conception date from ultrasound

[joscadje]

On 8/11/2015, the gestational age was 19w1d. On 8/19/2015, the gestational age was 19w4d. The mother swears she didn't realize she was pregnant until July. She did not have any prenatal care until these two ultrasounds. How accurate is the due date if it is only calculated using these two ultrasounds as a baseline?  The doctor estimated the due date between 12/30/15-1/4/15 based on the first ultrasound. I am already concerned that over an eight day period, there was only 3 days of measurable growth. Thank you.

[joscadje]

She had sex with 3 boys in a 4 week period. She told another boy she had a miscarriage in March. I knew there was a potentially larger window using the 19th week as a due date estimation. I offered to pay for the prenatal paternity test and was told absolutely not because she just knows this is my son's baby. I am just trying to be prepared. I guess the paternity test after the baby is born will tell us what we need to know.

[AnnieBrooke]

Are you asking if the baby's health might be at risk or mostly trying to find out if the dates point to your son?  As far as I know, her youth would not cause slow growth of the fetus.  The fact that the doctor gave a couple of different estimates rather close together does not really mean that much, since there is a pretty wide margin for error in the 19th week (it would be plus or minus ten days by now).  Why does she feel it is your son's baby, did she not have sex with anyone else near to the time she was having sex with him?

[joscadje]

The first estimated due due she was given was 12/30/15 based off the ultrasound done on 8/11/2015. She had NO prenatal care up to that point. She did not even take a pregnancy test until late July. My other concern is that she is only 14 years old. Could she be further along and the baby just be experiencing slow growth due to lack of prenatal care and her age?

[AnnieBrooke]

By the 19th week, it is not reliable, to use an ultrasound to try to determine when conception was.  I don't know why the two ultrasounds don't agree.  What was the very first estimated due date she was given, and when was she given that date?  (I.e., in July?)

[joscadje]

Both ultrasounds were done at the same office by the same doctor. The mother had sex with 3 different boys over a 5 week period, one of them being my son. The mother insists the baby belongs to my son. I am not saying he is not the father. I am just looking for the validity of the due date based on these two ultrasounds. Ultimately, the only thing that matters is that the baby is healthy but the lack of growth over an 8 day period is also concerning me.  

[AnnieBrooke]

Were  both ultrasounds done at the same place and read by the same doctor, or was one done at the ER and one at an ob-gyn's office?   That could easily explain the difference.