Co-Twin Control Studies: Natural Events, Experimental Interventions and Rare Happenings/Twin Research: Cancer Risk in Overweight Twins; Prognosis After Fetal Loss of One Twin; Twin Concordance for Parkinson's Disease; Neuroanatomy of Musically Discordant MZ Twins/News Articles: Twin Birth with Two Wombs; Twins' Prenatal Interactions; Switched-at-Birth Twins; Fetus-in-Fetu; Unsolved Paternity.

Co-twin control is a well-known methodological twin research design, but its variations and complexities are less well known. Various issues and illustrations are presented with reference to studies involving natural events, experimental interventions and rare happenings that underlie monozygotic (MZ) twins' environmental differences. This discussion is followed by summaries of recent twin research pertaining to cancer risk in overweight twins, the physical risk to surviving twins after fetal loss of a co-twin, a 20-year update of twin concordance for Parkinson's disease, and neuroanatomical differences in musically discordant MZ twin pairs. Several twin-related items that have attracted attention in the news are also summarized.

Two is a Crowd: Two is a Crowd: On the Enigmatic Etiopathogenesis of Conjoined Twinning.

In this article, we provide a comprehensive overview of multiple facets in the puzzling genesis of symmetrical conjoined twins. The etiopathogenesis of conjoined twins remains matter for ongoing debate and is currently cited-in virtually every paper on conjoined twins-as partial fission or secondary fusion. Both theories could potentially be extrapolated from embryological adjustments exclusively seen in conjoined twins. Adoption of these, seemingly factual, theoretical proposals has (unconsciously) resulted in crystallized patterns of verbal and graphic representations concerning the enigmatic genesis of conjoined twins. Critical evaluation on their plausibility and solidity remains however largely absent. As it appears, both the fission and fusion theories cannot be applied to the full range of conjunction possibilities and thus remain matter for persistent inconclusiveness. We propose that initial duplication of axially located morphogenetic potent primordia could be the initiating factor in the genesis of ventrally, laterally, and caudally conjoined twins. The mutual position of two primordia results in neo-axial orientation and/or interaction aplasia. Both these embryological adjustments result in conjunction patterns that may seemingly appear as being caused by fission or fusion. However, as we will substantiate, neither fission nor fusion are the cause of most conjoined twinning types; rather what is interpreted as fission or fusion is actually the result of the twinning process itself. Furthermore, we will discuss the currently held views on the origin of conjoined twins and its commonly assumed etiological correlation with monozygotic twinning. Finally, considerations are presented which indicate that the dorsal conjunction group is etiologically and pathogenetically different from other symmetric conjoined twins. This leads us to propose that dorsally united twins could actually be caused by secondary fusion of two initially separate monozygotic twins. An additional reason for the ongoing etiopathogenetic debate on the genesis of conjoined twins is because different types of conjoined twins are classically placed in one overarching receptacle, which has hindered the quest for answers. Clin. Anat. 32:722-741, 2019. © 2019 Wiley Periodicals, Inc.

Diprosopus: Systematic review and report of two cases.

BACKGROUND: Diprosopus is a subtype of symmetric conjoined twins with one head, facial duplication and a single trunk. Diprosopus is a very rare congenital anomaly. METHODS: This is a systematic review of published cases and the presentation of two new cases born in Argentina. We estimated the prevalence of conjoined twins and diprosopus using data from the National Network of Congenital Anomalies of Argentina (RENAC). RESULTS: The prevalence of conjoined twins in RENAC was 19 per 1,000,000 births (95% confidence interval, 12-29). Diprosopus prevalence was 2 per 1,000,000 births (95% confidence interval, 0.2-6.8). In the systematic review, we identified 31 diprosopus cases. The facial structures more frequently duplicated were nose and eyes. Most frequent associated anomalies were: anencephaly, duplication of cerebral hemispheres, craniorachischisis, oral clefts, spinal abnormalities, congenital heart defects, diaphragmatic hernia, thoracic and/or abdominal visceral laterality anomalies. One of the RENAC cases and three cases from the literature had another discordant nonmalformed twin. CONCLUSION: The conjoined twins prevalence was similar to other studies. The prevalence of diprosopus was higher. The etiology is still unknown. The presence of visceral laterality anomalies may indicate the link between diprosopus and the alteration or duplication of the primitive node in the perigastrulation period (12-15 days postfertilization). Pregnancies of more than two embryos may be a risk factor for diprosopus. Given the low prevalence of this defect, it would be useful to perform studies involving several surveillance systems and international consortiums. Birth Defects Research (Part A), 2016. © 2016 Wiley Periodicals, Inc. Birth Defects Research (Part A) 106:993-1007, 2016. © 2016 Wiley Periodicals, Inc.

The conjoined twin sisters Helen and Judith (1701-1723) and their pictorial impact in later 18th-century science.

Given the uniqueness of the Hungarian conjoined twin sisters Helen and Judith (1701­1723) and their lasting influence as an anatomical showcase if not model for mental or social deviant states, we present here a closer scrutiny of their introduction into the scientific literature of the later 18th century by analyzing depictions of the twins from 1707 onwards.

Parapagus (dicephalus, tetrabrachius, dipus) conjoined twins and their rehabilitation.

A case of female parapagus conjoined twins living as unseparated is presented in this report. The twins had two heads, four arms and two legs. As a result of their fusion, operative care had been considered to be unacceptable, and the family had refused to take care of them. At three years of age, they were referred to the Rehabilitation Department with the complaint of inability to walk. While designing the rehabilitation program, somatosensory evoked potential evaluation was performed and showed that twin 1 controlled the right leg and twin 2 controlled the left. The program consisted of coordinated pacing training by verbal commands, upper and lower extremity reeducation, and balance and coordination exercises. After two months of inpatient rehabilitation, they were able to walk independently with a specially designed walker. Currently, the twins are 11 years old with normal academic achievement, and they are able to walk, run and climb the stairs independently.

Conjoined hearts in thoracopagus twins.

This study aimed to identify the anatomic and pathologic structural cardiac abnormalities in conjoined twins and to focus on those that have prevented the successful separation of conjoined hearts. A retrospective review was undertaken to examine consecutive cases of thoracopagus conjoined twins with conjoined hearts evaluated at The Children's Hospital of Philadelphia from 1 January 1980 through 6 October 2008. The records included autopsy and surgical findings as well as clinical reports. The study group included nine sets of conjoined twins with a mean gestational age at birth of 33.8 ± 5.5 weeks. Three twin pairs were stillborn. Five twin pairs died afterward. One pair died of cardiopulmonary failure. The median age at death was 22 days (range, 0-345 days). Major congenital heart disease was present in 94.4% (17/18) of the hearts, and 72.2% (13/18) of the hearts had single-ventricle physiology. Total anomalous pulmonary venous return occurred in 39% (7/18) of the cases. The clinical outcome for thoracopagus twins with conjoined hearts remains poor because of inability to separate conjoined and single ventricles. Surgical nonintervention and palliative care should be strongly considered for these patients.

Coagulation changes in a siamese twin in SIRS after death of the other twin: a case study.

BACKGROUND: Conjoined twins represent a rare case of embryonic failure. Siamese twins' final outcome is usually associated with poor prognosis due to complications, among which the inflammatory and septic disturbances are often present. CASE REPORT: The article describes Siamese twins of craniopagus type. One of the twins died of heart and aortic failure after 48 hours of life. The decision regarding surgical separation then became an emergency. At the same time laboratory results for the surviving twin I indicated steadily worsening coagulation functions and processes, which we believed were caused by the death of twin II, as well as by systemic inflammatory response syndrome (SIRS). CONCLUSIONS: Due to vascular conjunction between the twins' brains' circulatory systems the sequenced progress of coagulopathy was noticed in the surviving twin.

Acardius anceps with neck cyst and cleft palate: Three dimensional skeletal computed tomography reconstruction with discussion of the literature.

Acardiac twinning is a rare anomaly of monochorionic twin pregnancies. Acardiac fetuses lack a functional heart but are passively perfused by arterial blood from their pump co-twin causing the acardiac body to be hypoxemic. In this report, we present an acardius anceps, therapeutically laser separated from its pump twin at 16 weeks. The healthy pump twin and macerated acardiac body were born at 40 3/7 weeks. A three dimensional (3D) reconstruction was made by CT images, showing cranial bones, spinal column, pelvis and lower extremities but absent arms. A cyst in the neck of the acardiac twin was identified by postnatal sonography; this was also described in four literature cases, and was additionally observed by us in two other acardiac twins. Median cleft palate was identified by oral cavity inspection but undetectable in the reconstruction. In the literature, we found 21 other acardiac anceps twins with a cleft palate. From the two larger published series, with 12 clefts in 21 acardiac anceps twins, a cleft palate occurs in over 50% during acardiac twinning. Our first hypothesis is that acardiac fetuses develop an oral cleft palate when acardiac onset starts prior to 11 weeks, because 11 weeks includes the period of embryonic oral cavity formation, and no cleft occurs when onset starts later than 11 weeks. Our second hypothesis is that cysts and cleft palates are more common in acardiac twins than currently known, likely reflecting that acardiac bodies are hypoxemic and that hypoxia contributes to the development of both cysts and clefts.

Pharmaceutical considerations with conjoined twins.

Sharing of the vascular system in conjoined twins creates pharmaceutical dilemmas that require individualization of protocols. One of the major goals for the medical team is to determine how medications should be administered, dosed, and monitored in each set of conjoined twins. In order to achieve these goals, the team must determine the extent of shared circulation, volume of distribution, effectiveness of enteral absorption, renal clearance, and develop processes to ensure medication safety. In this article, we discuss unique challenges in medication practices in conjoined twins and present general principles that can be applied to determine optimal pharmaceutical strategies.

Conjoined twins: Pre-birth management, changes to NRP, and transport.

The management of conjoined twins is complex and requires careful preparation. Pre-birth management includes prenatal counseling, which is important due to the overall poor prognosis. In instances of trial of life, the delivery must be tailored to address the anticipated anatomy based on prenatal imaging and anticipated physiology. A multidisciplinary team is essential to anticipate and address the ergonomic challenges and medical issues related to organ fusion, cross-circulation and associated anomalies. There are several suggested modifications to the current Neonatal Resuscitation Program algorithm including modifications to initial assessment, airway management, administration of chest compressions, obtaining emergency access, and medication dosing. Simulation is essential to address challenges, practice Neonatal Resuscitation Program modifications, delineate clear roles during delivery and practice communication. This paper offers a discussion of unique issues associated with delivery of conjoined twins and recommendations on how to approach these challenges based on our experience and available literature.

Nutritional considerations in the care of conjoined twins.

Conjoined twins represent an interesting nutritional challenge as nutrient delivery and absorption is greatly affected by anatomy and, therefore, unique to each twin pair. Nutritional support is essential to optimize growth and development in the neonatal period; however, very little data exists on the topic in this population. Conjoined twins require individualized nutritional assessment that focuses on the interaction between the metabolic rate, nutrient uptake, and nutrient delivery of each twin in the dyad. This report describes one center's experience with monitoring growth, establishing nutrient requirements, and determining substrate utilization in three sets of conjoined twins.

Conjoined Twins.

Reported here is a case of conjoined twins presented to ante-natal outpatient department of Paropakar Maternity and Women's Hospital on 21st August 2015 on a 20 year "Primigravida at 27 weeks and 6days of gestation not in labor" referred from a polyclinic following ultrasonography diagnosis for better management. After confirming the diagnosis and counseling the patients regarding mode of delivery and possible outcomes, elective caesarean section was performed and delivered male conjoined twins of Parapagusdicephalus type with poor Apgar score. No resuscitation attempted except oxygen supplementation as per wish of parents and early neonatal deaths occurred at one hour of life. Keywords: conjoined twins; monozygotic twins; siamese twins; twinning; twin pregnancy.

Nursing considerations and interdisciplinary coordination in the care of conjoined twins.

Traditional nursing care strategies may require modification to meet the unique needs of conjoined twins. Here we discuss the strategies found to be useful in planning for and responding to distinctive circumstances encountered throughout hospitalization, as well as lessons learned. Areas of focus include ensuring privacy, designing adequate unit accommodations to meet space and equipment needs, staffing considerations and adaptations to typical neonatal intensive care nursing interventions. The utility of a team-based approach to interdisciplinary care coordination is also discussed. With adequate preparation and thoughtful innovation, most tertiary neonatal intensive care units can readily adapt to the unique needs of conjoined twins.

Therapy services and specialized devices for conjoined twins: Unique challenges with conjoined twins and the importance of physical and occupational therapy.

Conjoined twins are a rare occurrence that offer unique challenges and circumstances to therapists. The overall goal of physical and occupational therapy treatment is to provide care that promotes developmental progression to two conjoined individuals with distinct personalities and potentially different physical and medical needs. The unique presentation of conjoined twins must be considered in determining therapeutic goals, interventions and plans of care. Providing therapeutic interventions throughout the NICU stay is a dynamic, evolving process, which challenges the therapy team to work together to find solutions. This paper aims to highlight the considerations, challenges, and strategies used to address barriers in the therapeutic care of conjoined twins.

Role of simulation in preparation for the care of conjoined twins-prenatal preparation to separation.

The rarity and complexity of conjoined twins creates a challenge for prenatal planning, delivery resuscitation, and postnatal management. The modality of simulation offers a safe practice environment for a multidisciplinary group consisting of neonatal providers, nurses, respiratory therapists, and surgeons in which to identify and address clinical decision making, procedural, and behavioral plans related to routine and emergency care of these patients. Simulation-based clinical rehearsals (SbCR) provide a unique opportunity to prepare for rare, complex, and patient specific clinical procedures and scenarios. This primer serves as a revisable tool that promotes the development of proper timing, technique, and confidence to allow for an optimal setting for delivery of safe care to conjoined twins. We describe the development and implementation of a simulation approach to all stages of care from the antenatal life, NICU care, to preparation for postnatal separation of conjoined twins.

Acardiac twin pregnancies part IV: Acardiac onset from unequal embryonic splitting simulated by a fetoplacental resistance model.

BACKGROUND: Benirschke postulated that acardiac twinning occurs when markedly unequal embryonic splitting combines with arterioarterial (AA) and venovenous placental anastomoses. We tested this hypothesis by model simulations and by comparison of outcomes with 18 "pseudo-" (twin fetus with beating heart but otherwise with clear signs of an acardiac) and 3 "normal" acardiac cases. METHODS: The smaller/larger cell volume ratio at embryonic splitting becomes the smaller/larger embryonic/fetal blood volume ratio (a). From a, we derived nonpulsating blood pressures using normal values (larger twin) and normal values at an appropriate earlier gestational age (smaller twin). These unequal pressure sources were used in a linear resistance fetoplacental network to calculate umbilical venous diameter ratios. Acardiac onset occurs when the smaller twin has 50% left of its normal, singleton placenta. Comparison with clinical cases approximated a by crown-rump-length-ratio to the 3rd power. Input parameters are a and the AA-radius at 40 weeks. RESULTS: Acardiacs can be small or large, can occur early or late, earlier at smaller a and larger AA, with larger umbilical venous diameter ratios at smaller a and smaller AA. Comparison with the 21 clinical cases was good, except for 2. CONCLUSION: Our analysis supports Benirschke's hypothesis. The smaller twin has to share its placental perfusion with the larger twin, which is a novel finding. The AA size is essential for the future of both fetuses but complicates easy understanding of (pseudo-)acardiac clinical presentations. Late acardiac onset occurs infrequently. Using nonpulsating circulations may have caused our extensive predictions of late onset. An improved model requires including hypoxemia in the smaller twin from chronic placental hypoperfusion. Birth Defects Research 109:211-223, 2017. © 2016 Wiley Periodicals, Inc.

Pygopagus Conjoined Twins: A Neurophysiologic Intraoperative Monitoring Schema.

Conjoined twins occur in up to 1 in 50,000 live births with approximately 18% joined in a pygopagus configuration at the buttocks. Twins with this configuration display symptoms and carry surgical risks during separation related to the extent of their connection which can include anorectal, genitourinary, vertebral, and neural structures. Neurophysiologic intraoperative monitoring for these cases has been discussed in the literature with variable utility. The authors present a case of pygopagus twins with fused spinal cords and imperforate anus where the use of neurophysiologic intraoperative monitoring significantly impacted surgical decision-making in division of these critical structures.

Separation of pyopagus conjoined twins: a New Zealand neurosurgical experience.

Conjoined twins represent a rare form of incomplete embryonic separation. They are classified into eight different subtypes, with 18% representing pyopagus conjoints. History is scattered with accounts of the various types of conjoints and it is only recently that strategies have been devised to enable surgical separation of such twins. It is estimated that approximately 20 cases of separation of pyopagus twins have been performed. We provide a historical look at pyopagus conjoint twins and report our neurosurgical experience of Australasia's first separation of pyopagus twin girls.