The trial's main limitation is the lack of blinding of participants and carers as all women attending MLU were known to be in the study intervention group. Those allocated to CLU care were not masked either, as the blinding of participants allocated to control groups in such situations has been criticised . Unavoidable potential bias thus exists for both randomised groups. Assessors for certain outcomes, such as laboratory tests, were blinded to study group. The outcome 'blood loss' was estimated, as per hospital protocols, and amounts are thus imprecise in both groups.
The focus of this study was on the relative effects of midwife-led care provided in the setting of an alongside MLU. As such, this study combines elements of midwife-led care including continuity of care in pregnancy and birth with settings for birth i.e. the MLU. We acknowledge that not all midwife-led models of care will take place in an alongside MLU nor, indeed, in a home-like environment . Further, not all alternative settings for birth will provide midwife-led care . Differentiating the effects of midwife-led care from the setting of that care is not possible within this study, a limitation that is not unique to our study. The potential confounding effect of practice settings such as MLU on the outcomes of midwife-led care is complex as are the interrelationships between philosophy and continuity of care .
In this study, the percentage of women transferring from MLU to CLU care in the antenatal period, in particular, is higher (at 45%) than quoted rates of 24% in some UK centres . The permanent transfer rates of 13% intrapartum and 0.5% postnatally are approximately the same as the 12-15% and up to 8% reported in the UK . Some of the reasons for permanent transfer such as induction of labour and premature labour should not automatically preclude women from being transferred back to MLU care in the postnatal period, if appropriate. Quality reviews and audits of reasons for transfer would assist in reducing these high rates to more normal levels.
The strength of this trial lies in its size, and in its serendipitous conduct prior to the introduction of MLUs, in Ireland, due to the enlightened vision of the (then) North-Eastern Health Board in planning service innovation formally within the framework of a clinical trial. The MidU study is likely to have good external validity, as the setting of the trial is similar to many birthing units in the UK and other countries. Identifying eligible women was done using clinical criteria of 'low risk' similar to, or sometimes more stringent than, those used in many other centres, and 43% of women met those criteria. As 50% of these women also agreed to join the trial, there is a large enough proportion to warrant introducing a new scheme. Furthermore, the MLU intervention described in the trial protocol and implemented in the trial itself for women allocated to the MLU arm can be regarded as standard practice for MLU care in the two study sites, since the relevant procedures were established in the context of the MidU trial. Similarly, the control intervention in MidU reflects standard practice for women receiving CLU care in these two sites.
We calculated the sample size for the MidU trial using estimates for induction of labour, episiotomy and augmentation of labour. We also calculated the effect sizes that this would allow us to detect for other important outcomes and included this information in the protocol for the trial and within this report. We thus had several "primary outcomes" because complex interventions such as models of maternity care involve a variety of people including pregnant women, practitioners, policy makers and the public, all of whom are likely to be interested in the results of a randomised trial. These people can have different priorities when assessing the evidence from a trial such as MidU, and it is unclear whose priorities should be given prominence by choosing a single primary outcome. This diversity of opinion was confirmed in many discussions before, during and after the trial and, so, by explicitly selecting several primary outcomes, we committed ourselves to making the findings for each of these available in the report of the study, including all adverse outcomes, as we have done here. In this way, we leave it to readers to use their own priorities to decide whether any single outcome, or combination of outcomes, is the most important for their interpretation of the findings of MidU.
The results reported here show that midwife-led care, as practised in this study in an 'alongside' MLU, is as safe as consultant-led care and is associated with less intervention. Women cared for in the MLUs were significantly less likely to receive continuous EFM, or have their labour augmented, with no statistically significant difference in adverse neonatal or maternal outcomes such as low Apgar scores, resuscitation, admission to SCBU, CS, instrumental birth or PPH. Other intervention rates, such as episiotomy and induction of labour, were similar in both groups.
The lower rate of EFM in the MLUs should be seen in the context of knowledge that the predictive ability of abnormal fetal heart rate patterns to identify fetal metabolic acidosis and hypoxic-ischemic encephalopathy is low . The Cochrane Review of continuous cardiotocography (CTG) during labour found that, in 12 trials with more than 37,000 women, continuous EFM was associated with a significant increase in CS rates and instrumental birth with no difference shown in cerebral palsy or neonatal mortality. EFM was, however, associated with a reduction in neonatal seizures . Despite the significantly lower use of EFM in women randomised to MLU, there was no difference in the CS rates between the groups. Although counter-intuitive, this finding is consistent with the Cochrane Review on midwife-led care . The lower rate of instrumental vaginal births is consistent with the Cochrane Reviews on both continuous CTG  and midwife-led care .
Augmentation of labour, through 'active management,' was introduced in the 1970s in Ireland to prevent prolonged primigravid labours and save 60% on birth costs . A review comparing routine care with early amniotomy and oxytocin for delay in first stage spontaneous labour found that early intervention was associated with a modest reduction in CS rates but there was insufficient evidence on maternal or neonatal outcomes . The higher augmentation rates for women in CLU in this study are not associated with a reduction in complications in the fetus or neonate, or with a decrease in operative or instrumental birth rates, and are therefore unnecessary in low-risk women.
Recent editorial commentary in the Lancet recommended that trialists should set their findings in the context of an up-to-date systematic review, in order to acknowledge the place of their results in the world literature . In line with this recommendation, a comparison of MidU primary and some secondary outcome results with the Cochrane Review of midwife-led versus consultant-led care was conducted,  and shows some differences but many similarities. Only those results where the addition of the MidU data did not lead to substantial increases in the I2 statistic for heterogeneity (greater than I2 = 75%) have been presented.
The addition of the MidU findings strengthens the findings of the review, increasing the statistical power of the meta-analyses and changing some results from statistically significant to non-significant for the secondary outcomes of 'antenatal hospitalisation' (RR 0.90 95% CI 0.81, 0.99 I2 = 32% without MidU, to RR 0.96 95% CI 0.89, 1.03 I2 = 49% with MidU); and 'fetal/neonatal loss before 24 weeks' (RR 0.79 95% CI 0.65, 0.97 I2 = 0% without MidU, to RR 0.82, 95% CI 0.67, 1.00 I2 = 0% with MidU). The addition of MidU also changes the results of the meta-analyses from non-significant to significant in favour of MLU for the outcome 'amniotomy' (RR 0.88 95% CI 0.75, 1.04 I2 = 41% without MidU; to RR 0.80 95% CI 0.66, 0.97 I2 = 74% with MidU), and in favour of CLU for the outcome 'shorter mean length of labour' (mean difference 0.27 95% CI -0.18, 0.72 I2 = 0% without MidU to mean difference 0.46 95% CI 0.22, 0.70 I2 = 0% with MidU). As in MidU, four studies included in the Cochrane Review  found significant reduced rates of augmentation of labour in MLUs, but the remaining six showed no difference. Overall, meta-analyses do not show a significant difference in this outcome, with or without the addition of MidU data . In the MidU study, induction of labour, PPH and low Apgar scores were not different between the two groups, in accord with the Cochrane Review findings. The MidU study, in common with eight others in the review, showed a reduction in instrumental birth in MLUs, which was not statistically significant. The increased power available in the Cochrane meta-analysis, before and after addition of the MidU data, continues to show a significant decrease in instrumental birth rates in favour of MLUs . Similarly, the MidU study, in common with five others in the Cochrane Review, showed a non-significant reduction in episiotomies for MLU women. One other study in the review showed no difference, but five showed a statistically significant difference in favour of MLU care. The increased power available in the Cochrane meta-analysis, before and after addition of the MidU data, shows a significant difference in episiotomy rate in favour of MLUs . Consistent with MidU, the Cochrane Review finds no significant difference in 'fetal loss/neonatal death equal to/after 24 weeks' before and after the addition of MidU data.
In summary, MidU adds to the totality of evidence available by substantiating and adding to the results of previous research. The similarity between MidU and other international studies in the Cochrane Review shows that our findings have good generalisability. Further research is necessary into ways of decreasing non-essential interventions for healthy women in normal labour, to increase the normal birth rate for healthy women at low risk to complications.