Fetal defecation

Alberto Sosa Olavarria, MD*, Eva Leinart, MD**

*  CEUSP, Valencia, Venezuela.
** Inner Vision Women's Ultrasound, Nashville, Tennessee, USA.


According to the previous concepts, the human fetus does not defecate in the uterus. Fetal defecation was thought to be a result of some stress insult which caused the anal sphincter to release meconium. Multiple studies performed during the last 15 years show that in-utero defecation is a normal physiological process and can be observed by a 2D, 3D-4D imaging or color Doppler.

Stool in the first half of the pregnancy has a whitish color. This was proved by amniocentesis performed immediately after the defecation was observed by ultrasound. The typical dark greenish color of meconium, as we see it after delivery, is caused by biliverdin which stains the bowel content. The metabolism after 20 weeks may be slower, so the intestinal content stays within the bowel for a longer period of time which facilitates staining the stool with biliary pigments. Biliverdin, product of bilirubin oxidation system, is probably first produced after 20 weeks of gestation. The combination of this two factors may explain a different color of the meconium in the first and second half of the pregnancy [1,2,3].

Fetal defecation happens throughout the whole fetal life. Physiological defecation is not a result of the fetal distress. The amniotic fluid clearance system consists of fetal swallowing, respiratory tract secretion and urination. All these physiological processes are in balance under the normal circumstances. The clearance mechanism of amniotic fluid can be affected by fetal distress. Which explains meconium stained amniotic fluid of compromised fetuses [4].

Case report

This is a case of a patient who was scanned at 20 weeks of gestation. The patient had non-contributive family and personal history and her pregnancy was uneventful. There were no anomalies detected on ultrasound except of the echoic protrusion attached to the caudal region resembling a tail. The finding changed during the time, after 2 minutes of ultrasound observation, the protrusion detached from the caudal region and was floating in the amniotic fluid near the buttocks. The diagnosis was fetal defecation and the tail-like protrusion was a fetal stool.

mages 1- 4: Images showing caudal region, note an echoic, tail-like protrusion which seems to be attached to the perineal region. This protrusion is fetal stool attached to the anus.


Images 5: This image shows that the stool is not attached to the anus anymore. The meconium is visible by the buttocks (arrow).


Videos 1,2: Videos showing the fetus passing meconium.

Videos 3,4: Videos 3 shows meconium still attached to the anus. Video 4 shows the completed defecation, the stool is not attached to the anus, but floating next to the buttocks.


1. Ciftçi AO, Tanyel FC.In utero defecation: a new concept.Turk J Pediatr. 1998; 40(1):45-53. 
2. Ramón y Cajal, C. L. and Martínez, R. O. Prenatal observation of fetal defecation using four-dimensional ultrasonography. Ultrasound in Obstetrics & Gynecology. 2005; 26: 794–795.
3. C. Lopez Ramon y Cajal,R.Ocampo Martınez. In-utero defecation between weeks 14 and 22 of gestation: stools are whitish. Ultrasound Obstet Gynecol. 2004; 23: 93–95.
4. C.LĂłpez RamĂłn y Cajal, R.Ocampo MartĂ­nez. Defecation in utero: A physiologic fetal function. American Journal of Obstetrics & Gynecology.2003; 188 (1),153-156.

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