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PATIENT STORY

A 22-year-old woman presents with last menstrual period approximately 2 months ago complains of morning sickness, but is otherwise feeling well. A urine pregnancy test confirms she is pregnant. Figure 79-1 shows a fetus of 9 weeks estimated gestational age (EGA).

FIGURE 79-1

Ultrasound examination of a fetus of 9 weeks estimated gestational age. The ultrasound was performed with a vaginal probe and the membranes are visible. (Reproduced with permission from E.J. Mayeaux, Jr., MD.)

INTRODUCTION

Obstetrical ultrasound has become a vital tool in our ability to properly care for the pregnant patient. Vast technologic improvements have made visualization of the pregnancy even better and improved our diagnostic capabilities, ranging from the normal pregnancy to the extremely early ectopic pregnancy. Ultrasonography (US) allows for a relatively detailed assessment of fetal gestational age, development, number of fetuses, fetal anatomy, placental location, and uterine or ovarian pathology. Most pregnancies in the United States undergo ultrasound imaging for various indications.

SYNONYMS

Dating scan.

EPIDEMIOLOGY

  • Women who receive antenatal care have lower maternal and perinatal mortality and better pregnancy outcomes.1 However, the optimal components of prenatal care have not been rigorously examined in well-designed studies.

  • In the United States in 2003, 84.1% of pregnant women obtained prenatal care in the first trimester, and only 3.5% received no care or initiated prenatal care in the third trimester.

  • A first trimester ultrasound is performed either transabdominally or transvaginally before 14 weeks.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Ultrasound is used to estimate gestational age and to calculate the expected date of delivery (EDD). Ultrasound is especially helpful when menses are irregular, the last menstrual period (LMP) is unknown, or in patients who conceived while using hormonal contraceptives. A Cochrane review noted that with more accurate dating, there was a reduction in intervention for postterm pregnancy.2 The earlier in pregnancy a scan is performed, the more accurate the age assessment from crown to rump length. The initial age assignment should not be revised on subsequent scans.3

  • The Routine Antenatal Diagnostic Imaging with Ultrasound (RADIUS) trial was a randomized trial of routine obstetrical ultrasound screening.4 It included more than 15,000 women in the United States. The trial showed that routine ultrasound screening was associated with a significantly increased detection of fetal anomalies, but no improvement in any perinatal outcome, including mortality, preterm birth, birth weight, and neonatal morbidity.

  • First trimester vaginal bleeding is found in 20% to 40% of pregnancies. The differential diagnoses include possible spontaneous abortion, ectopic pregnancy, and gestational trophoblastic disease.

  • Ectopic pregnancy causes a significant degree of morbidity and mortality if untreated, often through tubal rupture with potentially life-threatening hemorrhage. Identification of an intrauterine pregnancy effectively excludes the possibility of ...

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