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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Excessive fluid accumulation in either the allantoic or amniotic cavity of the pregnant uterus
  • Hydrops allantois is related primarily to placental dysfunction/insufficiency, contributing to fluid accumulation within the allantoic space of the fetal membranes
  • Hydrops amnion is attributable to abnormalities of the fetus, contributing directly to fluid accumulation by virtue of congenital anomalies. Segmental aplasias (primarily GI in origin) preclude swallowing and processing and/or recycling of amniotic fluid. The fetus may be delivered alive but rarely is viable

Pathophysiology!!navigator!!

  • Dysfunction of either the placenta or the fetus results in accumulation of excessive amounts of allantoic or amniotic fluid, undermining the dam's health by excessive weight of modest to rapid accumulation, contributing to her dehydration, compromised GI function, and labored respiration
  • There is a possibility that a hydropic condition may in some cases be related or secondary to the development of placentitis. A link has been proposed in human medicine and as a potential etiology in areas where leptospirosis is endemic (equids)
  • Clinical management for both conditions is the same—induction of parturition, to save the dam's life, and to prevent rupture of the ventral abdominal wall and/or the uterus

Systems Affected!!navigator!!

Reproductive—dam and fetus.

Genetics!!navigator!!

There may be a hereditary role in development of hydropic conditions.

Incidence/Prevalence!!navigator!!

Rare

Signalment!!navigator!!

  • No breed or age predisposition, although more cases have been reported in draft mares
  • Abnormal accumulation of fluid (up to 100 L) in the allantoic cavity; abdominal size is abnormally large for stage of gestation
  • Commonly occurs from 6 to 10 months of gestation
  • Frequently has a rapid onset occurring over a few days to a few weeks
  • Most mares develop a tremendous amount of ventral abdominal edema
  • Abdominal and/or uterine rupture can result due to the excessive weight of allantoic or amniotic fluid

Signs!!navigator!!

  • Modest to rapid accumulation of fluid within the uterus (allantoic or amniotic)
  • Rapid increase in abdominal size/shape
  • Abdominal pain (moderate to severe), severe ventral edema, elevated pulse, labored respiration due to pressure on the diaphragm, difficulty walking, recumbency as the condition progresses
  • TRP reveals an abnormal accumulation of fluid
  • The fetus is difficult or impossible to detect (transrectal palpation or ballottement)

Causes!!navigator!!

N/A

Risk Factors!!navigator!!

Draft mares.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Twin pregnancy—mid-to-late gestation
  • Prepubic tendon rupture
  • Herniation or rupture of ventral abdominal wall
  • Possibly, uterine torsion

CBC/Biochemistry/Urinalysis!!navigator!!

  • Possible increased or decreased PCV (secondary to hypovolemia or dehydration, respectively)
  • Possible increase in blood urea nitrogen and creatinine secondary to dehydration
  • Serum titer for leptospirosis. Interpretation of a titer's significance is made with caution, i.e. a 4-fold increase in the antibody titer would provide strong support for a leptospirosis diagnosis

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

US

  • Fluid compartments are grossly enlarged, either allantoic or amniotic
  • Torso/abdomen of the hydramnios fetus may have a grossly widened diameter as a result of ascites
  • Fetal activity and its heart beat/rate may be difficult to monitor or detect because of the enlarged fluid volume within which it is located

Other Diagnostic Procedures!!navigator!!

  • US and TRP
  • Abdominocentesis, US guided, may be of use to detect abnormal free fluid in abdomen and in cases of uterine rupture

Pathologic Findings!!navigator!!

  • Placental insufficiency secondary to placentitis
  • Hydrops amnion—fetal swallowing defects (segmental aplasia(s) preventing swallowing and processing of amniotic fluid, which leads to its accumulation in excessive amounts)
  • Fetal defects such as growth retardation and hydrocephalus have been reported, as well as brachygnathia
  • Torsion of the umbilical cord and amnion has been reported

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Manual dilation of the cervix, completed gradually over a 10–20 min period
  • Measured, controlled drainage of allantoic/amniotic fluid via aseptic insertion of a sterile drain tube through the cervix and fetal membranes.
  • Slow removal of fluid is important to prevent hypovolemic shock in the mare
    • A sudden loss of pressure on the abdominal vessels may result as the uterus is drained, and lead to vascular pooling. Monitor PCV and plasma proteins throughout
    • If removal can be well- managed, achieving a gradual decrease in volume over a 12–24 h period is best
    • 1 method—manually dilate cervix, serial cloprostenol administration (250 µg at 12 h interval; 2–4 doses). Place nasogastric tube through membranes, tying off around tubing to facilitate controlled fluid removal, 5–10 L at a time, clamping off in between increments to keep mare stabilized
    • Continue with IV fluid delivery and care, as follows
  • For the dam:
    • IV fluids—balanced electrolyte solutions, lactated Ringer's solution, or hypertonic saline solution
    • Corticosteroids—prednisolone sodium succinate. Initial dose is 50–100 mg IV or IM. Initial IV should be given slowly (30 s to 1 min)
    • Flunixin meglumine (0.7 mg/kg IV every 24 h) to decrease the likelihood of hypovolemic shock
    • Oxytocin is often ineffective due to chronic stretching (uterine atony/inertia)
  • Once sufficient fluid has been removed by a slow, controlled rate removal, the CA membrane should be ruptured and the fetus removed by forced extraction
    • Note—in some cases the CA membrane may be thickened and difficult to rupture, in which case, the membrane should be pulled caudally, into the anterior vagina, to facilitate easier opening of the membrane and extraction of the fetus
    • Continue monitoring the mare, fluids, and antibiotic administration, as indicated

Nursing Care!!navigator!!

Close monitoring of the mare for signs of shock and/or infection after removal of fluids and fetus.

Activity!!navigator!!

Limited by inability of dam to move.

Diet!!navigator!!

N/A

Client Education!!navigator!!

Mares that appear excessively large for stage of gestation should be evaluated, particularly if signs of systemic disease or disability develop.

Surgical Considerations!!navigator!!

  • Induction of parturition
  • Caesarean section, but keep in mind that fetal survival is uncommon/unlikely

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Since most hydrops mares spontaneously abort, treatment should be directed at terminating the pregnancy
  • The use of oxytocin is usually not effective since most of these mares will have uterine inertia (atony) due to the stretching of the uterine musculature
  • During or soon after attempted slow, controlled drainage of allantoic fluid, treatment for hypotensive shock may be necessary:
    • Hypertonic saline solution 2–4 mL/kg (7.2%) IV (Bimeda Inc., Le Sueur, MN)
    • Hetastarch (colloids) 10 mL/kg IV (Hespan; Braun Medical Inc., Irvine, CA)
    • Plasma-Lyte A 30 mL/kg/h IV (Baxter Healthcare Corp., Deerfield, IL)

Contraindications!!navigator!!

N/A

Precautions!!navigator!!

N/A

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Once a diagnosis is made, termination of pregnancy is appropriate
  • In a few rare cases that do not become dramatically enlarged until nearer term, the vertical depth of allantoic fluid can be monitored at weekly intervals, with delivery of a smaller than normal, but viable, foal
  • It is imperative to monitor the dam for signs of respiratory distress, as well as for her general health and stability of her vital signs
  • Fetal biophysical parameters, including serial recording of fetal heart rate (resting and notation of accelerations during periods of fetal activity)
  • Serial measures of the combined thickness of the uterus and placenta at/near the cervical star and for areas of possible placental separation

Prevention/Avoidance!!navigator!!

  • Hydrops amnion—breed to different sire once mare recovers from either controlled vaginal delivery or C-section
  • Hydrops allantois—as the abnormal placentation may reflect ineffective placental attachment because of an abnormal endometrium, placentitis, or primary placental failure, rebreeding may result in a similar outcome
  • Adventitious placentation has been reported in cattle and is an effort by the placenta to generate additional, however ineffective, sites for placental transfer (oxygen in, removal of fetal waste)

Possible Complications!!navigator!!

  • Loss of pregnancy
  • Prepubic tendon rupture
  • Rupture of ventral belly wall
  • Maternal death

Expected Course and Prognosis!!navigator!!

  • Prognosis for fetal survival is poor
  • Prognosis for survival of the dam is guarded, if parturition is induced before more serious damage occurs
  • Prognosis for future reproduction:
    • Guarded for a mare with a hydrops allantois as it is a reflection of insufficient placental attachment sites and more likely to be repeated with a subsequent pregnancy. If the breed permits embryo transfer, the mare could be flushed for embryos following breeding
    • Guarded for the pregnancy of a hydrops amnion mare. The recommendation would be for her to be bred to a different stallion once she has recovered from the delivery/abortion

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Placentitis
  • Adventitious placentation has been reported in cattle

Age-Related Factors!!navigator!!

Older, multiparous mares, but has been reported in all ages.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

A pregnancy-related condition.

Synonyms!!navigator!!

N/A

Abbreviations!!navigator!!

  • CA = chorioallantoic
  • GI = gastrointestinal
  • PCV = packed cell volume
  • TRP = transrectal palpation
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Baker LP, Bridges ER, Lovelady A. Hydrops allantois in a mare with twin pregnancy. Clin Theriogenol 2016;8(3):368.

Canisso IF, Schnobrich MR. Disorders of the reproductive tract: hydrops of the fetal membranes. In: Reed SM, Bayly WM, Sellon DC, eds, Equine Internal Medicine. St. Louis, MO: Elsevier, 2018: 1289–1290.

Christensen BW, Troedsson MH, Murchie TA, et al. Management of hydrops amnion in a mare resulting in birth of a live foal. J Am Vet Med Assoc 2006;228(8):1228–1233.

Honnas CH, Spensley MS, Laverty S, Blanchard PC. Hydramnios causing uterine rupture in a mare. J Am Vet Med Assoc 1988;193:332–336.

Löfstedt RM. Abnormalities of Pregnancy. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Philadelphia, PA: Wiley-Blackwell, 2011:2441–2445.

Morrison MJW, Back B, McClure JT, et al. Hydroallantois and prepubic tendon rupture in a Standardbred mare. Clin Theriogenol 2016;8(3):359.

Shanahan LM, Slovis NM. Leptospira interrogans associated with hydrallantois in 2 pluriparous Thoroughbred mares. J Vet Intern Med 2011;25(1):158–161.

Vandeplassche M, Bouters R, Spincemaille J, Bonte P. Dropsy of the fetal sacs in the mare: induced and spontaneous abortion. Vet Rec 1976;99:67–69.

Waelchli RO. Hydrops. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction. Wiley-Blackwell, 2011:2368–2372.

Author(s) ⬆

Author: Carla L. Carleton

Consulting Editor: Carla L. Carleton