# Twin pregnancy with the first twin in breech presentation: Survival and neurodevelopmental outcome of preterm infants at a corrected age of 2 years

Camille Dhonneur, Cyril Flamant, Jean-Christophe Rozé, Valérie Rouger, Norbert Winer, Vincent Dochez

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## To cite this version:

Camille Dhonneur, Cyril Flamant, Jean-Christophe Rozé, Valérie Rouger, Norbert Winer, et al.. Twin pregnancy with the first twin in breech presentation: Survival and neurodevelopmental outcome of preterm infants at a corrected age of 2 years. European Journal of Obstetrics & Gynecology and Reproductive Biology, 2026, 317, pp.114868. 10.1016/j.ejogrb.2025.114868. hal-05493245

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Full length article

# Twin pregnancy with the first twin in breech presentation: Survival and neurodevelopmental outcome of preterm infants at a corrected age of 2 years

<figure><img src="image_4.png" /></figure>

Camille Dhonneur<sup>a</sup>, Cyril Flamant<sup>b</sup>, Jean-Christophe Rozé<sup>b</sup>, Valérie Rouger<sup>c</sup>, Norbert Winer<sup>d</sup>, Vincent Dochez<sup>e,†</sup>

## ARTICLE INFO

### Keywords:

- Twin pregnancy

- Breech presentation

- Preterm birth

- Neurodevelopmental outcome

## ABSTRACT

**Objectives:** To compare survival and neurodevelopmental outcomes at 2 years' corrected age for preterm twins (≤33+0 weeks) with the first twin in breech presentation, according to planned mode of delivery (planned vaginal delivery [PVD] vs planned caesarean delivery [PCD]). Secondary objectives were survival at discharge, survival without morbidity at discharge, neonatal outcomes, and maternal morbidity.

**Methods:** We conducted a retrospective cohort study of women with preterm breech first twins born after preterm labour (≤33+0 weeks) at Nantes University Hospital (2008–2019). A propensity score estimated each mother's risk of caesarean. Outcomes (survival at discharge, survival at discharge without morbidity, and survival with normal neurodevelopment at 2 years) were adjusted for gestational age, sex, and propensity score. Sensitivity analyses included multiple imputation for missing data and exclusion of births < 26+0 weeks.

**Results:** Among 413 preterm twin deliveries, 61 women were included: 15 in the PVD group (30 newborns) and 46 in the PCD group (92 newborns). After adjustment for propensity score and gestational age, no significant differences were observed in survival at discharge (aOR 1.9, 95 % CI 0.28–12.7, P = 0.51) or survival without morbidity (aOR 0.3, 95 % CI 0.06–2.21, P = 0.27). Survival with normal neurodevelopment at 2 years trended lower with PVD (aOR 0.3, 95 % CI 0.07–1.22, P = 0.09). Maternal morbidity was higher in the PCD group.

**Conclusion:** Planned mode of delivery did not significantly influence survival in preterm breech-first twins, but confidence intervals were wide. A trend toward poorer neurodevelopment at 2 years was observed after planned vaginal delivery, whereas maternal morbidity was higher after planned caesarean delivery. These findings support individualized decision-making, balancing neonatal and maternal risks.

## Introduction

The incidence of twin gestations has increased over the past 40 years. In 2021, twins accounted for about 3.2 % of all births in France [1]. Twin pregnancies have a higher risk of complications such as preterm birth, foetal growth restriction, and perinatal mortality and morbidity [2]. The risk of preterm birth is 10 times higher for multiple than for singleton pregnancies: in 2021 in France, 5.5 % of singleton births occurred before 37 weeks of gestation, compared with 52.6 % of multiple pregnancies [1]. Determining the safest mode of delivery for twin pregnancy is more

complex than for singletons, since not only gestational age, but also birth order, various presentation combinations, estimated foetal weight, and chorionicity must be considered.

In the French guidelines, which date from 2009, experts concluded that the lack of strong evidence prevented them from recommending one mode of delivery rather than another in twin pregnancies, regardless of gestational age at birth [3]. The more preterm the birth, the more common noncephalic presentation is for first twins (T1); this rate decreases with gestational age [4]. Potential complications of vaginal birth in preterm breech presentations, such as head entrapment or, rarely,

<footnote><sup>a</sup> Nantes Université, CHU Nantes, Service de Gynécologie-Obstétrique, F-44000 Nantes, France</footnote>

<footnote><sup>b</sup> Nantes Université, CHU Nantes, Service de Médecine Néonatale, INSERM, CIC 1413, F-44000 Nantes, France</footnote>

<footnote><sup>c</sup> Réseau de suivi des enfants vulnérables (RSEV-GE/LIFT), Institut National de la Santé et de la Recherche Médicale, CIC 1413, CHU Nantes F-44000 Nantes, France</footnote>

<footnote><sup>d</sup> Nantes Université, CHU Nantes, Service de Gynécologie-Obstétrique, INRAE, UMR 1280 PhAN, F-44000 Nantes, France</footnote>

<footnote><sup>e</sup> Nantes Université, CHU Nantes, Service de Gynécologie-Obstétrique, Mouvement - Interactions - Performance, MIP, UR 4334, F-44000 Nantes, France</footnote>

<footnote>* Corresponding author.
E-mail address: vincent.dochez@chu-nantes.fr (V. Dochez).</footnote>
foetal interlocking may increase perinatal mortality [5]. Morbidity can result from trauma during extraction manoeuvres. On the other hand, caesarean delivery (CD), especially with the potential technical difficulties at low gestational ages, can lead to both short- and long-term maternal morbidity [6]. The frequent need for a vertical uterine incision can have significant implications for the woman's reproductive future.[7] Most recent retrospective studies of mode of delivery for preterm twins excluded cases with the first twin in breech presentation. Several studies examined modes of delivery for first twins in cephalic presentation and failed to find that CDs produced better perinatal morbidity or mortality in these situations [8–12].

Because the literature about the mode of delivery of preterm twin gestations with T1 in breech presentation is sparse, we sought to analyze the association between planned mode of delivery and survival with normal neurodevelopment at a corrected age of 2 years in preterm twin pregnancies in this situation. Secondarily, we examined the association between the planned mode of birth and neonatal outcomes: survival at discharge and survival at discharge without morbidity.

## Methods

Prospectively collected data came from the birth register of a tertiary university hospital center in western France and covered these births from 2008 through 2019. We included all twin pregnancies who delivered between 22<sup>-0</sup> and 33<sup>+0</sup> weeks with T1 breech presentation. We excluded all such pregnancies accompanied by foetal pathology (twin-twin syndrome, any serious malformation, intrauterine death, or medical termination) or intervention during pregnancy (such as embryo reduction for a triplet pregnancy). We also excluded all women for whom a vaginal delivery was impossible because of an emergency (e.g., placental abruption, cord prolapse, metrorrhagia, preeclampsia) or appeared inappropriate (e.g., foetal growth restriction [FGR] with a pathologic Doppler or foetal heart rate abnormalities), or because of our maternity's recommended protocol (systematic caesarean for monochorial monoamniotic twin pregnancies). We thus included all women in preterm labour who did not meet these exclusion criteria. There was no formal institutional protocol for mode of delivery in this situation; the planned mode of delivery was decided on a case-by-case basis by a senior obstetrician according to gestational age, estimated foetal weights, chorionicity, presentation of the second twin (T2), maternal history (including previous caesarean), and maternal condition. Women were counselled about the potential maternal and neonatal risks of each option, and their preferences were taken into account. The cephalic presentation of T2 was not an exclusion criterion. There were no intrauterine foetal deaths at the onset of labour. We compared women with a planned vaginal delivery (PVD) to those with a planned caesarean delivery (PCD), according to the intended mode of delivery at admission, even when this plan was not followed (e.g., intrapartum caesarean in the PVD group).

Most women were admitted in preterm labour on an emergency basis. In women known to be at high risk of preterm birth, counselling about mode of delivery was sometimes initiated during antenatal visits, but the timing of these consultations relative to delivery was not systematically recorded. The final decision about the planned mode of delivery was always taken at admission by a senior obstetrician, after a discussion with the woman about the respective risks and benefits. Continuous electronic foetal heart rate monitoring was used during labour whenever technically feasible, typically from around 24 weeks' gestation; at earlier gestational ages, monitoring could be intermittent or of limited quality. All births took place in a tertiary-level maternity unit with on-site neonatal intensive care. A neonatologist or senior pediatrician attended all deliveries from 24 weeks' gestation, and earlier when active management was planned. Neonatal resuscitation and intensive care followed contemporary national guidelines, including respiratory support, surfactant administration, hemodynamic stabilization, and neuroprotective care as appropriate.

## Outcomes

We recorded maternal and delivery characteristics. Neonatal outcomes at birth were recorded: birthweight, Apgar scores at 1 and 5 min, and blood gas values: arterial pH, venous pH, lactates (the highest) and base excess (the lowest). For neonatal outcomes, we also recorded the survival rate at discharge and at discharge without morbidity, that is, without bronchopulmonary dysplasia (BPD) or moderate or severe necrotizing enterocolitis (NEC) or a severe intraventricular haemorrhage (IVH) during hospitalization. Their neurological development at 2 years of corrected age was collected from the Loire Infant Follow-up Team (LIFT) cohort (of which the twins studied here are a specific subcohort) by a pediatrician blinded to their study group (PVD and PCD).[13] These data enabled us to classify them into 3 levels of neurodevelopment: normal, intermediate (mild difficulty with language, comprehension, etc.), and abnormal (significant neurodevelopmental impairment). All infants, including those who died after head entrapment, were included in the analyses of survival and in the composite outcome contrasting normal neurodevelopment versus intermediate or abnormal neurodevelopment or death. Only three children with a genetic syndrome diagnosed after birth were excluded from the neurodevelopmental classification at 2 years.

## Statistics

First, we used univariate analysis to examine the association between exposure (PVD) and maternal and obstetric characteristics. After accounting for the correlation between twins with a generalized estimating equation (GEE), we calculated a propensity score, defined as the probability of being in the PCD group, based on maternal age, maternal body mass index, parity (nulliparous or not), assisted reproduction, gestational age, and birth weight Z-score. Second, we analysed the association between the exposure and both of the neonatal outcomes (survival at discharge; survival at discharge without morbidities (i.e., severe IVH, NEC, or BPD) without any adjustment, then in two separate adjusted models. Model 1 adjusted for gestational age and female sex, which are strong predictors of neonatal outcome. Model 2 adjusted for gestational age and the propensity score to account for confounding by the baseline variables included in the score while avoiding over-adjustment and collinearity that could arise from including each individual covariate separately in addition to the propensity score. Results are reported as crude and two sets of adjusted odds ratios. The same procedure was applied to analyse the association between exposure and outcomes at 2 years of corrected age (normal neurodevelopment versus intermediate or abnormal neurodevelopment or death).

Two sensitivity analyses used multiple imputations of missing 2-year outcome data, one in the general population and one in children born at or after 26<sup>+0</sup> weeks. All tests were 2-sided, and *P* < 0.05 was considered statistically significant. All analyses were performed with SPSS 29.0.

## Results

From 2008 through 2019, our hospital had 413 preterm twin pregnancies delivered ≤ 33<sup>+0</sup> weeks' gestation (Fig. 1). After excluding 196 sets of twins (for foetal pathology, intervention during pregnancy, impossibility of vaginal delivery due to emergency situations, etc.), 217 women were in preterm labour for all T1 presentations. T1 was in breech presentation for 61 women, and all 122 twins were available for analysis. This study of T1 breech births thus includes 15 women in the PVD group and 46 in the PCD group.

Maternal and obstetric characteristics did not differ between the 2 groups (that is, by planned mode of delivery), except for BMI (*P* = 0.009) (Table 1). In the PVD group, 13/15 women (86.7 %) delivered both twins vaginally, and 2/15 (13.3 %) required intrapartum caesarean delivery for both twins. Among these 15 pairs of twins with T1 in breech presentation, 5 had T2 in cephalic presentation, with vaginal delivery
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Flow chart. MCMA: Monochorionic-monoamniotic twin, PCD: Planned caesarean delivery, PVD: Planned vaginal delivery.</figcaption></figure>

probably planned in view of the prematurity. In the PCD group, 45/46 women had caesarean delivery as planned, and 1 delivered vaginally because labour progressed too rapidly to allow caesarean (Table 2). All but one pair of twins had foetal heart rate monitoring during labour; in the remaining case, the decision not to monitor was taken by the senior obstetrician because of extremely early gestational age and poor prognosis. A neonatologist or senior pediatrician attended almost all deliveries, and active management was undertaken for all but the most extremely preterm infants according to national guidelines.

In the PVD group, no emergency caesarean was required for a second twin after vaginal delivery of T1. In the PCD group, a vertical uterine incision was used for 7% (n = 3) of the deliveries and a low uterine

incision for 91% (and 1 vaginal birth). There were 2 initial vertical incisions, with a third made after an initial low incision because it was required to extract the second twin.

Two head entrapments occurred in the PVD group, both at 24 weeks of gestation and involving the second twin. In both cases, the deliveries were managed by a senior obstetrician using standard breech extraction manoeuvres, including suprapubic pressure and traction, together with intravenous nitroglycerin (nitronal) to achieve uterine relaxation. One neonate died in the delivery room and the other during hospitalization. Head entrapment occurred once in the PCD group, involving the second twin at 29 weeks' gestation during caesarean delivery; it was managed with intravenous nitroglycerin and an additional vertical hysterotomy,
<table><caption>**Table 1**
Demographic Characteristics.</caption><caption>Maternal & Obstetrical Characteristics Planned Mode of Delivery</caption><thead><tr><th></th><th>PVD</th><th>PCD</th><th>P</th></tr></thead><tbody><tr><td>Age (years)</td><td>n = 15 (%)</td><td>n = 46 (%)</td><td>0.051</td></tr><tr><td>mean ± SD</td><td>34 ± 5</td><td>31 ± 5</td><td></td></tr><tr><td>&lt;25</td><td>1 (6.7)</td><td>7 (15.2)</td><td></td></tr><tr><td>25-35</td><td>7 (46.7)</td><td>30 (65.2)</td><td></td></tr><tr><td>&gt;35</td><td>7 (46.7)</td><td>9 (19.6)</td><td></td></tr><tr><td>BMI (kg/m²)</td><td>22 ± 7</td><td>24 ± 5</td><td>0.009</td></tr><tr><td>mean ± SD</td><td>13 (86.7)</td><td>32 (70)</td><td></td></tr><tr><td>&lt;25.0</td><td>2 (13.3)</td><td>14 (30)</td><td></td></tr><tr><td>≥25.0</td><td></td><td></td><td></td></tr><tr><td>Nulliparous</td><td>8 (53.3)</td><td>30 (65.6)</td><td>0.54</td></tr><tr><td>Previous caesarean delivery</td><td>0</td><td>6 (13.0)</td><td>0.31</td></tr><tr><td>Assisted medical reproduction</td><td>5 (33.3)</td><td>21 (45.7)</td><td>0.09</td></tr><tr><td>Dichorionic</td><td>15 (100.0)</td><td>40 (87.0)</td><td>0.52</td></tr><tr><td>Antenatal steroids</td><td>8 (53.3)</td><td>36 (78.3)</td><td>0.57</td></tr><tr><td>Magnesium sulfate</td><td>6 (40.0)</td><td>13 (28.3)</td><td>0.56</td></tr><tr><td>Gestational age</td><td></td><td></td><td></td></tr><tr><td>mean ± SD</td><td>28 ± 3</td><td>30 ± 2</td><td>0.052</td></tr><tr><td>&lt;26 weeks</td><td>7 (46.7)</td><td>2 (4.3)</td><td></td></tr><tr><td>26-27 weeks</td><td>0</td><td>6 (13.0)</td><td></td></tr><tr><td>28-29 weeks</td><td>1 (6.7)</td><td>11 (23.9)</td><td></td></tr><tr><td>30-33 weeks</td><td>7 (46.7)</td><td>27 (58.7)</td><td></td></tr><tr><td>Presentation of second twin</td><td></td><td></td><td></td></tr><tr><td>Cephalic</td><td>5 (33.3)</td><td>11 (23.9)</td><td>0.51</td></tr><tr><td>Breech</td><td>8 (53.3)</td><td>20 (43.5)</td><td>0.56</td></tr><tr><td>Transverse</td><td>2 (13.3)</td><td>15 (32.6)</td><td>0.19</td></tr></tbody></table>

BMI: Body mass index; PCD: Planned caesarean delivery; PVD: Planned vaginal delivery; weeks: Weeks of gestation.
Values are numbers (%) or means ± standard deviation.

<table><caption>**Table 2**
Descriptive analysis of deliveries.</caption><caption>Characteristics of deliveries Planned mode of delivery</caption><thead><tr><th></th><th>PVD<br>n = 15 (%)</th><th>PCD<br>n = 46 (%)</th></tr></thead><tbody><tr><td>First twin</td><td>13 (86.7)</td><td>1 (2.2)</td></tr><tr><td>Vaginal delivery</td><td></td><td></td></tr><tr><td>Caesarean low incision</td><td>2 (13.3)</td><td>42 (91.3)</td></tr><tr><td>Caesarean vertical incision</td><td>0</td><td>3 (6.5)</td></tr><tr><td>Second twin</td><td>13 (86.7)</td><td>1 (2.2)</td></tr><tr><td>Vaginal delivery</td><td></td><td></td></tr><tr><td>Caesarean low incision</td><td>2 (13.3)</td><td>42 (91.3)</td></tr><tr><td>Caesarean vertical incision</td><td>0</td><td>3 (6.5)</td></tr><tr><td>Head entrapment first twin</td><td>0</td><td>0</td></tr><tr><td>Head entrapment second twin</td><td>2 (13.3)</td><td>1 (2.2)</td></tr><tr><td>Postpartum haemorrhage</td><td>1<br>(6.7)</td><td>7<br>(15.2)</td></tr><tr><td>Embolization</td><td>0</td><td>1 (2.2)</td></tr><tr><td>Hysterectomy</td><td>0</td><td>1 (2.2)</td></tr><tr><td>Vaginal tears</td><td>2 (13.3)</td><td>0</td></tr><tr><td>OASI</td><td>0</td><td>0</td></tr></tbody></table>

OASI: Obstetrical anal sphincter injury; PCD: Planned caesarean delivery; PVD: Planned vaginal delivery.
Data reported as numbers (%).

and the neonate survived. The rate of postpartum haemorrhages was higher in the PCD group. Among 7 haemorrhages, 2 were severe: one required embolization, and the other an emergency hysterectomy.

The two groups did not differ significantly for the 5-minute Apgar score (P = 0.13), which exceeded 7 in both groups. Other neonatal outcomes at birth differed significantly between them, however. In the PCD group, birth weight was significantly lower for second twins (P = 0.04), and lactates were significantly higher for both twins (T1, P = 0.01 and T2, P = 0.02) vs PVD.

Our cohort population contained 122 new-borns. Three were

excluded from the 2-year analysis due to the postnatal diagnosis of a genetic syndrome, and 11 more due to missing data at 2 years. This analysis therefore included 108 children. A sensitivity analysis used multiple imputations to take the 11 children into account (Fig. 2).

Neonatal survival at discharge in the PVD group was 67 % versus 93 % in the PCD group, and at discharge without morbidity, 43 % versus 78 % respectively. Normal neurodevelopment at 2 years was 39 % in the PVD group and 79 % in the PCD group. In the PVD group, 33 % of the neonates died — all before 26 weeks of gestation. The death rate in the PCD group was 6 %.

The univariate analyses revealed significant differences between the two groups for survival at discharge, survival at discharge without morbidity, and for normal development at the corrected age of 2 years (Table 3). After adjustment for gestational age and foetal sex, however, survival at discharge was not significantly different between the two groups. However, survival with normal neurodevelopment at 2 years of corrected age, however, trended lower (aOR<sup>a</sup>, 0.28; 95 % CI, 0.08–1.02, P<sup>a</sup> = 0.055) in the PVD group.

The sensitivity analyses using multiple imputations in all cohorts found that the adjusted OR for the association between the exposure and survival with an optimal examination at 2 years was 0.34, 95 % CI; 0.08–1.39, P = 0.13 and in children born at 26<sup>+0</sup> weeks of gestation and later, 0.21 (95 % CI, 0.04–1.26, P = 0.08).

## Discussion

### Principal findings

After adjustment for the confounding variables, our study did not find a significant difference between the PVD and PCD groups in survival with normal neurodevelopment at a corrected age of 2 years for preterm twins ≤ 33<sup>+0</sup> weeks with T1 in breech presentation. Adjusted survival at discharge and adjusted survival without morbidity were also not significantly different between the groups. Nonetheless, after each set of adjustments, normal development at 2 years corrected age showed a borderline lower trend in the PVD group.

### Results in the context of what is known

Our results show that some factors favour PCD for these births while others favour PVD. In support of planned caesarean, the adjusted results for survival and neurological status at 2 years showed a borderline significant trend towards poorer neurological status in the PVD group. We conducted a sensitivity analysis, with multiple imputation to avoid bias due to loss to follow-up. The result of this analysis was consistent with this trend (aOR, 0.34; 95 % CI, 0.08–1.39, P = 0.13). Finally, we performed an analysis that excluded all twin pregnancies where the delivery was < 26<sup>+0</sup> weeks, given that the many deaths occurring before that point in the PVD group could explain this trend). Nonetheless, the neurological prognosis still showed a poorer trend in the PVD group, without reaching statistical significance (P = 0.08). A larger study would be necessary to obtain better evidence about these trends.

However, given that the main criticism of planned vaginal delivery is the risk of head entrapment, it is notable that PCD did not avoid this complication (one case in this group). Maternal morbidity was also lower in the PVD group, with 2 severe postpartum haemorrhages in the PCD group (one embolization and one emergency hysterectomy) and none in the PVD group. Moreover, 3 mothers (7 %) of the PCD group had a vertical uterine incision (which affects prognosis in future pregnancies for mothers and children). These results are consistent with what has already been described in the literature in situations of extreme prematurity.[14,15] Accordingly, a study of maternal morbidity and these patients' prognosis in subsequent pregnancies might be of interest.
<figure><img src="image_6.png" /><figcaption>Fig. 2. Flow chart of the child population.</figcaption></figure>

<table><caption>**Table 3**
Univariate and adjusted analysis of neonatal outcomes.</caption><thead><tr><th>PVD</th><th>OR<br>(95 %CI)</th><th>P</th><th>aOR<sup>a</sup> (95 %CI)</th><th>P<sup>a</sup></th><th>aOR<sup>b</sup> (95 %CI)</th><th>P<sup>b</sup></th></tr></thead><tbody><tr><td>Survival at discharge</td><td>0.14<br>(0.36-0.54)</td><td>0.005</td><td>1.70<br>(0.20-14.7)</td><td>0.63</td><td>1.90<br>(0.28-12.7)</td><td>0.51</td></tr><tr><td>Survival<br>without morbidity</td><td>0.21 (0.06-0.68)</td><td>0.009</td><td>0.32 (0.05-1.94)</td><td>0.21</td><td>0.30 (0.06-2.21)</td><td>0.27</td></tr><tr><td>Survival and normal<br>neurodevelopment at<br>2 years age corrected</td><td>0.16<br>(0.05-0.48)</td><td>0.001</td><td>0.28 (0.08-1.02)</td><td>0.055</td><td>0.30 (0.07-1.22)</td><td>0.09</td></tr></tbody></table>

PVD: Planned vaginal delivery.

OR and P: Univariate analysis.

aOR: adjusted odds ratio.

aOR<sup>a</sup> and P<sup>b</sup>: analysis adjusted for gestational age and sex (female).

aOR<sup>b</sup> and P<sup>b</sup>: adjusted for propensity score and gestational age.

## Clinical implications

After an extensive systematic search of Medline, we could not find any published studies specifically about preterm twins ≤33+0 weeks with T1 in breech presentation. Several studies about twin pregnancies in breech presentation do include preterm twins in their populations. A Dutch cohort study published in 2018 compared neonatal mortality and morbidity in very preterm twin pregnancies (26-32 weeks) by intended mode of delivery among women in preterm labour. The groups did not differ significantly for mortality in the subgroup analysis (414 women) of the breech/cephalic sets of twins compared with the breech/breech or transverse sets. Neonatal morbidity for T1 was significantly higher in planned caesarean than planned vaginal deliveries; maternal morbidity was also higher for the planned caesarean births [8]. Other articles have included preterm deliveries in studies comparing mode of T1 delivery, probably to ensure adequate power, but did not perform subgroup analyses by gestational age. None of these studies found evidence of excess mortality for vaginal delivery [16-19]. In our study, maternal morbidity was higher after planned caesarean delivery, with severe postpartum haemorrhage and vertical uterine incisions observed only in this group.

Given the potential long-term obstetric consequences of classical or extended incisions, these maternal risks should be explicitly discussed with women when weighing the uncertain neonatal benefit of caesarean delivery in this rare clinical situation.”

The scientific literature on the delivery of breech preterm singletons is richer but equally contradictory. A 2013 systematic review included 4 RCTs (for a total of 116 patients) of singleton pregnancies with both cephalic and breech presentations for woman in preterm labour before 37 weeks of gestation and found no difference between vaginal and caesarean delivery for perinatal morbidity and mortality even in the subgroup in breech presentation [20]. A recent systematic review and *meta*-analysis by Demertzidou et al. assessed the effect of mode of delivery in severe preterm singleton pregnancies and found that vaginal delivery was associated with increased neonatal and perinatal mortality for foetuses in breech presentation, but not for those in cephalic presentation [21]. These findings suggest that both presentation and prematurity modify the balance of risks between vaginal and caesarean delivery. In our twin cohort with a breech first twin, we did not observe a statistically significant difference in survival by planned mode of delivery, but we found a trend toward poorer neurodevelopment at 2 years
in the planned vaginal delivery group, with wide confidence intervals. Together, these data indicate that results from singleton breech preterm births cannot be directly extrapolated to twin pregnancies and underline the need for twin-specific evidence. It is thus unsurprising that various observational studies aiming to determine the optimal mode of delivery have produced contradictory results. A Dutch study published in 2015 included a large cohort of 8356 women, with outcomes analysed by planned mode of delivery and gestational age group. The subgroup giving birth at 28-32 weeks by planned caesarean delivery had significantly less composite mortality and severe morbidity than the comparable group with planned vaginal delivery [22]. Nonetheless, this article's notable methodological limitations have been noted [23]. On the contrary, well-conducted French studies applying rigorous methods suggest that a policy of planned vaginal delivery for preterm breech was not associated with a detectable increased risk of neonatal death or severe morbidity. The principal risk of vaginal delivery is head entrapment, which occurs rarely [5,6,24].

In our study, the rate of head entrapment was 13% (2/15) in the PVD group; both times it occurred at 24 weeks of gestation for the second twins. One foetus died in the delivery room, the other before discharge. This rate varies between studies. Lorthe et al. compared neonatal outcome and outcome at 2 years of age of preterm breech singletons from 26 weeks of gestation by planned mode of delivery. The PVD group in this French study included 143 new-borns; only one died after head entrapment [6]. Another French study from 2021 assessed the safety of planned vaginal delivery of extremely preterm (25-27+6 weeks) foetuses in breech presentation. It found a head entrapment rate of 27.4% (31/113), and 29% of these were followed by neonatal death in the delivery room. Half of these foetuses were born at 25 weeks of gestation [25]. This finding appears to confirm the report by Bodmer et al. that the incidence of head entrapment seems highest before 28 weeks; their 1986 study reported 7 deaths caused by head entrapment among 55 breech presentations before 28 weeks, compared with 2 of 211 ≥ 28 weeks [26]. Nonetheless, caesarean delivery does not completely protect against head retention, as there was one such case in our PCD group.

Moreover, maternal morbidity must also be considered in choosing the mode of delivery, particularly in preterm births, which can result in severe maternal morbidity [14]. Some studies suggest an association between low gestational age and increased maternal morbidity in caesarean deliveries [15]. In addition to the increased risk of postpartum haemorrhage, surgical wounds, and thromboembolism, the vertical incision made in early preterm caesareans negatively affects the patient's obstetric prognosis for future pregnancies (risks of uterine rupture, placenta accreta spectrum disorder, etc.). An Australian observational study published in 1997 and covering a period of 9 years showed that at 24 weeks, 20% of caesareans used vertical incisions. This incidence fell to less than 5% at 30 weeks' gestation and to less than 1% at 34 weeks [27]. But also since the publication in 2000 of the Term Breech Trial, caesarean sections have become the preferred mode of delivery for preterm breech presentation in many hospitals [28-30].

## Research implications

Even though several French studies have produced results that encourage planned vaginal delivery in twin pregnancies, with reassuring results, in 2021 caesareans were planned for 37% of the twin pregnancies in France (compared with 10% of singleton pregnancies), and ultimately 58% of twin deliveries were caesarean (compared with 20% for singletons) [1]. The lack of a consensus of the optimal mode of delivery for preterm twins probably explains this very high percentage of caesarean births for them.

Caesarean sections are also a source of neonatal complications, as there are sometimes extraction difficulties that can cause anoxia and trauma, but also long-term complications. Recent research suggests that it can lead to impaired immune development, with higher risks of allergy, asthma, obesity, and reduced gut microbiome diversity compared

to vaginal births [7].

## Strengths and limitations

The main limitation of our study is its retrospective observational character, which cannot provide as high a level of evidence as a randomized controlled trial. Another important limitation is the small sample size, especially in the PVD group (15 women, 30 infants). As a result, the study is underpowered to detect modest differences between groups, and the wide confidence intervals around several estimates mean that we cannot exclude clinically relevant effects of the planned mode of delivery, even when p values are not statistically significant. Preterm birth is also a heterogeneous syndrome, and our classification based only on gestational age and clinical presentation at admission does not capture the etiologic subtypes recently described in functional taxonomies of preterm birth [31]. We were not able to reliably classify our small cohort according to these phenotypes, which may influence both mode-of-delivery decisions and outcomes. Finally, the single-centre design can be considered a limitation because it reduces variation in clinical practice and may limit generalizability; conversely, it may reduce confounding due to differences in policies between hospitals. In this specific clinical context, conducting a randomized—and even a multicentre—trial is virtually impossible, given the heterogeneity of practices across centres and the rarity of this clinical situation. Most randomized studies have focused on twin pregnancies beyond 32 weeks of gestation [32,33]. Our study, which specifically addresses pregnancies before 33^10^ weeks, is therefore unique in its design.

To reduce the impact of these limitations, we used a rigorous methodology. We compared two groups defined by the intended mode of delivery rather than the actual route of birth, to limit classification bias. We focused on preterm labour and excluded preterm deliveries for maternal or foetal indications, in order to reduce confounding by indication, which may limit generalizability but increases internal validity. We assessed neurologic development at 2 years of corrected age, when robust clinical conclusions can be drawn. The propensity score adjustment was used to minimize confounding, but residual confounding by unmeasured factors cannot be excluded. Finally, the comparability of our population to those in previous studies and the consistency of our findings with theirs support the internal and external validity of our results.

## Conclusion

Our study did not show a statistically significant difference in survival according to the planned mode of delivery for preterm labour in twin pregnancies with the first twin in breech presentation, but confidence intervals were wide. A trend toward a lower rate of normal neurodevelopment at a corrected age of 2 years was observed after planned vaginal delivery, although this finding did not reach statistical significance and should be interpreted with caution. Maternal morbidity, including severe postpartum haemorrhage and vertical uterine incisions, appeared to be higher in the planned caesarean group and should be taken into account when choosing the mode of delivery. In view of these results and the limitations of our study, we do not support a single uniform recommendation. As for singleton breech presentations at term, decisions about the mode of delivery for preterm twins with a breech first twin should be individualized, taking into account gestational age, foetal condition, maternal risks, and the woman's informed preferences.

## Funding Statement

This research received no external funding.

## Ethics

The LIFT cohort (Grandir ensemble en Pays de la Loire) is funded by
the Regional Health Agency of the Pays de la Loire and registered with the French Data Protection Authority for clinical research (Commission Nationale de l'Informatique et des Libertés or CNIL, No. 851,117). The study received a favorable assessment from the relevant ethics committee (GNEDS, Groupe Nantais d'Ethique dans le Domaine de la Santé). Written consent was obtained from parents before children were included in the cohort.

## Data sharing statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## CRediT authorship contribution statement

Camille Dhonneur: Writing – original draft, Methodology, Data curation, Conceptualization. Cyril Flamant: Supervision, Project administration. Jean-Christophe Rozé: Methodology. Valérie Rouger: Data curation. Norbert Winer: Writing – review & editing. Vincent Dochez: Writing – original draft, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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