Pregnancy After Breakup & New Relationship: Seeking Guidance

Question
Hi, Im currently in a dilemma at the moment with my pregnancy,i was with my boyfriend for 4 years until january 09 (this year) we split and i began seeing someone else, the last time i slept with my new partner was on 15/04/09 we didnt use protection. we then split as id be speakin to my ex again, we decided to give things ago and the first time i slept with him was friday 01/05/09. then on the 19th may i took a clear blue conception inicator test which said i was 2-3weeks pregnant. (i havent a clue when my last perid was)i then went to the midwife who sorted out a date scan for me on july 10th, the ultrasound staff said i was 11weeks 5 days so said 12weeks in my notes and give me a due date of 22nd jan. ive done numourous conception calculators etc which show i conceived beginning of may. ive just got this constant doubt in my mind tho that it could be the man i was with from feb till april 09. ive been so careless and its a constant worry even tho everything is pointing to my partner now (whom i was with 4 years)at the beginning of may,but i didnt no whether the ultrasounds can be out by 17 days or not? (2 and a half weeks). and that do the ultrasound scans base your size including the 2 weeks before you actually conceive? my current partner is white and my previous mixed race so when she finally arrives id know for certain but i just dont want to have to wait till shes actually born to find out? is there any way that my baby could be from my partner in april? as my 20week scan sizes were all what they should be too?

Answer
Hi Halley,

Ultrasounds cannot be out by 17 days as they measure the fetus, at 12 weeks a fetus will measure around 5.4cm, at 14 weeks a fetus will measure 8.7cm, so it would definitely pick that up. Try not to worry as I would be very surprised if your ex partner was the babies father. Good luck!