In vitro simulation of acute feto-fetal transfusion in case of single intrauterine fetal death in monochorionic twins

INTRODUCTION

Thanks to shared circulation in monochorionic twins, single intrauterine fetal death (IUD) may lead to acute feto-fetal transfusion (aFFTR). The objective of the study was to describe our model of aFFTR simulation after IUD in monochorionic (MC) twins.

METHODS

Prospective study analyzed 99 fresh MC placentas with the physiological course. A specially designed protocol was used for the preparation and analysis of the placentas. A pair of infusion sets fixed together using a mechanical mercury sphygmomanometer cuff was connected to the cannulated umbilical arteries. The tonometer was pressurized up to 30 and 40 mmHg. A positive finding of aFFTR was determined as the amount exceeding 1 ml of dye flowed out of the umbilical cord simulating a dead fetus. The number and types of anastomoses, types, and distances between cords insertions, and the size of the placental areas for each fetus were also statistically analyzed. The placental angioarchitecture with and without proven aFFTR was statistically compared, odds ratio (OR) and multivariable logistic analysis were performed.

RESULTS

A total of 49/99 (49.5%) cases of aFFTR was proven, and the average transfusion time of 1 ml was 30 s (19-46 s). aFFTR was present in 49/78 (62.8%) of placentas with arterio-arterial (AA) anastomosis. The median diameter of AA anastomoses with the present, and absent aFFTRF was 2.0 mm and 1.0 mm, respectively. The proven interfetal transfusion was 8%, 31%, and 61% in AA anastomoses with a diameter below 0,5 mm, 0,5-1,5 mm, and above 1,5 mm, respectively (p < 0,001). AA anastomoses diameter >1.5 mm had OR of 44.2 (95% CI 5.54-352.39). In the case of coexistence of AA anastomosis and umbilical cord distance ≤5th percentile, the aFFTRF occurred in 90.9%.

DISCUSSION

The potential risk of aFFTR in monochorionic twins is mainly due to the presence and nature of AA anastomoses. The diameter and length of the vessels play a crucial role, which is clinically related to the distance of the umbilical cords insertions.

Acardiac twin pregnancies part VI: Why does acardiac twinning occur only in the first trimester?

BACKGROUND

Clinical observation suggests that acardiac twinning occurs only in the first trimester. In part, this contradicts our previous analysis (part IV) of Benirschke's concept that unequal embryonic splitting causes unequal embryo/fetal blood volumes and pressures. Our aim is to explain why acardiac onset is restricted to the first trimester.

METHODS

We applied the vascular resistance scheme of two fetuses connected by arterio-arterial (AA) and veno-venous (VV) anastomoses, the small VV resistance approximated as zero. The smaller twin has volume fraction α < 1 of the assumed normal larger twin, and has only access to fraction X < 1 of its placenta; the larger twin's larger mean arterial pressure accesses the remaining fraction. Before 13 weeks, embryos have a much smaller vascular resistance than placentas. After 13 weeks, when maternal blood provides oxygen, smaller twins can increase their vascular volume by hypoxemia-mediated neovascularization. Estimated AA radii at 40 weeks, r_AA (40), are 0.5-1.3 mm.

RESULTS

Embryos with α < 0.33 unlikely survive 13 weeks and acardiac twinning occurs under appropriate conditions (AA-VV, small placenta). Acardiac body perfusion occurs because of a much smaller vascular resistance than the placenta. When α > 0.33 and r_AA (40)=1.3 mm, modeled survival is >32 weeks.

CONCLUSION

Before 13 weeks, embryos with α < 0.33 cannot survive and may result in the onset of acardia. Beyond 13 weeks, fetuses with α ≥ 0.33 survive because r_AA (40) is too small for acardiac onset. Following fetal demise, exsanguination from the live twin increases its blood volume and, we assumed also, its vascular resistance. Perfusion then occurs through the lower resistance placenta.

Aortic distensibility as a surrogate for intertwin pulse pressure differences in monochorionic pregnancies with and without twin-twin transfusion syndrome

OBJECTIVES

Twin-twin transfusion syndrome (TTTS) complicates 10-15% of monochorionic diamniotic (MCDA) twin pregnancies. The donor response to hypovolemia allows the transfer of vasoactive mediators to the recipient, causing increased recipient afterload and hypertension. Our objective was to apply a novel speckle-tracking technique to measure the aortic fractional area change (AFAC) during the cardiac cycle in MCDA twins with and without TTTS, and identify intertwin differences in AFAC and parameters of cardiac function.

METHODS

High-frame rate four-chamber views of the fetal heart, including the mid-thoracic aorta, were collected prospectively in MCDA twin pairs referred to our center between June 2014 and April 2015. Using speckle-tracking software, the endovascular border of the aorta was traced manually during systole, with guidance on cardiac cycle timing by anatomical M-mode. AFAC, defined as the difference between maximum and minimum area divided by minimum area, expressed as a percentage, was calculated offline and averaged over three cardiac cycles. Tissue Doppler and displacement were used to measure long-axis cardiac function. Intra- and interclass correlation coefficients were used to test observer variability.

RESULTS

Fifty-one MCDA twin pregnancies were included, comprising uncomplicated MCDA (n = 14), TTTS Stages 1/2 (n = 21) and TTTS Stages 3/4 (n = 16). Median gestational age was 20.4 (range, 16.2-27.5) weeks. Mean ± SD heart rate was 142.6 ± 7.2 bpm with no significant intertwin pair differences. AFAC was significantly higher in recipients than in donors of TTTS pairs (Stages 1/2: 72.3 ± 29.9% vs 43.7 ± 19.3%, P < 0.001; Stages 3/4: 75.2 ± 29.2% vs 42.5 ± 18.4%, P = 0.002), consistent with higher recipient pulse pressure. No intertwin differences in AFAC were seen in uncomplicated MCDA pairs. Inter- and intraclass correlation coefficients for AFAC were 0.894 and 0.888. AFAC correlated significantly with combined cardiac output (r = 0.252, P = 0.011) and left and right E/E' ratio (left: r = 0.302, P = 0.004; right: r = 0.247, P = 0.030).

CONCLUSION

AFAC is a quantifiable and reproducible method to assess aortic distensibility and is a promising tool to monitor the response to prelaser therapeutic interventions in pregnancies with TTTS. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Twin-to-twin transfusion syndrome (TTTS)

Twin-to-twin transfusion syndrome (TTTS) is a severe complication of monochorionic (MC) twin pregnancies, characterized by the development of unbalanced chronic blood transfer from one twin, defined as donor twin, to the other, defined as recipient, through placental anastomoses. If left untreated, TTTS is associated with very high perinatal mortality and morbidity rates, due to a combination of fetal and/or obstetric complications. The reported prevalence is 10-15% of all MC twins, or about 1 in 2000 pregnancies. This consensus document reviews available evidence and offers practical guidance to clinicians by providing recommendations on various aspects concerning diagnosis and management of TTTS.