Complicated Monochorionic Twin Pregnancies Research Articles

Vasoactive Management of Pulmonary Hypertension and Ventricular Dysfunction in Neonates Following Complicated Monochorionic Twin Pregnancies: A Single-Center Experience.

Twins resulting from a complicated monochorionic (MC) twin pregnancy are at risk for postnatal evolution of pulmonary hypertension (PH) and cardiac dysfunction (CD). Both pathologies are important contributors to short- and long-term morbidity in these infants. The aim of the present retrospective single-center cohort study was to evaluate the need for vasoactive treatment for PH and CD in these neonates. In-born neonates following a complicated MC twin pregnancy admitted to the department of neonatology of the University Children's Hospital Bonn (UKB) between October 2019 and December 2023 were screened for study inclusion. Finally, 70 neonates were included in the final analysis, with 37 neonates subclassified as recipient twins (group A) and 33 neonates as donor twins (group B). The overall PH incidence at day of life (DOL) 1 was 17% and decreased to 6% at DOL 7 (p = 0.013), with no PH findings at DOL 28. The overall incidence of CD was 56% at DOL 1 and decreased strongly until DOL 7 (10%, p = 0.015), with no diagnosis of CD at DOL 28. The use of dobutamine, norepinephrine, and vasopressin at DOL 1 until DOL 7 did not differ between the subgroups, whereas the dosing of milrinone was significantly higher in Group B at DOL 1 (p = 0.043). Inhaled nitric oxide (iNO) was used in 16% of the cohort, and a levosimendan therapy was administered in 34% of the neonates. One-third of the cohort was treated with oral beta blockers, and in 10%, an intravenous beta blockade (landiolol) was administered. The maximum levosimendan vasoactive-inotropic score (LVISmax) increased from DOL 1 (12.4 [3/27]) to DOL 2 (14.6 [1/68], p = 0.777), with a significant decrease thereafter as measured at DOL 7 (9.5 [2/30], p = 0.011). Early PH and CD are frequent diagnoses in neonates following a complicated MC twin pregnancy, and an individualized vasoactive treatment strategy is required in the management of these infants.

Cardiac adaptation and malformation in twin-twin transfusion syndrome and selective fetal growth restriction: A systematic review.

This systematic review explores cardiac adaptation in monochorionic (MC) twins with twin-twin transfusion syndrome (TTTS) or selective fetal growth restriction (sFGR) and assesses the risk of congenital heart defects (CHDs). Adhering to PRISMA guidelines, 63 studies were reviewed (49 on cardiac adaptation, 13 on CHD, one on both). A narrative synthesis of cardiac adaptation patterns was performed. Additionally, a meta-analysis compared the livebirth prevalence of CHD in TTTS and sFGR against uncomplicated MC twins. In TTTS recipients, cardiac function may be impaired for diastolic, systolic, as well as global functions, while in donors, cardiac function is generally preserved. In sFGR, large twins may show hypertrophic cardiomyopathy, and small twins may show impaired systolic function. Co-occurrence of TTTS and sFGR magnifies cardiac impact but is often underreported. Meta-analysis for CHD prevalence revealed a relative risk ratio of 3.5 (95% CI: 2.5-4.9) for TTTS and 2.2 (95%CI: 1.3-3.5) for sFGR compared with uncomplicated MC twins. This study highlights the well-documented cardiac adaptation in TTTS, contrasting with limited understanding in sFGR. Elevated CHD risks were observed in both conditions. Enhanced cardiovascular surveillance is warranted in complicated MC twin pregnancies. Future research should explore cardiac adaptation in sFGR and its long-term consequences.

New radiofrequency ablation procedure for selective reduction in complicated monochorionic twin or triplet pregnancy using multistep, incremental expansion technique.

Radiofrequency ablation (RFA) is the preferred approach for selective reduction in complex monochorionic (MC) multiple pregnancies owing to the ease of operation and minimal invasiveness. To optimize the RFA technique and reduce the risk of adverse pregnancy outcome resulting from the heat-sink effect of RFA therapy, we used an innovative RFA method, in which an electrode needle was expanded incrementally and stepwise. This study aimed to assess the efficacy and safety profile of this novel multistep incremental expansion RFA method for selective fetal reduction in MC twin and triplet pregnancies. This was a single-center retrospective cohort study of all MC multiple pregnancies undergoing RFA between March 2016 and October 2022 at our center. The multistep RFA technique involved the use of an expandable needle, which was gradually expanded during the RFA procedure until cessation of umbilical cord blood flow was achieved. The needle used for the single-step RFA method was fully extended from the start of treatment. In total, 132 MC multiple pregnancies underwent selective reduction using RFA, including 50 cases undergoing multistep RFA and 82 cases undergoing single-step RFA. The overall survival rates were not significantly different between the multistep and single-step RFA groups (81.1% vs 72.3%; P = 0.234). Similarly, the rates of preterm prelabor rupture of the membranes within 2 weeks after RFA, procedure-related complications, spontaneous preterm delivery and pathological findings on cranial ultrasound, as well as gestational age at delivery and birth weight, did not differ between the two groups. However, there was a trend towards a prolonged procedure-to-delivery interval following multistep RFA compared with single-step RFA (median, 109 vs 99 days; P = 0.377). Moreover, the fetal loss rate within 2 weeks after RFA in the multistep RFA group was significantly lower than that in the single-step RFA group (10.0% vs 24.4%; P = 0.041). The median ablation time was shorter (5.3 vs 7.8 min; P < 0.001) and the median ablation energy was lower (10.2 vs 18.0 kJ; P < 0.001) in multistep compared with single-step RFA. There were no significant differences in neonatal outcomes following multistep vs single-step RFA. Overall survival rates were similar between the two RFA methods. However, the multistep RFA technique was associated with a lower risk of fetal loss within 2 weeks after RFA. The multistep RFA technique required significantly less ablation energy and a shorter ablation time compared with single-step RFA in selective fetal reduction of MC twin and triplet pregnancies. Additionally, there was a trend towards a prolonged procedure-to-delivery interval with the multistep RFA technique. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

SFM Fetal Therapy Practice Guidelines: Radiofrequency Ablation of Fetal Umbilical Cord

AbstractIn radiofrequency ablation (RFA), the ions in the tissue surrounding the probe's uninsulated tip are noticeably stirred up by the electrode's high-frequency alternating current. The surrounding tissue experiences thermal coagulation necrosis as a result of the frictional heat.RFA is used in complicated monochorionic twin pregnancies with selective fetal growth restriction (FGR), TRAP, and TTTS. RFA may also be considered in giant chorioangioma with favorable vascular anatomy and giant sacrococcygeal teratoma with imminent hydrops. It serves as a substitute to laser.

The impact of placental anastomoses and umbilical cord insertions’ sites on monochorionic twin pregnancy outcomes: Evidence from color-dye injection studies

IntroductionOur knowledge of monochorionic pregnancies’ complications is largely based on the extensive ongoing research on monochorionic placental structure. Previous studies on the concordance of umbilical cord insertions are limited. This study aimed to evaluate placental anastomoses and cord insertions as independent risk factors for neonatal adverse outcomes. MethodsThis was a prospective study conducted at Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy from April 2021 to December 2022. Seventy-six women with a monochorionic pregnancy were enrolled at their first-trimester scan. After delivery, all placentas that were confirmed to be monochorionic were analyzed according to standard protocols, including those of complicated monochorionic twin pregnancies. The primary outcomes were a Composite Monochorionic Pregnancy Outcome (CMPO) and a Composite Neonatal Adverse Outcome (CNAO). The secondary outcome was the birth weight discordance between the neonates. ResultsThe CMPO occurred in 15.8 % pregnancies, and the CNAO occurred in 67.1 % pregnancies. The analysis confirmed a significant association between velamentous cord insertions and neonatal adverse events (p = 0.003). Also, a significant positive association (p = 0.0326) between twin birth weight discordance and discordance in twins umbilical cord insertions’ sites was found. No significant association between the number and type of the anastomoses and both the CMPO or CNAO was detected. DiscussionOur data suggest that the routine sonographic assessment of umbilical cords' insertion sites during the first trimester could be helpful in predicting fetal and neonatal adverse events. We believe that this sonographic assessment should start to be implemented in our routine care of monochorionic pregnancies.

Placental DNA methylation analysis of selective fetal growth restriction in monochorionic twins reveals aberrant methylated CYP11A1 gene for fetal growth restriction.

Fetal growth restriction (FGR) is associated with increased susceptibility to perinatal morbidity and mortality. Evidence suggests that epigenetic changes play critical roles in the regulation of fetal growth. We sought to present a comprehensive analysis of the associations between placental DNA methylation and selective fetal growth restriction (sFGR), which is a severe complication of monochorionic twin pregnancies, characterized by one fetus experiencing restricted growth. Genome-wide methylation analysis was performed on 24 placental samples obtained from 12 monochorionic twins with sFGR (Cohort 1) using Illumina Infinium MethylationEPIC BeadChip. Integrative analysis of our EPIC data and two previous placental methylation studies of sFGR (a total of 30 placental samples from 15 sFGR twins) was used to identify convincing differential promoter methylation. Validation analysis was performed on the placentas from 15 sFGR twins (30 placental samples), 15 FGR singletons, and 14 control singletons (Cohort 2) using pyrosequencing, quantitative real-time polymerase chain reaction, western blot, and immunohistochemistry (IHC). A globe shift toward hypomethylation was identified in the placentas of growth-restricted fetuses compared with the placentas of normal fetuses in monochorionic twins, including 5625 hypomethylated CpGs and 452 hypermethylated CpGs, especially in the regions of CpG islands, gene-body and promoters. The analysis of pathways revealed dysregulation primarily in steroid hormone biosynthesis, metabolism, cell adhesion, signaling transduction, and immune response. Integrative analysis revealed a differentially methylated promoter region in the CYP11A1 gene, encoding a rate-limiting enzyme of steroidogenesis converting cholesterol to pregnenolone. The CYP11A1 gene was validated to have hypomethylation and higher mRNA expression in sFGR twins and FGR singletons. In conclusion, our findings suggested that the changes in placental DNA methylation pattern in sFGR may have functional implications for differentially methylated genes and regulatory regions. The study provides reliable evidence for identifying abnormally methylated CYP11A1 gene in the placenta of sFGR.

Surveillance of pregnancy outcome of monochorionic twins at Tu Du Hospital

Background: Monochorionic twins are a high risk pregnancy and are associated with special complications that are unique to sharing a placenta and because of the hemodynamic imbalance caused by placental vascular anastomoses. Therefore, the outcome of monochorionic twins is still being researched and reported to looking for the best evidence to perform the optimal interventions.&#x0D; Objectives: To describe the outcome of monochorionic twins to determine the proportion of special complications. Moreover, exploring the rate of fetal death in uterus, premature delivery, the successful vaginal birth in complicated monochorionic twins after bipolar cord coagulation.&#x0D; Materials and Methods: Case series report of monochorionic twins which was managed pregnancy and delivered at Tu Du hospital between January 2018 and January 2019, comprised 166 cases with 81 complicated monochorionic twin pregnancies.&#x0D; Results: The series comprised 85 uncomplicated monochorionic twins (51.2%) and 81 complicated cases (48.8%) with 15% twin-twin transfusion syndrome (TTTS) and 28.3% selective intrauterine growth restriction (sIUGR). Nineteen cases of bipolar cord coagulation perfomed included seven TTTS, eight sIUGR, three cases with serious malformation, and one twin reversed arterial perfusion sequence (TRAP).&#x0D; Conclusions: TTTS and sIUGR are complications unique to monochorionic twins and diagnosed in the early stage after 23 week’s gestation. Bipolar cord coagulation is an effective procedure in complicated monochorionic pregnancies to improve pregnancy outcome.

Perinatal outcome after selective fetal reduction in monochorionic twin pregnancies: A comparison of techniques over a 20-year period.

To assess the perinatal outcome after fetal reduction in complicated monochorionic (MC) twin pregnancies by comparing different techniques. A retrospective cohort study at a national referral center comparing data between four techniques: interstitial laser coagulation, radiofrequency ablation (RFA), fetoscopic laser coagulation (FLC) and bipolar cord coagulation (BCC). The primary outcome was the mortality of the co-twins. Secondary outcomes were preterm pre-labor rupture of membranes (PPROM), gestational age at delivery and neonatal morbidity. 259MC twin pregnancies underwent selective fetal reduction: 29 IL, 64 RFA, 85 FLC and 81 BCC. The perinatal mortality rate was 29% and fetal demise of the co-twins occurred in 19%. The lowest mortality rate was seen after BCC (17%, p=0.012). PPROM occurred in 18% patients without significant differences between techniques. The mean gestational age at delivery in liveborn children was 35weeks and did not differ between techniques. Severe cerebral injury and neonatal morbidity were reported in 4% and 14%, respectively, without significant differences between techniques. Selective fetal reductions in MC twins are precarious procedures with an increased risk of perinatal mortality of the co-twins. Our results show the lowest mortality rates after BCC. However, high PPROM rates were seen irrespective of the technique.

Does Progesterone Prevent Preterm Labor in Complicated Monochorionic Twin Pregnancies after Radiofrequency Ablation of One Fetus?

Background: Twin pregnancies have a higher risk of preterm labor than singletons. Otherwise, progesterone using to reduce the risk of preterm labor in twin pregnancies remains controversial. Therefore, this study evaluated the effect of intramuscular progesterone to prevent preterm labor in complicated monochorionic diamniotic twin pregnancies after Radiofrequency Ablation (RFA) of one fetus.&#x0D; Methods: Pregnant women with monochorionic diamniotic twin pregnancies of 16 to 26 weeks of gestational age in an academic center were randomly assigned to receive intramuscular 17-hydroxy progesterone caproate weekly until 36 weeks of gestational age after RFA of one fetus and a control group who did not receive intervention after RFA. Demographic and obstetrical characteristics, as well as maternal, fetal and neonatal outcomes were compared between groups.&#x0D; Results: In total, 79 participants were recruited in the study. The mean±SD of gestational age at delivery in case and control groups were 34.6±3.8 and 34.6±5.1 with no significant difference (p=0.967). Neonatal outcomes including birth weight (p=0.870), intensive care unit admission (p=0.415), premature preterm rupture of membrane (p=0.115) and pregnancy outcome (live birth, fetal demise or neonatal death) (p=0.524) were not different either. Indeed, gestational age at delivery was inversely related to cervical length at the time of procedure and maternal body mass index, but these differences were not statistically significant. Also, there was no significant difference in terms of gestational diabetes, which was a worrying complication of 17-hydroxy progesterone caproate.&#x0D; Conclusion: Although 17-hydroxy progesterone caproate seems to be safe with no apparent maternal and neonatal side effects, it does not prolong pregnancy after RFA. Further studies with longer follow up and larger sample size are suggested.

Long-term follow-up of complicated monochorionic twin pregnancies: Focus on neurodevelopment.

Monochorionic twin pregnancies have an increased risk of morbidity and mortality. Due to the advancements in screening and treatment strategies, mortality rates have decreased. Improving survival rates demands a shift in scope toward long-term outcomes. In this review, we focus on neurodevelopmental outcome in survivors from complicated monochorionic twin pregnancies, including twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), acute peripartum TTTS, acute perimortem TTTS, selective fetal growth restriction (sFGR) and monoamnionicity. Our aim is to provide an overview of the current knowledge on the long-term outcome in survivors, including psychomotor development and quality of life, and provide recommendations for future research and follow-up programs.

Twin Reversed Arterial Perfusion Sequence.

Twin Reversed Arterial Perfusion Sequence.

Success Rate and Perinatal Outcomes of Selective Reduction by Radiofrequency Ablation in Monochorionic Multiple Pregnancies with a Hydropic Fetus; A Prospective Interventional Single-Arm Study.

Selective reduction of the fetus is one of the therapeutic methods in complicated monochorionic twins. The present study aimed to investigate the success rate and perinatal outcomes of selective reduction using radiofrequency ablation (RFA) in monochorionic multiple pregnancies with a hydropic fetus. This prospective interventional single-arm study was conducted in a referral hospital from 2017 to 2019. Totally, 27 complicated monochorionic twin and triplet pregnancies underwent RFA to occlude the umbilical vein of the hydropic fetus. The participants were followed until 2 months post-delivery. Procedure success rate, survival rate, gestational age at delivery, and neonatal outcome were evaluated. The umbilical cord in 26 (96.2%) cases was successfully occluded by RFA with no maternal complications. Live birth was within 75%. The mean±SD age at delivery was 34.4±3.83 weeks. The gestational age at delivery in TTTS (twin-to-twin transfusion syndrome)-induced hydrops was significantly lower than the non-TTTS hydrops group (P=0.003). Four cases experienced preterm premature rupture of the membranes (PPROM) before 34 weeks. Of all viable neonates, 8 cases were admitted to the neonatal intensive care unit (NICU). In 2 months follow-up post-delivery, all neonates had normal findings without any adverse outcomes. Selective reduction by RFA in complicated monochorionic pregnancies with a hydropic fetus may be a safe method with a high success rate and 100% neonatal survival. This method may be optimal for feticide in non-TTTS hydropic twins.

Acardia anceps- A case report

Twin-Reversed Arterial Perfusion(TRAP) sequence or Acardia twin refers to a unique complication of mono-chorionic twin pregnancy in which a twin with an absent or rudimentary non functioning heart (acardiac twin) is perfused by its co-twin (pumping twin) through a large artery to artery placental shunt, often accompanied by a vein to vein shunt. Here we discussed about a clinical case of TRAP sequence came in established preterm labour and its management.

Twin-to-twin transfusion syndrome: new macroscopic and microscopic findings

Abstract Background Twin-to-twin Transfusion Syndrome (TTTS) is a serious complication of monochorionic twin pregnancies. Affects about 10% to 15% of pregnancies and it is associated with high fetal and neonatal mortality, as well as cardiac and neurological morbidity in surviving fetuses. The main objective was to characterize a series of fetuses with TTTS since the pathophysiology of the syndrome is not fully understood and the clinical spectrum is broad. Methods Post-mortem macroscopic and microscopic examination of 26 fetuses (from 2010 to 2020) with TTTS syndrome. Results The most frequent macroscopic findings in placenta were discrepancy in size and pallor/placental congestion. Other macroscopic findings not described in the literature were calcifications, areas of infarction and hematomas. Infarction areas and villi heterogeneity growth were the most common microscopic findings, described in the literature. Regarding the fetus, the restriction of intrauterine growth, the alteration of anthropometric parameters and the presence of a plethoric/anemic fetus were the main characteristics associated with this syndrome. The most common microscopic findings were signs of anoxia and congestive organs, already described in the literature. We also found frequently pulmonary abnormalities as new findings in our study. Conclusions The results allowed the identification of TTTS aspects that can contribute to the characterization of this syndrome. Given that the progression of TTTS remains unpredictable and the mortality rate for both fetuses is 90%, it becomes increasingly important to identify strategies for diagnosing and characterizing the syndrome.

Perinatal outcome in monochorionic twin pregnancies after selective fetal reduction using radiofrequency ablation.

To study the perinatal outcomes in women with complicated monochorionic twin pregnancies undergoing selective fetal reduction using radiofrequency ablation (RFA). This retrospective study included 44 patients with monochorionic twin pregnancies, between 14 and 28weeks of pregnancy, who underwent RFA for selective fetal reduction. Perinatal and maternal outcomes and procedure-related complications were analyzed. The procedure was technically successful in all 44 cases. Indications for selective fetal reduction included twin-to-twin transfusion syndrome (52.3%), twin reversed arterial perfusion (20.5%), twins discordant for anomaly (15.9%), and selective fetal growth restriction (11.4%). Median gestational age at procedure was 222/7 weeks (range 14-266/7 ). Live birth rate was 77.3% with three neonatal deaths; so overall survival was 70.5%. Median procedure-to-delivery interval was 123/7 weeks (range 24/7 -23). There were eight losses before 24weeks of pregnancy, which included two co-twin deaths. Median gestational age at delivery was 35weeks (interquartile range 321/7 -37weeks). The preterm delivery rate was 66.7% (24/36) and preterm prelabor rupture of membranes (PPROM) occurred in 22.7% (10/44) of patients. Selective fetal reduction using RFA is safe and effective in complicated monochorionic pregnancies. However, the rates of PPROM and preterm delivery remain high.

Call to action: long‐term neurodevelopment in monochorionic twins

Call to action: long‐term neurodevelopment in monochorionic twins

Perinatal and Long Term Outcome of Monochorionic Twins Complicated by Twin-Twin Transfusion Syndrome

Twin-twin transfusion syndrome (TTTS) is the most harmful complication of monochorionic twin pregnancies. Fetoscopic laser coagulation of placental vascular anastomoses represents the causative and first-line treatment for the disease. Substantial improvements in survival rates and long-term outcome have been achieved during the last 20 years of practice. This is due to improvements in antenatal detection of the condition, surgical skills and centralization in the referral fetal therapy unit, as well as postnatal intensive care and follow up programs. Major morbidity issues concern cardiologic, renal and cerebral functions and are mainly caused by intrauterine haemodynamic imbalances and prematurity. This review summarizes the current evidence on the prognosis of monochorionic twins survivors after TTTS treated by laser surgery, focusing on perinatal and long-term outcomes.

Perinatal Outcomes following Radiofrequency Ablation in Complicated Monochorionic Multiple Pregnancies

Background Radiofrequency ablation (RFA) is considered as an optional treatment method in complicated monochorionic (MC) twin pregnancies. The purpose of this study is to investigate the main factors of fetal death after such treatment procedure. The study also compares the perinatal outcomes among various groups of indication and gestational age (GA) at procedure. Materials and Methods: This prospective cohort study considers 195 cases of MC multiple pregnancies including one twin with twin-twin transfusion syndrome, selective intrauterine growth restriction ,sever anomaly and twin reversed arterial perfusion sequence(TRAP) which underwent selected reduction using RFA from 2016 to 2018 at Yas Hospital, Tehran, Iran. The GA at RFA categorized as 16- 19+6 wks., 20-23+6 wks., and 24-28 wks. The analysis of risk factors of fetal death after RFA is based on multivariable logistic regression model. Results: The result of analysis reveals that the rate of co-twin anemia after RFA in anomaly indication was higher than the other indications significantly (p=0.038) while according to GA categories, it is significantly lower in 20-23+6 weeks. (p=0.016). Three independent significant factors contributing in fetal death after RFA were co-twin anemia after RFA, TRAP and anomaly indications of RFA and GA at RFA, respectively. Conclusion The co-twin anemia after RFA was found the most contributing factor of fetal death. As the results showed that the rate of co-twin anemia after RFA is significantly low in 20-23+6 weeks of GA, such GA is suggested for RFA procedure to reduce the fetal death.

Radiofrequency ablation for selective fetal reduction in complicated Monochorionic twins; comparing the outcomes according to the indications

BackgroundTo evaluate the perinatal outcomes in women with complicated monochorionic diamniotic twins who underwent selective reduction using radiofrequency ablation (RFA).MethodsThis retrospective study included patients with complicated monochorionic diamniotic twins between 16 to 28 weeks who underwent selective reduction using RFA.ResultsDuring the study period, 143 women with complicated monochorionic twins underwent RFA including 52 with selective fetal growth restriction (sFGR), 48 with twin to twin transfusion syndrome (TTTS), 33 with major fetal anomalies in one of the twins, and 10 with reversed arterial perfusion sequence (TRAP). The overall survival was 71.3% (102/143). The procedures were technically successful in achieving selective termination in all cases. The mean ± SD of gestational age at the time of the procedure was 21.0 ± 2.3 weeks. The mean ± SD of gestational age at delivery was 34.6 ± 3.3 weeks. The mean ± SD of overall procedure-to-delivery time was 12 ± 1.7 weeks. The pregnancy success rates among sFGR, TRAP, TTTS and anomaly groups were 82.7, 80, 73 and 60.7% respectively. There were no maternal complications.ConclusionRadiofrequency ablation for fetal reduction in complicated monochorionic twin pregnancies appears to be a reasonable option. The pregnancy success rate following RFA selective reduction was highest among sFGR and TRAP groups and lowest in the anomaly group.

Acardiac twin pregnancies part V: Why does an acardiac twin with renal tissue produce polyhydramnios?

BackgroundAcardiac twinning is a complication of monochorionic twin pregnancies. From literature reports, 30 of 41 relatively large acardiac twins with renal tissue produced polyhydramnios within their amniotic compartment. We aim to investigate the underlying mechanisms that cause excess amniotic fluid using an established model of fetal fluid dynamics.MethodsWe assumed that acardiac onset is before 13 weeks, acardiacs with renal tissue have normal kidney function and produce urine flow from 11 weeks on, and acardiac urine production requires a pressure of half the pump twin's mean arterial pressure. We apply a resistance network with the pump twin's arterio‐venous pressure as source, pump umbilical arteries, placenta, placental arterio‐arterial (AA) anastomoses and acardiac resistances. Acardiac amniotic fluid dynamics excluded acardiac lung fluid secretion, swallowing and the relatively small intramembranous flow.ResultsIn small acardiacs with sufficient urine production, polyhydramnios will occur due to the lack of amniotic fluid resorption. Urine production is dependent upon having sufficient mean arterial pressure, which requires nearly a two‐fold larger resistance within the acardiac as compared to the placental AA resistance. Subphysiologic arterial pressure may result in renal dysgenesis.ConclusionOur findings suggest the potential for prediction of which clinical acardiac cases may or may not develop polyhydramnios based upon noninvasive assessments of renal tissue, blood flow and urine production. This information would be of great value in determining early obstetric interventions as opposed to conservative management. These findings may also contribute to an improved knowledge of the fascinating pathophysiology that surrounds acardiac twinning.