My first ultrasound was done at 16 weeks and 2 day I woundering if a that far along acurrate in deteriming how you are or could it be off by like 4 weeks?

The accuracy of an ultrasound in determining gestational age depends on several factors, including the skill and experience of the ultrasound technician, the quality of the ultrasound equipment, and the gestational age of the fetus. In general, ultrasounds performed in the first trimester (before 14 weeks) are considered more accurate for determining gestational age compared to those performed later in pregnancy.

At 16 weeks and 2 days of gestation, an ultrasound is typically quite accurate in determining gestational age, with a margin of error of about 5-7 days. This means that your estimated due date based on the ultrasound may be off by a few days, but it is unlikely to be off by 4 weeks.

However, it is important to note that there can be some variation in fetal growth and development, and some fetuses may be larger or smaller than average for their gestational age. Additionally, certain factors, such as maternal obesity or uterine abnormalities, may affect the accuracy of the ultrasound measurement.

Therefore, it is important to discuss the results of your ultrasound with your healthcare provider, who can consider all relevant factors and provide you with the most accurate estimate of your due date.