Routinely offering all pregnant women an ultrasound scan in their third trimester could reduce rates of undetected breech presentation by more than two-thirds, according to a new study led by St George's University Hospital NHS Foundation Trust in London and Norfolk and Norwich University Hospital NHS Foundation Trust in Norwich.
In the study, published in PLOS Medicine, The team noted that the incidence of breech presentation at term is 3-4% and breech vaginal birth is associated with an increase in perinatal mortality and morbidity, as well as maternal morbidity. Women with known breech presentation at term can be effectively counselled about their options – external cephalic version, planned vaginal birth, or elective Caesarean section – and the inherent risks and perceived benefits of each.
Missed Breach Presentations 'Unacceptably High'
However, they said, there are "unacceptably high rates of missed breech/non-cephalic presentations", and there is "substantial evidence that clinical examination is not accurate enough for determination of foetal presentation". For example, the sensitivity of abdominal palpation is poor, at just 50-70%.
The researchers set out to study whether implementing policies of either routine third trimester ultrasound by sonographers (at St. George's), or point-of-care ultrasound (POCUS)with a handheld device by trained midwives (at Norwich), had been effective in reducing the proportion of undiagnosed term breech presentations when comparing pre- and post-screening epochs.
Due to the rarity of adverse outcomes, they explained, they employed Bayesian regression analysis with informative priors – a statistical tool that permits updating previous findings with new data to generate new evidence. This enabled them to update prior estimates from a similar previous study with new data from their own study to yield likelihood estimates.
Women with multiple pregnancy, preterm birth prior to 37 weeks, congenital abnormality, and those undergoing planned Caesarean for breech presentation were excluded.
The observational retrospective study also assessed the effects of routine ultrasound on related adverse perinatal outcomes.
Undiagnosed Breech 'Reduced Drastically' by Ultrasound
Undiagnosed breech presentation – either women presenting in labour or with ruptured membranes at term who were subsequently discovered to have a breech presentation, or women attending for induction of labour at term and found to have a breech presentation before induction – "reduced drastically in the post-screening epoch" following the implementation of the screening policies, they reported.
The primary outcome of the proportion of all term breech presentations that were undiagnosed decreased from 14.2% to 2.8% with routine third trimester sonographer ultrasound, and from 16.2% to 3.5% with POCUS.
Bayesian regression analysis with informative priors showed that the rate of undiagnosed breech was 71% lower after the implementation of the policy of universal ultrasound (relative risk [RR] 0.29; 95% credible interval [CrI] 0.20 to 0.38) with a posterior probability greater than 99.9%.
Along with the lowered rate of undiagnosed breech, the emergency Caesarean rate was reduced from 12.9% to 11.5% (P=0.029) comparing the periods before and after the introduction of the screening policies. However the rate of elective Caesarean delivery was higher during the universal scan epoch (13.0% versus 12.0%, P=0.029).
In addition, analysis of the secondary outcomes showed associated improvements in short-term adverse perinatal outcomes among pregnancies with diagnosed breech presentation at term, including reductions in:
- Low Apgar score (<7 at 5 minutes)
- Hypoxic ischaemic encephalopathy
- Unexpected neonatal unit admission
- Extended perinatal mortality rate
Policy Change Could Lead to a 'Significant Reduction' in Undiagnosed Breech Births
The team concluded that use of a policy of either routine third trimester ultrasound by sonographers or routine third trimester POCUS by trained midwives was associated with "a significant reduction in the proportion of all breech presentations that were undiagnosed at term", when compared with standard antenatal care.
They added that other studies had shown that universal third trimester ultrasound would "virtually eliminate" the proportion of all term breech presentations that were undiagnosed.
"Accurate knowledge of foetal presentation at term is crucial for optimal antenatal and intrapartum care," they said. "Routine third trimester scan by a sonographer/clinician or use of POCUS by trained midwives can both achieve this objective.
"Although evidence suggests that a planned breech vaginal birth may be offered after careful case selection and counselling, a large proportion of maternity units in the UK and worldwide lack skilled providers for vaginal breech births. Antenatal identification of breech presentation would allow healthcare providers to offer unbiased information such that pregnant women feel empowered to make an informed decision and have a positive birth experience."
They also noted that "the major obstacles to routine third trimester scan policy include the costs incurred", and that a National Institute for Health Research Health Technology Assessment review had suggested that handheld portable ultrasound might readily close this gap as a low-cost device that antenatal care providers like midwives could to detect foetal presentation with minimal training.
The number needed to scan to prevent one case of undiagnosed breech presentation was 255 (95% CI 192 to 376), they said.
While the cost-effectiveness of POCUS needs to be explored further for feasibility, "a policy of using POCUS in community clinics and the labour ward by healthcare providers, after a short period of training, appears to be as effective as a policy of routine third trimester formal departmental ultrasound".
Offering Options for Breach Presentation Reduces Morbidity
Asked to comment by Medscape News UK, Professor Alexander Heazell, clinical director of the Tommy's Stillbirth Research Centre in Manchester, said: "This is a welcome study that confirms what an earlier study from the UK has already found, that scanning is a reliable way to detect breech presentation, and that offering options to manage breech presentation reduces morbidity.
"The National Institute for Health Research recently had a call-out for a trial to address this research question to provide higher grade evidence; until then we should wait before instituting routine ultrasound scans to determine fetal presentation."
Also commenting to Medscape News UK, Elizabeth Duff, senior policy advisor at the National Childbirth Trust (NCT), said: "An additional scan in late pregnancy to detect breech positions could be helpful to women, enabling them to have more time to make decisions about their birth plan and discuss this with caregivers.
"However, many maternity services are currently severely understaffed and under pressure, and sadly in reality, many hospitals may not be able to offer an additional scan at this current time."
The authors declared no external funding for the study. AK is a Vice President of the Royal College of Obstetricians and Gynaecologists, and a Trustee (and the Treasurer) of the International Society of Ultrasound in Obstetrics and Gynecology. AK has lectured at and consulted in several ultrasound-based projects, webinars, and educational events.