Trying to Conceive After a Break & One Unprotected Encounter: What's the Timeline?

Question
right ok... me and my boyfriend have been together 2 years and decided to start trying for a baby recently. However just after christmas 2010 we did brake up for a few months but got back together on ...MARCH 19TH... so since March 19th i have only slept with my partner and we have been trying for a baby. while we were split i had one very sTupid drunken night and ended up sleeping with another guy on ...MARCH 12TH... I am not 100% sure if we used a condom. (big mistake!) Now basically from what i can remember i had a normal period on the ...11TH APRIL... this lasted untill the 15th of april. and on the ...19TH MAY... I did a clear blue test and found out i was pregnant. it said 2-3 weeks but not sure how accuarte they are. was really happy and booked in to see the midwife at about what i thought would be about 10 weeks. however We had to go to hospital before we met the midwife as i noticed the tinyest amount of what i thought may be blood in my urine. they booked me in for a internal scan on ...14TH JUNE... at the hospital. It was in a internal vaginal scan and they dated me 8 weeks 1 day. the crl was 16mm. everything was fine they found the heart beat and i even got a cute picture to take home. the baby looked like a bean :) so this was on the 14TH JUNE i was told i was 8 weeks 1 day. the day after i saw my midwife and all was good. i was booked in for my 12 week scan on the 11th july. 11TH JULY... had 12 week scan yet again eveything was fine the baby measured 56.4mm and was dated 12WEEKS 1DAY... again got a picture and the difference was amazing i could see a little nose :).on the 5TH SEPTEMBER i went for my 20 week scan and again eveerything was fine got a good picture and found out im having a boy. (sorry if i have confused you with anything!) now... what i need desperatly is peace of mind. the guy i had sex with on MARCH 12TH... before me and boyfriend got back together... is now trying to tell me he could be the dad!!! i dont think he can be as theres like a 5 week difference between when i last slept with him and when the scans are saying i fell pregnant. well actually there is a 7 week difference in when they they say i concieved and when i slept with the other guy.  if it wasnt my boyfriends then both my scans must of been wrong by 7weeks conception dates! is this at all possible? especially as i had my early internal scan at 8 weeks. is that possible FOR it to be wrong by 7 weeks? so instead of being 8weeks it could be 15 weeks old baby and they were mistaken at the scan? i really dont think its possible but just need a proffesional oppinion as i am a hairdresser not a midwife lol! thanks for reading this and please ask me if i have confused you with anything. sorry it is sooo long!! x

Answer
Lily,

The other man can't possibly be the father. Not possible. No way. Zip. Zero. Nada.  Unless you slept with someone other than your boyfriend after April 15th, then it's his baby.  Based on your dates you most likely conceived around May 2nd.


Best,
Catherine Beier MS CBE
Giving Birth Naturally:
Empowering Women to Trust Their Bodies