How to Manually Reduce Twins between 60 and 120 Days Gestation Using Cranio-Cervical Dislocation

Cranio-cervical dislocation between 60 - 110 days of gestation appears to be a viable new method for twin reduction by either rectal manipulation or flank laparotomy. This alternative procedure does not compromise the integrity of the uterus or damage the remaining fetus. By performing the twin reduction before placentation is complete, the remaining fetus is allowed to grow to its full potential, producing a healthier normal sized foal at birth.

1. Introduction

For mares to be reproductively efficient, they need to have regular ovulatory estrous cycles, be bred, conceive, maintain their pregnancy, and raise the foal successfully. Therefore, when twin pregnancies occur and both fetuses are lost, leaving a mare barren for 1 yr, there is a profound economic impact. In the past, the incidence of twin births has been documented as occurring in 1 - 2% of the equine population [1] with twinning accounting for 6 - 30% of abortions in the mare [2-4]. When twin pregnancies are present, gestation proceeds normally until competition for uterine space/placenta arises and death with or without mummification of one fetus leads to abortion (5 - 9 mo) [5]. Lactation commonly occurs when one foal dies, which causes premature mammary gland development [5]. Many veterinarians in the past have tried to reduce the chance of twins by using extreme management practices such as not breeding mares with two major follicles, breeding mares after the second ovulation, or breeding mares if both follicles ovulate to short cycle the mare [6-8]. However, these strategies have led to loss of valuable estrus periods during the breeding season, resulting in decreased number of pregnancies and increased economic loss [6].

Fortunately, with the use of ultrasound and an increased understanding of the mechanisms involved in twinning, better approaches to the management of breeding and reduction of twins have been developed [9-11].

Pregnancies can be diagnosed as early as 9 days post-ovulation; optimum detection of twin pregnancies occurs between day 13 and 15 of gestation when embryonic vesicles are still mobile and recognition of asynchronous twin embryonic vesicles can be achieved [12-14]. Natural reduction before day 11 of gestation does not occur and is negligible between days 11 and 15 [7,13,15]. Therefore, twin pregnancies detected during the mobility phase (days 9 - 15) can best be managed by manually crushing one embryonic vesicle [5]. The smaller vesicle or the one that needs the least amount of uterine manipulation is preferentially destroyed [16]. Survival rates of the remaining vesicle have been described as exceeding 90% [16,17].

Fixation of the embryonic vesicles occurs between days 16 and 17 of gestation. Ginther [18] determined natural reduction to a single conceptus to occur ~83% of the time for unilateral fixation as opposed to minimal reduction (4%) when fixed in different horns. In addition, the probability of natural reduction occurring decreases as gestational age increases to day 40 [13,19]. If the vesicles can be separated at this time, 90% of unilateral twins can be manually crushed successfully between days 17 and 20 [10,20]. Seventy-five percent of bilateral twins may be successfully reduced to a single pregnancy by crushing one vesicle before day 30 of gestation. However, with bilateral twins of gestational age >35 days, there is a greater risk of abortion of both at later stages [7,10]. It has been speculated that this may be caused by fluid release and loss of chorioallantoic and endometrial contact [21].

There are several other methods to reduce twins before and during the fetal stage (day 40) and endometrial cup formation (day 36). Between days 21 and 49 of gestation, sudden temporary reduction of food intake by mares for 2 - 4 wk has a 60% chance of reduction [8]. Manual manipulation transrectally without vesical rupture between days 28 and 42 has a 28% chance of a single viable foal [18]. Surgical removal of one conceptus between days 41 and 65 of gestation caused 5 of 8 mares with bilateral fixation to deliver a single foal and 0 of 7 mares with unilateral fixation to deliver a viable foal [21]. Transvaginal ultrasound-guided aspiration of the allantoic fluid of one conceptus between days 20 and 71 has varying results (unilateral twins [33%]; bilateral twins [75%]). When transvaginal ultrasound-guided aspiration was performed on unilateral twins before or at day 36, 40% of mares had a viable single vesicle 10 days later; when performed after day 36, only 10% of mares had a viable single vesicle 10 days later [22]. In subsequent studies, 31% of unilateral twin reduction produced live foals with all successful procedures being performed before 35 days of gestation [23]. Further results have been conflicting: 0 - 9% single live foals are delivered in unilateral twins depending on gestational age, and 25% single live foals are delivered in bilateral twins [24]. Therefore, it has been concluded that transvaginal ultrasound-guided twin reduction is best performed before day 35 of gestation [25]. There are a variety of factors that influence the success and limitations of this procedure, including day of gestation at time of reduction, unilateral verses bilateral fixation because of the close proximity of the fetuses and associated membranes, operator experience in not damaging the adjacent vesicle or traumatizing the uterus excessively during penetration of the needle, and leakage of fluid from the aspirated vesicle that can cause separation of placental membranes from the endometrium [24,25]. Transcutaneous ultrasound-guided twin reduction in the mare has been performed between day 66 and 168 of gestation. This procedure injects potassium chloride (KCl) into the heart of the smaller fetus with 38 - 40% of mares delivering a normal single live foal [24,26]. Subsequent twin reductions have concluded that the procedure is best performed between 115 and 130 days of gestation, and it results in 49% of mares delivering a single live foal; 60% of mares deliver a single live foal when injected with procaine penicillin [a] instead of KCl [20]. Unfortunately, the success of this procedure depends heavily on the experience of the operator and the prevention of iatrogenic infection or prostaglandin release. Additionally, a proportion of the single live foals that are born seem to have some degree of placental insufficiency, because they are weak, small at birth, and unthrifty; many times, a lot of expense is invested in these foals that are of little value, especially colts [24].

When the above procedures fail to produce a single viable conceptus after day 36 and endometrial cup formation has occurred with subsequent loss of both conceptuses, the mare is unable to cycle back until the endometrial cup regresses (80 - 120 days). This will leave mares barren for the breeding season, which has a severe economic impact.

Therefore, the authors developed a procedure that could be performed after natural reduction had the opportunity to occur or when twins were identified for the first time post-endometrial cup formation but before placental formation when one fetus would compromise the other.

2. Materials and Methods

When twins are present at 60 - 110 days of gestation, a new procedure with two different techniques has been attempted for fetal reduction. The first involves trans-rectal manipulation of one of the twins. This procedure has been performed between days 60 and 90 of gestation. The mare is restrained either in stocks or with a twitch in the doorway. Detomidine HCl [b] (10 - 20 mg/kg, IV) is used for sedation in combination with other sedatives, if needed. However, sedation may relax the uterus; this can move the fetuses cranially in the abdomen and out of reach. Propantheline bromide [c] (30 mg or 1 ml, IV) should be administered to help relax the smooth muscle in the uterus and rectum so that the fetuses can be identified and manipulated more easily. Flunixine meglamine [d] (1 mg/kg, IV) should also be administered before the procedure is performed. Preferably, the smaller fetus or the fetus that has less contact with the endometrium and minimal space to grow is reduced. When the identified fetus is located, the head must be isolated. This is done by finding the dome-shaped structure and confirming its identity by the mandible or by moving distally and recognizing the cervical vertebrae. Cranio-cervical dislocation is created by stabilizing the head between the thumb and forefinger and bending the head from side to side, breaking down the ligaments attaching the head and neck. Dislocation is then created by placing your thumb at the base of the cranium and applying pressure proximal and dorsally. If dislocation is achieved, a pop is felt, and the thumb and forefinger can be placed in the space between the head and neck. Mares should be placed on altrenogest [e] (.088 mg/kg, orally) once daily for the next 3 - 4 wk. When dislocation is performed, death with loss of fetal heart beat is usually evident within 24 h to 1 wk. Examination of fetal viability should be done 1 wk later and then every 2 wk for 1 mo.

The second technique is surgical and is required if manual transrectal reduction can not be completed. This procedure has been preformed to date on twins between gestational ages of 58 and 110 days. Transabdominal ultrasound is used to identify the horn in which the most viable fetus is located. This is determined again by the fetus with the largest size and the greatest surface area attached to the endometrium for future growth. Propantheline bromide (30 mg or 1 ml, IV), flunixin meglamine (1 mg/kg, IV), procaine penicillin (20,000 - 50,000 IU/kg, q 12 - 24 h, IM), and gentocin sulfate [f] (6.6 mg/kg, q 24 h, IV or IM) is administered pre-operatively. A standing flank incision is performed on the side of the horn containing the fetus identified for reduction. The uterus is located within the abdominal cavity with one arm, and the twin is isolated transrectally as previously described. Cranio-cervical dislocation is performed by manipulating the fetus through the uterus without incising or invading the uterine lumen. The flank incision is routinely closed when the procedure is completed. With this technique, it may take 24 h-6 wk before death is evident in the manipulated fetus. Mares should continue on flunixine meglamine, procaine penicillin, and gentocin for the next 2 days; trimethoprin sulpha [g] (24 mg/kg, q 12 h, orally) should be administered for 1 wk, and altrenogest (.088 mg/kg, q 24 h) should be administered once daily for 1 mo. It has been observed that greater success, resulting in viability of the remaining fetus and continued pregnancy, occurs when death of the manipulated twin occurs sooner versus later.

3. Results

At this time, small numbers of twins have been reduced by these methods; however, results have been encouraging. Seven sets of twins have been reduced with transrectal manipulation. These have varied from between 55 and 90 days of gestation. Five of seven delivered a normal-sized single fetus. Two aborted both fetuses 30 - 60 days after the procedure was performed. Three of seven had to be manipulated two or three different times, 10 days apart, before cranio-cervical dislocation was successful. The remaining four sets of twins were able to be reduced during the first treatment. When cranio-cervical dislocation was achieved, it took 1 - 3 wk before the reduced fetus had no viable heartbeat. Two of five normal single twins born were manipulated more than once, whereas only one of the aborted twins was manipulated multiple times.

When performing cranio-cervical dislocation using flank laparotomy, five pairs of twins were reduced between days 60 and 110. Of these, two mares delivered normal-sized single foals, one mare aborted both fetuses, one mare was found empty at 110 days of gestation, and one mare is currently still pregnant with only a single viable heartbeat present. Therefore, three of five pregnancies have single viable foals. Manipulation consisted of a one-time treatment with the reduced fetus loosing their heartbeat from 1 - 40 days post-procedure. Two mares maintained two viable fetal heartbeats for extended periods of time. The first mare had two viable heartbeats for 30 days with the single fetus still viable, and the second mare had two viable heartbeats for 40 days at which time the mare was discovered to have aborted both fetuses.

4. Discussion

It is the hypothesis of the veterinarians involved in developing these techniques that early twin reduction, before placental development, may decrease the amount of impingement on the nutrient supply; this allows the remaining twin to develop normally. Cranio-cervical dislocation is unlike transcutaneous ultrasound-guided reduction in which a large percentage of delivered single foals are considered undersized, weak, and disappointing [h]. This is believed to be caused by the time of reduction, which is late in gestation. Therefore, the advantages of performing this procedure, according to the authors, far outweigh the disadvantages. The fact that there are no other procedures that are successful at this stage of gestation (60 - 110 days of gestation) is important, because reduction before placental formation is optimum for normal growth. By performing this procedure at a later stage of gestation than transvaginal ultrasound-guided aspiration, size is easier to differentiate between the fetuses; additionally, it is easier to identify the fetus with the most endometrial contact and subsequently, the fetus that will be more viable. Additionally, this procedure does not invade the integrity of the uterus with needles, and therefore, there is no chance of leakage of fluid from the reduced conceptus. When leakage occurs, there is disruption of the fetal membranes separating them from the endometrium, which compromises oxygenation and nutrition exchange of the remaining conceptus [21,24].

Concurrently, by not transversing the abdominal wall and entering the lumen of the uterus, there is less chance of bacterial contamination that can result in placentitis or endometritis. The disadvantages of cranio-cervical dislocation mostly relate to the isolation of the fetus. When the mare is at this stage of gestation, identifying the correct fetus within the uterus is inexact. It is absolutely imperative that the uterus is relaxed enough for identification of the body parts. Additionally, at this time, there is no documented evidence on the amount of trauma or prostaglandin release that occurs with manipulation of the fetus through the uterus.

The procedure does not take a long time from isolation to dislocation, and therefore, there should not be severe inflammation. However, proficiency and time may impinge on the outcome. Finally, the long duration of time that a fetus can survive with a dislocated head was extremely surprising to the authors. The heart beat of two of the fetuses done using laparotomy remained viable for a long period of time; there is no current explanation, but incomplete severage of the spinal cord may have occurred. For these two fetuses, there were abnormalities that developed in the shape of the chest and in the clarity of other organs on ultrasound when a heartbeat was present. It was deduced, by the fact that one of these mares aborted both foals, that an earlier death in the reduced fetus increases the chance of the single pregnancy going to term. The incision site, when using flank laparotomy, heals well, and if a seroma does form, the bottom can be opened easily. No scars have been evident, and all of the mares' incisions healed normally.

At this time, cranio-cervical dislocation, a procedure where the head is dislocated from the proximal cervical vertebrae to sever the spinal cord, seems to be a viable alternative as a method of twin reduction between 60 and 110 days gestation by either transrectal manipulation or flank laparotomy. By performing this procedure, reduction of a twin occurs before placenta formation; this allows the remaining twin to grow to its full potential by using all of the mare's endometrial surface.

Footnotes

1. Rocaine Penecillin, Durvet, Blue Springs, MO 64014.
2. Ermosedan, Orion Corporation, Fl-02101 Espoo, Finland.
3. Ropantheline Bromide, compounded at Hagyard-Davidson-McGee, Lexington, KY 40511.
4. Anamine, Schering-Plough, Union, NJ 07083.
5. Egumate, InterVet, Dallas, TX 75252.
6. EntaMax, Phoenix, St. Joseph, MO 64503.
7. Ulfamethoxazole and trimethoprim tablets, Mutual Pharmaceuticals, Philadelphia, PA 19124.
8. Eimer J. Lexington, KY. Personal communication. 2003