Early placenta previa vs. threatened abortion


In February 1988, the patient, a 26-year-old married woman, experienced moderate vaginal bleeding. She contacted her gynecologist, who referred her to an ultrasound clinic for a sonographic workup.

In February 1988, the patient, a 26-year-old married woman, experienced moderate vaginal bleeding. She contacted her gynecologist, who referred her to an ultrasound clinic for a sonographic workup.

In February 1988, the patient, a 26-year-old married woman, experienced moderate vaginal bleeding. She contacted her gynecologist, who referred her to an ultrasound clinic for a sonographic workup.

History established that the patient’s last menstrual period (LMP) was 7.4 weeks earlier. Although she had missed one period, she did not know whether she was pregnant at the time.

Real-time sonography (Scans A and B) revealed chorionic sac with an embryonic heart beat of 151 beats per minute. Blood was identified around the sac.



A. Transabdominal, saggital sections of the uterus (two planes of view)



Scan B: Transverse section of the uterus.

Data analysis (using the Basic Baby II program) indicated embryonic heart rate (EHR) to be 150.9 beats per minute, corresponding to a fetal age of 7.3 weeks. (Scan C). Crown-rump length was 10.8 mm, suggesting a fetal age of 7.2 weeks.

Scan C: Sagittal M-mode tracing measured from the embryo at the center of the chorionic sac. Note: the body marker incorrectly indicates transverse.


Case Outcome

Retrospective Outcome Diagnosis, Blood, decidua parietals, chorionic sac, (decidua capsularis), gestational ring, uterine segment, case study, ultrasound, sonogram

Blood between the decidua parietals and the chorionic sac (decidua capsularis), with the gestational ring in the lower uterine segment.


 Clinical Diagnosis

Based on these findings, what is your clinical diagnosis?

  • Adenomatous polyp

  • Choriocarcinoma with cystic degeneration and elevated hCG

  • Dysgerminoma with amenorrhea

  • Early placenta previa

  • Impending 1st trimester miscarriage (spontaneous abortion)

  • Trophoblastic disease with coexistent embryo

The scans do not reveal evidence of either adenomatous polyps or uterine cancer. Embryonic heart rate of 151 B/M indicates pregnancy rather than some form of uterine cancer.

Dysgerminoma may be a cause of primary amenorrhea, but this condition usually involves solid tumors of the ovary.

Choriocarcinoma is associated with elevated hCG and may have variable consistency.


These unusual scans represent a case of very early placenta previa – the earliest that this sonographer has ever seen. The pregnancy was at the midpoint of the first trimester, so early that the woman did not yet know she was pregnant. Due to the unusual appearance, the initial diagnosis was impending 1st trimester miscarriage (threatened abortion). Trophoblastic disease would have a more granular appearance rather than the single cyst shown here.

The patient did not return to our clinic for follow-up, because she was managed by her own physician. Some time later, a subsequent conversation with the obstetrician revealed that, at 30.5 weeks of gestation, the patient had begun bleeding heavily. Her doctor conducted an ultrasound scan, confirmed the diagnosis of complete previa, and immediately delivered the baby through C-section. At birth, the child was a normal and healthy 30-week old male weighing 1265 grams. Both mother and child had continued to do well in the years that followed.



Placenta previa is a condition that results when any part of the placenta implants in the lower uterine segment covers the internal os of the cervix (birth canal). The three forms of placenta previa are:

  • marginal – placental edge is located within 2 cm of the cervical os but does not cross the os (also called low implantation)

  • partial – part of the os is covered by placenta

  • total – cervical os is completely covered

Placenta previa can lead to severe bleeding and is potentially fatal to both the mother and the fetus. The problem occurs in approximately 1 out of every 200 pregnancies. Although the cause is unknown, the risk increases in

  • older women

  • smokers

  • women with a history of uterine abnormalities such as fibroids

  • patients with endometrial damage due to prior pregnancy, induced abortion, or previous cesarean section.

Virtually all cases of placenta previa are diagnosed in the late second or early third trimesters, with a peak incidence at 34 weeks. Often the only symptom is painless vaginal bleeding; the blood is usually bright red and ranges in volume from scant to heavy. However, in about one case out of four, the patient also may experience uterine contractions. Continued blood loss can lead to anemia. Usually, though, the initial bleeding episode resolves spontaneously, and then bleeding recurs later in pregnancy.

The case presented here is highly unusual, since it occurred in a young woman in her first pregnancy and since it triggered symptomatic bleeding before the eighth week of gestation.

Approximately 12% of placentas are low-lying in pregnant women between 18 and 20 weeks of gestation. Perhaps 90% or more of cases of previa diagnosed in the second trimester resolve spontaneously. The placenta usually migrates toward the top of the uterine cavity as term approaches. For this reason, conservative (expectant) management is often all that is required, depending on the stage of fetal development and assuming bleeding is not excessive. The mother’s activity should be restricted. If possible, she should be urged to have complete bed rest. She should also be counseled to avoid sexual intercourse and douching. Her hemoglobin should be maintained at or above 10 mg/dL.

However, in cases where the placenta does cover the os, 40% will not resolve spontaneously and will require C-section eventually.

At or before 36 weeks, or whenever fetal lung maturity has been documented, a diagnosis of placenta previa requires immediate delivery by C-section. Even gentle cervical exam can trigger hemorrhage which necessitates emergency delivery of the baby. For this reason, cervical exam is performed in suspected cases of placental previa only when immediate surgical delivery can take place.

Severe and life-threatening hemorrhage is an indication for C-section regardless of the stage of fetal development or gestational age. Low vertical uterine incision is probably safer in patients with anterior placenta.

Sonographers are in a good position to identify placenta previa. Up to 97% of cases can be detected through ultrasound, especially if transvaginal, translabial, or transperineal ultrasound is performed in combination with transabdominal scanning. If early ultrasound has revealed the condition, but no bleeding occurs and fetal growth is adequate, ultrasound does not need to be repeated until 30 weeks of gestation. If the condition is confirmed, then the mother should be counseled to restrict activity. Ultrasound can be performed again just prior to C-section unless there are medical reasons for scanning earlier.

More discussion on this case appears in DuBose TJ, Fetal Sonography. Philadelphia, WB Saunders, 1996:361-362. 



This case points up a problem in the semantics of medical terminology. Some terms have specific meaning in one area of medicine, yet may not be exactly applicable in the area of diagnostic sonography. There are several types of spontaneous abortion that are clinical diagnoses, but are generally referred to a "miscarriage" by the lay public.(1), (2)

Threatened abortion is defined vaginal bleeding in the first trimester which may or may not be associated with pain or a mild ache in the lower abdomen. This is a specifically defined term which is the reason that the current case was referred for sonographic study. According to the above references between 20% and 25% of all pregnant experience some vaginal bleeding during the 1st trimester, and approximately 50% of those who threaten, or 10%-12.5% of all pregnancies, will eventually abort.

Inevitable abortion is accompanied with bleeding and a partially open cervix as well as cramping.(1), (2) While the appearance of the current case made the sonographer think it was inevitable that the pregnancy would be lost, the sonographic diagnosis did not meet the criteria for this clinical diagnosis.

Incomplete abortion involves all of the above with the additional condition of "...passage of products of conception,...." .(1), (2) This case did not meet this definition at all. It also did not meet the conditions for missed abortion, fetus dead for some time (weeks) without passage; or the definition of recurrent abortion.

Therefore, it appears that this case does not exactly meet the conditions for a sonographic diagnosis of any of the above except the clinical diagnosis of threatened abortion.

Even though, this case presented with a bizarre sonographic appearance at 7 weeks, it did not miscarry. Since at 30 weeks the patient presented with hemorrhage, and a complete placenta previa diagnosed by sonography and at emergency Caesarian section, the suggestion of an early placenta previa can be made. This is a retrospective view of the case in which the decidua basalis is shown to be implanted over the internal os.

In addition to the above complexities of making the diagnosis of threatened abortion from sonographic findings, researchers studying the problem of bleeding in early pregnancy found the following: "Some bleeding about the time of expected menses may be physiological, analogous to the placental sign described by Hartman (1929) in the rhesus monkey. In these animals, there is always at least microscopic bleeding. The blood apparently makes its way from ruptured blood vessels and eroded uterine epithelium into the uterine cavity." (2)

The diagnosis of placenta previa has been avoided early in pregnancy because of the propensity of placenta previa to resolve before the term is reached. Perhaps, with the addition of sonographic information, it is time to add a diagnosis of "threatened placenta previa" to the repertoire of diagnoses. A diagnosis such as this would at least alert the clinician of the possibility and would require a follow-up sonogram before the onset of labor.




1. Bennett MJ: Abortion, in Hacker & Moore, editors: Essentials of Obstetrics and Gynecology, 2nd Edition; W. B. Saunders Co., 1992, p. 415-416.

2. Cunningham FG, MacDonald PC, and Grant NF: Williams Obstetrics, 18th Edition; Appleton & Lange, 1989; p. 496-498.

Fore More Information:

Placenta Previa

When conducting an Internet search for information on this topic, be sure to follow the search engine’s instructions for entering placenta previa as a single phrase. For example, in Infoseek or AltaVista, enter the phrase "placenta previa" within double quotation marks.

An INFOSEEK Net search on "placenta previa" turned up 400 links. The following are among the better options:


To learn more about estimating gestational age from the embryonic heart rate, search for "embryonic heart rate" on the OBGYN.net site.

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