Pregnancy Baby Size.

How big are most babies when they are born?
The weight varies greatly from baby to baby. However, the average weight of a baby at term is 7 to 7-1/2 pounds (2.6 to 3kg).

Is there any way to estimate from my size how big my baby will be?
It's very hard to estimate the weight of any baby before birth. Many doctors will guess and give a range of a couple pounds. It's not uncommon to estimate a baby will weigh 8-1/2 (3.4kg) pounds and find it's only a 7-pound (2.6kg) baby when it's born.

My doctor said that ultrasound can be used to gauge a baby's weight. Is that true?
Ultrasound is sometimes used to estimate fetal weight, but errors do occur. However, the accuracy of predicting fetal weight with ultrasound is improving.

How does ultrasound measure a baby's weight?
A formula has been established to help estimate fetal weight with ultrasound. Several measurements are used, including the diameter of the baby's head, circumference of the baby's abdomen and length of the femur (thighbone) of the baby's leg. Occasionally, other fetal measurements are taken.

How accurate is ultrasound in measuring a baby's weight before birth?
It is the test of choice to estimate fetal weight. However, estimates may vary as much as half a pound (225g) in either direction.

I'm 13 weeks' pregnant and read that my baby's head is about half or 50% of its body length. Can this be true?
Yes, at this point the head is about half the crown-to-rump length (measurement from top of the head to the baby's buttocks). In 2 months, when you are 21 weeks' pregnant, the head will be about 1/3 of the fetal body. At birth, your baby's head will be 1/4 the size of its body.