Equis ISSN 2398-2977

Placenta: retained

Synonym(s): Retained fetal membranes, RFM

Contributor(s): Jean Pierre Held, Rob Lofstedt, Graham Munroe, Philippa O'Brien, Vetstream Ltd, Elaine Watson


  • Fetal membranes are comprised of the allantochorion (placenta), amnion and umbilical cord.
  • Fetal membranes are said to be retained if they are not passed in their entirety within 3-6 h post-partum.
  • The placenta is classed as retained if it has not passed within 3-6 h post-partum.
  • The placenta in the non-gravid horn of the uterus is most often retained.
  • Most common after dystocia   Reproduction: dystocia  , induction of parturition   Reproduction: parturition - induction  , Cesarean section   Uterus: caesarean section  or abortion   Abortion: overview  .
  • Cause: often unknown; can follow apparently normal foalings but can also be associated with dystocia, atony, twins, etc.
  • Signs: sometimes the membranes may be seen protruding from the vulva post-foaling. In cases where only a small portion is retained, no membranes are visible externally and the mare may present with signs of endotoxemia 24-48 h post-foaling.
  • Diagnosis: vaginal examination, transrectal ultrasonography.
  • Treatment: depends on duration of retention and presence/absence of metritis-laminitis-septicemia complex. Manual traction, the use of hormones, eg oxytocin, or by uterine infusion.
  • Antimicrobial therapy, is required in most cases and sometimes anti-inflammatory therapy as well.
  • Intrauterine manipulation should be kept to a minimum in order to reduce the risk of complications developing.
  • Prognosis: good to guarded.



  • Exact cause still unknown.
  • Thought to be a combination of hormonal imbalance and uterine inertia   Uterus: inertia  .
  • Placental adhesion has been identified in draft mares in particular.

Predisposing factors



  • In normal passage of the fetal membranes, separation of microvilli from the endometrial crypts begins at the gravid horn, assisted by involution and contraction of the uterus and expulsive efforts from the mare. The horns of the allantochorion invaginate as they are released and pass through the ruptured cervical star. As the allantochorion passes through the vulval opening, increased weight of the membranes hanging down from the vulva encourages release of the non-gravid horn.
  • Retention of membranes results from delayed separation of the allantochorion (chorioallantois) from the endometrium.
  • The allantochorion is thicker in the non-gravid horn. It is also more folded and the villi are longer than in the gravid horn. All these factors lead to a greater degree of attachment than in the gravid horn and can be responsible for retained placenta.
  • Uterine inertia may result from low calcium levels, overstretching of the myometrium (following hydrops or twin pregnancy) or myometrial exhaustion due to dystocia or advanced maternal age.
  • Periglandular fibrosis of the endometrium may result in placental adhesion.


  • The placenta is usually expelled within 90 min of foaling.
  • Retained placenta is usually considered to be pathologic after 3-6 h post-partum.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Crabtree J (2012) Peripartum problems in mares 2. Postpartum problems. In Pract 34 (8), 462-471 VetMedResource.
  • Rapacz A et al (2012) Retained fetal membranes in heavy draft mares associated with histological abnormalities. Equine Vet Sci 32 (1), 38-44 VetMedResource.
  • Boerma S, Back W & Sloet van Oldruitenborgh-Oosterbaan M M (2012) The Friesian horse breed: A clinical challenge to the equine veterinarian? Equine Vet Educ 24 (2), 66-71 VetMedResource.
  • Hudson N P H, Prince D R, Mayhew I G & Watson E D (2005) Investigation and management of a cluster of cases of equine retained fetal membranes in Highland ponies. Vet Rec 157 (3), 85-89 PubMed.
  • Sevinga M, Hesselink J W & Barkema H W (2002)  Reproductive performance of Friesian mares after retained placenta and manual removal of the placenta. Theriogenology 57, 923-930 PubMed.
  • Sevinga M, Barkema H W & Hesselink J W (2002) Serum calcium and magnesium concentrations and the use of a calcium-magnesium borogluconate solution in the treatment of Friesian mares with retained placenta. Theriogenology 57, 917-941 PubMed.
  • Haffner J C et al (1998) Equine retained placenta - technique for and tolerance to umbilical artery injections of collagenase. Theriogenology 49 (4), 711-716 PubMed.

Other sources of information

  • Threlfall W R (2011) Retained Fetal Membranes. In: Equine Reproduction. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. 2nd edn. Wiley-Blackwell. pp 2520-2529.
  • Frazer G S (2004) Management of Retained Fetal Membranes. In: Proc 43rd BEVA Congress. Equine Vet J Ltd, UK. pp 231.
  • Allen W E (1988) Fertility and obstetrics in the horse. Blackwell Scientific Publications.
  • Held J P (1987) Retained Placenta. In: Current Therapy in Equine Medicine.Vol 2. Ed: N E Robinson. pp 547-550.
  • Arthur G H, Noakes D E & Pearson H (1983) Veterinary Reproduction and Obstetrics. 4th edn. Balliere Tindall, UK.
  • Rossdale P D & Ricketts S W (1980) Equine Stud Farm Medicine. 2nd edn. Balliere Tindall, UK.