Management of monozygotic twins in the mare

Twin management in the mare: A review

“…The technique is performed by rectal manipulation and involves the isolation of the smallest or most easily accessible fetus with compression of its fetal neck/thorax between the ultrasound probe and the mare's pelvic brim/lateral abdominal wall by applying constant, increasing pressure to cause cardiac arrest, but without rupturing the chorioallantois. [51][52][53][54] Successful application results in faint valve movements or cardiac arrest immediately after performing the reduction or within 24 h. Cardiac arrest can be presented after a single session, however manipulation may need to be repeated on consecutive days. 52 The combination of a tocolytic, spasmolytic drug and NSAIDs can be administered at the time of the procedure to facilitate the isolation of the fetus, prevent rectal straining and inhibit prostaglandin release.…”

“…52 Regular ultrasonographic monitoring following this procedure is suggested to assess both the demise of the reduced fetus and the viability of the remaining fetus as an unsuccessful outcome is often not immediately apparent and abortion usually only occurs about 1 month after the procedure. 52,53 The thoracic compression technique is currently favoured and most effective between 55 and 65 days of gestation [52][53][54] and a live foal success rate of 60% (6/10; unilateral fixed twin pregnancies) can be expected. 53 Recently, Arnold et al 52 also reported a successful reduction to a singleton in 9 out of 10 (90%) dizygotic twins, seven of which have resulted in the birth of a normal sized single foal (70%).…”

“…52,53 The thoracic compression technique is currently favoured and most effective between 55 and 65 days of gestation [52][53][54] and a live foal success rate of 60% (6/10; unilateral fixed twin pregnancies) can be expected. 53 Recently, Arnold et al 52 also reported a successful reduction to a singleton in 9 out of 10 (90%) dizygotic twins, seven of which have resulted in the birth of a normal sized single foal (70%). Disadvantages and factors that negatively impact the outcome are: time spent to perform the procedure, multiple manipulations in consecutive days, operator's experience and insufficient isolation of the targeted fetus.…”

“…Disadvantages and factors that negatively impact the outcome are: time spent to perform the procedure, multiple manipulations in consecutive days, operator's experience and insufficient isolation of the targeted fetus. 52,53…”

“…81 The placental architecture of monozygotic twins and triplets indicates the embryonic stage at which the embryo splits. 82 In the horse, there are a few described sets of dichorionic diamniotic monozygotic twins, 53,77,79 but most reported cases have been monochorionic diamniotic/diallantoic, suggesting that these pregnancies most likely arise from the division of the inner cell mass (ICM) within one blastocyst. 78,81,82 Monochorionic diamniotic/diallantoic monozygotic twins or triplets are characterised by the presence of two or more embryonic bodies, each with their own amnion and developing allantois, but sharing a single yolk sac.…”