Outcome of monochorionic twin pregnancy with selective intrauterine growth restriction according to umbilical artery Doppler flow pattern of smaller twin.
Management of sIUGR in MC twin pregnancy is challenging. There are no randomized controlled trials on how to manage and when to deliver these pregnancies. Furthermore, the natural history and clinical evolution of sIUGR in MC twins have not yet been ascertained completely, precluding an evidence-based approach to their management in clinical practice.
Classification of sIUGR based on the UA Doppler flow pattern of the smaller twin provides a valuable tool to stratify the obstetric risk of these pregnancies. However, it may not reflect entirely the natural history of the anomaly because management choices, such as fetal therapy, can affect perinatal outcome. Therefore, the different types of sIUGR may not reflect accurately progression of disease severity.
Type I sIUGR most likely represents the milder spectrum of growth restriction in MC twins; the degree of unequal placental sharing between the twins is smaller than for the other types of sIUGR, thus precluding a large discrepancy in fetal size. Furthermore, the relatively small number of arterioarterial anastomoses compared with the other sIUGR types allows relative hemodynamic stability between the twins, which is reflected in the lower occurrence of perinatal death and postnatal brain damage. In the absence of Doppler abnormalities, it seems reasonable to follow up these pregnancies conservatively with weekly ultrasound scans.
Type II sIUGR pregnancies are affected commonly by severe discordance in fetal weight and by progressive abnormalities in arterial and venous Doppler, requiring delivery at an earlier gestational age. However, the latency between onset of UA flow anomalies and delivery is usually longer than that in singleton and dichorionic twin gestations.
Type II sIUGR is usually characterized by a progressive deterioration of fetal status, requiring
early delivery. The optimal prenatal management of these pregnancies is yet to be established and should. be tailored according to the gestational age at diagnosis, the degree of fetal weight discordance and the severity of Doppler abnormalities. A closer follow up with biweekly scans in the presence of absent or reversed end-diastolic flow in the UA, followed by delivery when venous Doppler abnormalities occur, represents the most reasonable option, although it would require confirmation in a prospective trial.
Prenatal therapy, such as cord occlusion or laser coagulation of placental anastomoses, can be considered before viability but it is affected by a relatively high rate of cotwin loss or maternal complications, such as preterm delivery, and is technically more difficult than when performed for TTTS.
early delivery. The optimal prenatal management of these pregnancies is yet to be established and should. be tailored according to the gestational age at diagnosis, the degree of fetal weight discordance and the severity of Doppler abnormalities. A closer follow up with biweekly scans in the presence of absent or reversed end-diastolic flow in the UA, followed by delivery when venous Doppler abnormalities occur, represents the most reasonable option, although it would require confirmation in a prospective trial.
Prenatal therapy, such as cord occlusion or laser coagulation of placental anastomoses, can be considered before viability but it is affected by a relatively high rate of cotwin loss or maternal complications, such as preterm delivery, and is technically more difficult than when performed for TTTS.
Type III sIUGR is characterized by the presence of intermittent absent or reversed end-diastolic flow in the UA of the smaller twin. This feature is unique to MC twins and is due to the peculiar vascular arrangement of Type III sIUGR placentae, which show significantly more large arterioarterial anastomoses compared with uncomplicated Types I and II sIUGR twins.
These large arterioarterial anastomoses allow continuous blood exchange between the umbilical cords of the twins, which is reflected in a specific appearance of the UA waveform. The intermittent Doppler pattern is mostly seen close to the placental insertion site of the umbilical cord and can be missed easily unless low sweep speed pulsed Doppler is used. The clinical course of pregnancies with Type III sIUGR is mainly determined by the magnitude and direction of blood exchange, which may lead to different clinical outcomes, even in twins showing the same degree of growth discrepancy.
Type III sIUGR is affected by a high rate of unexpected fetal demise, even in the case of stable Doppler findings, thus questioning the actual role of Doppler ultrasound in managing these pregnancies. Management of Type III sIUGR is arbitrary; several factors such as gestational age
at diagnosis, degree of growth discordance and severity of Doppler anomalies may help the decision planning, but parents should be counseled about the unpredictable clinical course of these pregnancies. Fetal therapy may be considered before viability although, as for Type II sIUGR, it may be challenging technically due to the short distance between the umbilical cord and the absence of twin oligohydramnios – polyhydramnios sequence.
Large multicenter prospective trials are needed to find the optimal management of these pregnancies
according to gestational age at diagnosis and type and severity of UA Doppler pattern and degree of BW discordance.
Type III sIUGR is affected by a high rate of unexpected fetal demise, even in the case of stable Doppler findings, thus questioning the actual role of Doppler ultrasound in managing these pregnancies. Management of Type III sIUGR is arbitrary; several factors such as gestational age
at diagnosis, degree of growth discordance and severity of Doppler anomalies may help the decision planning, but parents should be counseled about the unpredictable clinical course of these pregnancies. Fetal therapy may be considered before viability although, as for Type II sIUGR, it may be challenging technically due to the short distance between the umbilical cord and the absence of twin oligohydramnios – polyhydramnios sequence.
Large multicenter prospective trials are needed to find the optimal management of these pregnancies
according to gestational age at diagnosis and type and severity of UA Doppler pattern and degree of BW discordance.
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