In the Cat Pregnancy Calendar, the time it takes for kittens to develop in their mother’s uterus or womb from conception to birth is called the “Gestation Period”. This takes an average of 63 to 65 days. But in cats this period can be very variable. It can be as short as 56 days to as long as 72 days.
The Cat Pregnancy Calendar can be divided into 3 Developmental Stages:
STAGE 1 Pre-Implantation to Implantation Stage
- Covers the first 2 weeks of pregnancy (Days 0-14).
- This is the stage when conception occurs. On Day 0, the female’s egg becomes fertilized by the male’s sperm at the female’s Fallopian tubes (also called oviducts) near her ovaries.
- The singe-cell fertilized egg (also called the zygote) then travels down from the Fallopian tubes to the uterus in the next few days.
- On its way to the to the uterus, the zygote starts dividing into a 2-layered, ball-shaped, multiple-celled structure called the blastocyst.
- The blastocyst implants or attaches to the wall of the queen’s uterus, more specifically at the uterine horns, at around Day 14 after conception.
- From Days 0-7 there are no detectable signs of pregnancy.
- The earliest that pregnancy can be detected by very high quality ultrasonography is at between Days 11-15 where they appear as discrete spherical swellings on the walls of the queen’s uterus.
STAGE 2 Embryogenesis Stage
- Covers the 3rd to 4th weeks of pregnancy (Days 15-28).
- This stage is called “Embryogenesis Stage” because it is when the embryonic kitten’s organ systems start to form and develop.
- The embryo is now a small spherical swelling at the uterine horns and can be felt by palpation (the process of using one’s hands to examine something) at around Days 17-25. Palpation should be done only by an experienced veterinarian.
- At around Days 20-25, it is the earliest the Relaxin Assay Test can be used to determine pregnancy, however, it is better to wait at around the 5th week of gestation. Relaxin is a hormone produced by the developing placenta(s) in the queen.
- At Days 25-35 the fetal heartbeat start becoming detectable through ultrasonography. When a heartbeat is detected, it implies that the kitten is now at least 3 weeks old.
- On around the third week of gestation, the hair around the queen’s nipples start to thin and the nipples themselves start to develop and swell slightly and “pink-up”.
STAGE 3 Fetal Growth Stage
- Covers the 5th to 9th weeks of pregnancy (Days 29-63).
- During this stage, the fetal organs in the different body systems have been established and they now begin to grow and develop.
- The glands begin to function and secrete their hormones.
- At Day 35 the fetal kittens are floating in a lot of amniotic fluid making palpation difficult at this stage until around Day 49.
- From Day 49 until the end of pregnancy, the amount of amniotic fluid surrounding the fetus becomes lesser and the kitten’s head becomes big enough to be felt as a firm nodular structure by palpation.
- The earliest the fetal skeleton can be seen on X-ray is Day 42 but it is better to perform this procedure for pregnancy diagnosis at Day 47 to give a clearer image. X-rays are not teratogenic (meaning causing birth defects) anymore to the fetus at this stage because the kitten’s internal organs have formed.
- On the 5th week of gestation, the queen’s belly start becoming visibly larger and her nipples become more pink and prominent and she will start to eat more.
- On the 8th week the queen may start to exhibit “nesting” behavior and search for birthing areas and at this time you will also be able to see the kittens moving inside her along her flanks, most noticeable when she is resting.
- On the 9th week the queen may start to go into labor and within 12 to 24 hours prior to labor you might observe already milky discharge from the nipples and clear watery discharge from the vulva.