Enter the gestational age in weeks and fetal measurements in mm to calculate percentiles.

How calculations are based

This estimated fetal weight calculator will calculate percentiles as well as the estimated fetal weights based ultrasound data and on many published formulas.* Calculations are based on the 4 common fetal measurements, biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference (AC).

What is the estimated fetal weight?

Fetal ultrasound measurements show how the baby is growing and also help detect abnormalities. The estimation of fetal weight during pregnancy is among the most important examinations done. These measurements may help your doctor determine whether the baby is too small (intrauterine growth restriction: IUGR) or too big (large for gestational age: LGA).

Why is fetal weight important?

Babies that are too small or too large have higher risks of complications. Because the early detection of growth abnormalities may help to manage complications more appropriately even before the baby is born, monitoring fetal growth is an important part of antepartum care. Monitoring can be done through several steps including palpating the uterus and the fetus, measuring the size of the uterus, and performing a sonogram. A sonogram will measure various parts of the fetus, including the head, abdomen, and upper thighbone.

What determines fetal weight?

The growth of the fetus (and the percentile of the ultrasound sonogram) during pregnancy is dependent on many factors such as genetic, placental and maternal factors. Under normal circumstances, the fetus' inherent growth potential yields a newborn of appropriate size (not too big or too small) with a wide range of ‘normal’ sizes. The maternal-placental-fetal units act in harmony to provide the needs of the fetus while supporting the physiologic changes of the mother. When there is a limitation of growth potential in a fetus, that is comparable to failure to thrive in the infant. The causes of both can be intrinsic or environmental. The key is to detect any growth issues as early as possible.

What is considered "small for gestational age"?

Small for Gestational Age (SGA) is a term that refers to an infant or fetus in the uterus that is smaller in size than is expected for an infant or a fetus of similar gender, genetic heritage, and gestational age. SGA or Intrauterine Growth Restriction (IUGR) are usually identified by ultrasound before birth or an examination after birth. Birth weight below the 10th percentile of the population, corrected for gestational age, has been the most widely used definition of SGA and IUGR. 

Neonatal growth restriction is recognized as a syndrome encompassing small size as well as specific metabolic abnormalities including hypoglycemia (low blood sugar level), hypothermia (low body temperature), and polycythemia (increased level of red blood cells).

* Published formulas for percentiles and estimated fetal weights are based ultrasound data and on many published formulas including those by Hadlock, Shepard, Woo, Shinozuka, Ott, Combs, Warsof, Campbell, and many others.