Baby's Length and Weight Explained
There are several ways of calculating a baby’s age, weight and length. We opted for the methods that most doctors use.
Your due date (and thus the fetal age of your baby) is counted from the first day of your last menstrual period (LMP). An average pregnancy lasts about 40 weeks (give or take).
When it comes to your baby’s length and weight, consider all of these measurements as guidelines; each baby develops differently in the womb. After 12 or 13 weeks, some sources will refer to what’s called the “fetal length,” namely from head to toe of the baby. Our numbers refer to the crown-rump length (CRL), which measures the distance from the top of the head (crown) to the tailbone (rump).