experience and views of women and clinicians will be published in full, separately.
Population
Potential participants were approached at Southmead Hospital, Bristol, United Kingdom. Figure 2 outlines the eligibility criteria for initial consent and allocation to the intervention if an operative vaginal birth for a clinical indication was required for prolonged second stage of labor or presumed fetal compromise—as defined by the Royal College of Obstetricians & Gynaecologists. Women were provided with study information through a verbal discussion, an information leaflet, and a video demonstrating the Odon Device.
Intervention
Odon Device–assisted births were conducted by 1 of 5 obstetricians who had undergone specialized training ( Supplemental Figure 2 ). If the Odon Device was unsuccessful, the obstetrician used their clinical judgment to complete the birth using forceps, vacuum, or cesarean delivery. After use (following high-level disinfection), devices were systematically examined by the study team and manufacturer. The device was used in women who had a fully dilated cervix, with the vertex presenting at or below the ischial spines, in any position.
Outcomes
The primary feasibility outcome was the proportion of approached and eligible women agreeing to participate. The primary clinical outcome was the proportion of births successfully assisted with the Odon Device. A birth was defined as “successful” if all of the following 6 criteria were met: (1) vaginal birth assisted with the Odon Device, (2) no serious maternal adverse reaction related to the use of the device, (3) no serious neonatal adverse reaction related to the use of the device, (4) no serious adverse device effect, (5) woman’s perception of her birth of >6 (Patient Perception Score [PPS] ) ( Supplemental Table 1 ), and (6) practitioner-reported outcome of >12 ( Supplemental Table 2 ).
The PPS has been previously validated for operative vaginal birth. Operators were asked their perceptions of the use of the device using a simple, nonvalidated tool ( Supplemental Table 2 ). Secondary outcomes included metrics related to study feasibility and safety (ie, maternal perineal trauma and measured blood loss, neonatal soft tissues trauma and pain, and device safety) ( Figure 3 ). Neonates were followed up to day 28 via notes review and mothers on days 7, 28, and 90 after birth via telephone consultation. Further details are contained in the published study protocol.
Sample size
Sample sizes between 24 and 50 have been recommended for feasibility studies. , A complete sample size of 40 women was fixed a priori to enable the estimation of a potential rate of successful operative vaginal birth of 80% to within a 95% confidence interval (CI) of ±12%. This sample size will demonstrate the use of a secondary instrument of 50% to within a 95% CI of ±15%.
Statistical analysis
Data were entered and stored on a bespoke study database (GeneSYS) designed and managed by the Clinical Trial and Evaluation Unit, University of Bristol, Bristol, United Kingdom. Data were analyzed using Stata (version 15.1, StataCorp, College Station, TX). Continuous variables were reported as mean and standard deviation or median and interquartile range; categorical variables were reported as frequency and percentages. Relationships among characteristics that affect the success of the Odon Device were explored using nonparametric tests, the Fisher exact test for categorical variables, and the Mann-Whitney test for continuous variables.
Ethics
This study was approved by South Central–Berkshire REC, United Kingdom, on September 3, 2018 (18/SC/0344), the Medicines and Healthcare Products Regulatory Agency on August 9, 2018, and the Health Research Authority on September 3, 2018.
Results
Recruitment
Women were recruited between October 2018 and January 2019 ( Figure 4 ). Pregnancy notes of 545 women were screened; 441 of 545 women (80.9%) were initially deemed eligible and approached. Furthermore, 57 of the approached women were then identified to be ineligible. Of the 384 women who were approached and eligible, 298 (77.6%) consented to participate should they require an operative vaginal birth ( Figure 4 ).
Of the 298 women who had consented, 224 (75.2%) did not have an operative vaginal birth: 139 (62.1%) had a spontaneous vaginal birth, 76 (33.9%) had a cesarean delivery, and 9 (4.0%) were not yet in labor when the recruitment target was reached. In addition, 72 women (24.2%) who had provided consent required an operative vaginal birth; the Odon Device was used in 40 cases (55.6%).
Data quality
There were minimal missing data: body mass index at 36 weeks’ gestation (6 of 40, 15%); umbilical artery pH and base excess (7 of 40, 18%); umbilical vein pH and base excess (4 of 40, 10%); Neonatal Infant Pain Score (NIPS) at 2 hours postnatal (1 of 40, 3%); and NIPS at 6 hours postnatal (5 of 40, 13%). Participants were deemed lost to follow-up if they did not respond within 4 days of the planned follow-up. Follow-up was not obtained from 3 (8%) and 4 (10%) women on day 28 and 90, respectively. A day 28 neonatal follow-up (3%) was not completed.
Demographics and characteristics
Table 1 summarizes the demographics and birth characteristics. Furthermore, 29 women (73%) had an operative vaginal birth for presumed fetal compromise and 11 women (28%) for prolonged second stage of labor. Birth was assisted in all cephalic fetal positions, at all stations at or below the ischial spines and with or without regional analgesia.
| Variable | Overall (n=40) |
|---|---|
| Maternal age (y) | 28.9±4.8 |
| BMI at booking | 25.3±5.5 |
| BMI at 36 wk | 29.4±5.7 a |
| Ethnicity | |
| White British | 32 (80.0) |
| Any other white background | 4 (10.0) |
| Black African | 1 (2.5) |
| Black Caribbean | 1 (2.5) |
| Indian | 1 (2.5) |
| Any other Asian background | 1 (2.5) |
| Parity | |
| 0 | 34 (85.0) |
| ≥1 | 6 (15.0) |
| Previous cesarean delivery | 1 (2.5) |
| Length of gestation (wk) | 39.0±1.3 |
| Birthweight (g) | 3198±542 3120 (2800–3602) |
| Head circumference (cm) | 34.0±1.6 |
| Duration of first stage of labor (min) | 342±199 321 (188–480) |
| Duration of second stage of labor (min) | 112±63 103 (67–152) |
| Induced labor | 34 (85.0) |
| Primary indication for operative vaginal birth | |
| Presumed fetal compromise | 29 (72.5) |
| Prolonged second stage of labor | 11 (27.5) |
| Fetal position | |
| OA | 31 (77.5) |
| OT | 4 (10.0) |
| OP | 5 (12.5) |
| Fetal head palpable per abdomen | |
| 0/5 | 40 (100.0) |
| 1/5 | 0 (0.0) |
| Station of fetal head | |
| Spines | 3 (7.5) |
| +1 cm below the spines | 18 (45.0) |
| +2 cm below the spines | 18 (45.0) |
| +3 cm below the spines | 1 (2.5) |
| Molding | |
| None | 9 (22.5) |
| + | 26 (65.0) |
| ++ | 4 (10.0) |
| +++ | 1 (2.5) |
| Caput | |
| None | 11 (27.5) |
| 1 cm | 9 (22.5) |
| 2 cm | 16 (40.0) |
| 3 cm | 4 (10.0) |
| Analgesia | |
| None | 1 (2.5) |
| Perineal infiltration | 12 (30.0) |
| Pudendal block | 1 (2.5) |
| Regional anesthesia | 34 (85.0) |
| General anesthesia | 0 (0.0) |
| Grade of operator | |
| Attending | 29 (72.5) |
| Trainee | 11 (27.5) |
Primary clinical outcome
The Odon Device was the only device required to assist birth in 19 of 40 cases (48%). There was no serious maternal or neonatal adverse reaction related to the use of the device during birth, and there was no serious adverse device effect. All practitioners found the device easy to use; however, 1 woman (3%) whose birth was assisted using the Odon Device reported her perception of the operative birth as poor. Therefore, by our a priori definition, the proportion of births that were “successfully” assisted with the Odon Device was 18 of 40 (45%).
Additional assistance was required to complete the birth in 21 of 40 cases (52%). Of the 40 cases, 18 (45%) were completed using nonrotational forceps, 1 (3%) required rotational forceps, and 2 (5%) required an emergency cesarean delivery (1 immediately following an unsuccessful Odon Device and 1 after a failed attempt using rotational forceps). The fetal vertex was at the level of the ischial spines in all cases requiring rotational forceps or cesarean delivery.
In addition, 39 of 40 devices (98%) were inspected after use, and 4 of 40 devices (10%) had a fault in the bulb pump mechanism, unable to inflate the air cuff. None of the faulty device had been successful, and in each case, the operator had raised concerns that the air chamber had not inflated adequately during use.
Characteristics that affect the success of the Odon Device
Table 2 summarizes the characteristics of 36 births, which were assisted with nonfaulty devices by success (19 cases) and failure (17 cases). Station ( P =.014) and degree of molding ( P =.022) were strongly related to the success of the device; higher fetal station and/or increased molding was associated with lower device success rates. Caput ( P =.057) may also affect the success of the device; greater degrees of caput were associated with a higher likelihood of failure. There was no evidence to support any relationship among device success and onset of labor ( P =.650), head circumference ( P =.368), primary indication for operative vaginal birth ( P =1.000), position of the fetal head ( P =.843), birthweight ( P =.272), length of the second stage of labor ( P =.814), and length of the first stage of labor ( P =.178).
| Successful Odon n=19 | Unsuccessful Odon n=17 | |
|---|---|---|
| Maternal age (y) | 28.10±5.40 | 29.90±4.20 |
| BMI at booking | 25.22±5.30 | 25.30±5.60 |
| BMI at 36 wk | 28.60±5.40 a | 29.60±6.00 b |
| Ethnicity | ||
| White British | 15 (78.9) | 15 (88.2) |
| Any other white background | 3 (15.8) | 0 (0.0) |
| Black African | 0 (0.0) | 1 (5.9) |
| Black Caribbean | 0 (0.0) | 0 (0.0) |
| Indian | 1 (5.3) | 0 (0.0) |
| Any other Asian background | 0 (0.0) | 1 (5.9) |
| Parity | ||
| 0 | 16 (84.2) | 14 (82.3) |
| ≥1 | 3 (15.8) | 3 (17.6) |
| Previous cesarean delivery | 0 (0.0) | 1 (5.9) |
| Length of gestation (wk) | 38.8±1.3 | 39.1±1.3 |
| Birthweight (g) | 3097±454 3044 (2730–3405) | 3207±(606) 3190 (2724–3604) |
| Head circumference (cm) | 34.00±1.50 | 34.00±1.50 |
| Duration of first stage (min) | 334±197 240 (180–485) | 357±217 314 (240–480) |
| Duration of second stage (min) | 97±54 100 (61–139) | 122±64 122 (75–158) |
| Induced labor | 17 (89.5) | 14 (82.4) |
| Primary indication for operative vaginal birth | ||
| Presumed fetal compromise | 14 (73.7) | 13 (76.5) |
| Delay in the second stage of labor | 5 (26.3) | 4 (23.5) |
| Fetal position | ||
| OA | 14 (73.7) | 14 (82.4) |
| OT | 2 (10.5) | 2 (11.8) |
| OP | 3 (15.8) | 1 (5.9) |
| Fetal head palpable per abdomen | ||
| 0/5 | 19 (100.0) | 17 (100.0) |
| 1/5 | 0 (0.0) | 0 (0.0) |
| Station of fetal head | ||
| Spines | 0 (0.0) | 3 (17.6) |
| +1 cm below the spines | 6 (31.6) | 10 (58.8) |
| +2 cm below the spines | 12 (63.2) | 4 (23.5) |
| +3 cm below the spines | 1 (5.3) | 0 (0.0) |
| Molding | ||
| None | 0 (0.0) | 0 (0.0) |
| + | 8 (42.1) | 1 (5.9) |
| ++ | 9 (47.4) | 13 (76.0) |
| +++ | 1 (5.3) | 3 (17.6) |
| Caput | ||
| None | 1 (5.3) | 0 (0.0) |
| 1 cm | 8 (42.1) | 1 (5.9) |
| 2 cm | 3 (15.8) | 6 (35.3) |
| 3 cm | 7 (36.8) | 7 (41.2) |
| Analgesia c | ||
| None | 1 (5.3) | 0 (0.0) |
| Perineal infiltration | 7 (36.8) | 2 (11.8) |
| Pudendal block | 0 (0.0) | 0 (0.0) |
| Regional anesthesia | 15 (78.9) | 15 (88.2) |
| General anesthesia | 0 (0.0) | 0 (0.0) |
| Grade of operator | ||
| Attending | 14 (73.7) | 13 (76.5) |
| Trainee | 5 (26.3) | 4 (23.5) |
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