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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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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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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 LMP ...