Aim of this study is to analyze determinants of breech presentation using information from two regional databases of Lombardy (Italy) including data on consecutive singleton breech and vertex deliveries occurred in the Region, between January 2010 and December 2015. Breech presentation occurred in 3.8% of all single deliveries. Main determinants of breech presentation at birth were: gestational age and birth weight (the lower, the higher the incidence of breech presentation), maternal age (the older the mother, the higher the risk of breech presentation), parity (the frequency of breech decreased with increasing parity) and previous cesarean section. Breech presentation resulted more frequent after assisted reproduction procedures.
The most common cause of breech presentation is preterm delivery [
Among maternal characteristics, older age, primiparity, and previous cesarean section have been suggested as risk factors for breech delivery, but their role is still controversial.
Only few population-based studies have been published on risk factors for breech presentation [
In Lombardy (an Italian region of about 10 million inhabitants), a standard form is used to register all births and neonatal discharges from public and private hospitals. Diagnoses of admission and discharge are codified according to the International Statistical Classification of Diseases 9th edition—Clinical Modification (ICD-9-CM), Italian version. For each delivery, both maternal and neonatal demographic and clinical data are reported (i.e., maternal country of birth, maternal cause of admission, neonatal sex, congenital abnormalities detected at birth or within the period of hospital admission). After delivery, a specific form is filled by midwifes including information on current pregnancy and its clinical course, on maternal characteristics and medical history, on type of conception (spontaneous/not spontaneous), on delivery (including fetus presentation), and on maternal outcome at birth.
Data on all deliveries and births in Lombardy from January 2010 to December 2013 and from January 2014 to December 2015 were included in the present analysis; multiple gestations were excluded from the analysis as they are characterized by significantly increased risk of noncephalic presentation; deliveries with transverse and oblique presentation were excluded.
Comparisons have been made between breech deliveries and vertex deliveries. Potential risk factors have been chosen based on previous literature. Crude Odds ratios (OR) with corresponding 95% confidence intervals (CI) were computed. Further, multivariate estimates, derived using unconditional logistic regression, fitted by the method of maximum likelihood, were also computed. Small for gestational age (SGA) at birth was defined according to previous publications [
According to Italian law, analysis of anonymous routine database do not require Ethics Committee application.
In the study period 450,104 deliveries were reported. After exclusion of stillbirths (493), twins (14346), newborns with gestational age <23 weeks or missing (537), and presentation different from vertex and breech (
Table
Distribution and corresponding odds ratios of cases with vertex and breech presentation according to selected factors. Lombardy, Italy.
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<25 | 43408 | 97.0 | 1344 | 3.0 | 1+ | 1+ | ||||
25–29 | 90850 | 96.6 | 3165 | 3.4 | 1.12 | 1.05 | 1.20 | 1.23 | 1.15 | 1.31 |
30–34 | 140980 | 96.1 | 5750 | 3.9 | 1.32 | 1.24 | 1.40 | 1.50 | 1.41 | 1.60 |
35–39 | 110433 | 95.9 | 4763 | 4.1 | 1.39 | 1.31 | 1.48 | 1.67 | 1.56 | 1.79 |
40+ | 29461 | 95.3 | 1448 | 4.7 | 1.59 | 1.47 | 1.71 | 1.84 | 1.69 | 2.00 |
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University | 118047 | 96.1 | 4844 | 3.9 | 1+ | 1+ | ||||
High school degree | 179993 | 96.1 | 7367 | 3.9 | 1.00 | 0.96 | 1.04 | 1.08 | 1.04 | 1.12 |
Primary/intermediate school or no education | 116464 | 96.5 | 4247 | 3.5 | 0.89 | 0.85 | 0.93 | 1.09 | 1.04 | 1.14 |
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Italian | 293243 | 95.9 | 12379 | 4.1 | 1+ | 1+ | ||||
Foreign | 123054 | 96.7 | 4146 | 3.3 | 0.80 | 0.77 | 0.83 | 0.95 | 0.91 | 0.99 |
Albanian | 11036 | 96.6 | 388 | 3.4 | 0.83 | 0.75 | 0.92 | |||
Chinese | 6277 | 97.5 | 163 | 2.5 | 0.62 | 0.53 | 0.72 | |||
Egyptian | 7189 | 97.2 | 205 | 2.8 | 0.68 | 0.59 | 0.78 | |||
Moroccan | 16206 | 97.1 | 478 | 2.9 | 0.70 | 0.64 | 0.77 | |||
Romanian | 14371 | 95.8 | 623 | 4.2 | 1.03 | 0.95 | 1.11 | |||
Other | 67975 | 96.7 | 2289 | 3.3 | 0.80 | 0.76 | 0.83 | |||
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0 | 210014 | 95.2 | 10689 | 4.8 | 1+ | 1+ | ||||
1 | 147313 | 97.2 | 4239 | 2.8 | 0.57 | 0.55 | 0.59 | 0.47 | 0.45 | 0.49 |
2+ | 51874 | 97.5 | 1311 | 2.5 | 0.50 | 0.47 | 0.53 | 0.40 | 0.37 | 0.43 |
Previous parity in unidentified number | 6932 | 96.1 | 282 | 3.9 | 0.80 | 0.71 | 0.90 | 0.55 | 0.48 | 0.63 |
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Nulliparous | 210014 | 95.2 | 10689 | 4.8 | 2.15 | 2.07 | 2.24 | NE | ||
0 | 133385 | 97.7 | 3156 | 2.3 | 1+ | 1+ | ||||
1 | 38316 | 95.5 | 1821 | 4.5 | 2.01 | 1.89 | 2.13 | 1.81 | 1.70 | 1.93 |
2+ | 7808 | 96.4 | 291 | 3.6 | 1.58 | 1.39 | 1.78 | 1.60 | 1.40 | 1.82 |
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No | 294791 | 96.1 | 11849 | 3.9 | 1+ | 1+ | ||||
Yes | 121506 | 96.3 | 4676 | 3.7 | 0.96 | 0.92 | 0.99 | 1.05 | 1.01 | 1.09 |
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Spontaneous conception | 408332 | 96.2 | 15959 | 3.8 | 1+ | 1+ | ||||
Assisted conception | 7965 | 93.4 | 566 | 6.6 | 1.82 | 1.67 | 1.98 | 1.14 | 1.04 | 1.25 |
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23-24 | 176 | 69.0 | 79 | 31.0 | 12.81 | 9.82 | 16.71 | 16.08 | 12.18 | 21.22 |
25-26 | 294 | 70.0 | 126 | 30.0 | 12.23 | 9.92 | 15.07 | 14.27 | 11.42 | 17.82 |
27-28 | 468 | 73.6 | 168 | 26.4 | 10.24 | 8.58 | 12.23 | 11.45 | 9.48 | 13.83 |
29-30 | 770 | 79.8 | 195 | 20.2 | 7.22 | 6.17 | 8.46 | 8.07 | 6.82 | 9.54 |
31-32 | 1532 | 86.9 | 230 | 13.1 | 4.28 | 3.72 | 4.92 | 4.67 | 4.03 | 5.42 |
33-34 | 3948 | 88.6 | 506 | 11.4 | 3.66 | 3.33 | 4.02 | 3.76 | 3.41 | 4.16 |
35-36 | 14626 | 91.3 | 1393 | 8.7 | 2.72 | 2.57 | 2.88 | 2.68 | 2.52 | 2.84 |
37+ | 394483 | 96.6 | 13828 | 3.4 | 1+ | 1+ | ||||
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Male | 215446 | 96.5 | 7781 | 3.5 | 1+ | 1+ | ||||
Female | 200847 | 95.8 | 8743 | 4.2 | 1.21 | 1.17 | 1.24 | 1.22 | 1.18 | 1.26 |
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No | 377022 | 96.4 | 14181 | 3.6 | 1+ | 1+ | ||||
Yes | 39271 | 94.4 | 2343 | 5.6 | 1.59 | 1.52 | 1.66 | 1.34 | 1.27 | 1.40 |
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416297 | 96.2 | 16525 | 3.8 |
In some cases the sum does not add up to the total because of missing values.
NE = Item risk not estimated because of collinearity with “previous deliveries” variable.
°Including all the above listed variables.
The risk of breech presentation was lower in parous women: the adjusted OR was 0.47 (95% CI 0.45–0.49) for women with one previous delivery and 0.40 (95% CI 0.37–0.43) for women with two or more previous deliveries compared to nulliparous women.
Breech presentation was significantly associated with a history of previous cesarean section (
Further, we conducted the same analysis in the subset of both vertex and breech births occurring at 37 weeks of gestation or more (Table
Distribution and corresponding odds ratios of cases with gestational age ≥37 weeks, with vertex and breech presentation, according to selected factors. Lombardy, Italy.
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<25 | 41162 | 97.4 | 1113 | 2.6 | 1+ | 1+ | ||||
25–29 | 86512 | 97.0 | 2690 | 3.0 | 1.15 | 1.07 | 1.23 | 1.23 | 1.14 | 1.32 |
30–34 | 134076 | 96.5 | 4862 | 3.5 | 1.34 | 1.25 | 1.43 | 1.46 | 1.36 | 1.57 |
35–39 | 104283 | 96.3 | 3965 | 3.7 | 1.41 | 1.31 | 1.50 | 1.58 | 1.47 | 1.71 |
40+ | 27365 | 96.0 | 1155 | 4.0 | 1.56 | 1.44 | 1.70 | 1.62 | 1.48 | 1.78 |
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University | 112538 | 96.4 | 4144 | 3.6 | 1+ | 1+ | ||||
High school degree | 170611 | 96.5 | 6183 | 3.5 | 0.98 | 0.95 | 1.02 | 1.06 | 1.02 | 1.11 |
Primary/intermediate school or no education | 109644 | 97.0 | 3446 | 3.0 | 0.85 | 0.82 | 0.89 | 1.07 | 1.01 | 1.12 |
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Italian | 278611 | 96.4 | 10453 | 3.6 | 1+ | 1+ | ||||
Foreign | 115872 | 97.2 | 3375 | 2.8 | 0.78 | 0.75 | 0.81 | 0.95 | 0.91 | 0.996 |
Albanian | 10544 | 97.0 | 323 | 3.0 | 0.82 | 0.73 | 0.91 | |||
Chinese | 6021 | 97.7 | 140 | 2.3 | 0.62 | 0.52 | 0.73 | |||
Egyptian | 6855 | 97.6 | 166 | 2.4 | 0.65 | 0.55 | 0.75 | |||
Moroccan | 15508 | 97.5 | 393 | 2.5 | 0.68 | 0.61 | 0.75 | |||
Romanian | 13365 | 96.3 | 509 | 3.7 | 1.02 | 0.93 | 1.11 | |||
Other | 63579 | 97.2 | 1844 | 2.8 | 0.77 | 0.74 | 0.81 | |||
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0 | 198363 | 95.6 | 9065 | 4.4 | 1+ | 1+ | ||||
1 | 140420 | 97.6 | 3515 | 2.4 | 0.55 | 0.53 | 0.57 | 0.41 | 0.39 | 0.43 |
2+ | 48980 | 98.0 | 1010 | 2.0 | 0.45 | 0.42 | 0.48 | 0.35 | 0.33 | 0.38 |
Previous parity in unidentified number | 6566 | 96.5 | 235 | 3.5 | 0.78 | 0.69 | 0.89 | 0.48 | 0.42 | 0.56 |
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Nulliparous | 198363 | 95.6 | 9065 | 4.4 | 2.30 | 2.20 | 2.40 | NE | ||
0 | 127389 | 98.0 | 2536 | 2.0 | 1+ | 1+ | ||||
1 | 35829 | 95.9 | 1530 | 4.1 | 2.15 | 2.01 | 2.29 | 1.41 | 1.31 | 1.50 |
2+ | 7132 | 97.0 | 221 | 3.0 | 1.56 | 1.35 | 1.79 | 0.96 | 0.82 | 1.11 |
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No | 279954 | 96.6 | 9990 | 3.4 | 1+ | 1+ | ||||
Yes | 114529 | 96.8 | 3838 | 3.2 | 0.94 | 0.90 | 0.98 | 1.03 | 0.99 | 1.07 |
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Spontaneous conception | 387371 | 96.7 | 13423 | 3.3 | 1+ | 1+ | ||||
Assisted conception | 7112 | 94.6 | 405 | 5.4 | 1.64 | 1.48 | 1.82 | 1.03 | 0.93 | 1.14 |
FIVET | 2234 | 95.1 | 116 | 4.9 | 1.50 | 1.24 | 1.81 | |||
ICSI | 2875 | 94.2 | 177 | 5.8 | 1.78 | 1.53 | 2.07 | |||
Other | 2003 | 94.7 | 112 | 5.3 | 1.61 | 1.33 | 1.95 | |||
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Male | 203560 | 97.0 | 6397 | 3.0 | 1+ | 1+ | ||||
Female | 190920 | 96.3 | 7430 | 3.7 | 1.24 | 1.20 | 1.28 | 1.23 | 1.22 | 1.31 |
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No | 382060 | 96.6 | 13290 | 3.4 | 1+ | 1+ | ||||
Yes | 8294 | 95.1 | 423 | 4.9 | 1.54 | 1.47 | 1.62 | 1.25 | 1.19 | 1.32 |
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394483 | 96.6 | 13828 | 3.4 |
In some cases the sum does not add up to the total because of missing values.
1+ Reference category
NE = Item risk not estimated because of collinearity with “previous deliveries” variable.
In this study, the main factors associated with a higher risk of breech presentation were: lower gestational age, low birth weight (SGA newborn), increasing maternal age, primiparity, a history of previous caesarean section, pregnancy after ART procedures, a history of previous spontaneous/induced abortion, and female sex. Most of these conditions remained significantly associated to breech delivery also in the subgroup of births at 37 weeks of gestation or more.
In particular, low birth weight, low gestational age, advanced maternal age, primiparity and a female baby emerged as independent risk factors for breech delivery in several previous papers [
Before discussing the results, potential limitations of our study should be considered.
Fetal position at delivery and relative risk factors were usually derived from birth and/or hospital records collected mainly for administrative reasons and not for scientific purposes. However, fetal presentation is an easy information to collect and it has a notable relevance in the indication, for example, of cesarean section. Further, the reported frequency of breech presentation was largely consistent during the study period and with data reported for other Italian Regions and World Countries [
Another limitation of this paper is that we have no information about factors such as maternal uterine anomalies, recurrence risk of breech presentation, and hereditary predisposition to breech presentation at birth: all these conditions are actually associated with an increased risk of breech presentation [
Among the strengths of this study, we should consider the population-based design and the large sample size. The large number of records gave us the possibility to adjust for several risk factors and it allowed more precise risk estimates. Moreover, to our knowledge, this is the first population-based contribution on this topic coming from Southern Europe and referring to a recent historical period.
Apart from preterm birth, it has been shown that the risk of breech presentation is associated with lower parity and increasing maternal age. In the study by Wiktop et al., a prenatal ultrasound was performed in more than 7000 pregnant patients and they observed that a noncephalic fetus at 35 weeks, in nulliparous women, had twice the chance of not turning in vertex position at delivery, compared to multiparous patients [
A history of cesarean section represents a risk factor for several adverse obstetric outcomes and it has already been described as a predicting condition for breech presentation [
An interesting finding of our analysis is the observation that breech presentation occurs more frequently in ART pregnancies. This association has been previously reported [
Our analysis showed that the risk of breech position is significantly higher in SGA children and that small fetal size at birth represents a risk factor independently of gestational age. This result was confirmed in the subgroup analysis of breech birth after 37 weeks. Moreover, the fact that most breech births (>80%) occurs at term supports our observation [
Different hypothesis have been so far proposed to clarify this consistent association between fetal size and breech position. One explanation is that some smaller fetuses might have a degree of intrauterine growth restriction (IUGR) and, in this situation, a low amniotic fluid amount or a less active fetus may reduce the chance of turning into cephalic position; however, birth weight and breech birth remain inversely associated up to the 90th percentile and a very few of these fetuses would have a IUGR. Another explanation is that a higher fetal weight, mainly distributed to fetal head, forced the fetus into cephalic position in uterus and it may help a spontaneous vertex version [
In conclusion, this study showed that breech presentation is associated with several maternal and fetal characteristics. Our results are in line with previous reported data but with the peculiarity of being referred to a large specific population in Southern Europe (Lombardy, Italy). These findings suggest that different, and still not well-defined, biologic mechanisms may be involved in determining breech position, including both genetic and acquired environmental factors. Due to the large sample size, this population-based study offers quantitative estimates of the role of different risk factors with narrow confidence intervals.
Assisted reproduction technology
Cesarean section
Small for gestational age
Intrauterine growth restriction
External cephalic version.
Data supporting the results reported in this article can not be found in public datasets as its owned by Regione Lombardia (The Health Authority).
The authors declare that they have no conflicts of interest.
The analysis was conducted in the framework of the Ricerca Corrente 2018.