Expert: Catherine Beier MS CBE - 10/22/2009

Question
Catherine
thanks for your earlier response

So I am now starting to think that maybe I had my LMP w/c 9th Feb - I just cant remember now.  I was sure it was the 2nd Feb.  but obv if it was the 9th Feb it would all make sense with my EDD.
I have had a look at online ovulation calendars if my LMP was 9th Feb and then my ov should have been the following:
1) Sunday, 22 Feb, 2009 - Friday, 27 Feb, 2009
2) 20th Feb - 25 Feb
3) 21st - 25 Feb

obviously the first website has got me worried but they do say that to get pregnant the night you actually do the deed is unlikey so assume I did it on the 28th in the early hours implantation should take 2-3 days after which would take me up to the 2nd Marchish.....so this would not  have been in my ov period - correct?  

so when I went for 12 week ultrasound scan (1st May) - I was 11+2 days.  If it was the other guy I would have been 8 weeks from conception......so again points to him not being father
Another thing I do not understand is if the scan was 11+2 - why when you count back it points to 11th Feb concpetion if EDD date points to a 24th Feb conception.......

if my egg had not been fertilised between the ov periods above..then surely it would have died.  and if I did it with the other chap on the 28th then there would have been no egg....

Sorry to witter on but serioulsy keeping getting down about this.....
after all the advice I have sought nothing points to the other guy being the Father but I just cant help but freak out about it.....suppose it must be the immense guilt!!

thanks in advance....

xx  

Answer
Sharon,


You are confused on how pregnancy dates are calculated.  Based on your ultrasound, you most likely conceived around February 24th, not the 11th.  Your last menstrual period would have been estimated to have started on Feb. 11th.  Ultrasound due dates automatically add in 2 weeks before conception.  So, if you were told that you were 11 weeks, 2 days pregnant, this means you were 9 weeks, 2 days from conception.


The first date of your last period is mostly irrelevant; most women don't have completely regular cycles and don't ovulate on the same day each month.


Basing a pregnancy due date on the first day of your last period is only accurate if you have 28 day cycles and always ovulate on day 14.  Since this is very, very rarely the case, then a due date calculated in this fashion is a guess at best.  In any case, babies come when they are ready - they don't know what due dates are.



So, based on all this information, it still looks clear that your partner is the father.  You most likely conceived from sperm deposited when you had intercourse with your partner on Feb. 21st, which you indicated in your first question.




Best,
Catherine