Pregnancy

10 Pregnancy




FREQUENTLY ASKED QUESTIONS



1) Can a bitch carry pups from more than one sire in a litter?

Yes. This phenomenon is called superfecundation. Because the spermatozoa from the male can live for up to a week in the bitch and may be present well before the eggs are ready to be fertilized, a bitch bred by more than one male has spermatozoa from all males involved adhering to the lining of the reproductive tract, available to fertilize the eggs once they are mature. Parentage testing can be done to determine who is the sire of the pups; DNA samples from the dam, all possible sires, and the pups in question are required.


2) My bitch had a litter of five pups with one runt. Was that small pup conceived later than the other four?

Probably not. Dogs release all their eggs over about a 24-hour span. Even if conception of that small pup occurred later than conception of the other pups, all the pups float around free for 17 days before implantation and formation of the placenta. Runt pups most likely are the same age as their littermates but had poor placentation.


3) My vet says gestation length from breeding can vary from 58 to 71 days. How can there be such a huge range if the dog only is bred once or twice?

Bitches stand to be bred for a large window of time around ovulation and spermatozoa from the male live in the bitch’s reproductive tract for an extended period, too. Date of breeding is not necessarily date of conception. If no workup was done to allow determination of ovulation date, more exact determination of likely whelping date cannot be made.


4) How many days before term can puppies be born safely?

That is a good question! Puppies lay down surfactant, which allows normal expansion of the lungs, very late in gestation. No one ever has done a study in which pups were removed by C-section various days before term to see when they would survive, nor is anyone likely to do such a study. If the ovulation date is known, I prefer not to take pups any earlier than 61 days from ovulation.


5) Do human early pregnancy tests (EPTs) work in dogs?

No. The hormone measured in human EPTs is human chorionic gonadotropin. This is produced only in humans. Dogs do not produce a similar hormone early in pregnancy.


6) I could see the pups moving in my pregnant dog yesterday but cannot see anything today. How can we determine whether the pups are okay?

Lack of movement does not necessarily mean there is a problem. The pups simply may be running out of room in there! The best way to determine whether the pups are okay is by ultrasound.


7) Is it safe to take x-rays late in pregnancy?

Yes. The amount of radiation used in x-rays is as safe for the pups as it is for the bitch and the humans performing the procedure. The pups are no longer developing and so are not sensitive to radiation as a cause of birth defects.


8) My Labrador retriever threw a litter of four pups. What are some reasons for this small litter size?

The most likely culprit is breeding at the wrong time. Optimal breeding day for litter size is 2 days after ovulation as determined by measurement of progesterone by your veterinarian. Other possible causes include hypothyroidism, uterine infection, and advanced age of the bitch.


9) I had x-rays taken at about 55 days from breeding, and the vet could see only one large pup. Is my dog going to have trouble whelping?

She may have trouble whelping. Pups grow to fill the size available to them, and this pup had the whole uterus to himself. Singleton pups also may be associated with prolonged gestation because the single pup may not be able to set off the hormone cascade that initiates labor. Talk to your veterinarian about emergency care or performance of elective C-section.


10) Are red raspberry tea leaves recommended for use during pregnancy in dogs?

There is no evidence that red raspberry tea leaves are beneficial during pregnancy.


11) I just lost a litter to canine herpesvirus. Do I need to worry about myself and my family getting herpes?

No. Canine herpesvirus cannot infect humans, and human herpesvirus cannot infect dogs.



I. PHYSIOLOGY AND ENDOCRINOLOGY


The eggs released by the bitch are fertilized in the uterine tubes and move into the uterus 8 to 9 days after ovulation. The conceptus implants and the placenta begin to be formed 16 to 18 days after ovulation. High concentrations of progesterone must be present throughout pregnancy. Progesterone during pregnancy decreases uterine contractility; stimulates secretions of the endometrial glands, which presumably provide nutrients to maintain the conceptus before implantation; and stimulates mammary development. Prolactin concentrations begin to rise at midgestation. Concentration of relaxin, released from the placenta, also rises beginning at midgestation (Figure 10-1).


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Figure 10-1 Hormone changes of pregnancy.


The body of the bitch responds to the presence of the enlarged uterus and developing fetuses with processes designed to maintain function in the bitch while promoting development and growth of the puppies. Physiologic changes in the bitch that occur during normal pregnancy include the following:


• Increased heart rate

• Increased packed cell volume (% of the blood made up of red blood cells)

• Increased oxygen consumption

• Slower gastric emptying time

• Increased blood flow to the kidney

Superfecundation is the presence in one litter of pups with different sires. This occurs readily in any bitch bred by more than one male. In some breeds, superfecundation is encouraged because it allows for greater genetic diversity in any given litter. This is especially useful in breeds with a small number of individuals. The American Kennel Club (AKC) does allow breeding a bitch to more than one male; genetic parentage testing of the pups is required before they can be registered (see Chapter 29).


Superfetation occurs when a pregnant animal is bred and a second conception occurs. This has not been documented to occur in dogs, nor is it likely because dogs ovulate all ova over a 24-hour period and because spermatozoa would be unable to reach the uterine tube past developed zonary placentas. If there are pups of grossly different size in one litter, it is most likely that the small pup had an abnormal placenta or developmental abnormality.


Gestation length in the dog most commonly is reported to be 63 days. However, that gestation length is from ovulation, not from breeding. It has been demonstrated that gestation length timed from ovulation in most bitches is from 62 to 64 days. Gestation length timed from breeding can vary from 58 to 71 days. Remember that bitches will stand to be bred for a large window of time around ovulation and that spermatozoa may live for more than a week after introduction into the bitch’s reproductive tract. Therefore if a bitch is bred very early and does not conceive until well after breeding, she will have an apparent prolonged gestation. Conversely, if a bitch is bred late and conceives very soon after breeding, she will have a shortened gestation.


Puppies do not lay down surfactant in their lungs until within days of term. Without surfactant their lungs are incapable of normal function and pups born without sufficient surfactant either die of lack of oxygen or develop respiratory disease. Little research has been done to determine exactly how early in pregnancy puppies can be taken by cesarean section and be viable, nor has research been done evaluating the usefulness of cortisone in promoting formation of surfactant, as is done in humans. Elective cesarean section should not be performed prior to 61 days from ovulation unless the bitch’s life is at stake.



II. DIAGNOSIS


Pregnancy diagnosis in the dog is complicated by the fact that all dogs go through the same sequence of hormone changes after estrus, whether or not they are bred. For that reason, blood tests are not as commonly used to diagnose pregnancy as are diagnostic methods that physically identify pregnancy. The various methods of pregnancy diagnosis that are commonly used vary in time during gestation when they can be used, accuracy, and ability to provide information beyond a simple “yes or no” answer (Table 10-1).



Table 10-1 Methods for Pregnancy Diagnosis in Dogs

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Human “early pregnancy tests” do not work in dogs. These tests identify the hormone human chorionic gonadotropin (hCG), which is produced only during pregnancy in humans. The human conceptus implants 6 days after conception; so, by the time a woman suspects she may be pregnant, 14 days after ovulation, there has been a functional placenta secreting hCG for about 8 days. No hormone of this type is known to be produced in dogs during pregnancy. Because dogs do not develop a functional placenta until after implantation on about day 17 after ovulation, creation of an early pregnancy test for dogs is not likely.



A. ABDOMINAL PALPATION


Palpation of the abdomen permits the experienced individual to feel amniotic vesicles. The amniotic vesicles are the developing pups within the amniotic membranes, surrounded by fluid. These turgid vesicles have the consistency of peeled, hard-boiled eggs and range in size at midgestation from a grape in very small dogs to an egg in large-breed dogs. The vesicles are not grasped but instead are allowed to slip through the fingers as the abdominal contents pass through the fingers (Figure 10-2). Abdominal palpation never has been documented to cause pregnancy loss in bitches, but repeated palpation day after day is not recommended.


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Figure 10-2 Abdominal palpation for pregnancy.


Abdominal palpation is best performed from about days 28 to 35 from ovulation. Amniotic vesicles are too small to feel much earlier than 28 days from ovulation. After about 35 days from ovulation, the amniotic vesicles fill with fluid and abut each other end to end, making them difficult to feel as individual entities. It is difficult to diagnose pregnancy in bitches that are tense, very thin, or very obese. Overall accuracy is reported to be 88%. If a mistake is made, it is more often a false-positive; feces in the colon can feel very much like amniotic vesicles, as can a segmented uterus affected with pyometra (see Chapter 16).


Abdominal palpation is not at all accurate as an indicator of litter size. Some of the abdominal space lies within the rib cage and cannot be palpated. Similarly, abdominal palpation is not an accurate indicator of fetal viability unless the pregnancy is very advanced and the person palpating can feel or see the pups kicking.



B. IMAGING



1. Ultrasound


Several types of ultrasound are described in the veterinary literature. Those used commonly in small animal medicine are Doppler and B-mode ultrasound. With any type of ultrasound, sound waves are sent into tissue and reflected back. The reflection may be audible, as in Doppler ultrasound, or visible, as with B-mode ultrasound. Doppler ultrasound is rarely used as a diagnostic tool in veterinary medicine but is a component of systems designed for management of high risk pregnancies and possible dystocias (WhelpWise, Whelp Watch; see Chapter 12). For pregnancy diagnosis, B-mode ultrasound most commonly is used (Figure 10-3).


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Figure 10-3 Performing abdominal ultrasound.


Amniotic vesicles easily are identified by B-mode ultrasound. The amniotic vesicles are balls filled with fluid, with a tiny developing puppy in the center. Fluid appears black on ultrasound, so B-mode ultrasound of a pregnant bitch’s uterus reveals multiple black spheres with gray material inside (Figure 10-4). There are reports of identification of pregnancy by B-mode ultrasound as early as 19 days after ovulation, but these amniotic vesicles are small and easily missed. Once the bitch is 24 days or more past ovulation, B-mode ultrasound is 94% to 98% accurate for pregnancy diagnosis.


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Figure 10-4 Sonogram of early pregnancy.


B-mode ultrasound is not the most accurate technique for determination of litter size, with reported accuracy of 32% to 36%. Because only a portion of the abdomen is being viewed at a time and the uterine horns can wind from side to side of the abdomen, it is easy to count a specific puppy more than once. Accuracy for determination of litter size is greater in litters of five or less because the puppies are spaced farther apart in the abdomen.


Ultrasound is the best technique available for determination of fetal viability. B-mode ultrasound is “real time”; beating hearts and movement of limbs readily are identified after midgestation. Fetal heart rate also can be used as an indicator of fetal distress. Fetal heart rate should be about twice that of the dam, usually greater than 200 beats per minute. Fetal heart rates of less than 150 beats per minute signal severe fetal distress and the need for immediate veterinary intervention.

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Related posts:

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  2. Embryology
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  4. Pharmacology

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Pregnancy

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