What is the best predictor of gestational age between 14-22 weeks?

The best predictor of gestational age between 14-22 weeks is head circumference. This measurement is particularly valuable during this period because the fetal head grows consistently and proportionately relative to gestational age.

In early pregnancy, the head is disproportionately larger in relation to the body, which allows for a more accurate estimation of gestational age through head circumference. It reflects the growth and development of the fetal brain and skull, which is crucial during this period of rapid fetal development.

While crown-rump length is another common measurement used to estimate gestational age, it is most accurate during the first trimester. As pregnancy progresses, the proportionality of the body parts begins to change, making head circumference a more reliable indicator in the specified weeks.

Femur length and abdominal circumference, while informative, do not correlate as strongly with gestational age in this specific timeframe compared to head circumference. Each of these measurements can serve as indices of fetal growth, but for the 14-22 week range, head circumference provides the clearest and most consistent estimate of gestational age.