Congenital heart disease (CHD) is the general medical term for heart defects that are present from birth. CHD accounts for up to 10% of neonatal deaths and up to 40% of all infant deaths when left undiagnosed (Thangaratinam et al, 2012). The incidence rate for CHD in the UK is estimated to be 7/1 000, or one in every 145 babies born (Brown et al, 2006; Thangaratinam et al, 2012). The term critical congenital heart disease (CCHD) refers to a subgroup of CHD (25%) which can cause serious and life-threatening problems including cardiac arrest and death. Infants with CCHD (Table 1) require surgery or other procedures within the first 28 days of life to ensure survival (Wren et al, 2008; Thangaratinam et al, 2012).
Table 1. Critical congenital heart disease defects
| Coarctation of aorta |
| Double-outlet right ventricle |
| Ebstein's anomaly |
| Hypoplastic left heart |
| Interrupted aortic arch |
| Pulmonary atresia (with intact septum) |
| Severe tetralogy of fallot: pulmonary atresia type |
| Total anomalous pulmonary venous connection |
| Transposition of great arteries |
| Tricuspid atresia |
| Truncus arteriosus |
Fetal circulation
The circulation of the blood in the fetal heart differs from that of a newborn infant. The fetus obtains oxygen from the maternal circulation through the placenta. The fetal circulation and heart are designed to send most of the oxygenated blood directly to the body organs mostly bypassing the lungs. The fetal heart has a small communication at atrial level (patent foramen ovale [PFO]) and a temporary vessel connecting the aorta to the main pulmonary artery (ductus arteriosus [DA]). The direction of the blood flow in utero is from the right to left heart with enough blood flowing to the lungs to allow growth before birth. The DA and PFO usually close within the first few days of life after birth.
Patent ductus arteriosus
In CCHD, postnatally, the DA is usually the only route that supplies blood to the lungs or to the rest of the body, depending on the type of defect. While there is a PDA, infants with CCHD may not demonstrate any clinical signs. However, the consequences following closure of the PDA in CCHD can be catastrophic with generalised hypoxemia leading to multi-organ failure, acidosis, cardiac arrest and death, if unrecognised.
Where CCHD has been diagnosed antenatally, the use of an intravenous prostaglandin infusion early in the postnatal period usually keeps the PDA open until the baby can be safely transferred to a paediatric cardiothoracic surgical centre for a catheter-based or surgical procedure to stabilise the heart before additional procedures later in life. Considering these problems, there are benefits of either antenatal or early postnatal detection of CCHD before the baby deteriorates (Wren et al, 2008).
Antenatal ultrasonography
Advances in antenatal ultrasonography and fetal echocardiography over the past few years have increased the prenatal CHD detection rate to approximately 60% (Uzun et al, 2018). However, cases of CCHD can still be missed even in specialist centres. Some structural lesions such as valvular stenoses may progress after the anomaly scan is performed at around 20-weeks' gestation. Ultrasonographic skills depend on individual sonographer experience and may vary between hospitals (Ewer, 2014).
Newborn screening
The term ‘newborn screening’ refers to investigations or assessments that can identify babies affected by a condition which, if detected and treated in a timely manner, may prevent disability or death early in life (Kemper, 2019). The newborn and infant physical examination (NIPE) is currently the only recommended national UK screening assessment for the detection of CHD. The efficacy of the physical examination alone for the detection of CCHD is quite low missing between 30%–50% of CHD. The level of experience of the examiner and/or the initial absence of symptoms are factors that contribute to missed diagnoses of CCHD.
Pulse oximetry
The pulse oximeter was invented in the early 1970s and is now widely used in all fields of acute medicine. It was a major technological advance; providing a reliable and non-invasive means for the measurement of the peripheral oxygen saturation in the blood. In fact, many health professionals refer to it as the fifth vital sign (Nitzan et al, 2014) along with heart rate, respiratory rate, temperature and blood pressure.
It can determine a patient's oxygen status using transmitted light through a translucent extremity site. However, it does have limitations. The accuracy of the pulse oximetry depends on factors including: skin pigmentation, anaemia, haemoglobinopathies, altitude/athmospheric oxygen pressure and poor technique (Nitzan et al, 2014).
Neonatal pulse oximetry screening
The use of pulse oximetry as a newborn screening tool involves measuring the oxygen saturations in newborn infants. Many studies are available worldwide advocating the use of NPOS as an additional screening tool for CCHD detection. There are differences in how saturations are measured; some studies advocate simultaneous measurement of pre-ductal (right hand) and post-ductal (lower limb) saturations. Others suggest a post-ductal saturation measurement is adequate. Many countries have adopted some form of universal NPOS as part of the newborn assessment (Thangaratinam et al, 2012). It has also been highlighted that NPOS can aid in the early identification of other conditions including sepsis and respiratory disease (Ewer et al, 2011; Jawin et al, 2015).
In 2015, a UK NPOS pilot study was conducted under the auspices of the National Screening Committee with the participation of 13 NHS Trusts including this unit (Evans, 2017). Following this study, concerns were raised regarding high false-positive rates, feasibility, cost-effectiveness and acceptability (Evans, 2017). In the UK, the routine use of NPOS is not yet recommended in current national screening guidelines.
A recent Cochrane systematic review and meta-analysis showed that the NPOS is a highly specific and moderately sensitive test for the detection of CCHD with low false-positive rates when performed after 24 hours of life. The review concluded that current evidence supported the introduction of routine NPOS for the improved detection of CCHD in asymptomatic newborn infants before discharging from hospital (Plana et al, 2018).
Postnatal assessment in this maternity unit
The NIPE of infants on the postnatal wards is conducted by different staff groups in this tertiary unit (The Rosie Maternity Unit, Cambridge University Hospitals NHS Trust): neonatal medical staff, neonatal advance nurse practitioners and by a cohort of midwives who have undergone formal training to perform the NIPE.
All infants admitted to the neonatal intensive care unit (NICU) are examined and have NPOS performed by neonatal staff. In addition, NICU staff have to perform the NIPEs on the postnatal ward for infants who 1) are <36 weeks of gestation 2) receiving nasogastric feeding 3) treated for symptomatic suspected sepsis with IV antibiotics 4) have a birthweight of <2.5 kg and 5) there are safeguarding concerns. All the remaining infants have their NIPEs performed by trained midwives. Currently, over 50 midwives have been trained to perform the NIPE, providing a seven-day service and performing over 50% of NIPE in this hospital.
Universal NPOS was introduced to this maternity unit in January 2014 with an agreed practice guideline for the assessment of infants on the postnatal wards and in the midwifery led birthing centre. Simultaneous measurement of pre-ductal and post-ductal saturations is used in this unit. NPOS is conducted separately to the NIPE. Prior to its introduction, all midwives and healthcare assistants received formal NPOS competency training delivered by a lead midwife and neonatal consultant (Singh et al, 2016). There were drop-in sessions to address any problems or concerns. A formal service evaluation of NPOS screening was conducted but no specific feedback from midwifery staff was obtained. NPOS has remained part of the wider postnatal assessment in this unit. All new midwives and now healthcare assistants starting in the Trust receive training to perform NPOS as part of their induction. All staff receive regular feedback on cases detected with NPOS during their on-going annual mandatory training.
NPOS is performed by midwives using MASIMO SET RAD 5 (Neuchatel Switzerland) oximeters. There are currently three pulse oximeters in use: one on the postnatal ward, one on the delivery ward and one in the community. The practice of reusable poseys or use of tape is advocated. The trust policy is that newborn infants are screened between the age of 4–8 hours of life as part of the postnatal assessment. If a positive NPOS result is obtained, midwives refer the baby to the NICU team for further management and investigation. This initial neonatal review may first take place on the postnatal ward by the NICU team who currently use portable pulse oximeters (Covidien NELLCOR OxiMax PM 10, Medtronic, Korea) which are a different model to the ones used routinely by midwives. Importantly, NPOS and the NIPE may not be performed at the same time or by the same midwife.
Midwifery survey
Objective
The primary aim of our study was to assess midwives' views and experience in performing NPOS prior to and over the four-year period since its introduction.
Methods
Survey design
An electronic survey of 10 questions was sent out via email to all midwives working in the unit (Appendix 1). The anonymity of the respondents was optional. The survey remained open for a six-week period (February 2018 to April 2018). Email reminders were circulated on a weekly basis to all the midwives.
The questionnaire requested feedback on the ease of NPOS utilisation prior to its introduction and four years after NPOS was implemented. On the feasibility scale, questions were scored on a scale from 1–10 with ‘1’ being ‘easy to perform with no disruption to care’ and ‘10’ being ‘difficult with problems including delayed discharges’. Other questions explored the respondents' perception on the usefulness of NPOS, their recollection of positive screening outcomes, the location of where they performed screening and whether they had additionally been trained to perform the NIPE. The final question was open-ended, prompting the midwives to give free-text comments to support their answers about their overall experience of using NPOS.
Data analysis
Data was collated in an Excel spreadsheet and later analysed using the Wilcoxon Signed Rank test, pairing each respondent's rankings before and after NPOS introduction. We used the Wilcoxon calculator on the Social Science Statistics Website (Socscistatistics.com, 2019).
Additional analysis included the percentage of the responding midwives who perform NPOS and also had been formally trained to undertake the NIPE. For those who had at least one positive NPOS result, we requested information about the final diagnosis following the positive NPOS result as per their recollection. Based on the free text replies, the comments were further categorised into three groups: positive, negative and neutral.
Results
Participants
Total respondents were 102 with complete responses from 99 out of 236 midwives (42% response rate). Two midwives missed one of the two main ranking questions and the third did not respond to most questions including whether they feel NPOS is an important screening tool.
Statistical analysis
The average scale rankings of 3.46 (pre) and 2.38 (post) indicate that the midwives were very positive about the NPOS after having performed it, compared to their initial perceptions (z-value of -4.5575; p-value of <0.001) (Figure 1 and Figure 2). A large proportion (n=96; 97%) of responding midwives stated that they routinely perform NPOS and 39% (n=38) of responding midwives had at least one positive screening result (Figure 3).
Figure 1. Scale of difficulty prior (pre) to newborn pulse oximetry screening introduction. 1=easy with no disruption to the service, 10=difficult with problems and delays to discharge 
Figure 2. Scale of difficulty four years after (post) newborn pulse oximetry screening introduction. 1=easy with no disruption to the service, 10=difficult with problems and delays to discharge 
Figure 3. Recollection of positive newborn pulse oximetry screening (NPOS) results
The diagnosis of a ‘cardiac anomaly’ was reported by 10 midwives. Other important conditions identified following a positive NPOS included sepsis, diaphragmatic hernia and situs inversus (Table 2). Some midwives reported more than one positive screen and gave additional information in the ‘other’ section. Nearly all of the respondents (99%) felt that the NPOS was an important screening tool. Of the midwives, 47% who routinely perform NPOS in the maternity unit were also trained and able to perform the NIPE.
Table 2. Recollection of diagnosis following positive newborn pulse oximetry screening (NPOS)
| Causes of positive NPOS | Number of midwives who reported |
|---|---|
| Cardiac anomaly | 10 |
| Sepsis | 24 |
| Diaphragmatic hernia | 3 |
| Situs inversus | 2 |
| Do not know outcome | 2 |
In terms of the location where they performed NPOS, 85% of the responding midwives reported they conducted screening only in the hospital. Of the responding midwives, 13% conducted screening in both in-hospital and community settings with the remaining 2% performing screens only in the community. In the hospital, the delivery unit was the place where most of the midwives performed NPOS (73%; 71 midwives out of 97), followed by the postnatal ward, the birthing centre and the recovery unit in a descending order.
In the free-text comment section, answers were divided in three categories: positive, negative and neutral based on the content. Positive comments from the midwives included that NPOS was quick, very easy-to-use and parents felt reassured by it. Negative comments included access to pulse oximeters and the need for more oximeters particularly in the community setting. They also reported some delays in medical reviews by the neonatal staff following positive screening. A few midwives felt the pulse oximeters used on the postnatal ward appeared to give lower readings compared to those used by neonatal staff on the NICU.
Discussion
We believe this study is the first UK qualitative study formally evaluating midwives' experience and level of acceptance in using NPOS in a tertiary maternity unit.
Our results show that the midwives in our unit are generally very positive about the NPOS and the test has been well-accepted since its introduction and is now seen as part of the routine postnatal assessment in line with, for example, the standard hearing screening test. While NPOS has identified cases on CCHD as expected in line with the published evidence from other studies, it has also helped in the earlier detection of other potentially life-threatening conditions such as sepsis and diaphragmatic hernia that could have resulted in postnatal collapse.
Limitations of our study
As in every questionnaire-based study, there is potential social desirability bias. Additionally, in our study, we asked the midwives to report positive outcome diagnoses and events which happened up to four years ago which may pose a risk of recollection bias.
No formal midwifery surveys had previously been conducted before or after the introduction of NPOS in 2014. The ranking scores presented in this paper are retrospective perceptions of the challenges that staff had felt in 2014 compared with current practice. The pre-implementation score could be considered to be of limited value four years later. However, one could also speculate that if staff are happy about screening now that they might underestimate their original pre-screening scores.
The total response rate of 42% appears a low value; which would indicate that the study might suffer from a non-response bias. We hypothesise two main reasons for a low response rate. Firstly, this being a busy tertiary maternity unit, some staff may have had insufficient time to complete the survey. Additionally, staff may suffer ‘survey fatigue’ as they are regularly asked to complete hospital surveys via their work email addresses. However, Beebe et al (2018) would suggest that a 42% response rate from a web-based study is an acceptable result and they regard web-based surveys as an increasingly viable method of data collection.
This was a single-centred study in a tertiary maternity unit where a high proportion of midwifery respondents have also received additional training to perform the NIPE and perhaps they could be considered to be more informed about potential neonatal problems. Further studies in non-tertiary maternity units with a different midwifery skill mix might provide different results.
Conclusion
Our single-centre survey shows that the NPOS is a well-accepted screening tool by the responding midwives. It is regarded as important and an easy-to-perform assessment which has become well-established in this maternity unit. We believe our results add further to the already strong evidence for the wider use of the NPOS as an additional screening test for the detection of CCHD in maternity units across the UK.