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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Often found in conjunction with high-risk pregnancies and impaired placental function; compromise fetal survival. Fetal stress is a normal physiologic response to potentially life-threatening situations. If not addressed, quickly progressed to distress, a pathophysiologic condition leading to fetal demise or delivery of a severely compromised foal.

Pathophysiology!!navigator!!

Maternal disease and/or compromised placental function including the following.

Preexisting Maternal Disease

  • PPID (formerly equine Cushing-like disease)
  • EMS/IR
  • Laminitis
  • Chronic, moderate to severe endometrial inflammation, endometrial periglandular fibrosis, and/or lymphatic cysts leading to impaired placental function

Gestational Maternal Conditions

  • Malnutrition
  • Colic
  • Enterocolitis
  • Hyperlipemia
  • Prepubic tendon rupture
  • Uterine torsion
  • Dystocia
  • Granulosa cell tumor
  • Laminitis
  • Musculoskeletal disease
  • Exposure to ergopeptine alkaloids in endophyte-infected fescue or ergotized grasses and/or grains
  • Exposure to other xenobiotics
  • Exposure to abortigenic infections, especially equine herpesvirus; bacterial contaminants on Eastern tent caterpillar setae

Placental Conditions

  • Placentitis; insufficiency; early separation; placental abnormalities reported with foals resulting from SCNT cloning procedures
  • Umbilical cord torsion or torsion of the amnion
  • Hydrops of fetal membranes
  • Mare reproductive loss syndrome

Fetal Conditions

  • Twins
  • Fetal abnormalities
  • Delayed fetal development, intrauterine growth retardation
  • Fetal trauma
  • Foals resulting from SCNT cloning procedures
  • Depending on the specific cause, the mechanisms can involve 1 or more of the following:
    • Maternal systemic disease; placental infection, insufficiency, torsion, separation; fetal abnormalities, all of which impede efficient fetal gas exchange and nutrient transfer
    • If impairment/stress is not resolved quickly the fetus responds pathophysiologically (i.e. distress) to alterations in oxygenation/nutrient supply (e.g. passing/aspirating meconium pre- or perinatally, decreased respiratory movements, irregular heartbeat), potentially leading to fetal compromise and death
    • Acute fetal stress may be premature birth of a nonviable foal
    • Fetal stress to distress results in fetal death and/or delivery of a severely compromised foal

Systems Affected!!navigator!!

  • Maternal—reproductive
  • Fetal—all organ systems

Risk Factors!!navigator!!

  • May be nonspecific
  • Thoroughbreds, Standardbreds, draft and American Miniature Horse mares, and related breeds predisposed to twinning
  • >15 years of age

Historical Findings

  • Previous examination with placentitis or fetal compromise
  • Previous abortion, high-risk pregnancy, or dystocia
  • History of delivering a small, dysmature, septicemic, and/or congenitally malformed foal
  • Preexisting maternal disease at conception (see Pathophysiology)
  • Previous exposure to endophyte-infected fescue or ergotized grasses and/or grains; abortigenic xenobiotics or infections

Physical Examination Findings

Maternal and Placental Signs

  • Anorexia, fever, other signs of concurrent, systemic disease
  • Abdominal discomfort
  • Mucoid, mucopurulent, hemorrhagic, serosanguineous, or purulent vulvar discharge
  • Premature udder development, dripping milk (except in cases of fescue toxicosis)
  • Premature placental separation (red bag)
  • Placentitis, placental separation, or hydrops of fetal membranes by TRP or transabdominal US
  • Excessive swelling along the ventral midline and evidence of ventral body wall weakening by TRP or transabdominal US
  • Excessive abdominal distention
  • Alterations in maternal circulating levels of progestins, estrogens, and/or relaxin reflect changes in fetal wellbeing and/or placental function

Fetal Signs

  • Clinical sign of fetal stress and/or distress might be premature delivery of a live or dead foal or late delivery of a severely compromised foal, unable to stand and suckle. Fetal hyperactivity or inactivity (concurrent with maternal or placental abnormalities) may suggest a less than ideal fetal environment and/or fetal compromise
  • Can be assessed by visual inspection or by TRP of the mare
  • Alterations in parameters assessed using TRP or transabdominal US

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Normal, uncomplicated, pregnancy with an active, normal fetus as assessed by TRP, transrectal or transabdominal US, and/or various laboratory tests.

CBC/Biochemistry/Urinalysis!!navigator!!

Maternal Assessment

  • Complete physical examination
  • CBC, serum biochemistry, determine inflammatory or stress leukocyte response, as well as other organ system involvement
  • Test for PPID or EMS/IR
  • ELISA or RIA analyses for maternal P4 may be useful at <80 days of gestation (normal levels vary from >1 to >4 ng/mL, depending on reference laboratory). At >100 days, RIA detects both P4 (very low > day 150) and cross-reacting 5α-pregnanes of uterofetoplacental origin. Acceptable levels of 5α-pregnanes vary with stage of gestation and the laboratory used. Decreased maternal 5α-pregnane concentrations during late gestation are associated with fescue toxicosis and ergotism and are reflected in RIA analyses for progestagens
  • Maternal estrogen concentrations can reflect fetal estrogen production and viability, especially conjugated estrogens, e.g. estrone sulfate
  • Decreased maternal relaxin concentration: with abnormal placental function
  • Decreased maternal prolactin secretion during late gestation—associated with fescue toxicosis and ergotism
  • Anecdotal reports of lower T3/T4 levels in mares with history of conception failure, EED, high-risk pregnancies, or abortion. The significance of low T4 levels is unknown
  • Feed or environmental analyses might be indicated for specific xenobiotics, ergopeptine alkaloids, phytoestrogens, heavy metals, or fescue endophyte (Epichloë coenophiala, formerly Neotyphodium coenophialum)

Fetal Assessment

  • Transrectal and transabdominal US can be useful in diagnosing twins, assessing fetal stress, distress, and/or viability, monitoring fetal development, evaluating placental health and diagnosing other gestational abnormalities, e.g. hydrops of fetal membranes
  • Predisposed individuals, i.e. barren, older mares, mares with prior high-risk pregnancy, placentitis, abortion, EED, conception failure, or endometritis, transrectal or transabdominal US should be performed on a routine basis during the entire pregnancy to assess fetal stress and viability
  • Confirmation of pregnancy and diagnosis of twins should be performed any time serious maternal disease occurs or surgical intervention is considered for a mare bred within the last 11 months
  • Twins confirmed by identifying 2 fetuses (easier by transrectal US when gestational age is <90 days) or by presence of a nonpregnant uterine horn (transabdominal US during late gestation)
  • By transabdominal US during late gestation—view fetus in both active and resting states for at least 30 min. Note abnormal fetal presentation and position
  • Abnormally high FHR after activity >100 bpm or >40 bpm difference between resting and active rates reflects fetal stress, rather than distress
  • Abnormal fetal heart rhythm by echocardiography may occur immediately before, during, or after foaling and might indicate distress from acute hypoxia
  • Abnormally low resting FHR is <60 bpm or <50 bpm after day 330 of gestation
  • Bradycardia and absence of heart rate variation with activity indicate central nervous system depression, probably from acute hypoxia. If persistent, correlates well with poor prognosis
  • Absence of fetal heartbeat is a reliable sign of fetal death
  • Absence of fetal breathing movements correlates well with fetal distress
  • Alterations in fetal fluid amounts
    • Normal range for maximal allantoic fluid depth, 4.7–22.1 cm
    • Normal range for maximal amniotic fluid depth, 0.8–14.9 cm; increased amounts reflect hydrops; low amounts indicate fetal distress and longstanding, chronic hypoxia
  • Increased echogenicity of fetal fluids may reflect distress earlier in pregnancy; can be normal during later gestation
  • Fetal ECG has been used to detect twins and to assess fetal viability and distress but largely has been replaced by transabdominal US with ECG capabilities
  • While a higher risk technique in horses than in humans, US-guided amniocentesis and/or allantocentesis and analysis of the collected fluids might become a future means to assess fetal karyotype, pulmonary maturity, and to measure fetal proteins
  • Samples might reveal bacteria, meconium, or inflammatory cells

Pathologic Findings!!navigator!!

  • Evidence of villous atrophy or hypoplasia on the chorionic surface of the fetal membranes
  • Thickening/edema of the chorioallantois or allantochorion
  • Endometrial biopsy (of nonpregnant mare)—presence of moderate to severe, chronic endometritis, endometrial periglandular fibrosis, decreased normal glandular architecture, lymphatic lacunae

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Monitoring/managing fetal stress/distress, including prolonged examination times required for complete serial transabdominal fetal assessments, is best performed at a facility prepared to manage high-risk pregnancies, especially if distress is severe and parturition (induction or cesarean section) is imminent
  • Early diagnosis is essential
  • Balance fetal distress and maintenance of pregnancy with the need to induce parturition (with or without cesarean section) if necessary to stabilize mare's health
  • Parturition requires close supervision in cases of fetal stress and distress. The neonatal foal will very likely require intensive care
  • Foal resuscitation during delivery or immediately postpartum, attention to airways, breathing, and circulation
    • Complications with dystocia or RFM

Activity!!navigator!!

  • For most cases, exercise will be limited and supervised
  • Prepubic tendon rupture, laminitis, fetal hydrops may necessitate severe restrictions/complete elimination of exercise

Client Education!!navigator!!

  • Discuss risk factors
  • Early diagnosis is essential for fetal survival
  • Predisposing conditions compromise fetal wellbeing, correct/manage for positive outcome
  • Induction of parturition and cesarean section are not without risk to dam and foal

Surgical Considerations!!navigator!!

  • Cesarean section may be indicated when vaginal delivery is not possible, or dystocia not amenable to resolution by manipulation alone
  • Surgical intervention indicated for repair of anatomic defects predisposing mares to endometritis
  • Certain diagnostic and therapeutic procedures might also involve some surgical intervention

Medications ⬆ ⬇

MEDICATIONS

Drug(s) of Choice

See specific conditions.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Mare and fetus need frequent monitoring until termination of pregnancy.

Prevention/Avoidance!!navigator!!

  • Recognition of at-risk mares
  • Correction of perineal conformation to prevent placentitis
  • Manage preexisting endometritis before breeding
  • Early monitoring of mares with a history of fetal stress, distress, and/or viability concerns
  • Complete breeding records, especially for recognition of double ovulations, early diagnosis of twins, embryonic or fetal reduction
  • Careful monitoring of pregnant mares for vaginal discharge/premature mammary secretions
  • Removal of pregnant mares from fescue pasture or ergotized grasses or grains during last trimester (60 days optimal, especially if bred on multiple cycles, with no US confirmation of pregnancy; minimum of 30 days prepartum, with adequate breeding dates and confirmation of pregnancy using US)
  • Use ET procedures with mares predisposed to EED or high-risk pregnancies
  • Avoid breeding or using ET procedures in mares which have produced multiple stressed, distressed, or dead foals due to congenital and potentially inheritable conditions
  • Prudent use of medications in pregnant mares
  • Avoid exposure to known toxicants

Possible Complications!!navigator!!

  • Abortion, dystocia, RFM, endometritis, metritis, laminitis, septicemia, reproductive tract trauma, and/or impaired fertility—all affect the mare's wellbeing and reproductive value
  • Neonatal foals compromised during pregnancy are more likely to be dysmature, septicemic, subject to angular limb deformities than foals from normal pregnancies

Expected Course and Prognosis!!navigator!!

  • The ability to prevent and treat conditions leading to stress/distress have improved. Successful management of at-risk pregnancies requires rigorous monitoring of mare, fetus, neonate
  • If predisposing conditions can be treated/managed, pregnancies diagnosed as stressed have a guarded prognosis for normal term gestation
  • If evidence of stress progresses to distress and distress continues during treatment the prognosis for successful term gestation is guarded to poor

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Synonyms!!navigator!!

  • Abortions, spontaneous infectious and noninfectious
  • High-risk pregnancy
  • Placental insufficiency
  • Twins

Abbreviations!!navigator!!

  • EED = early embryonic death
  • ELISA = enzyme-linked immunosorbent assay
  • EMS = equine metabolic syndrome
  • ET = embryo transfer
  • FHR = fetal heart rate
  • IR = insulin resistance
  • P4 = progesterone
  • PPID = pituitary pars intermedia dysfunction
  • RFM = retained fetal membranes
  • RIA = radioimmunoassay
  • SCNT = somatic cell nuclear transfer
  • T3 = triiodothyronine
  • T4 = thyroxine
  • TRP = transrectal palpation
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Bucca S. Ultrasonographic monitoring of the fetus. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:39–54.

Burns TA. Effects of common equine endocrine diseases on reproduction. Vet Clin North Am Equine Pract 2016;32(3):435–449.

Evans TJ, Blodgett DJ, Rottinghaus GE. Fescue toxicosis. In: Gupta RC, ed. Veterinary Toxicology: Basic and Clinical Principles, 2e. San Diego, CA: Elsevier, 2012:1166–1177.

McKinnon AO, Pycock JF. Maintenance of pregnancy. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:2455–2478.

Powell DG. Mare reproductive loss syndrome. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:2410–2417.

Pozor MA, Sheppard B, Hinrichs K, et al. Placental abnormalities in equine pregnancies generated by SCNT from one donor horse. Theriogenology2016;86(6):1573–1572.

Vaala WE. Monitoring the high risk pregnancy. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:16–38.

Author(s) ⬆

Author: Tim J. Evans

Consulting Editor: Carla L. Carleton