Fetal age is counted from the moment of conception. Thus, it is 14 days less than the gestational age, assuming a regular menstrual cycle of 28 days. Health care providers generally measure fetal age through ultrasounds.

Do you use gestational or fetal age?

While gestational age is measured from the first day of your last menstrual period, fetal age is calculated from the date of conception. This is during ovulation, which means that fetal age is about two weeks behind gestational age. This is the actual age of the fetus.

What if gestational age is more than fetal age?

A discrepancy between gestational age estimated by last menstrual period and biparietal diameter may indicate an increased risk of fetal death and adverse pregnancy outcome.

Is ultrasound accurate for baby weight?

Ultrasound is not very reliable for estimating fetal weight near term. For a 9-pound baby, an ultrasounds predictive accuracy is typically 15 to 20 percent off. Which means we may over- or underestimate by more than a pound.