Uterine inertia is an important cause of ineffective labor. Inertia is classified as primary (insufficient stimulation to start uterine contractions) or secondary (caused by uterine muscle fatigue after prolonged straining). Giant-breed dogs seem to be predisposed to uterine inertia.
Primary Uterine Inertia
The two conditions associated with primary uterine inertia are failure to go into labor by 67 days after ovulation and failure to progress from stage one to stage two labor within 24 hours. Causes of failure to initiate labor include a small litter (particularly a single puppy), overstretching of the uterus by a large litter, the stress and anxiety of being a first-time mother (dams can voluntarily prolong, delay, and even interrupt the normal birthing process for up to 24 hours), and occasionally, a calcium deficiency called hypocalcemia.
If more than 65 days have passed from the date of first breeding and the mother shows no signs of whelping, notify your veterinarian because gestation may be prolonged. (Alternatively, the pups may not yet be mature.) An X-ray can be taken to determine the number of puppies and their sizes.
Treatment: Hypocalcemia can be diagnosed by a blood test and treated by giving oral or intravenous calcium. If postmaturity is suspected, your veterinarian may wish to confirm this with a progesterone level test and then do a cesarean section.
If the cervix is dilated, oxytocin may be effective. Oxytocin should never be used when the cervix is closed or in cases of suspected physical blockage because of the danger of uterine rupture. If primary uterine inertia does not respond to medical treatment, a cesarean section is required.
Secondary Uterine Inertia
After a mechanical blockage has been removed, the uterus may be too tired for labor to resume.
Treatment: This usually involves cesarean section.