Methods

The trial protocol28 and results30 have been previously published and parts of the published articles are reproduced throughout this report. These have been reproduced with permission from Knight et al.28 [This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.] and Knight et al.30 [This article is available under the terms of the Creative Commons Attribution License (CC BY 4.0) ‘Beyond maternal death’. You may copy and distribute the article, create extracts, abstracts and new works from the article, alter and revise the article, text or data mine the article and otherwise reuse the article commercially (including reuse and/or resale of the article) without permission from Elsevier. You must give appropriate credit to the original work, together with a link to the formal publication through the relevant DOI and a link to the Creative Commons user license above. You must indicate if any changes are made but not in any way that suggests the licensor endorses you or your use of the work.]

Design

The A randomised controlled trial of prophylactic ANtibiotics to investigate the prevention of infection following Operative vaginal DElivery (ANODE) trial was a multicentre, randomised, blinded, placebo-controlled trial conducted in the UK.

Ethics approval and research governance

The ANODE trial protocol was approved by the Health Research Authority National Research Ethics Service Committee South Central – Hampshire B (study reference number 15/SC/0442).

Local approval and site-specific assessments were obtained from each NHS hospital site.

Patient and public involvement

The research question was initially prioritised by the user advisory group to the NIHR ‘Beyond maternal death’ programme, which generated the initial information about sepsis risk in association with operative vaginal birth.9 To obtain the perspective of a group more representative of the wider maternity population, we contacted the PRIME (Public and Researchers Involvement in Maternity and Early pregnancy) group. PRIME is a patient and public involvement group that was set up in collaboration with the University of Birmingham Collaborations for Leadership in Applied Health Research and Care (CLAHRC). PRIME group members helped design the trial processes and materials, particularly assisting with designing our approach to consent. The group was represented among the co-applicant group to continue to advise throughout the trial.

Participants

Inclusion criteria

• Women aged ≥ 16 years who were willing and able to give informed consent.
• Women who had had an operative vaginal delivery at ≥ 36⁺⁰ weeks’ gestation.

Exclusion criteria

Women were not eligible to enter the trial if any of the following applied:

• A clinical indication for ongoing antibiotic administration post delivery [e.g. because of a confirmed antenatal or intrapartum infection, third- or fourth-degree tears (obstetric anal sphincter injury)]. Note that receiving antenatal antibiotics (e.g. for maternal group B streptococcal carriage or prolonged rupture of membranes) was not considered a reason for exclusion if there was no indication for ongoing antibiotic prescription post delivery.
• Known allergy to penicillin or to any of the components of co-amoxiclav, as documented in hospital notes.
• History of anaphylaxis (a severe hypersensitivity reaction) to another β-lactam agent (e.g. cephalosporin, carbapenem or monobactam), as documented in hospital notes.

Setting

The trial was conducted in 27 consultant-led obstetric units in England and Wales (see Appendix 1).

Informed consent and recruitment

Information about the trial was made widely available throughout the maternity units in the form of posters and leaflets [with QR (Quick Response) codes to the trial website]. Written information about the trial was available to all women at participating centres during their pregnancy through different routes, depending on the centre, for example at their antenatal booking visit, as part of their hand-held notes or at their 19- to 21-week scan visit.

On admission, women in labour or admitted for induction were reminded about the trial by their health-care professional and information about the trial could be provided if not previously seen. After the clinical decision for operative vaginal birth had been made, the following approaches were used by the woman’s midwife, obstetrician or anaesthetist to obtain informed consent, depending on the clinical circumstances (Figure 1):

1. If there was no time constraint (e.g. in cases of operative vaginal birth for delayed second-stage progress or if birth was already completed), the health-care professional discussed the trial with the woman and provided her with the participant information leaflet. If she was happy to join the trial, then informed written consent was obtained.
2. If there was a time or other constraint (e.g. in cases of operative vaginal birth for suspected fetal compromise, or if an approach for written consent was considered inappropriate by the health professionals in attendance), women were approached to give verbal consent. It is possible that urgent deliveries are associated with a lower standard of asepsis, and so it was particularly important that these women were able to participate in the trial. If the attending obstetrician or midwife felt that it was appropriate, the woman was provided with verbal information about the trial and asked if she was willing to participate, in principle; if she agreed, she was randomised. Verbal consent was documented by the clinician recruiting the woman and countersigned by a witness. All women enrolled under this procedure were approached before discharge by trial midwives to give full written consent for inclusion of their data in the trial and for participation in the planned follow-up.

FIGURE 1 Consent and randomisation processes. Reproduced from Knight et al.28 This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/. The text includes minor additions and formatting changes to the original text. (Figure not reproduced here; see the original article.)

Intervention

Centres were supplied with sealed sequentially numbered indistinguishable packs containing trial treatment [a single dose of intravenous co-amoxiclav (1 g of amoxicillin/200 mg of clavulanic acid)] or placebo (a single dose of intravenous sterile saline), as designated. Bottles of 1000 mg/200 mg of co-amoxiclav, in the form of sterile powder for solution, were supplied for making up as an injection reconstituted with sterile water, which was also supplied. The placebo (0.9% saline) was supplied as 20 ml single-use vials of clear liquid. Reconstitution was not required.

As co-amoxiclav, when reconstituted, has a distinct colour and odour, it was impossible to blind those preparing and checking the intervention to women’s allocation. The investigational medicinal product (IMP) (co-amoxiclav or placebo) was made up in an opaque-coloured syringe so that the woman herself remained blinded to allocation. To ensure that awareness of allocation could not influence outcomes, it was specified that the research nurse/midwife conducting telephone follow-up should not have prepared or checked the intervention. Sites were instructed to give the intervention as soon as possible after women had given birth, and no later than 6 hours after birth of the baby.

Randomisation, blinding and code-breaking

A randomisation list was generated by the Senior Trials Statistician at the National Perinatal Epidemiology Unit Clinical Trials Unit (NPEU CTU) using permuted blocks of variable size to ensure balance and unpredictability overall. Pack numbers were added by the Senior Trials Programmer at the NPEU CTU, who liaised directly with the packaging and distribution company. Sites were provided with a series of sequential packs and stocks were replenished from the global sequence as required. Women were randomised by the allocation of the next sequentially numbered indistinguishable pack once consent and eligibility were established. Pack use was recorded by the recruiting site and reviewed by NPEU CTU.

An emergency code-breaking procedure was not required. As only a single dose of co-amoxiclav was administered, there was no need to code-break if further antibiotics were required. Centres were advised that if a woman had an anaphylactic reaction, she should be treated as if she had been given the active drug.

Internal pilot

We conducted an internal pilot during the first 9 months of the trial, when 1034 recruits were predicted, to test our recruitment and retention assumptions. The predefined stop–go criteria were:

• If recruitment was ≥ 75% (n ≥ 775), then the target sample size was clearly achievable and Trial Steering Committee (TSC) recommendation to Health Technology Assessment (HTA) programme would be to continue directly with the main trial.
• If recruitment was between 50% and 75% (517 ≤ n ≤ 775), then the TSC recommendation to the HTA programme would be to recruit more centres and review again in 6 months.
• If recruitment was < 50% (n < 517), then urgent discussions were required between the Project Management Group and the TSC to undertake a detailed review of options to subsequently recommend to the HTA programme.

Outcomes

Primary outcome

Confirmed or suspected maternal infection within 6 weeks of delivery, as defined by one of the following:

• a new prescription of antibiotics for presumed perineal wound-related infection, endometritis or uterine infection, urinary tract infection with systemic features or other systemic infection
• confirmed systemic infection on culture
• endometritis, as defined by the US Centers for Disease Control and Prevention (CDC).31

An episode of endometritis defined according to the CDC required meeting at least one of the following criteria:

• Organisms are cultured from fluid (including amniotic fluid) or tissue from endometrium obtained during an invasive procedure or biopsy.
• The woman exhibits at least two of the following signs or symptoms: fever (> 38 °C), abdominal pain (with no other recognised cause), uterine tenderness (with no other recognised cause) or purulent drainage from uterus (with no other recognised cause).

Secondary outcomes

Systemic sepsis

This was defined according to modified systemic inflammatory response syndrome (SIRS) criteria for pregnancy used in previous population-based surveillance studies,3,32 namely:

• any woman dying from infection or suspected infection
• any woman requiring level 2 or 3 critical care (or obstetric high-dependency unit-type care) because of severe sepsis or suspected severe sepsis
• a clinical diagnosis of severe sepsis (two or more of the following) –
  • a temperature of > 38 °C or < 36 °C measured on two occasions at least 4 hours apart
  • a heart rate of > 100 beats per minute measured on two occasions at least 4 hours apart
  • a respiratory rate of > 20 breaths per minute measured on two occasions at least 4 hours apart
  • a white cell count of > 17 × 10⁹/l or < 4 × 10⁹/l or with > 10% immature band forms, measured on two occasions.

Perineal wound infection

This was defined according to the Public Health England Surveillance definition of surgical site infection (SSI),33 which falls under the following headings.

Superficial incisional infection

Superficial incisional infection is a SSI that occurs within 30 days of surgery, involves only the skin or subcutaneous tissue of the incision and meets at least one of the following criteria:

• purulent drainage from superficial incision
• culture of organisms and pus cells present in fluid/tissue from superficial incision or wound swab from superficial incision
• at least two symptoms of inflammation – pain, tenderness, localised swelling, redness, heat AND EITHER (1) incision deliberately opened to manage infection OR (2) clinician’s diagnosis of superficial SSI.

Deep incisional infection

Deep incisional infection is a SSI involving the deep tissues (i.e. fascial and muscle layers) within 30 days of surgery (or 1 year if an implant is in place), and the infection appears to be related to the surgical procedure and meets at least one of the following criteria:

• purulent drainage from deep incision (not organ space)
• organisms from culture and pus cells present in fluid/tissue from deep incision or wound swab from deep incision
• deep incision dehisces or deliberately opened and patient has at least one symptom of fever or localised pain/tenderness
• abscess or other evidence of infection in deep incision – re-operation/histopathology/radiology
• clinician’s diagnosis of deep incisional SSI.

Organ/space infection

Organ/space infection is a SSI involving the organ/space (other than the incision) opened or manipulated during the surgical procedure, that occurs within 30 days of surgery and the infection appears to be related to the surgical procedure and meets at least one of the following criteria:

• purulent drainage from drain (through stab wound) into organ space
• organisms from culture and pus cells present in fluid or tissue from organ/space or swab from organ/space
• abscess or other evidence of infection in organ/space – re-operation/histopathology/radiology
• clinician’s diagnosis of organ/space infection.

Perineal pain/use of pain relief/dyspareunia/ability to sit comfortably to feed the baby/need for additional perineal care/breastfeeding

This was identified using standard questions developed for the HOOP study34 and the PREVIEW study.35

Maternal quality of life

This was elicited by the EuroQol-5 Dimensions, five-level version (EQ-5D-5L), questionnaire.36

Hospital bed stay/hospital and general practitioner visits/wound breakdown/antibiotic side effects

This was identified through specific questions included in the maternal questionnaire.

Sample size

Observational studies of operative vaginal birth estimate postnatal infection to occur in between 2% and 16% of women.29 The single existing trial of antibiotic prophylaxis at operative vaginal birth found a 4% rate of postnatal infection.10 We therefore used this more conservative estimate of the maternal infection rate following operative vaginal birth. We assumed an estimated relative risk reduction of 50% in this rate with antibiotics to 2% in the treatment arm. The single trial relating to operative vaginal birth suggests a greater reduction than this, but this rate of reduction is based on that seen in the more robust antibiotic prophylaxis for caesarean section trials.6 We used the absolute difference (i.e. a reduction from 4% to 2%) to calculate the sample size. To detect such a difference with 90% statistical power at the two-sided 5% level of significance required 1626 participants per group; with an estimated 5% loss to follow-up, the trial required 1712 participants per group, which was a total of 3424 women.

Statistical analyses

Statistical analyses were carried out according to a prespecified statistical analysis plan finalised and agreed prior to unblinding. In summary, demographic and clinical data were summarised with counts and percentages for categorical variables, means [standard deviations (SDs)] for normally distributed continuous variables and medians (with interquartile or simple ranges) for other continuous variables. Women were analysed in the groups to which they were randomly assigned, comparing the outcome of all women allocated to active treatment with all those allocated to placebo, regardless of deviation from the protocol or treatment received (referred to as the intention-to-treat population). Binary outcomes were analysed using risk ratios, while continuous outcomes were analysed using either a mean or a median difference, as appropriate. As randomisation did not involve stratification or minimisation, the primary analysis was based on unadjusted estimates of effect. Two-sided statistical testing was performed throughout. A 5% level of statistical significance was used for analyses of the primary outcome, and 1% for secondary outcomes. 95% CIs are presented for analyses of the primary outcome and 99% CIs for secondary outcomes.

Sensitivity analyses

Four planned sensitivity analyses were carried out:

1. examining the primary outcome restricted to women who had not received antibiotics in the 7 days prior to birth, in case any masking of a prophylactic effect occurred by inclusion of pre-treated women
2. examining the primary outcome excluding women prescribed antibiotics (other than the trial intervention) within 24 hours of birth in case these women were already infected prior to administration of the intervention
3. a repeat analysis of the primary outcome restricted to women whose primary outcome was obtained based on data obtained between 6 and 10 weeks after women had given birth
4. a sensitivity analysis including centre as a random effect.

Data collection

Data were collected at hospital discharge by extraction of information from a woman’s clinical records by the research midwife and at 6 weeks post partum by telephone interview with a research midwife to obtain information on the primary outcome. Following this, each woman was sent a postal or online questionnaire (as preferred by each woman) for collection of data on secondary outcomes.

Text reminders for completion of the questionnaire were sent and women were offered the option for telephone completion in the event of a delayed response to ensure a high response rate. Information about any hospital re-admissions and results of any microbiological investigations when a woman indicated that she had a suspected or confirmed infection were collected from hospital records by the site research midwife.

Basic demographic, medical and obstetric details were collected for all women, including details of any antibiotic treatment in the 7 days before women gave birth and the indication for antibiotic prescription.

Data on maternal anaphylaxis were collected up until hospital discharge. Data on other secondary outcomes were collected at 6 weeks post partum using standard instruments, when possible, as detailed below.

Surgical site infection (perineal)

This was identified using the items included in the Public Health England ’surgical wound healing post discharge questionnaire’.33

Perineal pain/use of pain relief/dyspareunia/ability to sit comfortably to feed the baby/need for additional perineal care/breastfeeding

This was identified using standard questions developed for the HOOP (Hands On Or Poised) study34 and the PREVIEW (PREVention of diabetes through lifestyle intervention and population studies In Europe and around the World) study.37

Maternal quality of life

This was elicited by the EQ-5D-5L.36

Hospital bed stay/hospital and general practitioner visits/wound breakdown/antibiotic side effects

This was identified through specific questions included in the maternal questionnaire, to include medications prescribed, critical care admission, hospital inpatient admissions, outpatient visits, and midwife and practice nurse visits. All side effects of the IMP were recorded.

Indications for maternal antibiotic prescription and causes of infection were independently coded by two clinical reviewers, blinded to allocation, into the following categories:

• perineal wound-related infection (including deep infections, such as abscess)
• endometritis/uterine infection
• urinary tract infection with systemic features (e.g. pyelonephritis)
• other systemic infection (sepsis)
• uncomplicated lower urinary tract infection (urinary tract infection with no other features specified)
• breast infection/mastitis
• respiratory infection (e.g. chest/throat)
• other infection (e.g. meningitis)
• other reason (non-infective)
• unknown reason.

Any discrepancies or disagreements between the two reviewers were resolved by discussion or referral to a third reviewer.

A ’blinded end-point review’ (BER) was conducted to derive the primary outcome for women who returned a questionnaire but did not complete a telephone interview. Two clinical reviewers, who were blinded to allocation, independently assessed each questionnaire to see if there was any evidence that might indicate that the woman had experienced the primary outcome (i.e. evidence of any condition that might have led to antibiotic prescription, endometritis or any hospital re-admission). Any discrepancies or disagreements between the two reviewers were resolved by discussion or referral to the BER committee chairperson. If there was a potential, but not definite, indication that a woman had experienced the primary outcome, information about any hospital re-admissions and the results of any microbiological investigations were collected from hospital records by the site research midwife.

Adverse event reporting

The safety reporting window for this trial was from administration of intervention to 6 hours post administration or discharge (whichever was sooner). Non-serious adverse events were not routinely recorded as the IMP is a licensed product being given at a standard dose. However, adverse events that were part of the trial outcomes were recorded in the case report form.

All serious adverse events (SAEs) were reported immediately, at least within 24 hours, except the following SAEs (which were not considered to be causally related to the trial intervention because these events occurred prior to the trial intervention being administered):

• birth defect/congenital anomaly
• hypertensive disorder of pregnancy (e.g. pre-eclampsia/eclampsia)
• post-partum haemorrhage with onset before the intervention.

Development safety update report

A development safety update report was submitted each year to the Competent Authority, the Ethics Committee and the sponsor.

Health-care resource use and cost analysis

As an additional analysis, not specified in the trial protocol, we conducted a within-trial comparison of health-care resource use and associated costs between trial arms. The perspective of the analysis was that of the UK NHS and the following categories of resource use were collected using the telephone interview and postal questionnaire at 6 weeks post delivery: antibiotic use (co-amoxiclav prophylaxis and new prescriptions), health-care professional visits [general practitioner (GP), nurse, midwife, health visitor and district nurse], outpatient hospital visits and all-cause hospital re-admissions.

Unit costs for co-amoxiclav were collected and estimated using the British National Formulary 2017.38 We did not have details of the antibiotics used for new prescriptions and, therefore, assumed that all new prescriptions were co-amoxiclav, a low-cost generic antibiotic, so that our estimate of costs was conservative. Although some women may have received more than one course of antibiotics, we assumed that all women who had a new prescription of antibiotics had a single 7-day course of co-amoxiclav with three daily doses, again so that our estimate of costs was conservative. Unit costs for GP visits and nurse/midwife services at general practice were collected from Unit Costs of Health and Social Care 2017.39 For other health-care resource categories, the unit cost was taken from NHS Reference Costs 2017/18.40 More details on sources and associated estimates of unit costs (expressed in 2017/18 Great British pounds) for the different categories of resource use are presented in Appendix 2, Tables 17 and 18. The costs associated with each category of resource use were estimated by multiplying resource use by unit costs.

We calculated the mean and SD of resource uses (number of visits for health-care professional and outpatient hospital visits, number of days for re-admissions) and costs for each category by trial arms. We also calculated overall mean (SD) costs at 6 weeks following delivery by adding up all individual cost categories, together with the cost for intervention (a single dose of intravenous co-amoxiclav). Mean differences in health-care resource use and costs were calculated and associated 99% parametric CIs were estimated.

The main analysis was based on complete cases among women who returned the postal questionnaire at 6 weeks post delivery and completed questions on usage for each specific health-care resource category. We compared the characteristics of women who returned the postal questionnaire with those who did not using the t-test for continuous variables and Pearson’s chi-squared test for categorical variables. A sensitivity analysis using multiple imputation with chained equations was conducted to evaluate the impact of missing data on our complete-case results. Fifty values were imputed for each missing data point by specifying separate regression models for each variable with missing data. Within each model, the remaining variables with missing data were used as predictors along with selected patient characteristics [maternal age, gestational age at randomisation in weeks, ethnic group, body mass index (BMI), any previous pregnancies of ≥ 22 weeks’ gestation, labour induction, episiotomy in current delivery, perineal tear in current delivery]. Imputation was performed using prediction mean matching (using five nearest neighbours) and for each trial arm separately.

Governance and monitoring

A monitoring plan for the trial, including responsibilities, was developed prior to the start of recruitment. Remote monitoring was carried out, with at least one monitoring assessment of each site. Site monitoring visits were carried out if remote monitoring identified any discrepancies.

The trial was supervised on a day-to-day basis by a Project Management Group. A TSC was convened comprising an independent chairperson, four other independent members, a patient and public involvement representative, the NPEU CTU Director and the chief investigator. A Data Monitoring Committee (DMC), independent of the applicants and of the TSC, reviewed the progress of the trial annually and provided the TSC with advice on the conduct of the trial.

Summary of changes to the trial protocol

The initial planned primary outcomes were defined as follows.

Confirmed or suspected maternal infection within 6 weeks of delivery, as defined by one of:

• a new prescription of antibiotics
• confirmed systemic infection on culture
• endometritis as defined by the US CDC.31

Following an interim review of the data by the DMC in February 2017, a change to the primary outcome was recommended to exclude women who were prescribed antibiotics for unrelated indications. This was because of concerns that the noise arising from antibiotic prescriptions for unrelated indications would mask the effect of the intervention. The primary outcome was therefore revised to the following.

Confirmed or suspected maternal infection within 6 weeks of delivery, as defined by one of:

• a new prescription of antibiotics for presumed perineal wound-related infection, endometritis or uterine infection, urinary tract infection with systemic features or other systemic infection
• confirmed systemic infection on culture
• endometritis as defined by the US CDC.31

Indications for antibiotic prescription were coded independently as described in Data collection by two clinically qualified staff, based on responses to the telephone questionnaire, the infection form or the postal questionnaire. The revised primary outcome could, therefore, be derived for all women already recruited into the trial and no additional processes were needed.

A summary of the other changes made to the original protocol is presented in Appendix 3.