Ultrasound-guided fetal thorax compression to reduce post-fixation twins in the mare.

Background: Management of twin pregnancy after conceptus vesicle fixation in the horse is challenging because the reduction techniques described are either invasive, difficult to perform or associated with disappointing success rates.

Objectives: To evaluate the success of transrectal ultrasound-guided fetal thorax compression for reducing post-fixation twin pregnancy in mares.

Study Design: Retrospective clinical study.

Methods: Sixteen mares were presented for twin reduction between 51 and 79 days of gestation. History obtained from the owner and/or referring veterinarian detailed information regarding the mare (age, breed), pregnancy (day of gestation, dizygotic versus monozygotic twins, unilateral versus bilateral fixation), treatment and outcome (one live fetus at discharge; live singleton at foaling) after twin reduction. Transrectal fetal thorax compression was performed under ultrasound guidance by two experienced operators.

Results: Overall 9 of 16 twin pregnancies were successfully reduced and the likelihood of success was significantly higher in dizygotic than monozygotic twins. The procedure was successful in 9 of 10 dizygotic twins but unsuccessful in all six cases of monozygotic twins. Among the dizygotic twins, two mares lost the pregnancy after discharge from the clinic, seven mares delivered a healthy foal of normal size.

Main Limitations: Small case number.

Conclusions: Transrectal ultrasound-guided fetal thorax compression is a minimally-invasive and successful technique for reducing dizygotic twin pregnancies at approximately 2 months of gestation, but does not lead to any live births in cases of monozygotic twins.