Management of Twins: Have We a New Option?
- Oct 15, 2001
As has been discussed in earlier issues of The Horse, twinning is highly undesirable in the mare. The advent of ultrasound has allowed earlier detection of multiple pregnancies from around Days 14 to 16 post-breeding, and the majority of clinicians are in agreement that twins are most effectively managed at this stage by manually crushing one of the vesicles. Certainly this author would agree that examination at this time should be routine, and if twins are found, a veterinarian should act immediately to reduce one of the pregnancies.
However, there are scenarios whereby a mare cannot be examined during this time period post-breeding.
Some owners prefer to see if their mare will return to estrus and delay the first examination for pregnancy until Day 18 or 19 post-breeding. If the twin vesicles have fixed together (i.e. are unilaterally located), it can be difficult to crush one of the vesicles without disrupting the other. It may be policy to leave twin pregnancies hoping for natural reduction to a singleton, but this will not occur in every case.
In other cases, the first examination may be delayed until three to four weeks post-breeding, perhaps for economic reasons or for convenience to coincide with the visit of the veterinarian for another purpose.
Alternatively, it may have been impossible to obtain the correct diagnosis on the first examination, and by the time of the second examination, the clinician is faced with twins so far advanced that manual crushing is unlikely to have a favorable outcome.
In many of these situations where only a diagnosis at a relatively late stage is possible, the best option may be to eliminate the pregnancy before Day 34 and formation of the endometrial cups, which produce a hormone (equine chorionic gonadotrophin; eCG), which will prevent the mare having fertile estrous cycles for several weeks. After Day 34, there are few options available other than aborting the mare and beginning early next breeding season.
Use of transabdominal ultrasound to guide a needle through the abdomen into one of the pregnancies is used by some clinicians to eliminate one of a twin pregnancy, and even surgical reduction of one of the pregnancies has been tried. Recently a technique that seems to offer an alternative approach when twin pregnancies are discovered at a relatively late stage has emerged--twin reduction by transvaginal ultrasound-guided puncture of the embryonic vesicle.
The technique was initially developed for cows and was first introduced to our Mare Fertility Clinic at Utrecht in 1992. There have been some modifications both in the actual technique and in our thinking as to the role of the technique in twin management since then.
Equipment and Pre-Puncture Evaluation
The ultrasound machine we use for the puncture is a Scanner 200 Vet (Pie Medical Ltd; Maastricht, The Netherlands) with a 7.5 MHz Sector Annular-array system. Immediately before the procedure, the mare is examined using transrectal ultrasound to evaluate the pregnancies and make a decision as to which one to puncture. If one pregnancy is obviously smaller or a few days younger than the other, that is the pregnancy that should be punctured. If both pregnancies appear identical on ultrasound examination, then the one easiest to puncture is selected.
At the time of this initial assessment the mare is given an injection of the anti-inflammatory drug flunixin meglumine (Banamine; Schering-Plough) to try and prevent regression of the corpus luteum, and daily treatment with the synthetic progestagen altrenogest (Regumate; Hoechst) is begun. After 30 minutes, she is brought back into the palpation stocks and prepared for the puncture procedure. This consists of bandaging the tail, emptying the rectum of manure, and instilling 50 ml of local anaesthetic locally in the rectum. The perineal area is then thoroughly cleaned prior to insertion of the transducer.
Needle Guidance System
Some form of casing around the ultrasound transducer is needed in order to guide the needle into the vesicle to be punctured. We use a 50 Cm long autoclavable stainless steel holder with a handle at one end to facilitate manipulation (at right). On the ultrasound image as displayed on the monitor, there is a needle/biopsy guideline that corresponds to the location and direction of the aspiration needle, making it possible to predict the direction of passage of the needle on the monitor screen. We use a 1.5 inch luer-lock disposable needle of either 20 gauge (for punctures less than 35 days post-breeding) or 18 gauge (for punctures more than 35 days post-breeding). We felt that for the earlier gestation punctures, a smaller diameter needle may be preferable to try and reduce the damage to the membranes lining the vesicle.
Some form of suction is necessary to aspirate the fluid from the pregnancy being punctured. Therefore, the needle is attached to sterile tubing connected to a suction pump.
The tip of the holder is covered with sterile plastic film to prevent vaginal mucus and other debris entering the opening of the needle guide, then sterile lubricant is applied. The transducer is gently inserted into the vagina as far as the side of the external opening of the cervix. The operator holds the transducer within its casing in one hand while with the other hand manipulates the uterus per rectum. By means of rectal manipulation, the uterus is positioned so that the pregnancy to be punctured is in the line of the needle by using the biopsy guide/puncture lines on the ultrasound monitor.
The stainless steel tube with the needle at the end is inserted by a second person into a guidance tube incorporated into the top of the protective casing. Care must be taken when inserting the needle into the guidance system that the needle goes smoothly through the hole at the end of the guidance device, otherwise a rough edge may develop making the needle more likely to be blocked by the fetal membranes during the puncture session. A marker indicates the extent the needle should be passed along the needle guide as it is, of course, important that at this stage the needle remains contained within its holder to avoid trauma to the vagina.
On the instruction of the operator manipulating the uterus, the needle is then advanced beyond the needle guide, through the vaginal wall, and into the pregnancy to be punctured. The instruction to advance the needle should only be given when the pregnancy has been steadily positioned on the puncture line seen on the monitor. A distinct "popping" sensation is felt when the pregnancy is entered and the echoic needle can be visualised within the pregnancy. As soon as the tip of the needle is seen to enter the pregnancy, suction is immediately applied and the pregnancy, as imaged on the ultrasound screen, begins to collapse.
The amount of fluid removed varies depending on the age of the pregnancy. Typically for a 30-day pregnancy, only 7-8 ml is removed (at left), whereas for a 50-day pregnancy, some 80-90 ml may be removed.
Immediately after the puncture session the result should be evaluated using trans-rectal ultrasound examination. The punctured twin should have a reduced volume of placental fluid and loss of shape, but is likely to still have a heart beat. The non-punctured twin should have a normal volume of placental fluid and shape with a clearly visible heart beat.
Mares tolerate the procedure very well and usually no additional restraint other than being placed in palpation stocks is necessary. There appears to be no discomfort during or following the procedure, and in more than fifty puncture sessions, no ill effects have been seen.
There is undoubtedly a learning curve with the technique, and it is important to develop a good understanding between the person manipulating the uterus and the person inserting the needle. The average time taken from insertion of the transvaginal transducer to completion of the puncture is around seven minutes, although this may be longer in later-stage pregnancies when the uterus is more difficult to manipulate. Most of this time is taken up by ensuring the uterus is fixed in the correct position with the pregnancy to be punctured in the biopsy line. Once the instruction to insert the needle is given, usually less than one minute of suction is necessary. It is important to accurately position the uterus as the needle should only be inserted once.
Regarding success rate, my colleague Herman Jonker presented a poster at the 1995 British Equine Veterinary Association Annual Congress based on our 1994 results. There was a 56% success rate in terms of mares pregnant one week later, and 31% actually had a foal born.
When we sat down and analyzed the results, it became clear that poorer results were obtained with pregnancies advanced beyond 35 days, particularly for unilateral pregnancies--which almost all failed. This was interesting as initially it had looked as if the main application of the technique may be those mares which had progressed beyond 35 days from breeding. While this may be true for bilateral twins, it appears that unilateral twins are not able to be effectively managed by twin puncture after Day 35.
Personally, I believe that technique is not the reason these late unilateral twin punctures fail. Although the technique of twin puncture has a learning curve and a good working understanding between the people involved is necessary, we think we have achieved the necessary expertise and our failures do not seem to correlate with a more difficult or particularly protracted puncture procedure. Other factors may be involved. For example, it may be that using a smaller diameter needle may improve our success rate. It is also possible that by using progestagens, alone or in combination with estradiol-17 beta, the success rate may be increased.
From talking to other colleagues experienced in the technique, particularly Margo Macpherson, DVM, from the University of Pennsylvania, loss of uterine tone could likely be a major factor in causing loss of the remaining vesicle. Consequently, some hormonal therapeutic regime may also provide some answers and improvement in the future success rate of the technique.
The loss of both pregnancies may be due to leaked fluid from the punctured vesicle, so it is crucial to attempt to aspirate as much fluid as possible. This means the needle should be left in the pregnancy as long as fluid is flowing, but if the uterus becomes difficult to fix, the needle should be withdrawn and the transducer removed. Infection may be the cause of the loss of the other pregnancy, in which case antibiotics may have a role to play in maintaining the other pregnancy.
The disappointing success with pregnancies above 35 days caused us to encourage earlier referral of cases for 1995. For 1995, therefore, we tried to puncture before Day 34, which I felt balanced between allowing us as long as possible for natural reduction against puncturing after endometrial cup formation. This gave us an ideal window for puncturing between 28 and 33 days post-breeding, although some pregnancies were not referred until a later stage. Obviously, the majority of these cases were unilaterally located twins, as bilateral twins can still be effectively managed by manual crushing up to day 33 in most cases. Our results from 26 punctures were 10 apparently normal singleton pregnancies after one week. The real success of the technique is the live foal numbers, which are not yet available for 1995.
I am excited about the technique, and my personal opinion is that it does have a role to play in the management of twin pregnancy in the mare...I am just not sure where its role is yet.
What is the optimal time for puncture? I have suggested before Day 33, as if we lose both pregnancies we should still be able to re-breed the mare. This means the technique will mainly be used in unilateral sets of twins. In this case, a high-quality ultrasound machine is necessary to give excellent image quality to allow visualization of the precise location of the needle. The live foal data may hold the key to an accurate assessment of the technique. If mares have a high subsequent abortion rate of the remaining singleton at a relatively late stage of gestation, it may be better to give prostaglandins to abort these unilateral twins discovered late and reserve twin puncture for after Day 34 post-breeding, when options for re-breeding are reduced.
Unfortunately, I believe we will be unable to get a high success rate with these late stage twin punctures. Would we be better to inject something into the fetus? Possibly, but there could be potential harmful effects to the other fetus from the injected toxin.
The main problem with establishing the role of this technique is access to sufficiently large numbers. I said at the beginning of this article that twins are best managed by early scanning and crushing of one of the vesicles. Essentially, transvaginal twin puncture is an "emergency/salvage" technique, and it is difficult to get enough numbers to form a clear judgement. It is possible that with small refinements of technique and use of medication following the puncture, success rates can be improved. We shall continue to work on the technique in the hope that we may be able to more accurately define the role it has to play in twin management in the mare.
Twin puncturing is a team effort at Utrecht, and I would like to acknowledge my co-workers in the technique: Herman Jonker, Joyce Parlevliet, Maarten Pieterse, Marcel Taverne, and Peter Vos. In addition, several of my ideas have been modified following discussions with other colleagues performing the technique, particularly Margo Macpherson and Dale Paccamonti.
About the Author
Jonathan F. Pycock, BVetMed, PhD, Dipl. ESM, MRCVS, operates Equine Reproductive Services, a first opinion and referral private equine practice based in Yorkshire, England. He has published many papers and book chapters on a variety of equine reproductive topics, and edited the book Equine Reproduction and Stud Medicine. His main interests include ultrasonography, breeding the problem mare, and artificial insemination. Currently, he is evaluating the use of oxytocin and depot oxytocin as a post-breeding treatment for mares.
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