In cats, the normal gestation range is given as 52-74 days, depending on the breed. As cats are induced ovulators, the luteinizing hormone only surges 24-40 hrs after copulation. If the copulation is not observed, it is difficult to determine when ovulation occurs.
After 5 days (post breeding) the fertilized ovum enters the uterus with the outer layer (zona pelucida) being shed 10-12 days after breeding. Implantation occurs at 12-13 days. Heart beats can be detected at 16 to 25 days.
Pregnancy diagnosis can be made by palpation for the gestational sacs 21-25 days post breeding. After 35 days, however, the sacs flatten and palpation becomes more difficult.
Ultrasound is the most sensitive and reliable method of pregnancy detection. With skilled technicians, fetal structures can be detected 11-17 days post breeding. It is less reliable to determine the number of fetuses. Heart rates can be monitored from day 25 onwards, and should be greater than 193 beats/min. Fetal movement can be observed at 28 days. After 40 days, the gestational age can be estimated using the foloowing two formulas:
Age = (25 x head diameter cms) + 3
Age = (11 x body diameter cms) +21
Mineralization occurs at 38-40 days. Xrays can then be used to determine the number of fetuses. Once mineralization begins, age of the fetuses can be estimated as seen in the table.
Use of hormones to determine pregnancy is dependent on the hormone. Progesterone is not reliable. Relaxin is specific to pregnancy as early as about 25 days. Prolactin is not reliable as it will spike in pseudopregnant animals.
Unlike in dogs, queens need a slow increase in calories beginning at 14 days.
Queens may have normocytic, normochromic anemia as well as mild neutrophilia. Other changes in bloodwork include decrease in proteins, increase in lactate dehydrogenase, increase in cholesterol, and decrease in creatinine.
For high risk pregnancies, monitoring of progesterone levels should be used. If a decrease in progesterone level is seen, females can enter pre-term labor, which may be stopped with exogenous progesterone or terbutaline.
Termination of pregnancies can be done either by spaying or, if fertility needs to be maintained, by using a variety of compounds such as estradiol cypionate.
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