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Chapter 2: The Prevalence of Neonatal Abstinence Syndrome

This chapter looks at the methods used to recruit infants of substance misusing mothers to the study and the rates of NAS found using the new community based health visitor assessment.

Recruiting to the study and measuring rates of NAS

Methods:

Identifying substance misusing mothers:

• Any infant born to an opiate using mother fulfilled the criteria for recruitment to the study. Active case finding of mothers was used to identify (more completely) infants born to substance misusing mothers. Eligible mothers were identified by their referrers, their own admission of substance misuse, urine screening or by the clinical diagnosis in the baby.

• Many of these mothers also took additional substances such as cocaine, amphetamines, ecstasy and methadone. Infants of mothers who used cannabis or benzodiazepines alone were excluded because there was little means of their being identified and if known, to distinguish between the complex overlap between social substance use and problem substance misuse.
• Notifications (of maternal substance misuse) continued to be shared by the multidisciplinary antenatal service and were also provided to the Study Nurse. The Study Nurse visited the neonatal unit and the postnatal wards on a daily basis (and developed a close working relationship with the maternity hospital staff). The peripheral maternity units were visited to explain the study and make personal contact. Links were made with health visitor groups, community midwives meetings, and substance misuse services. All GPs were provided with written information and contact numbers. These links were essential in case finding and for the next phase of the study, namely delivering the new intervention.

Recruitment to the study:

• Once an eligible mother was identified, a carefully planned recruitment process followed. Difficulties in recruitment were anticipated because of sensitivities about stigmatisation, confidentiality, criminal issues and child protection. To ensure consistency in the approach to the family, information given and receiving consent, only the Study Nurse recruited.
• The mother's own midwife informed her about the study and advised that the Study Nurse would offer to see her. The midwife confirmed with the mother that the Study Nurse could be given the mother's name. Fathers were included if they were available or wished at a later date to participate: in most cases parental rights resided with the mother. Once the Study Nurse was informed of an eligible infant, she visited the parent(s) in the postnatal ward or Neonatal Unit. The parent(s) were given the information sheet, the study was described and questions answered. The parent(s) were given 24 hours to consider the study, unless the infant was being discharged and the parents were willing to give consent that day. Two consent forms were obtained: one was filed in the infant's medical notes and one was given to the parent(s).
• Parents who did not wish to participate in the study were reassured that their infant would be offered an appointment at clinic, and would receive exactly the same hospital service as that available before the inception of the study. Prevalence was recorded for all infants irrespective of whether the parents agreed to participate in the study.

Identifying infants with NAS:

• In order to determine the prevalence of continuing and delayed onset neonatal abstinence syndrome in infants of substance misusing mothers, a community based structured health visitor assessment was developed ( see Appendix 1). Recruitment of infants into the study took place between June 2002 and December 2003; all infants were followed up to the age of six months.

• Infants with NAS were identified in the Aberdeen Maternity Hospital and the prevalence compared to previous audit data. The diagnosis was made by the nursing and medical staff using the scoring system developed by Finnegan et al in 1975, modified in 1986.

• The Study Nurse recorded information about infants with NAS on her daily visits to the NNU and the postnatal wards. The infant's medication was also noted: this was initially morphine, with phenobarbitol being added as required.

The project team met weekly to discuss individual infants and their follow up, to address issues about recruitment or assessment, and to review the overall progress of the study.

Results

Prevalence of infants of substance misusing mothers

• 110 infants fulfilled the study criteria during the recruitment period from June 2002 to the end of December 2003. 72 infants were recruited to the study giving a recruitment rate of 65.5%.

Rate of NAS

110 infants of substance misusing mothers were born during the 18 month recruitment period, of whom 84 were admitted to the Neonatal Unit ¹. Of these 9 were preterm ² and showed no signs of NAS and the other 75 were admitted because of NAS. These figures, when compared with those for the years 2000 and 2001 (see Table 1), suggest an increasing trend.

The problem of mothers misusing substances in the Grampian area would appear to be a contributor to the higher rate of preterm births. Maternal drug use should be considered when planning future neonatal services for the area. Maternal substance misuse is known to contribute to the prematurity rate, with Slattery and Morrison (2002) reporting a rate of 25%. In the study group the rate was 21.8% compared with the overall preterm birth rate of 8.5% which occurred in the two overlapping years of the study.

Table 1 shows that the proportion of study infants of substance misusing mothers who develop NAS has increased from 57.3% to 68.2% when compared with the 2000 year cohort. The reasons for this are likely to be complex. As access to antenatal services continues to improve, better and earlier identification may occur. Mothers with a continuing and deteriorating drug habit and who are known to the paediatric service because of a previously affected infant are having further infants. There may also be an increasing severity of maternal substance misuse in the Grampian population.

Table 1: NAS incidence in the study period compared with previous years

Measuring the incidence of continuing NAS

Methods

The identification of infants of substance misusing mothers, including those with NAS, provided the basis for the next phase of the study, namely the use of a new assessment tool to determine Continued or Delayed Onset NAS in the community.

Prior to discharge from the neonatal unit or the postnatal wards the Study Nurse discussed the infant's follow up (whether or not recruited) with the relevant consultant. The most usual criterion for hospital review was discharge on medication or continuing mild NAS. Parents of all non-recruited infants were offered a hospital follow-up clinic appointment which was made and the parent(s) notified prior to discharge.

During the study period there was a gradual change in practice in the neonatal unit, with more infants being prescribed phenobarbitol as an adjunct to morphine, and more being discharged home on treatment. This was intended to promote earlier discharge from the neonatal unit and to reduce any continuing symptoms of NAS.

For all families that had consented to participate in the study, the Study Nurse contacted the family health visitor to implement the new assessment. The protocol was explained (and equipment and forms provided) and a joint home visit arranged with the Study Nurse and family health visitor (this allowed for family health visitor training on the assessment tools). Continuing and Delayed Onset NAS were evaluated in the community using a further modification of the Finnegan score ( Appendix 1). This community NAS score excluded the signs specific to the neonatal period or to technical hospital observation. It is a subjective tool, which required information from parental reporting in addition to direct nursing observation. Only one statement was chosen from each section on the form ( Appendix 1) with the exclusion of 'Feedings', 'Fluid Intake' and 'Excoriations' where it could be necessary to choose more than one statement.

Infants were assessed by the family health visitor using the community NAS score at 2, 4, 8, 12 and 24 weeks from the date of birth. (If the infant was still in the maternity hospital the Study Nurse completed the early assessments). Once assessments and the relevant forms had been completed, they were posted to the Study Nurse and entered on to the database. The Study Nurse continued to advise and support the family health visitors.

If the Study Nurse or family health visitor identified an infant with a community NAS score of >8, Continuing or Delayed Onset NAS was suspected. An urgent appointment was offered at the hospital follow up clinic, usually for the next working day. The community score was repeated in the hospital follow up clinic, a database form completed, and treatment adjusted or if necessary prescribed. During the hospital appointment the infant was examined, growth and development were checked and, if needed, referrals made to other services. A plan for future reviews was agreed with the parent(s).

Results

Attendance rates for NAS services

All recruited infants were seen by their own health visitor. 17 of the non-recruited (38) group, were never seen at the hospital follow up clinic. 8 of these were either discussed with their health visitor or follow up was arranged at other specialist clinics. One baby had died and 2 had moved away from the area. The corrected rate of infants never seen was 5.5% (6/110).

At specialist NAS follow-up hospital out patient appointments

A total of 61 infants were offered appointments in hospital clinics for follow up. 202 appointments were arranged and 115 were attended, an attendance rate of 57% (compared with an attendance rate of 51% in 2001). Half of these infants were discharged after their first visit. Of those infants who were offered Royal Aberdeen Children's Hospital clinic visits, only 23% required more than two visits.

At the first outpatient visit:

• Several parents gave a history of continued NAS, which had resolved, meaning the opportunity for intervention and support had been missed.
• Other infants showed no signs of NAS at first hospital follow up; these infants were discharged i.e. their visit was probably unnecessary.

A considerable number of children were not seen by the follow up service and little was known of their progress. Given the possibility of continuing NAS and the vulnerability of these children and parents, this was not satisfactory (Oei et al, 2001). Data were available on all these aspects of the previous service from the audits of 2000 and 2001: these were compared with results from this study.

Health Visitors assessments

In contrast, out of the 72 recruited infants in the study, only 10 were involved in missed appointments: of 360 HV assessments required, 346 were completed (a completion rate of 96%).

Prevalence of continuing NAS

• 42/110 infants were discharged home on treatment with phenobarbitol ³. This is 42 of the 75 infants who initially had NAS.

Using the new intervention of the structured community follow up for these infants, 42 out of the whole study group (110) were found to have continuing NAS after being discharged home. The rate had increased in the study period compared with previous years. This could be due either to better identification of clinical signs as a result of the use of an assessment tool, or to more prolonged withdrawal due to more serious maternal drug problems. The study figures provide a secure baseline against which to evaluate future trends.

Delayed onset NAS

• Of the 26 infants who were asymptomatic initially 12 developed delayed onset NAS, and 7 required treatment. The high scores found by the health visitor assessments were confirmed by the hospital follow up clinic in all infants, confirming the accuracy of the assessment tool when used by nursing staff (or possibly by non-medical personnel) working in the community. The infants were identified at different assessment points as shown below in Table 2.

Identification of these infants with Delayed Onset NAS allowed prompt referral to the hospital follow up clinic. Parents or foster parents (carers) were able to join professionals in deciding whether or not treatment was needed. Medication was not prescribed in 5 cases as the carers felt the symptoms were improving and did not warrant treatment.

Table 2: Infants with Delayed Onset NAS and assessment point when identified

Table 3: Rates of Continuing /Delayed NAS in the study period compared with previous years

* Statistically, very significant
** Statistically, highly significant
The new tool therefore increased very significantly the diagnosis rate of both delayed and continuing NAS.

Duration of Treatment for Continued or Delayed onset NAS

In this group of 54 infants only 49 needed treatment. The majority of treated infants (37/49) had ceased treatment and were asymptomatic by the age of 20 weeks. A significant proportion did require longer treatment and follow up (12/49). The longest period of treatment was 151 days.

Summary

• During the study period (June 2002-December 2003) 110 infants were born to substance misusing mothers; 75 of these were admitted to the neonatal unit with NAS symptoms;
• 72 of the 110 eligible infants were recruited to the study;
• The new community based assessment developed for this study was completed by the family health visitor (or the Study Nurse if the infant was still in hospital) on the 72 infants recruited to the study. This was completed at 2, 4, 8, 12 and 24 weeks after birth and provided a community NAS score;
• For the study period, attendance rates at hospital appointments for infants identified as being born to substance misusing mothers was 57%; completion of Health Visitor community assessments was 96%;
• The new community assessment identified (and therefore offered appropriate treatment to):

i. 42 infants with continuing NAS
ii. 12 infants with delayed onset NAS.

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