Page 979 - Small Animal Internal Medicine, 6th Edition
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CHAPTER 54   The Practice of Theriogenology   951


            actual time of conception in the bitch, and the length of time   elective intervention is best delayed until stage I labor has
            semen can remain viable in the bitch reproductive tract   begun (see Chapter 55) or prolonged gestation is confirmed
  VetBooks.ir  (often > 7 days). Breeding dates and conception dates do not   ultrasonographically.
                                                                   Fetal age determination by ultrasonography is accom-
            correlate closely enough to permit very accurate prediction
            of whelping dates, and clinical signs of term pregnancy are
                                                                 tures or by measuring certain parameters. Measurements
            not specific. Radiographic appearance of fetal skeletal min-  plished by either the first appearance of certain visible struc-
            eralization varies at term, and fetal size varies with breed and   such as the gestational sac diameter, fetal occipitosacral
            litter size. Because the queen is an induced ovulator (ovula-  (crown-rump) length, and fetal head (biparietal) diameter
            tion follows coitus by 24-36 hours), gestational length can be   can be obtained ultrasonographically, relate closely to fetal
            predicted more accurately from  breeding  dates,  assuming   age, and permit estimation of gestational length and parturi-
            copulation provided adequate coital stimulation for the LH   tion dates, especially useful if ovulation timing was not per-
            surge and subsequent ovulation, and a limited number of   formed (Figs. 54.27, 54.29, 54.30; Video 54.4). Variation in
            copulations were permitted. The gestational length of queens   breed size (especially in the dog), brachycephalic canine and
            ranges from 52 to 74 days from the first to last breeding. The   feline breed variation, and individual variation in measuring
            mean gestational length is 65 to 66 days. Because of the poor   technique are sources of inaccuracy in predicting fetal age
            outcome with the delivery of premature puppies and kittens,   with ultrasound (Box 54.6).




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               1.92cm                                               1.22cm




            FIG 54.29                                            FIG 54.30
            Pregnancy ultrasound feline; gestational age 30 days. Cursors   Pregnancy ultrasound canine; gestational age 39 days.
            mark the occipitosacral (crown-rump) length in centimeters.   Cursors mark the biparietal (head) diameter in centimeters.

                   BOX 54.6
            Formulas to Predict Gestational Age and Days Before Parturition in the Dog and Cat

             Gestational  age  (GA)  is  based  on  days  post–luteinizing   Days before parturition in the dog
             hormone (LH) surge in the dog and days postbreeding in the   DBP = 65 − GA
             cat.  Gestational  sac  diameter  (GSD),  crown-rump  length
             (CRL),  head  diameter  (HD),  and  body  diameter  (BD)  mea-  Gestational Age in the Cat (±2 Days)
             surements are in centimeters. Days before parturition (DBP)   Greater than 40 days
             is based on 65 ± 1 days post-LH surge in the dog and 61   GA = 25 × HD + 3
             days postbreeding in the cat.                       GA = 11 × BD + 21

             Gestational Age in the Dog (±3 Days)                Days before parturition in the cat
             Less than 40 days
                                                                 DBP = 61 − GA
             GA = (6 × GSD) + 20
             GA = (3 × CRL) + 27                                 Novel feline gestational aging using crown-rump length
                                                                 Y = 0.2423 × GA − 4.2165
             Greater than 40 days
                                                                   Y is mean litter CRL (cm)
             GA = (15 × HD) + 20                                   GA is the gestational age
             GA = (7 × BD) + 29                                    (Solve for GA)
             GA = (6 × HD) + (3 × BD) + 30
            Data modified from Nyland et al: Small animal diagnostic ultrasound, ed 2, Philadelphia, 2002, Saunders.
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