Ultrasound Due Date Accuracy First-trimester ultrasound is the gold standard for gestational dating because embryonic growth is highly uniform. Crown-rump length measured before 14 weeks predicts gestational age within ±5 to 7 days, outperforms LMP when cycles are irregular or uncertain, and helps determine whether to change the due date. ACOG Redating Thresholds The LMP-based…
hCG Levels Chart by Week: Beta-hCG Ranges and Doubling Time HCG (human chorionic gonadotropin) is a pregnancy-specific placental hormone detectable in blood about 8–11 days after ovulation and in urine around 10–14 days after conception. In early viable pregnancy, levels typically double every 48–72 hours until approximately 6–7 weeks’ gestation, then rise more slowly thereafter….
Calculation of Pregnancy: How to Calculate Pregnancy Weeks and Due Date Obstetric gestational age is counted from the first day of the last menstrual period (LMP), not from conception. A typical pregnancy lasts 40 weeks (280 days), about 9 calendar months plus one week, or ten four-week months, rather than nine months. Clinical Formulas for…