Prolonged intermittent reversed end-diastolic flow in a monochorionic twin pregnancy associated with twin-to-twin transfusion syndrome and absence of Hyrtl's anastomosis

The role of the absence of Hyrtl's anastomosis in monochorionic pregnancy: Friend or foe?: A case report

INTRODUCTION

Hyrtl's anastomosis, an intra-arterial shunt, plays a protective role when the placental territories supplied by the umbilical arteries are different in size. Its absence is associated with an increased risk of poor outcomes in singleton pregnancy. However, the literature and studies on the effect of absent Hyrtl's anastomosis in twin placentas are rare.

CASE PRESENTATION

We present a case of a monochorionic diamniotic twin pregnancy complicated with type I selective fetal growth restriction (SFGR). Despite discordance in placental territory and cord insertion sites, the patient had an overall good pregnancy process, suggesting that the absence of Hyrtl's anastomosis may have played a benign role.

CONCLUSIONS

The absence of Hyrtl's anastomosis in our case seemed to show a favorable effect, representing a finding of opposite effects in monochorionic placentas compared with singleton placentas.

Incidence and characteristics of umbilical artery intermittent absent and/or reversed end-diastolic flow in complicated and uncomplicated monochorionic twin pregnancies

OBJECTIVE

To evaluate the incidence and clinical relevance of intermittent absent and/or reversed diastolic flow on umbilical artery Doppler in different groups of monochorionic twin pregnancies.

METHODS

This was a prospective study involving three groups of monochorionic pregnancies: Group 1: controls followed fortnightly from the first trimester (n = 80); Group 2: cases with selective intrauterine growth restriction (n = 40); and Group 3: cases with severe twin-twin transfusion syndrome (n = 50). The presence and persistence over time of intermittent absent and/or reversed end-diastolic flow on umbilical artery Doppler was recorded. Placentas were examined and placental sharing and the presence of large arterioarterial anastomoses (AAA) was assessed. Perinatal outcome was recorded in all cases.

RESULTS

Intermittent absent and/or reversed diastolic flow was present in 5% (4/80) of cases in Group 1, 45% (18/40) in Group 2 and 2% (1/50) in Group 3 (P < 0.0001, Group 2 vs. 1 and 3). Placental examination was performed in 76.4% (130/170) of cases and sharing was 58% for Group 1, 81% for Group 2 and 73% for Group 3 (P < 0.0001, Groups 2 and 3 vs. 1). Large AAA were identified in all examined cases with intermittent flow (18/18) and in 3.6% (4/112) of those without. The in-utero mortality rate was 0% in Group 1 and in Group 2 fetuses without intermittent flow. However, it was 19.4% in Group 2 cases with intermittent diastolic flow.

CONCLUSIONS

Intermittent absent and/or reversed end-diastolic flow may be considered to be a characteristic sign of monochorionic pregnancy, and seems to result from the existence of large AAA. Its incidence is significantly increased in the context of selective intrauterine growth restriction, indicating a high risk for poor pregnancy outcome in these cases.