Both prolonged and shortened pregnancies carry the risk of increased mortality of the offspring. The main causes of early delivery are genetic factors, bacterial and viral infections, corpus luteum insufficiency and pathologies of the placenta. Antepartum luteolysis is due to the activity of prostaglandin F2α. A decrease in the progesterone concentration activates the sensitivity of the uterine muscles to oxytocin. Calcium ions move into the myocytes and bind to calmodulin, starting enzymatic reactions necessary for muscle contraction. Oxytocin promotes prostaglandin F2α release. Cholesterol and magnesium stimulate the binding of oxytocin to its receptors. A premature delivery is caused by a disorder of the balance between contractility and relaxation of the myometrium, which is regulated by many signalling pathways. Birth in humans can be postponed by the use of many different tocolytic medications, β-adrenergic drugs (ritodrine, hexoprenaline, fenoterol, terbutaline), magnesium salts, prostaglandin synthesis inhibitors (indomethacin, naproxen), pentoxifylline, metoprolol, calcium antagonists – calcium channel blockers (nifedipine), oxytocine antagonists (atosiban), nitric oxide donors (nitroglycerin) as well as progesterone and its synthetic analogs. In dogs and cats, in the presence of endogenous hormone deficiency, progesterone and its derivatives (gestagens) are recommended. In small animals with the risk of premature delivery, terbutaline has successfully been used. Premature delivery is a serious problem in both human and veterinary medicine, and experience from human medicine is being gradually introduced into veterinary practice.
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