However if an egg is fertilised in due course then menstruation does not occur. Naegele’s Rule is used to calculate gestational age, which is based on the average human pregnancy lasting 280 days from the first day of the last monthly period. This involves adding 7 days and subtracting 3 months to give the expected date of delivery.

This calculation is based on ovulation occurring approximately two weeks into your menstrual cycle therefore the gestation of your baby is calculated from the dates you have input. However, in women who have irregular menstrual cycles or women who have recently been on the pill then this method can be inaccurate, it is therefore recommended that an ultrasound scan is performed as a more accurate means to date your pregnancy. Please visit our Packages and Fees Page to see all of our available packages and our Special Offers Page for up to date offers on our 3D and 4D ultrasound scans.