You might look up photos of embryos at 6 weeks and then at 8 weeks. Babies put on an incredible amount of growth in that time, I think the number I read once was something astonishing, like a million cells a minute. (That sounds unreal but the number really was inconceivable.) If you had an ultrasound at 6 weeks 3 days, the ultrasonographer would not have been looking at an 8th week baby and identified it as 6w3d. They look too different! And an ultrasound in your sixth week is quite reliable for purposes of sorting out whether the baby came from sex on a specific day in February. (You would not be able to sort out the difference between February 7 and February 10, but you can rule out February entirely if the baby was conceived in January.) The calculator gives the following based on your last menstrual period. Did you get an estimated due date from the doctor at that early ultrasound?
First day of last menstrual period: January 11
Probable date of ovulation: January 25
Possible dates of conception: January 21 to 29
Due date: October 18 (40 weeks)
The start point for a baby is the moment sperm meets egg, and they all do grow at the same rate for at least a while. According to the numbers you have given, sex on February 10 was after you had been pregnant at least 11 days and more like 15 or 16.
Yes I had it done by a doctor I had another
Done at a hospital on march 3 and they said I was
But I posted this in pregnancy 18_21 and everyone is
Saying the dates are to close and ultrasounds are not
On the one hand you have a medical doctor who has probably been in practice for a while, who is reading your medical records and your ultrasound report. On the other, you have 18-21 year olds in an online medical chat room. Because of what the 18-21 year olds say, you think a doctor would be looking at the ultrasound that measured your actual baby, and be unable to correctly identify at what growth stage it is, or even to come close. I guess I can't really help you with that. If you have no faith in doctors, well, you have no faith in doctors. Some people don't. All you can do if so is to get a DNA test once the baby is born, to put the question to rest once and for all.
The ultrasound would have to be many days wrong for the February guy to be the dad, and it is hard for a sixth-week ultrasound to be that many days wrong. By the time you are in your 39th week, babies who are the same age can measure as much as two weeks different than average. But not at 6 weeks.
Oh, there was supposed to be a question mark, "because of what the 18-21 year olds say, you don't think your doctor can correctly measure the baby?" In other words, I was teasing you -- "anonymous teenagers online say this, trained medical doctor in person says that, what to do, what to do."
But in all seriousness, if you really are thrown by their remarks (I might add, a lot of times the kind of advice one gets online is based on hearsay and misinterpretation) it might be more a case of your conscience than your dates. It sometimes happens that someone who wishes to forget she had rash sex, focuses instead on her dates in kind of a quest for certainty that she is not going to somehow be punished by a higher power. If that is what is happening for you, it's possible to get knocked off your certainty by idle gossip or half-understood stories repeated over again. If you do trust your doctor, I urge you to talk to him or her. I think he or she can put your mind at ease about how ultrasounds work.
Do you know if irregular periods make a difference?
Not to an ultrasound. It would matter if you are using a little wheel or counting on a calendar, but the ultrasound has viewed the actual baby. It backtracks to an assumed first day of last period, and counts forward to the due date, all based on the baby's real size and development milestones as seen by the ultrasound.