QuestionQUESTION: i had split up with my boyfriend and had sex with someone on the 16th march.i missed my period at the beginning of april but put it down to stress as i had just lost a good friend.i took a home pregnancy test a few days later it was negative.i then got back with my boyfriend and started having sex with him about the 18th april.i missed my next period so took another test at a clinic and it was negative,she said it could be that i was pregnant but only in the first couple of weeks as their tests show when you are 3 weeks pregnant.i went back the week after and it was positive.i arranged an early scan on the 16th may and it said i was about 4 and a half weeks no baby was shown.had my next scan june 27th and it said i was 11 weeks and 2 days.is there any chance at all that these scans could be as much as 4-5 weeks out and the other person could be the father??very worried.
ANSWER: Early ultrasound scans are extremely accurate in dating a pregnancy. During the first ten weeks, they are generally no more than 1 or 2 days off. Particularly since you had a scan putting you at 4.5 weeks, there is no possible way that baby could have been conceived in March. Your conception date should be somewhere between April 24 and April 30. Your second scan agrees with this.
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QUESTION: thank you very much you have helped put my mind at ease even though i keep worrying myself i don't know why.can i just ask how many days are they usually accurate to after 10 weeks seen as though i was told i am 11 weeks 2 days?i was a bit suprised they said it that exact.thanks again
AnswerBy the end of the first trimester, ultrasound dating can be off by as much as a week. The dating is done using charts of average fetal size. In the first trimester, the ultrasound technician will measure the length of your baby from the top of the head to the bottom of the spine, and then will compare it to a chart to determine the age. Most embryos develop at about the same rate for the first ten weeks, which is why these early scans are more accurate. However, after 10 weeks, natural genetic variability begins to show, and a baby that is larger or smaller than "average" will be incorrectly dated.
