There are many reasons for pregnancy loss in the female. Unfortunately, loss earlier than 21 days is hard to substantiate as there is a lack of a definitive pregnancy test within this period. After 21 days from ovulation, pregnancy can be diagnosed via ultrasound, by a relaxin blood assay 21 days from the lutenizing surge, and via X-ray after 42 to 45 days of gestation.
Fetal death during the first half of pregnancy normally results in either fetal resorption or unobserved abortion, whereas in the second half of pregnancy usually results in either abortion or stillbirth. Abortion may be difficult to be noticed as sometimes the bitch eats the aborted materials. Late in gestation in the presence of continuous hormonal (luteal) influence fetal death can result in mummified fetus when fetal and placental fluids are resorbed leaving a dry, deformed structure in the uterus.
What Should be Done When Pregnancy Loss is Determined?
The most important approach in the diagnosis and prevention of future loss is to conduct pathological tests on the aborted fetus and placenta. Additional tests include vaginal swab taken from the bitch for microbiological culture and cytological examination, full blood and urine analysis, and serum progesterone level measurement.
Future pregnancy must be monitored by ultrasound weekly in bitches with a history of pregnancy loss as fetal heart rates are good indicators of fetal health.
There are numerous potential causes of pregnancy loss and some are still unclear to us. Those known can be separated into two main categories: infectious and non-infectious causes.
Infectiou Causes for Pregnancy Loss
They are the most common causes of pregnancy loss and are often determined from testing of the aborted fetus and placenta, and bitch vaginal swab and serum. Vaginal swabs alone are not diagnostic for infection as the reproductive tract of the bitch contains colonies of normal bacteria that will give positive culture results. However, any bacterial species are capable of overgrowth and can in turn cause infection and subsequent pregnancy loss. Diagnosis in such cases is made via cultures from aborted material and inflammatory cytology from smears taken from the vagina or uterus.
Routine use of antibiotics in the bitch during pregnancy is strongly discouraged as such administration can lead to an overgrowth of E. coli or Mycoplasma which may affect the developing fetus.
Apart from overgrowth of normal bacterial flora, other infectious causes of pregnancy loss include:
a. Salmonella: Salmonella is not found in the normal flora. The bitch acquires infection from contaminated food, water or faeces. Diagnosis is made by culturing aborted material or vaginal discharge. A cure can be achieved in some cases by administering appropriate antibiotics. However, antibiotics may prolong the period that the affected bitch carries the infection in some cases. Infected bitches must be isolated.
b. Campylobacter: Campylobacter has been known to cause abortion and fetal resorption. Diagnosis can be confirmed by testing aborted material and vaginal culture. The infection can be successfully treated with appropriate antibiotics.
c. Mycoplasm: This organism is most likely to cause reproductive issues in overcrowded kennels. Antibiotics help to reduce the number of organisms present, but once the antibiotic ceases the number rises unless husbandry issues are addressed.
d. Canine herpesvirus: The bitch affected with this virus during the last three weeks of pregnancy develops generalised infection together with placental infection, which then results in abortion and mummification of the fetus. Diagnosis is achieved by isolating the virus from the aborted fetus or placenta. No successful treatment is available, but isolation of the pregnant bitch from other dogs commencing the last three weeks of pregnancy can prevent infection.
e. Canine parvovirus I: This virus causes fetal death and resorption in early pregnancy. Affected bitches show no clinical signs. Diagnosis is difficult and treatment is unavailable.
f. Other viruses: Both calicivirus and canine distemper virus have also been implicated in pregnancy loss. Diagnosis is made by identifying the virus in the aborted material.
g. Protozoa: Toxoplasmosis is an uncommon cause of canine abortion. Bitches acquire the infection via ingestion of contaminated cat faeces and raw meat. Diagnosis is made with a specific blood test.
Non-Infection Causes of Pregnancy Loss
a. Maternal health: There are several illnesses affecting the bitch that may result in pregnancy loss.
Hormonal diseases: such as low thyroid hormone levels, Cushings Disease, Addisons Disease and Diabetes Mellitus.
Cystic endometrial hypoplasia: It may affect the uterus to the extent that fetal growth cannot be supported to term. There is no known treatment available.
Dietary deficiencies: such as magnesium, vitamin A and iodine in the bitch may cause fetal loss, though this is uncommon these days due to improved feeding.
Significant abdominal trauma: can result in abortion or resorption. Severe exercises such as field training, agility or flyball carry an increased risk of trauma and, therefore, should be suspended during pregnancy.
Exposure of the bitch to chemicals: such as heavy metals and various organic solvents may have adverse effects in relation to pregnancy.
Difficulties in birth: can greatly increase the fetal mortality rate. They can often be overcome with strict monitoring during late pregnancy.
b. Gamete aging: Sperms may be aged by the time fertilisation occurs if bitches are bred too early in their cycle. On the contrary, bitches that are bred late in their cycle may only have near 'end of functional life' eggs. Such situations have been known to increase the risk of abortion in humans though this is not known in dogs.
c. Genetic and chromosomal causes: Fetal mortality rate is higher in pure breed dogs than hybrid dogs. Inbred dogs and bitches usually have lower conception rates and fewer live births than outbred dogs. Lethal chromosomal deaths are thought to be responsible for embryo deaths and resorption though the incidence of such conditions is presently unknown.
d. Drug administration: The first trimester (day 6 to day 20 gestation) is the critical period for embryotoxicity. Drug administration where possible should be avoided during this period, in particular drugs known to cause pregnancy loss (e.g. corticosteroids, chemotherapy drugs and organophosphates).
e. Hypoluteodism: A lack of sufficient progesterone to maintain pregnancy has been known to cause pregnancy loss. Care must be taken when assessing this as the cause of abortion because the progesterone level declines rapidly following abortion from any cause. In bitches progesterone higher than 2ng/ml is required to maintain pregnancy, and values higher than 20 ng/ml are common. It is often advisable to monitor the progesterone level at least weekly when progesterone levels fall to 5 to 10 ng/ml. Supplementation has to be given when progesterone levels fall to 5 ng/ml with more than a week of gestation left. Ideally progesterone supplementation should be avoided during the first trimester of pregnancy due to the risk of masculinising female fetuses. Progesterone supplementation has to be stopped 2 to 3 days before expected parturition so that fetuses are not retained for too long and milk production is not suppressed. Care should also be taken in the progesterone supplement administered so as to reduce the chance of side effects to the fetuses.