This tool applies the gestational-age prediction equations derived by Chervenak and colleagues (AJOG 1998) from a population of 152 singleton, 67 twin, and 19 triplet IVF pregnancies — gestations in which the true conceptional age was known precisely, removing the menstrual-dating imprecision that limits most other dating formulas.

You enter the fetal measurements; the tool selects the most accurate published equation for the parameters you have, returns the estimated gestational age, and shows the 95% confidence range (±2 SD) taken directly from the random error reported in the paper. For twins and triplets it applies the paper's validated combination and correction rules.

Validated range: 14–22 weeks. The authors explicitly note that prediction beyond 22 weeks requires further investigation, and HC becomes less reliable later as landmarks blur. The tool will flag estimates that fall outside this window.