Placenta and umbilical cord
premature detachment of the placenta from the maternal wall.
elongated duct that contributes to the development of the umbilical cord.
maternal surface of the placenta.
cord insertion into the margin of the placenta.
spontaneous uterine contraction occurring throughout pregnancy.
the portion of the chorion that develops into the fetal portion of the placenta.
chorion around the gestational sac on the opposite side of implantation.
fetal surface of the placenta.
vascular projections from the chorion at the implantation and placental site.
a placental condition in which the chorionic plate of the placenta is smaller than the basal plate.
occurs when the cord is completely wrapped around the fetal neck at a minimum of two times.
abnormal proliferation of the trophoblastic cells in the first trimester.
premature separation of the normally implanted placenta from the uterus.
growth of the chorionic villi superficially into the myometrium.
growth of the chorionic villi deep into the myometrium.
growth of the chorionic villi through the myometrium.
placenta completely covers the internal cervical os.
as the uterus enlarges and stretches, the attached placenta appears to “move” further from the lower uterine segment.
area behind the placenta composed of the decidua, myometrium, and uteroplacental vessels.
additional placenta tissue (lobes) connected to the body of the placenta by blood vessels.
failure of the anterior abdominal wall to close completely at the level of the umbilicus.
occurs when the intramembranous vessels course across the cervical os.
mucoid connective tissue that surrounds the vessels within the umbilical cord.
Placenta
Anatomy (fig. 28-1)
• Formed by the decidua basalis and decidua frondosum.
• Separated from the uterine myometrium by the retroplacental complex.
Normal sonographic appearance
First trimester
Second and third trimesters
• Solid, homogeneous medium-gray structure.
• Hyperechoic chorionic plate.
• Cystic areas directly behind chorionic plate (fetal vessels).
• Anechoic or hypoechoic sonolucent areas within placenta (placental lakes) are insignificant and commonly displayed after 25 weeks.
• Hypoechoic retroplacental complex.
• Myometrium appears as a thin hypoechoic layer posterior to the retroplacental complex.
Placental maturity and grading
• Grading dependent on echogenicity attributed to calcium and fibrous deposition with advancing age.
• Maternal hypertension, cigarette smoking, intrauterine growth restriction, and multifetal gestation may cause premature maturation.
• Delayed maturation is most commonly associated with maternal diabetes mellitus.
Placenta previa
• Placental placement in front of the fetus relative to the birth canal.
• Primary cause of painless vaginal bleeding in the third trimester.
• Risk factors include advanced maternal age, multiparity, and previous cesarean section, therapeutic abortion, or closely spaced pregnancies.
• Complications of placenta previa include premature delivery, life-threatening maternal hemorrhage, and increased risk of placenta accreta, stillbirth, and intrauterine growth restriction.
• Only 5% of cases diagnosed with placenta previa in the second trimester remain at term, a result of placental migration.
| TYPE | CLINICAL FINDINGS | SONOGRAPHIC FINDINGS | DIFFERENTIAL CONSIDERATIONS |
| Complete | Painless vaginal bleeding | Placenta covers the entire cervical os | Myometrial contractionOverdistention of the urinary bladderUterine leiomyomaImproper technique |
| Partial (incomplete) | Painless vaginal bleeding | Placenta covers one side of the cervical os | Myometrial contractionOverdistention of the urinary bladderUterine leiomyomaImproper technique |
| Marginal | AsymptomaticPainless vaginal bleeding | Edge of the placenta abuts the cervical os | Myometrial contractionOverdistention of the urinary bladderUterine leiomyomaLow-lying placenta |
| Low-lying | Asymptomatic | Edge of the placenta lies close but does not abut the cervical osWithin 2 cm of the internal os | Myometrial contractionOverdistention of the urinary bladderUterine leiomyomaMarginal previa |
| Vasa previa | BleedingCord compressionProlapsed cordTransverse fetal lie | Fetal vessels cross over the internal os | Normal free-floating cordVelamentous cordSuccenturiate placentaMyometrial contraction |
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| ABNORMALITY | INFORMATION | SONOGRAPHIC FINDINGS | DIFFERENTIAL CONSIDERATIONS |
| Abruption | Premature placental detachmentClinical findings include severe pelvic pain and vaginal bleedingRisk factors include maternal hypertension, smoking, diabetes, trauma, placenta previa, and short umbilical cord | Hypoechoic retroplacental massPlacental thickeningWell-defined marginsElevation of placental edgesSubamniotic or preplacental locations are rare | Normal retroplacental complexAmniochorionic separationMyometrial contractionUterine leiomyoma |
| Accreta | AccretaChorionic villi of the placenta are in direct contact with the uterine myometriumAttributed to complete or partial absence of the decidua basalisRisk factors include multiparity, placenta previa, and previous cesarean sectionIncreta—placenta invades the uterine myometriumPercreta—placental vessels invade the uterine serosa or urinary bladder | AccretaObscured or absent retroplacental complexNumerous placental lakesIncretaExtension of villi into the myometriumPercretaExtension of villi outside of the uterus | AdenomyosisMyometrial contractionUterine leiomyoma |
| Amniochorionic separation | Amnion can be separated from the fetal surface of the placenta but cannot be separated from the umbilical insertion siteChorion can be separated from the endometrial lining but cannot be separated from the placental edge | Localized fluid between the fetal side of the placenta and the amniotic membraneMembrane may move | Placental abruptionNormal venous lakes |
| Battledore placenta | Cord inserts into the end margin of the placenta | Insertion of the cord into the end margin of the placenta | Normal cord lying adjacent to the placental marginVelamentous cord |
| Calcifications | Sign of maturing placentaAssociated with maternal cigarette smoking or thrombotic disorders | Hyperechoic focus within the placental tissuePosterior acoustic shadowing | Molar pregnancy |
| Circumvallate placenta | Abnormal placental shape in which the membranes insert away from the placental edge toward the centerIncreases risk for abruption, intrauterine growth restriction, premature labor, and perinatal death | Rolled up placental edgeIrregular fold or thickening of the placentaUpturned placental edge contains hypoechoic or cystic spacesThick placental cord insertion | AbruptionAmniotic shelfSynechiae |
| Fibrin deposits | More commonly located along the subchorionic region of the placentaAttributed to the regulation of intervillous circulation | Hypoechoic area beneath the chorionic plate of the placentaTriangular or rectangle in shape | Venous lakeSubchorionic hematoma |
| Intervillous thrombosis | Presence of thrombus within the intervillous spacesOccurs in one third of pregnanciesLittle risk to fetus | Anechoic or hypoechoic intraplacental massNonvascular | ChorioangiomaPlacental lakes |
| Placental infarct | Result of ischemic necrosisOccurs in 25% of pregnanciesNo clinical risk when small | Hypoechoic focal placental massCalcification may occur | Intervillous thrombosisPlacental lake |
| Placental lakes | Also called venous lakes | Anechoic or hypoechoic area within the placentaInternal blood flow | Intervillous thrombosisPlacental infarct |
| Placentomalacia | Small placentaIntrauterine growth restrictionIntrauterine infectionChromosomal abnormality |