Interval Vaginal Delivery of Term Twins From Bilateral Horns of a Uterus Didelphys: Insight Into Labor Initiation and Progression

ABSTRACT

Uterus didelphys, characterized by two separate uterine cavities and cervices, is associated with increased obstetric complications. Twin pregnancy with one fetus in each horn is exceptionally rare, often managed by cesarean or resulting in preterm birth. We report the first known case of term vaginal deliveries from both horns, occurring 6 days apart. A 28‐year‐old woman with uterus didelphys spontaneously conceived twins, with one fetus in each horn. At 37 + 4 weeks of gestation, labor began spontaneously in the left uterus. The cardiotocogram initially showed asynchronous contractions between the horns during the latent phase, becoming synchronous in the active phase. The first twin was delivered via forceps due to non‐reassuring fetal status. The right uterus showed weak contractions but did not progress to labor. Six days later, labor was induced, and the second twin was also delivered via forceps. This case offers rare clinical insight into labor initiation and inter‐horn coordination.

1. Introduction

Uterus didelphys, or “double uterus,” arises from the failure of fusion of the Müllerian ducts, resulting in two distinct uterine cavities and cervices. This anomaly accounts for roughly 5%–10% of all Müllerian duct anomalies [1]. It is associated with higher rates of miscarriage, preterm labor, and obstetric complications [2]. Concurrent pregnancy in both uterine horns is extraordinarily rare, occurring in about 1 in 1 000 000 pregnancies [3]. Only about 20–30 such cases have been described worldwide in the past 100 years. Most reported cases have resulted in cesarean delivery or preterm birth [4, 5, 6, 7, 8, 9]. However, no case has been reported in which labor occurred independently in each uterine horn and both fetuses were delivered vaginally at term.

Uterine contractions during labor are primarily induced by the action of hormones such as oxytocin and prostaglandin F2α (PGF2α) on the myometrium, and the importance of uterine sensitivity to these mediators is well recognized [10]. However, the precise regulatory mechanisms remain insufficiently understood, partly due to the ethical limitations of conducting interventional studies on human labor. In this context, observing fetal and uterine activity during vaginal delivery of twins in a uterus didelphys offers a unique opportunity to gain clinical insight into the regulation and onset of labor.

Here, we present a case of term vaginal delivery of twins from the bilateral horns of a uterus didelphys, with deliveries occurring 6 days apart.

2. Case Presentation

A 28‐year‐old woman (gravida 3, para 1) with uterus didelphys presented with a spontaneous twin gestation, with one fetus developing in each uterine cavity. Her obstetric history included one prior term pregnancy with forceps delivery from the right uterus, during which a longitudinal vaginal septum was resected, and one first‐trimester miscarriage at 5 weeks. In the current pregnancy, serial ultrasound examinations demonstrated appropriate growth of both fetuses without obstetric complications or signs of threatened preterm labor, although tetralogy of Fallot was prenatally diagnosed in the right fetus.

At 33 + 4 weeks of gestation, pelvic magnetic resonance imaging was performed to evaluate the birth canal. The scan demonstrated that both cervices and lower uterine segments maintained normal morphology, and both fetuses were in cephalic presentation (Figure 1). Based on these findings, a trial of vaginal delivery was planned.

FIGURE 1.

T2‐weighted coronal magnetic resonance image at 33 + 4 weeks of gestation.

At 37 + 4 weeks of gestation, the patient developed painful, regular uterine contractions every 4–5 min, indicating the onset of labor. On examination, the cervix of the left uterus was 4 cm dilated (70% effaced, −3 station, soft), and the fetal head was more engaged than that of the right‐sided fetus, whose cervix remained closed. Two cardiotocogram monitors with external tocodynamometers were applied to each uterine horn, and both fetuses exhibited reassuring fetal status. The left uterus exhibited strong, regular contractions at 4–5‐min intervals, whereas the right uterus showed irregular activity that was not synchronized with the left (Figure 2). After membrane rupture and transition to the active phase of labor in the left uterus, contractions in the right uterus, though remaining weak, became synchronous with those of the left, while continuous monitoring of the fetal heart rate in the left uterus became unreliable during the second stage of labor (Figure 3). A bedside ultrasound indicated non‐reassuring fetal status, prompting forceps‐assisted delivery. The first twin, delivered from the left uterus, weighed 2645 g, with Apgar scores of 8 and 9 at 1 and 5 min, respectively, and an umbilical arterial pH of 7.297. Throughout the delivery of the first twin, fetal monitoring of the second twin (in the right uterus) remained reassuring. After placental delivery, weak contractions continued in the right uterus at 3‐min intervals, and the cervix progressed to 4 cm dilation, 50% effacement, and −3 station. However, spontaneous labor did not develop, and uterine activity gradually ceased. The following day, she began breastfeeding the first infant, and conservative management of the second twin was continued, with the expectation that prolonging the pregnancy would support fetal growth and reduce the risk of respiratory complications, especially in light of the prenatally diagnosed tetralogy of Fallot. Conservative management of the second twin was undertaken using non‐stress testing performed at least twice daily, including during breastfeeding. Despite ongoing breastfeeding, non‐reassuring fetal status episodes were not observed during this period.

FIGURE 2.

Cardiotocogram during labor before the active phase. Paper speed: 3 cm/min. Blue and red arrows indicate left and right uterine contractions, respectively. Approximately 40 s after the peak of the second left uterine contraction (blue arrow), a smaller contraction peak was observed, potentially representing the detection of a right uterine contraction. Other contractions occurred independently, indicating that left and right uterine contractions were asynchronous.

FIGURE 3.

Cardiotocogram during the active phase of labor. Paper speed is 3 cm/min. Blue and red arrows indicate left and right uterine contractions, respectively. No subjectively perceived uterine contractions were noted during the intervals between the indicated contractions. In this panel, the effective left uterine labor contractions (blue arrows) and painless right uterine contractions (red arrows) were synchronous.

Six days later, at 38 + 3 weeks of gestation, labor was induced for the second fetus, as the patient reported fatigue from continued conservative management while breastfeeding the first infant. Due to non‐reassuring fetal status, a second forceps delivery was performed. The second infant, delivered from the right uterus, weighed 3179 g, with Apgar scores of 8 and 9 at 1 and 5 min, respectively, and an umbilical arterial pH of 7.238. Both infants were delivered vaginally at term, 6 days apart, and the postpartum course was uneventful.

3. Discussion

We experienced a case of term vaginal delivery of twins from the bilateral horns of a uterus didelphys, with deliveries occurring 6 days apart. During the course of labor, only one uterus progressed to delivery. Contractions between the two horns were initially asynchronous, but became synchronous during the active phase, illustrating alternating patterns of coordination and independence. These characteristics provide a rare clinical glimpse into the mechanisms regulating the onset and progression of labor.

Our case provides insight into the synchrony of uterine contractions of both horns during labor, a topic that has been rarely addressed in clinical literature. The rhythm of uterine contractions is believed to be influenced by pulsatile secretion of oxytocin, the autonomic nervous system (particularly the hypogastric and pelvic nerves), and the pacemaker activation [11, 12]. A previous report analyzing contraction patterns in a uterus didelphys during simultaneous labor in both horns found that more than 90% of contractions were asynchronous, suggesting independent regulation by pacemaker sites in each horn [4]. In contrast, in our case, although the contractions between the two horns were initially asynchronous, the non‐laboring horn exhibited synchronized contractions with the laboring horn during the active phases of labor. This finding implies that the mechanisms governing uterine contraction may differ depending on whether the uterus is actively laboring or not, and that the contractions observed in the non‐laboring horn may represent a distinct physiological phenomenon. The absence of anatomical communication between the two horns makes gap junction‐mediated electrical coupling unlikely. Therefore, the synchronized contractions in the non‐laboring horn during the active phase of labor may have been mediated by systemic signals, such as pulsatile oxytocin release or reflex neural stimulation via shared autonomic pathways.

This case also offers an important clinical perspective on the initiation of labor. In previously reported cases of twin pregnancies involving a uterus didelphys, where each fetus is located in a separate uterine horn, it has occasionally been observed that preterm labor occurs in one horn while the other remains quiescent, resulting in discordant delivery timing [8, 13]. This phenomenon has been attributed to gestational age‐related factors, such as uterine overdistension and functional progesterone withdrawal, which are known contributors to the onset of labor. However, in our case, despite both fetuses reaching term gestation, spontaneous labor occurred only in one uterine horn. While the non‐laboring horn exhibited cervical ripening, it demonstrated only weak uterine contractions and did not proceed to labor spontaneously. After the delivery of the first infant, the patient continued breastfeeding the first infant in anticipation that nipple stimulation would induce oxytocin release and promote the onset of labor; however, spontaneous labor did not occur. This suggests that myometrial sensitivity, rather than gestational age alone, plays a critical role in the initiation of labor, and that local functional changes within the myometrium may be necessary to trigger effective contractions.

In conclusion, we experienced a case of term vaginal delivery of twins from the bilateral horns of a uterus didelphys, with deliveries occurring 6 days apart. Simultaneous cardiotocography of both uterine horns during labor of the first fetus provided a rare opportunity to examine the dynamic interplay between anatomical separation and physiological coordination of uterine activity, offering novel clinical insight into the mechanisms regulating human labor.

Author Contributions

Daiki Hiratsuka: conceptualization, data curation, investigation, writing – original draft, formal analysis. Takayuki Iriyama: conceptualization, investigation, supervision, writing – review and editing. Seisuke Sayama: review and critical comments. Keiichi Kumasawa: review and critical comments. Miyuki Harada: review and critical commetns. Yasushi Hirota: review and critical comments.

Disclosure

The authors have nothing to report.

Ethics Statement

The study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of the Faculty of Medicine of the University of Tokyo (IRB number: 3053).

Consent

Written informed consent was obtained from the patient for publication of this case report.

Conflicts of Interest

Dr. Yasushi Hirota and Dr. Takayuki Iriyama are Editorial Board members of this submitted JOGR Journal and co‐authors of this article. To minimize bias, they were excluded from all editorial decision‐making related to the acceptance of this article for publication.

Hiratsuka D., Iriyama T., Sayama S., Kumasawa K., Harada M., and Hirota Y., “Interval Vaginal Delivery of Term Twins From Bilateral Horns of a Uterus Didelphys: Insight Into Labor Initiation and Progression,” Journal of Obstetrics and Gynaecology Research 52, no. 2 (2026): e70206, 10.1111/jog.70206.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.