Introduction

Monoamniotic twin pregnancies constitute a rare event, representing 1% of all pregnancies. Nonetheless, it determines more than 10% of the perinatal mortality, the primary cause being the spontaneous or iatrogenic prematurity⁽¹⁾. Particularly, monoamniotic twin pregnancies associate a significant high mortality, up to 30-70%⁽²⁾, with the most frequent cause being the umbilical cord entanglement (70%), but also the abnormal placental insertion, abnormal vascularization, prematurity, intrauterine growth restriction and congenital anomalies⁽³⁾.

The septostomy of the dividing amniotic membrane in diamniotic twin pregnancies is identified mostly in monochorionic pregnancies. Spontaneous septostomy is defined in literature when amnionicity is confirmed early in the pregnancy and is associated with one of the following elements: umbilical cord entanglement (diagnosed either prenatal or postnatally), twin-to-twin transfusion syndrome (TTTS) and fetuses occupying both parts of the membrane⁽⁴⁾. Chmait et al. (2009) presented in a series of cases of complicated monochorionic twin pregnancies that the rate of spontaneous septostomy counts for 1.8% of monoamniotic pregnancies⁽⁴⁾.

Based on a review from 1991 to 2011 which included 15 cases describing spontaneous septostomy, Fleming and Miller (2012) revealed that nine out of 15 cases were properly diagnosed as such antenatally. Umbilical cord entanglement was identified in almost half of cases. Five pregnancies ended with the death of at least one of the fetuses. Confirming the incidence of prematurity in twin pregnancies, 11 out of 15 cases (73%) ended before 35 weeks of gestation. Most frequently, the negative prognosis transpired when the diagnosis was established after birth⁽²⁾.

The objective of this article is to further gather data from 2011 to 2024, continuing the work of Fleming and Miller (2012). There are such identified 10 new cases following similar characteristics with the prior review. An important difference found is the moment of diagnosis; in the last decade, succeeding is identifying this modification antenatally in eight out of 10 cases.

Materials and method

This literature review includes data from articles in databases such as PubMed, MEDLINE and Embase, following specific research of cases with spontaneous septostomies in twin diamniotic pregnancies from 2012 to 2024. All patients who suffered invasive procedures prior to establishing the diagnosis of septostomy were not included in the study, thus underlining the real “spontaneous” cases. We identified six new articles describing case-controls and one paper including a case series, the gathered data being summarized in Table 1.

Results

The search yielded a number of seven papers, reporting 10 cases of spontaneous septostomies in diamniotic twin pregnancies during 2012-2024. In all of the cases, the chorionicity and amnionicity diagnosis was established at the first-trimester ultrasound scan and, subsequently, confirmed after birth by the clinical assessment and histopathology examination of the placenta. In two cases, the septostomy diagnosis was established postnatally, and in the other eight cases antenatally, in the second trimester, between 24 and 28 weeks of gestation. Hvelplund et al. (2018) describe the clinical presentation that concludes the diagnosis by identifying the fetus A with a wide transparent band similar to the amniotic membrane, tightly bound periabdominally, but the fetus presented normal movement and limb circulation⁽¹²⁾. All cases were upheld as spontaneous since there were no extrinsic interventions which could have produce such event.

It is noticed that three out of 10 cases were obtained by in vitro fertilization. All pregnancies benefited from a satisfactory prenatal monitoring matching to the standard of care in each country, having anomaly scans in first and second trimester, biochemical screening and other noninvasive prenatal screening tests – all the results were within normal limits, presenting no pathological morphological elements and with low risk in trisomy screening. From the parity point of view, seven patients were primipara, two were secundipara, and one tertipara. The ages of the patients varied from 25 to 40 years old.

One of the most important and most severe complications of the monoamniotic pregnancies is represented by the umbilical cord entanglement. Amongst the cases found, 60% present different forms of complexity of the cord entanglement.

The gestational age at the moment of birth ranged from 24 to 37 weeks, with the majority of 70% being over 32 weeks. We noticed the decision of the medical staff to deferral the moment of birth in order to diminish the risks of prematurity. In six cases (which all finalized by the birth of alive newborns) the patients received corticotherapy with the purpose of fetal pulmonary maturation, delaying the moment of birth.

As delivery methods, in four cases identified by Suzuki (2013) it is not mentioned the type of delivery; however, there is a mention that no choice for caesarean section is offered⁽¹⁰⁾. For the other cases, five ended through emergency caesarean section and one assisted vaginal birth (being confirmed in utero fetal demise for both fetuses at 24 weeks of gestation).

Considering the fetal status at birth, there are three cases of in utero fetal demise (two cases with one of the children stillbirth and one case for both fetuses) and one case in which one of the fetuses died two days after birth from acute respiratory distress syndrome in the context of hyaline membrane disease.

A histopathological examination of the placentas was performed in the totality of cases in order to confirm the diagnosis of septostomy and to extend the study of the possible etiologies and associated complications. Thus, Hvelplund et al. (2012) obtained a histopathological aspect of the membrane with double amniotic layer without a chorion, a characteristic element to the monochorionic diamniotic pregnancy; also, unilaterally presents “amnion nodosum” which is habitually associated to severe oligohydramnios⁽¹²⁾. Bevilacqua et al. (2014) described the presence of the umbilical cord entanglement and a close placental insertion of the two umbilical cords⁽⁷⁾. Chada et al. (2009) described folded layers of the amnion disposed above the placenta, the membranes being found completely separated at the insertion point with the exception of a minimal area; the cord insertions were found at 1 cm distance between each other, presenting signs of vascular anastomosis⁽⁴⁾. In the case identified by Leeet al. (2012)¹³⁾, it is depicted a fused placental disk, with cord insertions at 3 cm between them, a cord entanglement with two and a half turns, and the presence of an amniotic fold.

To complete the literature review, we also report the case of a 30 years-old gravida, without any significant prior medical history, primipara, the pregnancy being spontaneously conceived. The first-trimester anomaly scan established a monochorionic diamniotic twin pregnancy. The pregnancy continued to have a proper monitoring, the patient benefiting from anomaly scans in the first, second and third trimesters, blood tests specific for each trimester, and being closely followed-up, respecting the current guidelines. Up to 36 weeks, there were no pathological elements to be reckoned. Considering the twin status, there was a common decision to terminate the pregnancy by caesarean section at 36 weeks of gestation. Intraoperatively, at the moment of birth, it was identified a complex cord entanglement possible by a spontaneous septostomy – diagnosis thus made postnatally (Figure 1). The fetal statuses at birth were reassuring, with fetus A weighing 2070 g, with an Apgar index of 9, and fetus B weighing 2280 g, with an Apgar index of 8. Both maternal and fetal outcomes were excellent.

Discussion

Monochorionic diamniotic pregnancies present the possibility of the interamniotic membrane to suffer ruptures both spontaneously, and also iatrogenically through amniocentesis or during the invasive procedures; all of these are considered afterwards pseudo-monoamniotic twin pregnancies. It is defined the pseudo-monoamniotic twin pregnancies that follows a septostomy in a diamniotic pregnancy, and it should be treated as a monochorionic monoamniotic pregnancy.

Once the membrane rupture occurs, the pregnancy becomes, from a functional point of view, a twin monoamniotic pregnancy with a high risk of developing cord entanglement (up to 50%) and an additional increase of perinatal mortality (up to 70%)⁽³⁾. It represents a rare event and a challenge, both considering the diagnosis and the management⁽⁵⁾.

In the majority of the studied cases, a suspicion of septostomy is raised during the ultrasound monitoring, and the diagnostic certainty is established at birth by the histopathologic exam. Generally, it is a challenge to identify the exact moment when the rupture occurred, since there is no associated symptom, neither a premature rupture of membranes, nor complications such as twin-to-twin transfusion syndrome (TTTS). Frequently, there is a supposition that the rupture occurs during the second trimester, considering the fine interamniotic membrane during the first-trimester scan (Table 2).

Currently, the proposed mechanisms for antenatal spontaneous rupture of the interamniotic membrane are the tight umbilical cords insertions to the placenta and fine interamniotic membrane with important active fetal movements in a limited uterine medium⁽³⁾.

The etiology of the spontaneous septostomy is frequently unclear, but it can include chorioamniotitis, mechanical rupture through fetal movement, amniotic band syndrome, developmental anomalies⁽¹⁾ or polyhydramnios, all related to risk factors such as multiparity and fetal structural or functional anomalies.

Chmait et al. (2009) found a rate of 1.8% spontaneous septostomies in a highly selected cohort of monochorionic diamniotic pregnancies in a tertiary referral center over a period of two and a half years. They described the following ultrasound signs that can suggest spontaneous septostomy: absence or interrupted interamniotic membrane, both fetuses occupying the same part of the membrane, umbilical cord entanglement and amniotic fluid excess with signs of TTTS⁽⁴⁾. Thus, there are ultrasound diagnostic criteria, such as very thin, interrupted or absent interamniotic membrane, double folded layers of amnion disposed above the placenta, fetuses occupying the same part of the ruptured membrane, umbilical cord entanglement, tight umbilical cord insertions on the placenta at less than 3 cm one from the other, and no membrane between the two umbilical cords, polyhydramnios and specific signs of TTTS⁽⁶⁾. The ultrasound diagnosis is established once we identify a fragment of free membrane or a loop of umbilical cord with different directions of the colored Doppler⁽⁷⁾.

The most important complication of the spontaneous septostomy is the umbilical cord entanglement, also representing the most frequent cause of perinatal mortality. It is reported in 70% of monoamniotic pregnancies, of which 50% are associated with perinatal demise⁽⁸⁾. In Nasrallah and Faden (2005) review, it is reported an incidence of 60% of the umbilical cord entanglement compared to the rate of 70% in true monochorionic monoamniotic pregnancies. The ultrasound sign for a true umbilical cord entanglement is described as “hanging noose”⁽⁹⁾.

The literature distinguishes the umbilical cord entanglement in 64% of cases of pseudo-monoamniotic pregnancies. Following the evolution of ultrasound technologies, nowadays we can identify it early, from the first trimester⁽¹⁾. The complexity of the entanglement can significantly influence the prognosis. Thus, these pregnancies require a careful management and monitoring to precociously identify the possible complications that can induce acute or chronic fetal distress, such as umbilical cord compression or occlusion.

The prognosis of pseudo-monoamniotic pregnancies versus monoamniotic ones does not differ, neither in the rate of umbilical cord entanglement, nor its complications⁽¹⁰⁾. Hence, the management of both of these types of pregnancies is to follow the guidelines in the management of monoamniotic pregnancies. The experts’ consensus comes with the proposition to deliver at 32-34 weeks of gestation, but individual studies notice that delaying up to 34 weeks with careful follow-up can be proposed with a favorable prognosis, without increasing the perinatal morbidity nor mortality.

Besides the complications secondary to the pseudo-amniotic environment (such as TTTS), septostomy can determine premature birth, which can be difficult to appreciate independently from the basal risk of multiple pregnancies or amniotic band syndrome⁽¹¹⁾.

The more precocious the diagnosis is made, the better outcome of the pregnancy is expected. However, in three cases, confirming the septostomy occurred at the moment of finding in utero fetal demise of at least one of the fetuses and associated extreme forms of umbilical cord entanglement. Moreover, the possible postnatal complications and the period of hospitalization are directly correlated to the prematurity status of the newborns.

Conclusions

The spontaneous rupture of the dividing amniotic membrane in monochorionic diamniotic pregnancy is an extremely rare event, and it remains a challenge in prenatal diagnosis. The cases mentioned beforehand in literature prove that a monochorionic diamniotic pregnancy that suffered a process of spontaneous septostomy should be managed as a monoamniotic pregnancy when considering monitoring, the moment and method of delivery, always taking in account the high morbidity and mortality in monochorionic monoamniotic pregnancies. These cases highlight the necessity of an attentive examination of the interamniotic dividing membrane at every prenatal visit, through different ultrasound sections, since it can profoundly change the management from a diamniotic to a monoamniotic pregnancy. 

Autor corespondent: Narcisa-Anamaria Covataru E-mail: narcisacovataru@gmail.com

CONFLICT OF INTEREST: none declared.

FINANCIAL SUPPORT: none declared.

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