Routine monitoring of early pregnancy
Keywords: equine, mare, pregnancy diagnosis, monitoringThis sequence of images illustrates the author’s philosophy in monitoring early pregnancies. Mare owners are encouraged to submit their mares for all of these steps in diagnosis. In this manner, twins can be managed properly, early embryonal death can be detected and the normal development of the conceptus can be monitored. Note the centimeter scale in all images.
Image A shows a conceptus presumed to be about 14 days old.
Image size 461 x 313px (full size).
In image A again, the echogenic line (a line of strong spectral reflections) that characterizes the uterine body (arrow) shows that the embryo is just cranial to the cervix.
The precise age of an embryo is unknown in common stud practice because mares are examined and usually inseminated at two day intervals (Mon-Wed-Fri) or three days intervals (Fri-Mon). This means that the precise time of ovulation is usually unknown.
| The embryonic vesicle migrates throughout the uterus until the embryo is about 16 days old then becomes "fixed". If there are twin embryos, they often become "fixed" together, complicating twin reduction; usually making it impossible. Therefore it is important to err on the side of shorter, rather than longer gestation when scheduling pregnancy diagnoses. Because the time of conception is usually unknown in common stud practice, pregnancy diagnosis is scheduled 14 to 16 days after an un-ovulated follicle was last seen, not after the first record of ovulation. In the latter case, twin embryos could be two or three days older than 14-16 days and already "fixed". |
Image B shows a conceptus that is approximately 16 days old.
Image size 461 x 313px (full size).
It has already become "fixed" in the uterine horn. The thick homogeneous "doughnut" that surrounds it is the tonic myometrium that characterizes early pregnancy in this species. The non-echogenic (black) center of the vesicle is almost entirely yolk sac. The embryo itself is not yet visible.
Image C shows a pregnancy is approximately 19 days of age.
Image size 461 x 313px (full size).
The sodium pump in the wall of the trophoblast is less active than earlier in gestation therefore the osmotic pressure within the trophoblast is lower and the trophoblast loses some of its turgidity at this time. This is normal and should not lead one to assume that embryonal death is about to occur. A small echogenic area on the lower right extremity of this vesicle is the embryo itself (arrow).
In image D, the embryo (green arrow) has lifted away from the ventral portion of the trophoblast about 23 to 24 days of age.
Image size 461 x 313px (full size).
The characteristic thickening of the uterine wall opposite the embryo (yellow arrow) is typical of this stage of pregnancy.
In images E and F, a pregnancy about 27 days old, the embryo itself is clearly visible and the embryonic membranes can be distinguished as well.
Image size 461 x 313px (full size).
These structures are delineated in image F.
Image size 461 x 313px (full size).
The heartbeat of the embryo clearly visible at this time, usually in the range of 120 to 160 bpm.
