People often say that you can’t be a "little bit pregnant". Either you are or you aren’t. When we’re talking dogs and cats we’ve got a little more of a gray area, and some areas are grayer than others.
First of all, they have multiple offspring, aka "litters". So, in that respect, you could be a little bit pregnant with one or two babies, or a whole lot pregnant with eight or ten (or more). If the pregnancy is part of your master plan to become wealthy by raising and selling beautiful pets, you’d like to have a lot of them. Eight is a nice number, since there are eight faucets on the old udder. With more than eight, you’ll probably need to do some supplemental formula feeding to help mom keep up with the demand.
As far as delivery of the babies is concerned, four to six is a nice number. It’s not so many that the mom gets totally exhausted (they don’t call it "labor" for nothing) and just quits before she’s through. With fewer pups or kittens, say one or two, they tend to be huge and hard to deliver. One baby gets all the nutrition available for a whole litter and he will be one big honker. The size of pups at birth depends mostly on the size of the mom and the number conceived. The size of dad will come into play later in life, but "Big Daddy" on small mommy really has no bearing on things at the time of birth.
Of course, sometimes the pregnancy is NOT part of your plan. Your actual plan was to get the baby-works removed before breeding took place, but you had a lot on your mind and time got away from you. Next thing you know there’s a whole lot of shaking going on. Your cute kitty appears to have taken up wrassling and opera-singing at the same time. Your sweet puppy has suddenly acquired an amazing number of new friends who are waiting in line to sign her dance card (or fighting each other instead of waiting their turn; pretty much everybody gets a turn, though).
So, you meant to keep closer tabs on things, but you just let her out for a minute, and you didn’t have your shoes on, and well, you know… Now what? Hey, maybe she didn’t get pregnant. I mean, you can’t get pregnant on the first date, can you? Aw, nuts.
So what are your options? You could become resigned to the situation and prepare for the babies in about nine weeks. ( Don’t forget those pre-natal checkups. ) You could terminate the pregnancy with prostaglandin injections. That works well and has no lasting side-effects. Unfortunately, you have to give the injections twice daily for four days, and they have to urinate, defecate, and vomit after every shot. It’s not cheap, either. You could pretend that she’s not pregnant and get on with the original plan to have her spayed (a complete removal of uterus and ovaries). You need to do that pretty quickly, though. You really don’t want to perform that kind of surgery in an advanced pregnancy.
Sure would be helpful if you knew whether she really got pregnant or not, wouldn’t it? Back in the dark ages when I first got out of veterinary school, we were pretty limited in our pregnancy tests for dogs. They tend to go through the hormonal changes associated with pregnancy even when they don’t get bred. So much for the progesterone EPT; that’s useless in dogs. An X-ray doesn’t show much until the last week of pregnancy. By eight weeks along, you’ve probably got a pretty good idea if she is or if she ain’t. For a long time, we couldn’t do much in the early stages beyond a touchy-feelie of the abdomen. You’re feeling through hair, skin, muscle wall, and the other guts. Pretty easy to miss things, particularly if the patient is a little tense (and who wouldn’t be?).
Things are better now. There is a blood test now for the hormone relaxin. You’ve got to be about halfway through before it shows up, though. Ultrasound exam will show up sooner than that (28 days of gestation). Since ultrasound also lets you observe fetal development and assess the health of the uterus, it’s the preferred method for early diagnosis. You can get a rough count of the babies with ultrasound, but it’s unlikely to be exact. It will certainly allow you to tell about how far along you are if the breeding date is somewhat uncertain. If you want a head count, you’re going to have to wait for that last week and take an X-ray. Then there is finally enough calcium in the fetal skeletons to get a good picture. While it is possible to make a mistake, at this point you can usually get a very accurate count of the babies, which is useful at the time of delivery (is that ALL of them?)
One side note here: I’ve mentioned spaying a pregnant female, which is obviously going to kill the little fetal puppies or kittens. That sounds pretty creepy, and it’s something I prefer not to do. The other side of the coin is that these are unwanted offspring who have no guaranteed homes. They are very likely to wind up in an overcrowded animal shelter. I spent several months working full-time in an animal shelter while I was in college. I had to put down a lot of animals that we just didn’t have room for. They had had their chance and had to make room for the newbies. That is really creepy. If I have to choose between spaying a pregnant female with BB-sized fetuses and putting down brown-eyed, waggy-tailed puppies, I’m going for the BBs. Sometimes life presents us with unpleasant choices and we just have to do our best.