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Pregnancy - Age accuracy of a fetus on an ultrasound

Today's date is Monday, 30-May

Does anyone know of an age range on an ultrasound that determines the age of a fetus?
I am in a situation in which I am now questioning whether or not I am the father.
She is/was my best friend for over three years.  We talked about everything, including significant others.  For the past year, she had sworn abstinence, serving as a leader of her church group with the emphasis on this practice.  Over the course of the past year (dating back to Jan. 2011), she had told me about the times she would date but not allow anything more than that.  She would also say that she would travel back to her home town from time to time and occasionally hang out with her ex, but that was it, no sex.
On New Year's Day, 01-Jan-2012, she had a party at her home.  I met two damn fine ladies and both were attracted to me, which she instantly noticed.  To cut to the meat of the story, she became jealous and didn't speak to me again until 14-Jan., after I called her.  After that emotional talk, she I and met at her house on the 16th, in which we had sex for the first time ever and we were not protected.  I did not ask the questions I should have, but it happens.
Sooooo, the next day she told me her next period was due on the 21st and she never missed a period, which raised a red flag.  On the 23rd her period hadn't come so she set up an appointment for her doctor.  On the 30th, she called me at work and told me the doctor stated she was pregnant.
Okay.  A high-risk pregnancy due to fibroid tumors, she has had four appointments since that date.  The baby is still fine as of today, but now I wonder about paternity.
The first ultrasound happened late February, very early.  The next ultrasound happened on Apr. 6th, in which the picture stated the fetus was 12 1/2 weeks.  I had had sex with her on Jan 16th or 10 weeks to the date.  I had questions and she quickly tabled them, stating I was the father.  Although I trusted her, I had reason to wonder, for there other signs which I won't get into.  The latest ultrasound happened last Friday, Apr-27th.  She didn't want me to go so she lied to me, for she called me and told me she went to the appointment and told me we were having a girl!  The ultrasound pic stated the fetus was now 16 1/2 weeks.  I was now real curious!  In speaking to a nurse, she insisted ultrasound dates are not totally accurate and could be off as much as two weeks either way.
The nurse all but assured me that it was highly unlikely the sex couldn't be determined before at least 18 weeks.  Can anyone out there confirm the earliest time sex could be determined?  I've been reading all weekend and I now know that a CVS could be used as early as 14 weeks.  I just don't know what type she has had.
She had been treating me like crap since the pregnancy began and our friendship is all but over.  She still to this day demands things of me that I don't feel I should have to do for her, but feel guilty because she's all alone.  So I still help out.
In closing, if an ultrasound is real accurate, then I feel the baby might not be mine!  If it is two weeks off either way, then two weeks earlier the sex really be determined and two weeks later the baby really wouldn't be mine... or could it still be.  She also looks like she is at least six months, for she is not a big woman.  The stress!!!  I now don't want the baby to be mine; I hope that doesn't sound too bad, but she doesn't want to have me as her man, so I don't want her to have my child.
There is more to my story, but this is the gist of it.

Jan 16 to Apr 27 is 14 weeks and four days and the ultrasound showed 16 weeks and 4 days.  I am real concerned.  For now I will continue to read up on this; she still has five or six months left and she is in pain frequently.

I look forward to any insights or stories anyone is willing to share with me, for I will check frequently.
6 Responses
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Avatar universal
I found out at exactly 17 weeks i was having a girl..so it is possible and like the other girls said they go by LMP.. so she is pregnant before she even has sex in the eyes of the doctor.. its confusing but sounds like ur the daddy
Helpful - 0
1947316 tn?1337300930
Sorry just re read your post again. And I had thought you were with her on Jan 14th not 16th. So I reentered the 16th....that puts her due date at October 8th and conception date at January 16th. Sorry if I confused you more
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Avatar universal
Ok, first of all, by the time a woman is expected to have her period, her fetus is already considered 4 weeks, even though conception typically happens at 2 weeks prior to missed period. They start counting from the first day of the LAST period.  Confusing, but that is the way it ia. So when she missed her period on the 21st or whatever, she was already 4 weeks pregnant, but conceived roughly 2 weeks before.... Making u most likely the father.

Second of all, I found out i was having a boy on exactly 17 weeks... 16 1/2 weeks is totally possible. Again, 16 1/2 weeks would translate into 14 1/2 weeks since conception.

You can always get a DNA test after she ia born. If you are truly her friend, you should just be supportive during her pregnancy. There are a lot of and downs and uncertainties for her.
Helpful - 0
1947316 tn?1337300930
Also every baby is different as to when you are able to tell the sex. I've heard of some people finding out as early as 13 weeks. My oldest son played peekaboo and it wasnt until 22 weeks with him. Most OBGYNs will do a gender ultrasound between 18-22 weeks but some do it sooner and it is just up to the baby on whether its ready to show what sex it is or not.

Also the earlier the ultrasound is preformed....the more accurate they are. It is the ones in later pregnancy that can be off..as every baby grows differently. But from what you have said, it sounds like they are pretty accurate
Helpful - 0
2109562 tn?1347253848
Also they can tell her the gender of the baby at 16w most don't until 18 but SOMETIMES it can be found even earlier than 16w.
Helpful - 0
1947316 tn?1337300930
First of all....did you know that the dates of aa pregnancy actually don't go from the day the baby was concieved? They base it on the first day of a womans last period. Most women ovulate approximately 2 weeks after their period and that is their most fertile time. A woman is technically pregnant for 38 weeks but by going by their last period it makes it 40weeks. That is where they are getting those extra 2 weeks. I went online and put in the date you had sex with her and it put in her due date as October 6,2012and that would be accurate that she is 17 weeks 2days. I'm sorry I understand how you feel...and not knowing her sexual history.....but it looks like you are very well the father. I am in a somewhat similar situation, I was with my babys father(one of my good friends) one time when she was concieved so I understand your doubts.....but it happens
Helpful - 0
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