All About Due Dates

Due Date Glossary

Abdominal Circumference (AC):  One of several ultrasound measurements that can be used to calculate an ultrasound due date.  The AC is also used to calculate the Estimated Fetal Weight (EFW).

Biparietal Diameter (BPD):  One of several ultrasound measurements that can be used to calculate an ultrasound due date.  The BPD measures the largest diameter formed by the parietal bones, the bones that form the top and sides of the skull.  The BPD is also used to calculate the Estimated Fetal Weight (EFW).

Estimated Date of Confinement (EDC):  This is a common term for the due date.  This term has historical roots in the Victorian era when it was common to use oblique terms to describe sensitive subjects.  It was a common practice at that time for a woman to be "confined" to bed during labor and for several days after childbirth.  Her friends and neighbors would come to her home to take care of her children and do her household chores while she was "in confinement."  EDC is an older term that is falling out of favor in some parts of the country in favor of EDD (see below). 

Estimated Due Date (EDD):  Another common term for the due date.  The abbreviation EDD can also stand for (depending on whom you ask and where you live) "Estimated Delivery Date" or "Estimated Date of Delivery."  EDD is a newer term that is coming into more common usage among care providers to replace the term EDC (see above).

Estimated Fetal Weight (EFW):  An estimate of how much the baby weighs (in grams) that is calculated by a mathematical formula using the BPD, HC, AC, and FL.  Ultrasound estimated fetal weights are not as accurate as many people believe.  Trying to estimate the weight of a fetus based on ultrasound measurements is the equivalent of trying to estimate a woman's weight by knowing her dress size.  You can get a "ballpark" number, but it's not going to be exact.  An ultrasound EFW has a built-in error (Standard Error of Mean) of 15-20% depending on how far along the pergnancy is at the time of the ultrasound.

Estimated Gestational Age (EGA):  Estimated gestational age means how far along you are in your pregnancy.  This is sometimes called Menstrual Age (MA), particularly in ultrasound reports.

Furmur Length (FL):  One of several ultrasound measurements that can be used to calculate an ultrasound due date.  The femur is the long bone between the hip and the knee.

Head Circumference (AC):  One of several ultrasound measurements that can be used to calculate an ultrasound due date.  The HC is also used to calculate the Estimated Fetal Weight (EFW).

Last Menstrual Period (LMP):  Last menstrual period refers to the FIRST DAY of your last menstrual period.  This is sometimes called "FDLMP" or "First Day, Last Menstrual Period" or even "FDLNMP" or "First Day, Last Normal Menstrual Period."