Fetal crown-rump length can be measured at 5 to 12 weeks and gives a good estimation of fetal age.

The estimated date of delivery (EDD) or the estimated date of confinement (EDC) is a specific date arrived at by certain calculations.

It is by no means the most accurate of calculations, in the sense that very rarely is a baby born on exactly that date.

By adding 14 days to the first day of the LMP and then further adding 266 days to it, the expected delivery date can be calculated.

This method may not always be accurate because cycle lengths vary greatly in women.

Computer software or web-based online calculators also give quite accurate results.

You can use the online Ovulation Schedule if you know the date of the first day of your last menstrual period (LMP) and length of menstrual cycle.

Or, to simplify it – (LMP 7 days) minus 3 months will give the EDC.

(If your LMP was on May 10 then the EDD is February 17). In women with longer cycles, you have to add 7 days to the first day of the LMP plus the number of days that the cycle extends beyond 28 days.

It can be felt as early as 14 to 16 weeks by a woman who has been pregnant before, while a first-time mother may not feel the first movements before 18 to 20 weeks.

Doppler ultrasound can detect fetal heart beats as early as 10 weeks of pregnancy and is another indirect means of arriving at an approximate due date.

If the exact date of ovulation is known, confirmed by a rise in BBT or an LH surge, you just need to add 266 days to it in order to calculate your pregnancy due date.