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INTRODUCTION

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Definitions

  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.

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OVERVIEW

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Transvaginal sonography (TVS) has become the method of choice for the detection and evaluation of early pregnancy. It affords detailed delineation of the choriodecidua and embryo/fetus and distinguishes living from nonliving embryos/fetuses by establishing the presence of heart motion. Most of the sonographic milestones used for assessment of early pregnancy can be established 1 week earlier with TVS than with conventional transabdominal sonography (TAS).1

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This chapter discusses the role of TVS in the basic evaluation of a first-trimester pregnancy that is within the uterus. Chapter 4 is devoted to the sonographic evaluation of ectopic pregnancy. Chapter 22 describes first-trimester screening for aneuploidy and anomalies. The American Institute of Ultrasound in Medicine (AIUM) Guidelines for Obstetrical Sonography in the First 10 Weeks is included as Appendix 3-1.

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CLINICAL INDICATIONS

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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.

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Approximately 20% to 50% of patients may experience bleeding in the first few weeks of pregnancy.2 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.2 This condition is probably related to an extension of a retrochorionic hemorrhage to involve more of the implantation site. The size of the retrochorionic hemorrhage can be correlated to clinical outcome.3

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Transvaginal sonography has a major role in evaluating patients with suspected ectopic pregnancy. Most importantly, TVS can accurately establish that the pregnancy is intrauterine, virtually excluding the possibility it is ectopic. This can be accomplished best by transvaginal scanning that can document an intrauterine pregnancy (IUP) as early as 4 to 5 postmenstrual weeks.4,5

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Thus, the major indications for TVS in the first trimester include

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  1. Establishment of intrauterine pregnancy, particularly when ectopic pregnancy is suspected

  2. Evaluation of complicated early pregnancy, such as retrochorionic hemorrhage, incomplete abortion, early pregnancy failure with resorption, or completed abortion

  3. Detection of embryonic/fetal life

  4. Precise localization of intrauterine contraceptive devices (IUCDs) associated with early pregnancy

  5. Detection of multiple gestations when clinically suspected

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INSTRUMENTATION AND SCANNING TECHNIQUE

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In most cases, TVS is the method of choice over TAS for evaluation of first-trimester pregnancies. This is primarily because of its improved resolution of the intrauterine contents and increased patient acceptance.4 Because of the theoretic potential ...

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