Australian and New Zealand Journal of Obstetrics and Gynaecology 2006; 46: 341–344

© 2006 The Authors 341Journal compilation © 2006 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists

Blackwell Publishing Asia Original ArticleUltrasound assessment of fetal presentation

Longitudinal ultrasound assessment of fetal presentation: A review of 1010 consecutive cases

Alice J. Sophia FOX and Michael G. CHAPMANUniversity of New South Wales, New South Wales, Australia

AbstractBackground: Abnormal presentation (detected in the early third trimester) causes concern for pregnant women andtheir carers. Definitive ultrasound-based data on the risk of persistence of abnormal presentation is lacking to allowappropriate counselling. Comparison of pregnancy outcome was made on the basis of maternal age at delivery.

Methods: Notes of 1010 women (426 primigravidae, 584 multigravidae), with singleton pregnancies, confinedbetween 1997 and 2005 were reviewed to extract: (i) the gestation based on 18–20-week ultrasound in conjunctionwith the patient’s recorded last menstrual period, and (ii) the presentation of each antenatal visit from 28+weeks until delivery. Previous obstetric history, maternal age, mode of delivery, birthweight and outcomes werealso documented.

Results: At 28–30 weeks, 216 babies presented abnormally. By 38+ weeks, 54 persisted as either a breech or atransverse lie. Thus, an abnormal presentation in the early trimester carries a 22.2% chance of persisting at term.Continuance of abnormal presentation at each subsequent week of the third trimester increased the risk of aCaesarean delivery at term. Conversely, in only six cases, a cephalic presentation at 28–30 weeks converted to abreech or other presentation during the third trimester – a risk of 0.75%.

Conclusion: These statistics provide a useful tool in advising women of the chances of abnormal presentation atterm based on the presentation at various stages of the third trimester, and prepare them for the potential require-ment of a Caesarean section.

Key words: antenatal, breech presentation, longitudinal study, pregnancy, third trimester.

Introduction

A number of procedures have become established as part ofthe routine of an antenatal visit during pregnancy. Amongthese is the palpation and recording of the presenting part ofthe expectant woman from around 28 weeks gestation. It isstandard teaching that in the early third trimester a signifi-cant percentage of babies have malpresentations.1 Over thecourse of the third trimester, an increasing number of babiespresent as a cephalic presentation.

For a pregnant woman, any abnormality that is detectedin her antenatal course creates concern. The finding of amalpresentation (such as breech presentation) can producesuch anxiety. With an increasing awareness of the implica-tions of the term breech study, that is, that vaginal breechdelivery is less safe than Caesarean section;1 pregnantwomen are understandably concerned if a breech, transverseor oblique presentation is discovered, even in the early partof the third trimester.2

Reassurance is then provided, relying on statistics collectedover many generations of midwives and obstetricians based

on abdominal palpation, which is notoriously inaccurate inthe early third trimester. Textbooks report incidences of 15–25% of all babies presenting by the breech at around 30 weeksgestation and declining to 3–4% at term.2–6 With the currenteducated patient seeking specific risk assessment of her chancesof a Caesarean section at each antenatal visit, accurate dataon the prognosis in relation to the presentation would beof benefit.

Since 1997, it has been the practice of one of the authors(MC) to scan patients at each antenatal visit in his private rooms.This has been a reassurance for the patients who seem to enjoyseeing their baby at each visit. At the time of the scan, pres-entation and fetal heart movements are documented in the

Correspondence: Professor Michael G. Chapman, University of New South Wales, c/o: Division of Women and Children’s Health, St George Hospital, Kogarah, NSW 2217, Australia. Email: m.chapman@unsw.edu.au

DOI: 10.1111/j.1479-828X.2006.00603.xReceived 20 December 2005; accepted 05 April 2006.

A. J. S. Fox and M. G. Chapman

342 © 2006 The AuthorsJournal compilation © 2006 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists; 46: 341–344

notes. Amniotic fluid volume is also assessed. The whole processtakes less than 1 min. We have conducted a retrospective reviewof the case notes of all patients delivered over this time toprovide a longitudinal study of ultrasound-determined fetalpresentation and its change during the third trimester.

Methods

The obstetric notes of women confined between 1 January1997 and 31 August 2005 were located from the filing sys-tem as part of an audit of MC’s practice at St George PrivateHospital. These notes were then reviewed to extract (i) thegestation based on 18–20-week ultrasound in conjunctionwith the patient’s recorded last menstrual period, and (ii) thepresentation at each antenatal visit from 28 weeks untildelivery. Maternal age, mode of delivery, birthweight andoutcomes were extracted. The previous obstetric history wasalso documented. All patients were delivered in the laboursuite in either St George Private or St George Public Hospital.Details of the deliveries were obtained from the hospital records.The data were collated on an Excel spreadsheet.

For this study, the inclusion criteria were a singletonfetus, documented ultrasound examinations conducted fromthe 28th week of pregnancy and every fortnight or weeklythereafter, and delivery at > 35 weeks gestation. For patientswith an abnormally presenting fetus, it was the obstetrician’spreference to not perform external cephalic version (ECV).

This study was part of retrospective audit of privatemedical records and no patient-identifying information was

used in the analysis. No investigations that were not the nor-mal practice of clinical care were undertaken. On this basisformal ethical committee approval was not sought.

This study was undertaken as part of a master’s year ofAF, who was a self-funding student.

Results

There were 1010 live singleton pregnancies; 584 were towomen who had had a previous delivery (multigravidae) and426 were to women in their first full-term pregnancy (primi-gravidae). At 28–30 weeks, 78.6% of the babies were foundto be in a cephalic presentation and 21.4% presented as abreech or transversely. By 38+ weeks, the presentations were94.7% cephalic and 5.3% breech or transverse. Table 1details the change in fetal presentation at each gestational ageperiod. It can be seen that, of the 216 breech and otherpresentations at 28 weeks, 162 (75%) converted to a cephalicpresentation by 38 weeks. This reveals that there was a 25%risk of persisting abnormal presentation. Of these cases, 95%had a Caesarean section delivery.

In six cases, a cephalic presentation converted to a breechor other presentation at some point in the third trimester. Thisoccurred in three primigravidae and three multigravidae,representing 11.1% of all abnormally presenting cases. Ulti-mately, in the 216 abnormally presenting cases at 28–30 weeks,breech or transverse position persisted in 54 to term. Of these54 cases, six mothers (all of whom were aged ≥ 35 years)were noted to have had a fibroid uterus (1 primigravida,

Table 1 Change in fetal presentation from week 28 to week 38+ at each gestational age. Figures in parentheses are percentages (n = 1010)

Gestational age (weeks)

Fetal presentation (n = 1010)Normal (cephalic) Abnormal (breech, transverse, oblique)

Primigravidae Multigravidae Total Primigravidae Multigravidae Total

28–29 352 442 794 (78.6) 74 142 216 (21.4)30–31 378 497 875 (86.6) 53 82 135 (13.4)32–33 393 520 913 (90.4) 36 61 97 (9.6)34–35 398 539 937 (92.8) 30 43 73 (7.2)36–37 399 549 948 (93.9) 28 34 62 (6.1)38 – Term 401 555 956 (94.7) 25 29 54 (5.3)

Table 2 The change in presentation with increasing gestational age for those with normal (cephalic) and abnormal (breech, transverse,oblique) at 28–29 weeks gestation. Figures in parentheses are percentages of the original presentation

Gestational age (weeks)

Fetal presentationNormal (cephalic) Abnormal (breech, transverse, oblique)

Primigravidae Multigravidae Total Primigravidae Multigravidae Total

28–29 350 (100.0) 438 (100.0) 788 (100.0) 74 (100.0) 142 (100.0) 216 (100.0)30–31 350 (100.0) 437 (99.8) 787 (99.9) 53 (71.6) 81 (57.0) 134 (62.0)32–33 347 (99.1) 436 (99.5) 783 (99.4) 33 (44.6) 60 (42.3) 93 (43.1)34–35 347 (99.1) 436 (99.5) 783 (99.4) 30 (40.5) 43 (30.3) 73 (33.8)36–37 347 (99.1) 436 (99.5) 783 (99.4) 28 (37.8) 33 (19.2) 61 (28.2)38 – Term 347 (99.1) 435 (99.3) 782 (99.2) 22 (29.7) 26 (18.3) 48 (22.2)

Ultrasound assessment of fetal presentation

© 2006 The Authors 343Journal compilation © 2006 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists; 46: 341–344

five multigravidae). Table 2 shows the outcome of normal(cephalic) or abnormal (breech, transverse, oblique) presen-tation at each gestation age.

Table 3 compares the maternal age of primiparous andmultiparous women with normal or abnormal fetal lie orpresentation at 38+ weeks. While women ≥ 35 years have aslightly higher risk of having a breech presentation or a trans-verse lie, this difference is not statistically significant.

In this practice, which sees a high percentage of infertilitycases due to the interests of the author, the mode of deliverywas skewed towards Caesarean section. The overall Caesareansection rate was 38.2%.

Discussion

This present study provides definitive longitudinal data touse in counselling patients in relation to the presentationof the fetus at various stages of the third trimester and thelikely outcome.

Not surprisingly, the frequency of abnormal presentationwas highest in the earliest documented gestational age group(216 cases at 28–30 weeks). The frequency of abnormalpresentation dropped rapidly from 30 to 31 weeks to a nadirof 5.3% after 38 weeks. Although gestational age is the singlegreatest determinant of fetal presentation, other causes havebeen ascribed, including uterine abnormalities (includingfibroids), abnormal placental implantation and age. Of the54 births with abnormal presentations, six mothers werefound to have had a fibroid uterus (predominately occurringin multigravid women). As can be seen in Table 3, there wasa trend towards more abnormal presentations with age ≥ 35years, but this trend was not significant as stated by Jollyet al.7

In a primigravida, an abnormal presentation at 28–30weeks leads to 30% chance of an abnormal presentation at38+ weeks, whereas for multiparae it is less at 18%. By 33weeks, an abnormal presentation provides a 66% risk ofabnormal presentation at term for a first pregnancy, and 43%for multiparae. Obviously, if an aggressive practice of ECV

is undertaken the percentages are likely to be halved, parti-cularly in multiparae.8,9

However, a cephalic presentation at 28–32 weeks resultsin a 0.85% risk of abnormal presentation in primiparae, anda 0.68% risk in multiparae by 38 weeks.

Conclusion

Abnormal presentation (breech, transverse, oblique) is oneof the more common obstetric complications that can occurin an otherwise straightforward pregnancy and one thatnaturally engenders concern to mothers regarding the healthand birth of their baby. With access to ultrasound scanningequipment, the majority of all non-cephalic fetal presentationsshould be diagnosed in the early third trimester, allowingeffective management and counselling by obstetricians usingthe statistics we have determined.

The significant result of this study is the definition of thesubstantial chances of abnormal presentation at term whenan abnormal presentation is found early in the third trimes-ter. This will be useful in advising patients and preparingthem for the potential requirement of a Caesarean section.

Acknowledgements

The pregnancy studies were the private patients of ProfessorChapman (MC). Alice Fox (AF) undertook the case recordof data extraction.

The plan for the study was primarily that of MC, withthe help of AF, who was involved in the data analysisand the drafting of the paper. MC undertook the editingof the paper.

This study was undertaken as part of a Masters year ofAF who was a self-funding student.

References

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2 Hannah M, Hannah W, Hewson S, Hodnett E, Saigal S, Wil-lan A. Planned Caesarean section versus planned vaginal birthfor breech presentation at term: a randomised multicentretrial. Term Breech Trial Collaborative Group. Lancet 2000; 356:1375–1383.

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Table 3 The age of (primiparous and multiparous) mothers withnormal or abnormal fetus lie at ≤ 34 weeks and at ≥ 35 weeksgestation. Figures in parentheses are percentages of each group(overall, primiparae and multiparae)

Age (years)≤ 34

(n = 747)≥ 35

(n = 263)

Normal presentation (cephalic) 708 (94.8) 248 (94.3)Primiparae 321 (94.4) 80 (93.0)Multiparae 387 (95.1) 168 (94.9)Abnormal presentation (breech, transverse lie)

39 (5.2) 15 (5.7)

Primiparae 19 (5.6) 6 (7.0)Multiparae 20 (4.9) 9 (5.1)

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344 © 2006 The AuthorsJournal compilation © 2006 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists; 46: 341–344

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9 Impey L, Pandit M. Tocolysis for repeat external cephalicversion in breech presentation at term: a randomised,double-blinded, placebo-controlled trial. BJOG 2005; 112:627–631.