What is a low-lying placenta?

Article Abstract:

Placenta previa is a term used to describe a placenta that lies in the lower part of the uterus, close to the os (the mouth of the uterus); it is traditionally classified as complete, partial, marginal, or low-lying, depending on its location. Transabdominal ultrasonography can be used to diagnose placenta previa, but transvaginal ultrasonography, in which the ultrasound probe is inserted into the vagina, can visualize the exact spatial relationship between the placenta and os. Results are reported of the application of this technique in 127 women with suspected placenta previa. The subjects were 33 weeks pregnant and delivered, on average, at 38 weeks. Fifty-two patients had placenta previa. Thirty-one patients had complete placenta previa (placenta completely covering the os) and underwent cesarean section. Seven of the remaining 21 patients required a cesarean section because of bleeding. In these cases, the average distance between the placental edge and the os was 1.1 centimeters (cm), compared with an average distance of 3.1 cm among the 14 women who did not require cesareans. One vaginal delivery took place by a woman whose placental edge lay within 2 cm of the cervical os. Cesarean section was not required for any patient with a placenta more than 2 cm from the os, but was required for seven of eight patients with placentas 2 cm from the os or closer. The terminology traditionally used to describe placenta previa is based on results of pelvic examination and does not provide much information about the clinical significance of a particular placental position. The authors suggest that high-resolution transvaginal ultrasonography, which enables measurement of the exact distance between placental edge and cervical os, makes traditional classification schemes obsolete. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Placenta praevia, Placenta previa

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The current status of maternal and fetal blood flow velocimetry

Article Abstract:

Three articles in the April 1991 issue of the American Journal of Obstetrics and Gynecology evaluate the use of ultrasonography, a noninvasive technology for imaging internal organs. This method can be used to visualize the developing fetus during pregnancy, as well as the internal organs of the mother. This article reviews the medical literature concerning ultrasonographic measurement of the blood flow between uterus and placenta, or blood flow within the fetus. When these circulations are impaired, maternal blood pressure may increase (hypertension), the fetus may not develop normally, or the fetus may not receive enough oxygen. Ultrasound can be used to measure both blood flow amount and flow velocity. Its predictive abilities with respect to maternal hypertension, fetal growth retardation, fetal distress, and low Apgar scores (a measure of physiological function of the infant immediately after birth) are discussed. In general, the value of Doppler velocimetry (measurement of flow velocity using one type of ultrasound) in clinical situations has not yet been demonstrated. Many factors that can cause measurement errors that can be controlled in carefully designed studies (such as maternal smoking and drug use), cannot be controlled in the clinical environment. At present, the method cannot be recommended as a diagnostic test for routine use. However, research to develop better ultrasound techniques for evaluating maternal and fetal blood flow should remain a high priority. (Consumer Summary produced by Reliance Medical Information, Inc.)

Blood flow, Measurement, Blood flow measurement, Doppler ultrasonography

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Limitations in the clinical prediction of intrapartum fetal asphyxia

Article Abstract:

An attempt to predict the occurrence of poor fetal oxygenation during labor by evaluating pregnancy and labor risk factors failed. Umbilical-cord blood samples were analyzed for adverse biochemical changes indicative of lack of oxygen after 1909 births. This occurred in 2.3% of the population. Records were then analyzed and the relationship with 20 known risk factors was examined. These risk factors accurately predicted only 3% of newborns with blood chemistry indications of lack of oxygen and 36% of the results were false positives. Next, the predictive value of these risk factors was examined for 100 cases of poor fetal oxygenation at birth in a population of 4368. Results of prenatal tests of fetal well-being were also included. Risk assessment accurately predicted only 3% of cases of fetal lack of oxygen in labor. Fifty-eight percent were false positives, and 23% were false negatives.

Health risk assessment, Asphyxia neonatorum

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