The stages of birth
In pregnancy, the kittens are spaced along each horn of the uterus. Each kitten is contained within its own membranes and has its own placenta through which it derives nourishment. The uterus may be considered as a muscular, sausage-shaped bag, capable of contracting both around its diameter and along its length. To help in its passage, each kitten is contained within a fairly tough double-layered bag of membranes, which are filled with slippery fluid in which the fetus floats. This serves as both protection and lubrication and provides a distending, stretching and dilating force when the uterus relaxes in front of it and contracts behind it during the course of birth.
Birth (parturition) is generally described in three stages, although in the cat the second and third stages are repeated with each kitten and the third stage is brief and nearly continuous with the second.
The first stage
This is essentially the stage of relaxation of the cervix and vagina and the start of contraction of the uterus. Uterine contractions must always be interrupted by periods of relaxation, otherwise, the blood supply to the kitten would be cut off. The pelvic muscles slacken and the perineum (the area between the anus and vulva) becomes looser and longer. Uterine contractions are not yet observable as straining, although movement of the kittens may be felt through the abdominal wall. There is little else to see at this stage except for repeated visits to the prospective kittening bed, and in the dependent type of cat, an apparent desire for reassurance from the owner. Some scratching up and bed-making occurs, and panting may be seen as a late first stage feature. Vaginal discharge is rarely seen and is usually locked away promptly by the cat. In the cat kittening for the first time, the first stage can be very prolonged, even lasting up to 36 hours without being abnormal.
The second and third stages of birth
After the relaxation of the first stage, the uterine contractions become stronger and more frequent and drive the first kitten, contained within its membranes, towards and into the pelvic opening. As the first kitten enters the pelvis, the outer layer of the membranes appears briefly at the vulva as the ‘water bag’, which bursts and sheds some fluid which is usually cleared up by the cat. The inner layer passes into the pelvis and retains some of the fluid which acts as a continuing lubricant to assist the passage of the kitten.
The cat pushes to help the kitten through the pelvis. This is usually the point at which the owner can see that the cat is actually straining. Normally, delivery of a kitten from the beginning of the second stage may take from five to 30 minutes. Once the head is out, one or two more strains should complete the passage of the kitten.
The third stage follows immediately and is seen simply as the passage of the membranes, complete with the dark flesh coloured mass of separated placenta, as the ‘after-birth’.
Normally, each set of membranes is passed immediately after each kitten. However, sometimes a second kitten will follow so quickly from the opposite uterine horn that the membranes from the first will be trapped temporarily and the two sets will be passed together.
As each kitten is born the cat will tear open the membranes and clear the mouth and nose area of the kitten, biting off the umbilical cord and subsequently eating the after-birth. Second and third stages of labour are repeated as each kitten is born. Intervals between kittens are variable, from as little as 10 minutes to up to an hour in the average case. While cats usually have an average of four kittens in each litter, this can range from one to 12 kittens. Larger litters are seen more frequently in pedigree breeds such as Oriental, Siamese and Burmese.
Sometimes, when one or more kittens have been born, the mother will cease straining and rest quite happily, suckling those kittens already born. She will accept food and drink and is in every way completely normal except that it is obvious from her size and shape, and the presence of movement, that there are still kittens waiting to be born. This resting stage may last up to 24 or even 36 hours, after which straining recommences and the remainder of the litter is born quite normally and easily.