Goubaa Mohamed MD Djerba Tunisia

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Ten pregnant women are scanned, for clinically suspected placenta previas. The initial study is performed transabdominally through a full urinary bladder and then transvaginally with an empty urinary bladder. Do the ultrasound findings support the clinical suspicion of placenta previas?

Dix patientes enceintes ont été examinées pour une suspicion clinique de placenta praevia, d'abord par voie abdominale avec vessie pleine puis par voie endovaginale.
L échographie confirmera-t-elle la suspicion clinique de placenta prévia?



Low-lying placenta
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Placenta bas isérée latéral
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case 2




Marginal (or partial) previa (Click on the image below)
Preavia marginal (ou partiel)(Cliquez sur les images en bas)

Case 1
Case 2

Case 3

Case 4


placenta completely previa(Click on the image below)
Placenta preavia total
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Normal : Differential
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Normal : Différentiel
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Normal : Differential

Click on the image below
Cliquez sur les images en bas



diagnosis diagnostic diagnostc arabic


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Placenta previa is defined as a placenta that is near or covering the internal cervical os.
Patients who are at increased risk for placenta previa include those with advanced maternal age, multiparous women, and those with a prior history of C-section. The most common symptom of placenta previa is painless bleeding in the third trimester, but patients may be asymptomatic. However, this does not mean that all cases of vaginal bleeding are caused by a placenta previa. Of the 3 to 5% of all pregnancies that are complicated by third trimester bleeding, only about 10% are due to a placenta previa.
The major complication, greater in a complete previa, is maternal hemorrhage at time of delivery. Others are premature delivery, intrauterine growth retardation, and perinatal death, presumably secondary to premature detachment of the placenta from the lower uterine segment.
Because trophotropism can cause significant changes in placental position, a previa is usually not formally diagnosed before 20 weeks unless symptoms are present. When detected after 20 weeks in an asymptomatic woman, a follow-up study should be performed at approximately 32 weeks to determine if the previa is still present. If a woman is symptomatic, particularly vaginal bleeding, more frequent ultrasound studies are often necessary.
Placenta previa has been classified into varying degrees to include low-lying placenta, partial previa, and complete previa. A low-lying placenta is within 2 cm of the os, a partial previa partially covers the os, and a complete previa extends completely across the internal cervical os.
The low-lying placenta and partial previa may migrate and alleviate the need for C-section. This process, which has been defined as trophotropism, describes the atrophy of the placenta in the region of the lower uterine segment with differential growth of other regions of the placenta toward more vascular-rich sites. Research has suggested that a placenta previa that is likely to need C-section is one that overlaps the internal cervical os by 20 mm in the third trimester.

Ultrasonography :
The following four defined methods exist for imaging of the lower uterine segment for identification of the location of the placenta in relationship to the internal os: trans-abdominal imaging, trans-labial imaging, endovaginal and endorectal imaging.
The most useful and inexpensive study is transvaginal ultrasonography that provides 100% accuracy in identifying a placenta previa. An alternative would be transrectal ultrasonography that can be equivalent to the standard transvaginal approach with less potential trauma to the pregnancy.
The ultrasound diagnosis of placenta previa is based on the position of the placenta to the internal cervical os. In the second trimester, in most cases, the lower uterine segment can be visualized through a distended urinary bladder. If not, it can frequently be evaluated with an empty urinary bladder scanning through the amniotic fluid. In the third trimester, however, both of these techniques may fail. The fetus is larger and may be persistently positioned in the lower uterus, and vaginal or endorectal scanning may be needed.
Endovaginal imaging is considered the gold standard for diagnosis of placenta previa. With trans-abdominal imaging, false-positive results may occur from an over-distended bladder, myometrial contractions, and shadowing of the cervix from the fetal head or other overlying fetal parts.
In a nondilated cervix, three ultrasound-based definitions are used in relation to the closed internal cervical os: a low-lying placenta where the placenta approaches but does not cover the os, a marginal (or partial) previa in which the placenta extends to the edge but does not cross the os, and a complete previa where the placenta crosses over and covers the internal os

Vasa Previa and velamentous umbilical cord :
Vasa previa describes vessels of fetal origin that completely or partially cover the internal cervical os.
Vasa previa may arise from velamentous cord insertion or marginal cord insertion or from the connecting vessels of an accessory or bilobed placenta. Vasa previa has also been seen with increased frequency in association with multiple gestations and low-lying placentas. These vessels are from the fetal circulation and can lead to significant fetal blood loss and fetal death at the time of rupture of membranes or delivery.
Sonographic Findings: An obstetric ultrasound should include visualization of the umbilical cord insertion into the placenta. Endovaginal ultrasound should be used in patients with risk factors for vasa previa, including patients in whom the placental cord insertion is not identified because of the limitations of transabdominal imaging that may be associated with maternal size or position of the maternal bladder. Color Doppler or power Doppler will usually be needed for confirmation of the diagnosis.

Reference :
* 1 : Heer IM, Muller-Egloff S, Strauss A. Placenta praevia--comparison of four sonographic modalities.
Ultraschall Med. 2006 Aug;27(4):355-9.

* 2 : Predanic M, Perni SC, Baergen RN, Jean-Pierre C, Chasen ST, Chervenak FA. A sonographic assessment of different patterns of placenta previa "migration" in the third trimester of pregnancy.
J Ultrasound Med. 2005 Jun;24(6):773-80.

* 3 : Lodhi SK, Khanum Z, Watoo TH. Placenta previa: the role of ultrasound in assessment during third trimester.
J Pak Med Assoc. 2004 Feb;54(2):81-3.

* 4 : Williams PL, Laifer-Narin SL, Ragavendra N. US of abnormal uterine bleeding.
Radiographics. 2003 May-Jun;23(3):703-18. Review.

* 5 : Mustafa SA, Brizot ML, Carvalho MH, et al: Transvaginal ultrasonography in predicting placenta previa at delivery: a longitudinal study. Ultrasound Obstet Gynecol 2002 Oct; 20(4): 356-9

* 6 : Chen JM, Zhou QC, Wang RR. [Value of transvaginal sonography in diagnosis of placenta previa]
Hunan Yi Ke Da Xue Xue Bao. 2001 Jun 28;26(3):289-90.

* 7 : Catanzarite V, Maida C, Thomas W, Mendoza A, Stanco L, Piacquadio KM. Prenatal sonographic diagnosis of vasa previa: ultrasound findings and obstetric outcome in ten cases.
Ultrasound Obstet Gynecol. 2001 Aug;18(2):109-15.

* 8 : Megier P, Gorin V, Desroches A. [Ultrasonography of placenta previa at the third trimester of pregnancy: research for signs of placenta accreta/percreta and vasa previa. Prospective color and pulsed Doppler ultrasonography study of 45 cases]
J Gynecol Obstet Biol Reprod (Paris). 1999 Jun;28(3):239-44.

* 9 : Sunna E, Ziadeh S. Transvaginal and transabdominal ultrasound for the diagnosis of placenta praevia.
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* 10 : Taipale P, Hiilesmaa V, Ylostalo P. Transvaginal ultrasonography at 18-23 weeks in predicting placenta previa at delivery.
Ultrasound Obstet Gynecol. 1998 Dec;12(6):422-5.

* 11 : Chen KH, Konchak P. Use of transvaginal color Doppler ultrasound to diagnose vasa previa.
J Am Osteopath Assoc. 1998 Feb;98(2):116-7.

* 12 : Taipale P, Hiilesmaa V, Ylostalo P. Diagnosis of placenta previa by transvaginal sonographic screening at 12-16 weeks in a nonselected population.
Obstet Gynecol. 1997 Mar;89(3):364-7.

* 13 : Dawson WB, Dumas MD, Romano WM, Gagnon R, Gratton RJ, Mowbray RD. Translabial ultrasonography and placenta previa: does measurement of the os-placenta distance predict outcome?
J Ultrasound Med. 1996 Jun;15(6):441-6.

* 14 : Tan NH, Abu M, Woo JL, Tahir HM. The role of transvaginal sonography in the diagnosis of placenta praevia.
Aust N Z J Obstet Gynaecol. 1995 Feb;35(1):42-5.