Fetal dating

Preterm is a full term pregnancy that is 37 to 42 weeks.

Any labor or birth prior to 37 weeks is considered preterm.

Trimester is approximately one-third or three months of a pregnancy.

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Understanding the stages of pregnancy can be difficult because the dating methods used by doctors don't exactly line up with the yearly calendar.Furthermore, pregnancy is divided into trimesters, or three periods of time.A working knowledge of the key terms used in pregnancy dating is helpful in the treatment of miscarriages and other pregnancy losses.A due date, for example, is the estimated date of delivery (EDD, or sometimes EDC) or the date when a pregnancy reaches exactly 40 weeks from the last menstrual period.Even though it seems strange to calculate a due date based on a time when you were not pregnant, it is the easiest way to estimate how long you have been pregnant until an ultrasound can be done.

Once you have an ultrasound, your due date may be changed based on the measurements the tech is able to take of some of the fetal body parts.

The date should only be changed if the ultrasound is more than five days different from your LMP, unless you are uncertain of your period.

Gestational age is the medical term for how many weeks and days of a pregnancy have passed.

It has a major impact on a fetus’s likelihood to survive a preterm birth.

Last menstrual period, often abbreviated as LMP, this is the first day of the last time you had your period before becoming pregnant.

It is used to calculate your due date before any ultrasound testing is done.