Pregnancy & Second trimester (Day 22 - 42)

The second trimester includes some of the most formative stages of fetal development. During this time, the pups are vulnerable to damage and birth defects so pay attention to your dog’s food, chemicals, and stress. In addition, during this period, you are finally going to find out if your bitch is pregnant! If all has gone well, it is really happening and pups are coming in four to six weeks.

What’s Happening?

At the end of the first trimester, and early into the second trimester, the embryonic puppies become elongated as their nervous system and organs begin to develop. They're now about 10 millimeters or one-third of an inch long, and 7 millimeters wide, regardless of breed.

Between Days 16 and 21 post ovulation, the embryos finally stop floating freely and implant in the lining of the uterus. The embryos space themselves throughout the two horns of the uterus before the puppy and the uterine lining connect through the placenta. The placenta is a temporary organ that supports the growing puppy with oxygen, nutrients, antibodies, and other substances, and removes waste products like urea and carbon dioxide.

Dogs have what is known as a zonary placenta. An unusual aspect of dog placentas is that during its development, some of the bitch's blood vessels are destroyed, releasing large amounts of blood at the edge of the placenta. This blood breaks down during the remainder of pregnancy, providing the puppy with iron, and leaving a green-colored mass. If you've ever whelped a litter, you know we see a lot of green when the pups are born due to this fetal blood.

During the early part of the second trimester, when the placenta and pup's organs are developing, both dam and pup are sensitive to a variety of insults, especially nutritional and toxins. The demands on the bitch's body are quite significant as she creates placentas and puppies so the care we provide is critical to a successful pregnancy.

By day 28 after ovulation, our embryonic pup becomes somewhat recognizable as a puppy, and is clearly visible on ultrasound. It's now known as a fetus. However, it's still only about the size of a walnut.

If we look at our bitches’ hormones progesterone remains relatively high in both pregnant and non-pregnant bitches until 24 days after ovulation. Then, relaxin and prolactin begin to rise in pregnant bitches but less so in non-pregnant bitches. Estrogen, which has been identical between pregnant and non-pregnant until now, begins to rise in our pregnant bitches and flat line in our non-pregnant bitches. As the second trimester draws to a close, we're likely to observe changes in our bitch that help us see whether or not they are pregnant.

The bitch may undergo physical and behavioral changes during this three-week period. Around day 35, some bitches will begin to show some mammary gland, minor mammary gland development as prolactin continues to elevate. Her coat may thin on her belly and her nipples may darken. She may begin to sleep more and more soundly. She is likely to run and play a little less. She may groom herself more than normal, insisting on keeping herself very clean. Not to worry, all of this is perfectly normal as her body prepares for whelping and lactation.

You also may notice that she is warmer than normal, panting even when the temperature feels cool to you. Carrying puppies heats bitches up so give her a cool place to rest and sleep.