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PREGNANCY DATING

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β-hCG (mIU/mL)

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  • Produced by cytotrophoblasts and syncytiotrophoblasts (primarily)

  • Ninety-two amino acid alpha subunit (identical to leutinizing hormone, follicle stimulating hormone, thyroid stimulating hormone (TSH)); 145 amino acid β-subunit (unique to hCG)

  • Serum/urine pregnancy tests are sensitive to levels of 1–20 mIU/mL (varies by test)

  • Within 24 hours of implantation (about 3 weeks after last menstrual period (LMP)), β-hCG is detectable in maternal serum. A sensitive pregnancy test can be (+) 1–2 days after implantation

  • Peak maternal levels reach about 100 000 mIU/mL (60–80 days after LMP); then decline; nadir about 16 weeks, and stay at this level for remainder of pregnancy (Figure 1-1)

  • After pregnancy (delivery or loss), it takes approximately 6–70 days for β-hCG to return to undetectable levels

  • Elevated levels also in molar pregnancy, renal failure with impaired hCG clearance, physiological pituitary hCG, and hCG-producing tumors (GI, ovary, bladder, lung)

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Figure 1-1

Mean concentration (95% CI) of human chorionic gonadotropin (hCG) in serum of women throughout normal pregnancy. (Used with permission from Cunningham F, Leveno KJ, Bloom SL, et al. Chapter 9. Prenatal care. In: Cunningham F, Leveno KJ, Bloom SL, et al., eds. Williams Obstetrics. 24th ed. New York, NY: McGraw-Hill; 2013.)

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Ultrasound

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See Table 1-1, Guidelines for Transvaginal Ultrasonographic Diagnosis of Pregnancy Failure in a Woman with an Intrauterine Pregnancy of Uncertain Viability

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TABLE 1-1

DIAGNOSTIC CRITERIA FOR NONVIABLE PREGNANCY USING TRANSVAGINAL ULTRASONOGRAPHY

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Establishing Estimated Date of Delivery (EDD)

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  • EDD is 280 days after the first day of the LMP (assumes regular, 28-day cycles, ovulation occurring at day 14, accurate recall)

  • Ultrasound in the first trimester (up to 13-6/7 weeks) is the most accurate method to establish/confirm gestational age (GA)—accuracy of ±5–7 days

  • If IVF pregnancy, age of the embryo, and date of transfer are used (day 5 transfer, EDD is 261 days from transfer date; day 3 transfer, EDD is 263 days from transfer date)

  • Average fetal heart rate (FHR) 90–110 bpm at 6 weeks. Poor prognosis if less than 90 bpm

  • See Table 1-2 for ...

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