- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- Prematurity—condition resulting from preterm birth (<320 days of gestation or less than a mare's normal gestational length). Normal 306–390 days in Thoroughbred mares
- Dysmaturity—condition in which foals are born after their expected gestational length, but are small and have some physical characteristics of premature foals. This definition typically includes foals with some degree of intrauterine growth retardation
- Typically, prematurity/dysmaturity results from placental insufficiency, umbilical abnormalities, maternal infection, fetal disease, or iatrogenic induction of parturition
- Any cause of insufficiency of the uteroplacental unit can affect its functional ability; diffusion of substances between the maternal and fetal circulation is disrupted and nutrient delivery, oxygen supply, and waste removal are reduced
- The final maturation of the foal's HPA axis occurs during the later stages of pregnancy. Any stressors to the fetus, either fetal or maternal in origin, can induce premature maturation of the fetal HPA axis and can culminate in a premature or dysmature foal
- Renal/urologic—placental insufficiency may decrease creatinine clearance from the fetus
- Gastrointestinal—intestinal motility dysfunction, gas accumulation, fecal retention, and gastric distention. In severe cases may develop necrotizing enterocolitis
- Endocrine/metabolic—insulin and glucose dysregulation, ACTH and cortisol dysregulation, and thermoregulatory abnormalities (related to triiodothyronine levels)
- Neuromuscular—weak, sometimes display signs of PAS
- Musculoskeletal—failure of ossification of cuboidal bones
- Cardiovascular—cardiovascular collapse and inconsistent response to vasoactive therapy
Out of a large subset of hospitalized foals, the prevalence of prematurity was 11–15% (unpublished).
Premature and dysmature foals are difficult to distinguish from one another from examination findings alone. Typically, foals are considered dysmature when signs of prematurity are present in a foal of normal gestational length.
Born earlier or later than expected, smaller than expected gestational size, history of maternal illness.
- Affected foals often have a low birth weight and are small in size; they may be thin with poor body condition, muscle weakness, and poor muscular development
- They often display a weak or uncoordinated suckle, have a slower than normal righting reflex, are slow to stand and nurse, and have thermoregulatory abnormalities, GI tract dysfunction, renal dysfunction, and poor glucose regulation
- Other findings may include periarticular laxity, hypotonia, a highly complaint thoracic wall, ± low lung compliance (“stiff lung”), a short, silky haircoat, domed forehead, entropion ± corneal ulceration, soft, floppy ears, and occasionally meconium staining
- An underlying cause is often not specifically determined
- Placental insufficiency or infection—premature placental separation, placentitis, twins
- Maternal illness—placentitis, systemic disease (colic, endotoxemia, etc.), chronic malnourishment or debilitating disease, pelvic anatomic abnormalities, uterine torsion, mare reproductive loss syndrome
- Fetal abnormalities—sepsis (bacterial or viral), malformation, hydrops amnion, umbilical abnormalities, endophyte-infected fescue toxicosis, congenital hypothyroidism (related to nitrate consumption by mare or iodine imbalances)
- Iatrogenic—inappropriate induction of parturition with exogenous oxytocin or prostaglandins or premature cesarean section
- Unknown/idiopathic
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS