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Key Terms

  1. Embryo: conceptus during early (<8 weeks) development when most organs are being formed.

  2. Fetus: conceptus during which time organs enlarge (>8 weeks).

  3. Subchorionic hemorrhage: bleeding beneath the chorion.

  4. Threatened abortion: characterized clinically by bleeding and cramping.

  5. “Implantation” bleeding: spotting associated with implantation (3-5 weeks).

  6. Incomplete abortion: bleeding, cramping with retained products of conception (RPOC) (fetus, choriodecidua, and membranes).

  7. Spontaneous abortion: bleeding associated with miscarriage (not induced or therapeutic Ab).

  8. Induced or therapeutic miscarriage or abortion: intentional use of medication and/or instrumentation to induce miscarriage.

  9. Ectopic pregnancy: implantation outside of endometrial lumen.

  10. Retained products of conception (RPOC): residual choriodecidua or embryo/fetal tissue within the uterine cavity after threatened, spontaneous, induced miscarriage, or pregnancy.


The extensive use of transvaginal sonography (TVS) has enabled improved evaluation of patients who are pregnant during the first trimester (up to 13 weeks) of pregnancy. TVS affords detailed delineation of the choriodecidua and embryo/fetus and distinguishes living from nonliving embryos/fetuses by establishing the presence of heart motion. It allows accurate assessment of the “developmental milestones” in first trimester pregnancy and reveals important information regarding abnormal or complicated early pregnancy. TVS can reveal detailed anatomic features of the fetus/embryo. Recently, 3D ultrasound has afforded even better anatomic resolution of the embryo and early fetus, both with volume and surface rendition (see Chapter 5).

This chapter discusses the role of TVS in the basic evaluation of an early first-trimester (before 13 weeks) pregnancy that is within the uterus. Chapter 4 is devoted to the sonographic evaluation of ectopic pregnancy. Chapter 5 describes sonographic assessment of the 11 to 18-week fetus, and Chapter 22 discusses the first-trimester screening for aneuploidy and associated anomalies. Recently, there have been major changes in the clinical and lab evaluations of first trimester with the use of cell-free DNA. Please refer to Chapter 5 for discussion of these changes. The American Institute of Ultrasound in Medicine (AIUM) Guidelines for Obstetrical Sonography in the First 10 Weeks is included as Appendix 3-1.


Transvaginal sonography has several clinical indications in the first trimester of pregnancy. The majority of these involve the establishment of the location of the pregnancy and the detection of embryonic/fetal life. Other indications include establishing the cause of vaginal bleeding and the prognosis of the pregnancy.

Approximately 20% to 50% of patients may experience bleeding in the first few weeks of pregnancy.1 This bleeding has been attributed to the anchoring of the choriodecidua as the blastocyst burrows into the decidualized endometrium. This bleeding is usually limited and not associated with uterine cramping. On the other hand, 20% to 30% of patients with bleeding will progress to a threatened abortion.1 This condition is probably related to an extension of a retro- or subchorionic hemorrhage to involve more of the implantation site. The size of ...

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