American Journal of Obstetrics and Gynecology
Expert reviewObstetricsUsing ultrasound in the clinical management of placental implantation abnormalities
Section snippets
PIA identification
The ultrasound identification of a PIA usually starts with the second-trimester fetal anatomic scan, which is most optimally performed at 18-22 weeks. One exception is a cesarean scar pregnancy, which can be detected in first-trimester ultrasound examinations.24, 25, 26 If at any time during gestation there is suspicion for placenta previa, low-lying placenta, or difficulty in transabdominal visualization of the entire placenta, a transvaginal examination may be considered for an accurate
Placenta previa with or without placenta accreta
The most common risk factor for placenta previa is when at the second-trimester ultrasound screening examination the internal cervical os is found to be covered completely or partially by placenta. Another risk factor for placenta previa is a history of ≥1 cesarean deliveries.1, 27, 28 Ananth et al27 reported relative risks for placenta previa of 4.5, 7.4, 6.5, and 44.9 for 1, 2, 3, and ≥4 previous cesarean deliveries. This translates to an exponential increase in the risk of placenta previa
Marginal/low-lying placenta
The definition of marginal/low-lying placenta is based on the relationship between the internal cervical os and the placental edge as determined by transvaginal ultrasound. If the placental edge reaches (touches) the internal os the diagnosis is marginal placenta previa. Low-lying placenta is diagnosed when the distance between the internal cervical os and the placental edge is 1-20 mm.9, 10, 11, 12, 13, 14, 22, 23 If the distance between the internal cervical os and the placental edge is >20
Vasa previa
Vasa previa is a condition characterized by the presence of fetal blood vessels crossing or running in close proximity to the internal cervical os. Accurate prenatal diagnosis and timed preterm delivery are crucial to avoid premature rupture of membranes (PROM) that can lead to vessel tearing and rapid fetal bleeding. Risk factors for vasa previa include velamentous cord insertion, accessory placental lobe, twin or in vitro fertilization pregnancy, and marginal/low-lying placentations.7, 8
Velamentous cord insertion
Velamentous umbilical cord insertion is a condition characterized by insertion of umbilical cord vessels into the chorioamniotic membranes. Thus, the umbilical vessels are vulnerable to compression changes since they are not supported by Wharton jelly. This umbilical cord abnormality is seen in approximately 1% of pregnancies with incidences ranging from 0.48–2.4%.4, 46, 47, 48, 49 In general, preterm delivery is not recommended; however, this condition has been associated with increased
Summary and conclusions
Cesarean delivery is one of the most common of all surgical procedures, occurring in every third delivery in the United States.51 One of the consequences of increasing cesarean delivery rates over the last few decades is an increase in PIAs. This implies that we should not expect any reductions of preterm deliveries due to PIAs in the near future. Therefore, it is important to focus on strategies of how to improve the management of these patients. For these patients, the decisions regarding the
References (52)
- et al.
Impact of multiple cesarean deliveries on maternal morbidity: a systematic review
Am J Obstet Gynecol
(2011) - et al.
Long-term maternal morbidity associated with repeat cesarean delivery
Am J Obstet Gynecol
(2011) - et al.
Placenta accreta: risk factors, perinatal outcomes and consequences for subsequent births
Am J Obstet Gynecol
(2013) - et al.
Risk factors and adverse pregnancy outcomes among births affected by velamentous umbilical cord insertion: a retrospective population-based register study
Eur J Obstet Gynecol Reprod Biol
(2012) - et al.
Maternal-fetal conditions necessitating a medical intervention resulting in preterm birth
Am J Obstet Gynecol
(2006) - et al.
What is a low-lying placenta?
Am J Obstet Gynecol
(1991) - et al.
Placental edge to internal os distance in the late third trimester and mode of delivery in placenta praevia
BJOG
(2003) - et al.
Placenta previa: distance to internal os and mode of delivery
Am J Obstet Gynecol
(2009) - et al.
The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis
Am J Obstet Gynecol
(1997) - et al.
Sonographic detection of placenta accreta in the second and third trimesters of pregnancy
Am J Obstet Gynecol
(2004)
Cervicovaginal fibronectin improves the prediction of preterm delivery based on sonographic cervical length in patients with preterm uterine contractions and intact membranes
Am J Obstet Gynecol
Rate of sonographic cervical shortening and the risk of spontaneous preterm birth
Am J Obstet Gynecol
Universal maternal cervical length screening during the second trimester: pros and cons of a strategy to identify woman at risk of spontaneous preterm delivery
Am J Obstet Gynecol
Improving the screening accuracy for preterm labor: is the combination of fetal fibronectin and cervical length in symptomatic patients a useful predictor of preterm birth? A systematic review
Am J Obstet Gynecol
Sonographic cervical length, vaginal bleeding, and the risk of preterm birth
Am J Obstet Gynecol
Cost-effectiveness analysis of cervical length measurement and fibronectin testing in women with threatened preterm labor
Am J Obstet Gynecol
Cost-effectiveness of transabdominal ultrasound for cervical length screening for preterm birth prevention
Am J Obstet Gynecol
Adherence to criteria for transvaginal ultrasound imaging and measurement of cervical length
Am J Obstet Gynecol
Rate of sonographic cervical shortening and biologic pathways of spontaneous preterm birth
Am J Obstet Gynecol
Perinatal diagnostic evaluation of velamentous umbilical cord insertion: clinical, Doppler, and ultrasound findings
Obstet Gynecol
Timing of indicated late-preterm and early-term birth
Obstet Gynecol
Vasa previa: the impact of prenatal diagnosis on outcomes
Obstet Gynecol
Placenta previa, placenta accreta, and vasa previa
Obstet Gynecol
Translabial ultrasonography and placenta previa: does measurement of the os-placenta distance predict outcome?
J Ultrasound Med
Diagnosis of low-lying placenta: can migration in the third trimester predict outcome?
Ultrasound Obstet Gynecol
Effect of a low-lying placenta on delivery outcome
Ultrasound Obstet Gynecol
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The authors report no conflict of interest.