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Identification of the Corpus Luteum in Early Pregnancy in the Mare Using Ultrasound
Non-Reviewed
IDENTIFICATION OF THE CORPUS LUTEUM IN EARLY PREGNANCY IN THE MARE USING ULTRASOUND John R. Newcombe B VetMed, MRCVS
Summary Two hundred mares of mixed breeding were examined with ultrasound for ovulation and at Days 13 to 16 for pregnancy. At this stage the visible presence of one or more corpora lutea (CL) were noted and tested for correlation with the side of ovulation. In 195 cases (94.6%) of 206 pregnancies a CL was seen ipsilateral to the side of ovulation. Cases where the CL was contralateral (3) or not seen (9) are discussed. While no longer palpatable in late diestrus, the CL can be imaged using ultrasonography. 1 In view of the continuing debate on the value of progesterone supplementation to prevent early embryonic failure, information on ovarian dynamics in early pregnancy would be beneficial. This case report demonstrates the usefulness of ultrasonography in determining the viability of the CL in early pregnancy.
Introduction Trans rectal ultrasonography provides a safe, non-invasive and relaAuthor's address: Warren House Farm, Barrracks Lane, Brownhills, West Midlands WS8 6LS, UK
Volume 14, Number 12, 1994
tively non-subjective method of visual assessment of the internal and external structure of the genital tract. 1 In particular the corpus luteum (CL) can be identified, measured, presence or absence of a central hypoechoic lacuna noted, a,3 and the level of echogenicity of the luteal tissue assessed, a The endometrium can be identified as of an even, moderately echodense texture (luteal) or with radiating bands of alternate hyper and hypoechoic areas (edema during follicular phase). 4 This study investigates the possibility of using the ultrasonic identification of the CL at Days 13 to 16 of pregnancy as a rapid method of assessing the viability of the CL without resort to blood progesterone analysis. Coincidentally, it also forms a basis for a retrospective diagnosis of the side of ovulation and of diestrous ovulations. A small number of pregnancies have been observed to fail associated with regression of the CL at about Day 15. As the mare returns to estrus the vesicle is aborted. Most of these pregnancies were probably associated with a nonviable conceptus and were destined to fail. They can, however, be maintained for variable periods by progesterone supplementation started on Day 15 or 16. Many fail to develop an embryo and the vesicle is aborted after removal of the progesterone support. A few otherwise viable pregnancies can be saved by the use of progesterone continued until either a viable CL is formed from a secondary ovulation, follicular luteinization after 45 days or until placental progesterone can safely be relied upon to take over at about 80 days. s This author concurs with recent opinions 6,7 that the vast majority of
pregnancies which fail up to Day 40 do not fail due to low plasma progesterone levels. In most cases of early embryonic death the CL remains ultrasonically identifiable for several weeks until exogenous prostaglandin is given to return the mare to estrus. The widespread use of progestagen supplementation to prevent early pregnancy loss is without a valid basis in all but a few cases. Recent work has clearly shown that h y d r o x y p r o g e s t e r o n e cannot maintain pregnancy in the absence of a viable CL. s There remain, however, a small percentage of cases where early recognition of a nonviable CL allows immediate progesterone supplementation to save the pregnancy.
Materials and M e t h o d s Two hundred mares of Thoroughbred, Cob, Irish draft, Shire and the majority of mixed breeding, all resident on one stud farm in 1992, were examined during 206 pregnancies. Examinations were made mostly in daylight in semi-open conditions. Mares were restrained in a crush and a nose twitch applied to limit movements. Examinations were made by rectal palpation and with ultrasound using a 5 MHz Linear transducer (DSL 300) every 48 hours during estrus until all significant follicles had either ovulated or begun to regress. Mares were reexamined 12 or 14 days after the first ovulation had been detected. All mares in this study were therefore pregnant between Days 13 and 16, (Day 1 = Day of ovulation), at the time of first examination. The uterus was examined by ultrasound primarily for the presence of one
653
Results Table 1, Numbers of mares with Corpora Lutea ultrasonically detectable on Days 13 to 16 of pregnancy.
Ovary ipsilateral to side of ovulation
Ovary contralateral to side of ovulation
177 (86%)
3 (1.4%)
clearly visible
18 (8.7%)
0
not visible
9 (4.3%)
clearly visible CL
CL not
References
CL
or more e m b r y o n i c vesicles but both ovaries were also examined for visual evidence o f one or more CL. Without knowledge or reference to the side of ovulation, note was made of the presence or absence o f a CL, its side and its level of CL echogenicity. The mature functional CL has a defined structure, usually 18 m m to 25 m m in diameter unless there remains an anechoic central lacuna formed in early diestrus. The echogenicity of the luteal tissue varies from slight to moderate but is rarely as highly echogenic as seen in early diestrus. The CL was designated as (a) clearly visible, (b) indistinctly visible with low echogenicity and/or ill-defined in outline, or (c) not visible. Most mares were re-examined for pregnancy after 4 or 6 days and the ovaries re-examined for CL's. Mares suspected of low peripheral plasma progesterone were immediately fitted with intravaginal progesterone releasing devices, a These devices contain 1.55 gm Progesterone in a slow release polymer. Studies in anestrous mares found mean p l a s m a progesterone levels of 2.03 ng/ml and 1.84 ng/m110 and 14 days after insertion, respectively, b
Discussion
In 86% o f mares, at least one apRID Sanofi,Watford, UK. bNewcombeJ.R. Unpublisheddata.
654
diestrous ovulations from the contralateral ovary. It is concluded that visualization of the CL with ultrasound in field conditions can be an accurate method of both determining the side of ovulation, including unsuspected diestrous ovulations from which a 'late' twin might develop, and the existence o f a viable CL.
clearly defined CL was seen on the side ipsilateral to the side of ovulation (or sides, where multiple ovulation had occured from both o v a r i e s ) . In 8.7% of mares only an ill-defined CL or one of low echogenicity was seen. In the normal cyclic mare the CL may still be visible on Day 15 but by D a y 16 has either disappeared or assumed a 'ghost' like appearance of defined border but low echogenicity. A small percentage of CL's in pregnant mares have a similar appearance. In only 9 (4.3%) mares no CL was identified at the first examination for pregnancy. In 5 of these cases a CL was found at a later (4-6 days) examination, one was not examined again and in another no CL could be identified 6 days later. Of the remaining two cases, one mare was in estrus 4 days later (Day 18) and had aborted, and the other was fitted with a PRID coil. The mare was repeatedly examined until Day 45 of pregnancy when a new CL was identified from a recent ovulation. At no time was the CL seen. In three mares a CL was identified only in the contralateral ovary suggesting a misdiagnosis. However, in two of these the CL was confirmed in the contralateral ovary at three subsequent examinations together with a CL in the ipsilateral ovary. In the third case a contralateral CL was confirmed but no ipsilateral CL found. It is thought that these were the result of undetected
1. Ginther OJ: Ultrasonic Imaging and Reproductive Events in the Mare. Equiservices. Cross Plains, Wl 1986. 2. Pierson RA, Ginther OJ: Ultrasonic evaluation of the corpus luteum in the mare. Theriogenology 1985;23:795-806. 3. TownsonDH, Pierson RA, Ginther OJ: Characterization of plasma progesteroneconcentrationsfor two distinct luteal morphologies in mares. Theriogenology 1989;32:197-204. 4. McKinnon AO, Squires EL, Carnevale EM, Harrison LA, Franz DD, McChesney AE, Shideler RK: Diagnostic ultrasonography of uterine pathology in the mare. Proceedings. Am Assoc Equine Pract 1987;605-622. 5. Holtan EW, Squires EL, Lapin DR, Ginther OJ: Effect of ovariectomy on pregnancy in mares. J Reprod Fert 1979;27:(Suppl)457-463. 6. Allen WR; Progesterone and the pregnant mare: unanswered chestnuts. Equine Vet J 1993;25:104-105. 7. Irvine CHG, Sutton P, Turner JE, Mennick PE: Changes in plasma progesterone concentrationsfrom Days 17 to 42 of gestation in mares maintaining or losing their pregnancy. Equine Vet J 1990;22:104-106. 8. McKinnonAO, Tarrida del Marmol, FigueroaS, NobeliusAM, HylandJH, Vasey JR: Equine Vet J 1993;25:158-160.
JOURNAL OF EQUINE VETERINARY SCIENCE
IDENTIFICATION OF THE CORPUS LUTEUM IN EARLY PREGNANCY IN THE MARE USING ULTRASOUND John R. Newcombe B VetMed, MRCVS
Summary Two hundred mares of mixed breeding were examined with ultrasound for ovulation and at Days 13 to 16 for pregnancy. At this stage the visible presence of one or more corpora lutea (CL) were noted and tested for correlation with the side of ovulation. In 195 cases (94.6%) of 206 pregnancies a CL was seen ipsilateral to the side of ovulation. Cases where the CL was contralateral (3) or not seen (9) are discussed. While no longer palpatable in late diestrus, the CL can be imaged using ultrasonography. 1 In view of the continuing debate on the value of progesterone supplementation to prevent early embryonic failure, information on ovarian dynamics in early pregnancy would be beneficial. This case report demonstrates the usefulness of ultrasonography in determining the viability of the CL in early pregnancy.
Introduction Trans rectal ultrasonography provides a safe, non-invasive and relaAuthor's address: Warren House Farm, Barrracks Lane, Brownhills, West Midlands WS8 6LS, UK
Volume 14, Number 12, 1994
tively non-subjective method of visual assessment of the internal and external structure of the genital tract. 1 In particular the corpus luteum (CL) can be identified, measured, presence or absence of a central hypoechoic lacuna noted, a,3 and the level of echogenicity of the luteal tissue assessed, a The endometrium can be identified as of an even, moderately echodense texture (luteal) or with radiating bands of alternate hyper and hypoechoic areas (edema during follicular phase). 4 This study investigates the possibility of using the ultrasonic identification of the CL at Days 13 to 16 of pregnancy as a rapid method of assessing the viability of the CL without resort to blood progesterone analysis. Coincidentally, it also forms a basis for a retrospective diagnosis of the side of ovulation and of diestrous ovulations. A small number of pregnancies have been observed to fail associated with regression of the CL at about Day 15. As the mare returns to estrus the vesicle is aborted. Most of these pregnancies were probably associated with a nonviable conceptus and were destined to fail. They can, however, be maintained for variable periods by progesterone supplementation started on Day 15 or 16. Many fail to develop an embryo and the vesicle is aborted after removal of the progesterone support. A few otherwise viable pregnancies can be saved by the use of progesterone continued until either a viable CL is formed from a secondary ovulation, follicular luteinization after 45 days or until placental progesterone can safely be relied upon to take over at about 80 days. s This author concurs with recent opinions 6,7 that the vast majority of
pregnancies which fail up to Day 40 do not fail due to low plasma progesterone levels. In most cases of early embryonic death the CL remains ultrasonically identifiable for several weeks until exogenous prostaglandin is given to return the mare to estrus. The widespread use of progestagen supplementation to prevent early pregnancy loss is without a valid basis in all but a few cases. Recent work has clearly shown that h y d r o x y p r o g e s t e r o n e cannot maintain pregnancy in the absence of a viable CL. s There remain, however, a small percentage of cases where early recognition of a nonviable CL allows immediate progesterone supplementation to save the pregnancy.
Materials and M e t h o d s Two hundred mares of Thoroughbred, Cob, Irish draft, Shire and the majority of mixed breeding, all resident on one stud farm in 1992, were examined during 206 pregnancies. Examinations were made mostly in daylight in semi-open conditions. Mares were restrained in a crush and a nose twitch applied to limit movements. Examinations were made by rectal palpation and with ultrasound using a 5 MHz Linear transducer (DSL 300) every 48 hours during estrus until all significant follicles had either ovulated or begun to regress. Mares were reexamined 12 or 14 days after the first ovulation had been detected. All mares in this study were therefore pregnant between Days 13 and 16, (Day 1 = Day of ovulation), at the time of first examination. The uterus was examined by ultrasound primarily for the presence of one
653
Results Table 1, Numbers of mares with Corpora Lutea ultrasonically detectable on Days 13 to 16 of pregnancy.
Ovary ipsilateral to side of ovulation
Ovary contralateral to side of ovulation
177 (86%)
3 (1.4%)
clearly visible
18 (8.7%)
0
not visible
9 (4.3%)
clearly visible CL
CL not
References
CL
or more e m b r y o n i c vesicles but both ovaries were also examined for visual evidence o f one or more CL. Without knowledge or reference to the side of ovulation, note was made of the presence or absence o f a CL, its side and its level of CL echogenicity. The mature functional CL has a defined structure, usually 18 m m to 25 m m in diameter unless there remains an anechoic central lacuna formed in early diestrus. The echogenicity of the luteal tissue varies from slight to moderate but is rarely as highly echogenic as seen in early diestrus. The CL was designated as (a) clearly visible, (b) indistinctly visible with low echogenicity and/or ill-defined in outline, or (c) not visible. Most mares were re-examined for pregnancy after 4 or 6 days and the ovaries re-examined for CL's. Mares suspected of low peripheral plasma progesterone were immediately fitted with intravaginal progesterone releasing devices, a These devices contain 1.55 gm Progesterone in a slow release polymer. Studies in anestrous mares found mean p l a s m a progesterone levels of 2.03 ng/ml and 1.84 ng/m110 and 14 days after insertion, respectively, b
Discussion
In 86% o f mares, at least one apRID Sanofi,Watford, UK. bNewcombeJ.R. Unpublisheddata.
654
diestrous ovulations from the contralateral ovary. It is concluded that visualization of the CL with ultrasound in field conditions can be an accurate method of both determining the side of ovulation, including unsuspected diestrous ovulations from which a 'late' twin might develop, and the existence o f a viable CL.
clearly defined CL was seen on the side ipsilateral to the side of ovulation (or sides, where multiple ovulation had occured from both o v a r i e s ) . In 8.7% of mares only an ill-defined CL or one of low echogenicity was seen. In the normal cyclic mare the CL may still be visible on Day 15 but by D a y 16 has either disappeared or assumed a 'ghost' like appearance of defined border but low echogenicity. A small percentage of CL's in pregnant mares have a similar appearance. In only 9 (4.3%) mares no CL was identified at the first examination for pregnancy. In 5 of these cases a CL was found at a later (4-6 days) examination, one was not examined again and in another no CL could be identified 6 days later. Of the remaining two cases, one mare was in estrus 4 days later (Day 18) and had aborted, and the other was fitted with a PRID coil. The mare was repeatedly examined until Day 45 of pregnancy when a new CL was identified from a recent ovulation. At no time was the CL seen. In three mares a CL was identified only in the contralateral ovary suggesting a misdiagnosis. However, in two of these the CL was confirmed in the contralateral ovary at three subsequent examinations together with a CL in the ipsilateral ovary. In the third case a contralateral CL was confirmed but no ipsilateral CL found. It is thought that these were the result of undetected
1. Ginther OJ: Ultrasonic Imaging and Reproductive Events in the Mare. Equiservices. Cross Plains, Wl 1986. 2. Pierson RA, Ginther OJ: Ultrasonic evaluation of the corpus luteum in the mare. Theriogenology 1985;23:795-806. 3. TownsonDH, Pierson RA, Ginther OJ: Characterization of plasma progesteroneconcentrationsfor two distinct luteal morphologies in mares. Theriogenology 1989;32:197-204. 4. McKinnon AO, Squires EL, Carnevale EM, Harrison LA, Franz DD, McChesney AE, Shideler RK: Diagnostic ultrasonography of uterine pathology in the mare. Proceedings. Am Assoc Equine Pract 1987;605-622. 5. Holtan EW, Squires EL, Lapin DR, Ginther OJ: Effect of ovariectomy on pregnancy in mares. J Reprod Fert 1979;27:(Suppl)457-463. 6. Allen WR; Progesterone and the pregnant mare: unanswered chestnuts. Equine Vet J 1993;25:104-105. 7. Irvine CHG, Sutton P, Turner JE, Mennick PE: Changes in plasma progesterone concentrationsfrom Days 17 to 42 of gestation in mares maintaining or losing their pregnancy. Equine Vet J 1990;22:104-106. 8. McKinnonAO, Tarrida del Marmol, FigueroaS, NobeliusAM, HylandJH, Vasey JR: Equine Vet J 1993;25:158-160.
JOURNAL OF EQUINE VETERINARY SCIENCE