Success rates and factors influencing pregnancy outcome after 464 transvaginal ultrasound‐guided twin reductions in the mare

Abstract

BackgroundTransvaginal ultrasound‐guided aspiration (TUA) is used for post‐fixation twin reduction in mares. However, there is limited information regarding factors that influence pregnancy outcome after TUA.ObjectivesTo evaluate the effect of day of gestation on which TUA is performed, aspiration volume, puncture of the conceptus, medication administered before and after TUA, embryo location, mare age and parity and operator experience on pregnancy and foaling rates after TUA.Study designRetrospective case series.MethodsData were collected from case records of 464 TUAs performed by 14 operators in 422 mares diagnosed pregnant with dizygotic twins in two different facilities between 2010 and 2019. Pregnancy status was determined by ultrasonography at 5–7 days and 3–4 weeks after the TUA was performed. Subsequent pregnancy and foaling results were obtained by follow‐up communication. The effects of mare, gestation‐ and TUA‐related variables on pregnancy and foaling rates were analysed by the chi‐square‐test for homogeneity and Fisher's exact test and logistic regression.ResultsTUA was performed between 21 and 82 days of gestation in unilaterally (267/359 [74.4%]) and bilaterally fixed (92/359 [25.6%]) twin pregnancies. A singleton pregnancy (218/381 [57.2%]), persistent twin pregnancy (60/381 [15.8%]), or the loss of both conceptuses (103/381 [27%]) was confirmed 5–7 days after TUA was performed. At 3–4 weeks post TUA 50.3% (163/324) of mares were diagnosed with a single viable pregnancy and 40.1% (127/317) went on to deliver a live single foal. TUA performed early in gestation (D 25–35) resulted in the birth of a live singleton foal in 49.3% (74/150) of mares.Main limitationsMissing retrospective data despite extensive follow‐up.ConclusionThis is the first large scale study to demonstrate that acceptable pregnancy and foaling rates can be achieved in mares diagnosed with twins when TUA is performed early in gestation (<40 days).

Twin management in the mare: A review

“…Transvaginal ultrasound guided aspiration or reduction (TUGR) is a well-known, suitable technique for management of post-fixation twins and is described to be performed between 16 and 70 days of gestation with more favourable results when performed before 40 days, with an optimal time window between 28 and 32 days of gestation (Figure 2). [40][41][42][43][44] Transvaginal ultrasound guided reduction, as illustrated in Figure 3, involves the puncture of a vesicle with aspiration of the yolk sac or allantoic fluid or alternatively, stabbing the embryo proper or fetus accompanied by minimal or no aspiration of fluid. 42 Prior to the TUGR procedure, the mare often receives NSAIDs to counteract prostaglandin release during uterine manipulation.…”

“…42 Prior to the TUGR procedure, the mare often receives NSAIDs to counteract prostaglandin release during uterine manipulation. 42,44 Prophylactic antibiotics could be administered, whereas their use is not routinely described in previous reports. Ideally, slight sedation (alfa2-agonist) in combination with a higher dose of an opioid analgesic is administered.…”

“…Ideally, slight sedation (alfa2-agonist) in combination with a higher dose of an opioid analgesic is administered. 44 A high dose of sedation could complicate rectal manipulations during the procedure and negatively impact the outcome due to the relaxing effect of sedatives, causing a more cranial and downward movement of the uterus into the abdomen. 45 The rectum can be relaxed by instillation of local anaesthetics or by mixing the local anaesthetics with a rectal lubricant and introducing it into the rectum at the time of the procedure.…”

“…by accidental aspirating and puncturing its membranes. 42,44,46 Performing TUGR by stabbing the embryo proper or fetus could be considered as a valid alternative to fluid aspiration in unilateral fixed twins. 42 However, a recent study showed more promising results if minimal fluid aspiration was performed only ('less is more').…”

“…42 However, a recent study showed more promising results if minimal fluid aspiration was performed only ('less is more'). 44 After a TUGR procedure, mares are often treated with progestins and NSAIDs to support the remaining pregnancy until the next ultrasonographic examination. 42,46 Regular ultrasonographic monitoring is important since, in most cases, death of the remaining twin most likely occurs within 10 to 14 days after the procedure or sometimes even later.…”