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Sirenomelia--a case report.


Sirenomelia is a rare and usually lethal congenital abnormality with multisystem involvement. The reported incidence is 1 in 100000 pregnancies. [1] Cases have been reported from all ethnic groups worldwide [2], and the Male: Female ratio is 2.7:1. [3] The most prominent feature is partial or complete fusion of lower limbs. This external appearance of the infant resembles the mermaids or sirens of Greek mythology. [4] We herein report a case of sirenomelia which had various morphological and visceral abnormalities.

Case Reports

Mrs X, 23 years, Primigravida at 31 weeks of gestation according to her last menstrual period presented with complain of pain abdomen since last four hours. There was no personal or family history of diabetes, any congenital malformation or teratogenic drug exposure; there was no history of any chronic medical disorder. Her present pregnancy was poorly followed up in local health centre with only one visit at around 30 weeks of gestation. Ultrasonography done then showed single live fetus at 30 weeks 2 days gestation with severe oligohydramnios (amniotic fluid index = 2 cm), three chambered fetal heart, bilateral hydronephrotic kidneys and dilated ureters. Musculoskeletal system showed normal long bones but digits could not be visualised due to overcrowding of fetal parts. On admission patient was hemodynamically stable. On per abdominal examination, fundal height corresponded to thirty weeks of gestation with cephalic presentation with normal fetal heart rate pattern with mild uterine contractions. On per vaginal examination cervix was3 centimetres dilated with bulging fetal membranes. She was put on conservative management and was given betamethasone cover. She gradually went into active labour and delivered a 1250 grams baby with following morphological abnormalities: (i) Swollen face with depressed nasal bridge; (ii) Absent external genitalia with an indistinct tag of tissue; (iii) Absent anal opening; (iv) Absent urethral meatus; (v) Fused lower segment of the body below the pelvis resulting into a single lower limb; (vi) Umbilical cord with single umbilical artery. Baby needed resuscitation after birth with positive pressure ventilation and expired within 5 minutes in spite of resuscitative efforts. Infantogram was done which showed sacral agenesis, hypoplastic pelvis, fused lower extremities with single femur, tibia and fibula. Parents refused autopsy of the baby and post-mortem ultrasonography. Mother got discharged on the second post natal day with an advice to follow up.


Sirenomelia is a rare congenital malformative disorder with uncertain aetiology. The clinching diagnostic point at birth is the phenotypic appearance with varying degrees of fused lower extremities. It is more commonly seen in monozygotic twins as compared to dizygotic twins and singletons, the reported incidence being 100-150 times higher. [5] It is usually associated with other visceral defects such as hypoplastic lungs, cardiac agenesis, absent genitalia, digestive defects, absent kidney and bladder, vertebral and central nervous system defects. [6, 7] Most babies with sirenomelia have single umbilical artery as seen in our case. [8] Stocker and Heifetz classified the sirenomelia sequence into 7 types [9]:

The exact cause is still unknown. Stevenson et al. [8] proposed a vascular steal hypothesis to explain the defects associated with sirenomelic fetus. It proposed that the single umbilical artery of vitelline origin, which originates high in the abdomen, diverts blood flow towards placenta. This leaves the lower body part poorly perfused with inadequate nutrient supply, which in turn results in agenesis of midline structures and subsequent abnormal approximation of lower limb fields.

Another well-known theory proposes that sirenomelia is a primary defect of blastogenesis that occurs during the final stages of gastrulation at the tail bud stage, corresponding to the third gestational week in human. [10] Experimental data suggests that sirenomelia has a genetic basis resulting from a defect in retinoic acid or bone morphogenetic protein signalling in the caudal embryonic region. [11, 12] Maternal diabetes mellitus [13] and heavy metal exposure [14] have also been linked to it.

Survival basically depends on the degree and type of visceral abnormalities specially the presence of a functioning kidney. The diagnosis, quite obvious at birth can also be established by antenatal ultrasonography. Sonography clues include oligohydramnios, renal agenesis and lower limb abnormalities.

In our case, the mother had no associated risk factor but due to the poor antenatal follow up, antenatal diagnosis could not be made on time but based on ultrasonography, the parents were counselled regarding the congenital anomaly in child.


Sirenomelia is usually incompatible with life depending on the underlying visceral abnormalities while the phenotype does not affect survival. With advances in reconstructive surgery, minor phenotypic defects can be corrected. Early antenatal diagnosis by anomaly scan can prevent the trauma of advanced termination of pregnancy or stillbirth.


[1.] Martinez-Frias ML, Garcia A, Bermejo E. Cyclopia and sirenomelia in a liveborn infant. J Med Genet. 1998; 35(3): 263-4.

[2.] Garrido-Allepuz C, Haro E, Gonzalez-Lamuno D, Martinez-Frias ML, Bertocchini F, Ros MA. A clinical and experimental overview of sirenomelia: insight into the mechanisms of congenital limb malformations. Dis Model Mech. 2011; 4(3): 289-99.

[3.] Valenzano M, Paoletti R, Rossi A, Farinini D, Garlaschi G, Fulcheri E. Sirenomelia. Pathological features, antenatal ultrasonographic clues, and a review of current embryogenic theories. Hum Reprod Update. 1999; 5(1): 82-6.

[4.] Messineo A, Innocenti M, Gelli R, Pancani S, Lo PR, Martin A. Multidisciplinary surgical approach to a surviving infant with sirenomelia. Pediatrics. 2006; 118(1): e220-e223.

[5.] Jaiyesimi F, Gomathinayagam T, Dixit A, Amer M. Sirenomelia without vitelline artery steal. Ann Saudi Med. 1998; 18(6): 542-4.

[6.] Tang TT, Oechler HW, Hinke DH, Segura AD, Franciosi RA. Limb bodywall complex in association with sirenomelia sequence. Am J Med Genet. 1991; 41(1): 21-5.

[7.] Rodriguez JI, Palacios J, Razquin S. Sirenomelia and anencephaly. Am J Med Genet. 1991; 39(1): 25-7

[8.] Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M Jr, Clericuzio C, et al. Vascular steal: the pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissues. Pediatrics. 1986; 78: 451-457.

[9.] Stocker JT, Heifetz SA: Sirenomelia. A morphological study of 33 cases and review of the literature. Perspect Pediatr Pathol. 1987; 10: 7-50.

[10.] Duesterhoeft SM, Ernst LM, Siebert JR, Kapur RP. Five cases of caudal regression with an aberrant abdominal umbilical artery: Further support for a caudal regression-sirenomelia spectrum. Am J Med Genet A. 2007; 143A(24): 3175-84.

[11.] Abu-Abed S, Dolle P, Metzger D, Beckett B, Chambon P, Petkovich M. The retinoic acid-metabolizing enzyme, CYP26A1, is essential for normal hindbrain patterning, vertebral identity, and development of posterior structures. Genes Dev. 2001; 15: 226-240.

[12.] Zakin L, Reversade B, Kuroda H, Lyons KM, De Robertis EM. Sirenomelia in Bmp7 and Tsg compound mutant mice: requirement for Bmp signaling in the development of ventral posterior mesoderm. Development. 2005; 132: 2489-2499

[13.] Assimakopoulos E, Athanasiadis A, Zafrakas M, Dragoumis K, Bontis J. Caudal regression syndrome and sirenomelia in only one twin in two diabetic pregnancies. Clin Exp Obstet Gynecol. 2004; 31: 151-153.

[14.] Orioli IM, Mastroiacovo P, Lopez-Camelo JS, Saldarriaga W, Isaza C, Aiello H, et al. Clusters of sirenomelia in South America. Birth Defects Res A Clin Mol Teratol. 2009; 85(2): 112-8.

Source of Support: Nil

Conflict of interest: None declared

Rakesh Kumar (1), Rajlaxmi Mundhra (2)

(1) Department of Paediatrics, Hindu Rao Hospital, Delhi, India

(2) Department of Obstetrics and Gynecology, Guru Teg Bahadur Hospital, Delhi, India

Correspondence to: Rakesh Kumar (

DOI: 10.5455/ijmsph.2013.071120132

Received Date: 21.10.2013

Accepted Date: 17.01.2014

Table-1: Stocker and Heifetz classification of sirenomelia

Type   Characteristic

I      All thigh and leg bones are present
II     Single fibula
III    Absent fibula
IV     Partially fused femurs, fused fibulae
V      Partially fused femurs
VI     Single femur, single tibia
VII    Single femur, absent tibia
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Title Annotation:CASE REPORT
Author:Kumar, Rakesh; Mundhra, Rajlaxmi
Publication:International Journal of Medical Science and Public Health
Article Type:Clinical report
Date:Feb 1, 2014
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