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The false negative test can happen due to fail to see a fetus; these false shadows may be occurred due to gas or fecal material. Fake positives might take place due to screening a loop of smaller intestine, but most often screening/imaging in a subsequent plane disclose that intestine turn into tubular form, whereas an ovulation sac does not. Visualization of ovulation sac is suggested to prove pregnancy. The enlargement of Uterine will lead the construction of the ovulation sac, but that is not a particular finding. Cardiac and fetal activities/movement is conventional cue of fetal feasibility. On the same day apparition of the embryo and cardiac activity typically take place. Cardiac activity appears initially as a flutter within the embryo’s tissue.
The maternal heat beat rate is two times less than the fetal heart rate. It is generally from 200 to 220 beats per minutes. Swallowing, hiccoughs, body and limb movements are the general fetal activities. A breeder can calculate ovulation age by assessing the being there of fetal structures meantime measuring the ovulation sac, head diameter, crown-rump and diameter of the body of the fetus. The appearance timeline of fetal structures is steady among breeds, and the observations should always be used with the measurements that are taken to most accurately expected ovulation age. At least two or more fetuses should be used to obtaining the measurements. Litter size not effect the accuracy but in toys and miniature breeds one day is additional to calculate the ovulation age. And in giant breed when their ovulation age calculated must subtract two days. The accuracy falls at about 50% in the last 3 weeks of gestation and the diameter of head should be used as it is the most consistent. Overall, the correctness of prediction of ovulation age at any time during ovulation, once it adjusted for body weight as explained above, is 88% ± 2 days from the expected age.
Ultrasound test never correctly and accurately can judge the fetal numbers. Only a little section of the reproductive area can be screened at single time only, allowing fetuses to be counted more than once or not at all, this is the only reason that ultra sound can not judge the fetal numbers. Fetal resorption may also be a factor. To overestimate the size of small litters and to the size of large litters underestimate is the tendency. One can be predict it is either a large or small litter but reliable accuracy is not there in ultrasound examine. From thirty to fifty days one study only quoted on eighteen percent and 8 percent only if it done after fifty days. There are many breeders and vets who has not awareness of these limitations of the ultrasound, thus with the prediction of ovulation age they are expecting to get fetal numbers.