Hello
It takes about seven days from fertilisation to implantation. For the three days following fertilisation, the egg will move toward the uterus, growing all the time.
http://health.ninemsn.com.au/article.aspx?id=2393
A pregnancy is usually referred to in weeks, starting from the first day of the last menstrual period (LMP). However, as generally occurs about 2 weeks into the menstrual cycle, the developing foetus is thus 2 weeks younger than the number of weeks a woman is referred to as being pregnant. This means a woman who is 6 weeks pregnant is carrying a 4 week old foetus.
http://www.hon.ch/Dossier/MotherChild/pregnancy/dating.html
In the first trimester Crown rump lenght is used to estimate gestation age and the maximum error by this way is 5 days. Also some researches state 45% pregnant women were not certain about their LMP as a result of poor recall,irregular cycle,Bleeding in early pregnancy,OCP use within two months of conception.
Check this link
http://www.storknet.com/cubbies/pregnancy/duedate.htm
Edited by dr_amitmunjal on August 30 2006 at 8:57 PM
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