2nd Trimester

Conception date/when you had sex to get pregnant

clpowers95clpowers95 member
edited June 2017 in 2nd Trimester
I need some advice I was told at my last ultra sound I was 9 weeks which would make me about 14 weeks and 6 days but I had a new ultrasound at a different place saying I'm actually 15 weeks and 5 days can anyone help me figure out when I had the sex that got me pregnant? Me and my boy friend broke up between March 17 and the 20 and I unfortunately spent a night with my ex... I just need to be sure I know who the father is and I need some advice because I know the conception date and the day you had sex are not exactly the same and they add a week or two to how far along you are but I don't quite understand it completely.

Re: Conception date/when you had sex to get pregnant

  • Agree with PP, the reliable way to know is paternity test.
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  • It can take 6-10 days from fertilization to implantation on average, and sperm can live up to 5 days, so I could be anywhere from 6-15 days between sex and the start of pregnancy. So you won't really get any reliable answers since you're cutting it a little close. A paternity test would be the only reliable way to tell for sure.
  • You can get a blood test now that will collect fetal blood cells from your blood stream, and do a DNA test.
    Me- 39 (turning 40 in April), TTC for the first time ever (since Jan 2015), low ovarian reserve
    Married 3/14/14 to my wonderful wife, but her sperm count is rather low
    TTC with frozen donor sperm and science

    7 IUIs, 7 BFNs.
    2 IVF attempts, both cancelled and converted to IUI, both BFNs.
    Decided that my tired old ovaries are ready to retire.
    Next step- reciprocal IVF, using my wife's eggs, my uterus!  
    fresh 5 day transfer (2 embryos) 4/17/17- BFP! 
    Identical twins "due" 1/2/17 (but anticipated arrival sometime December)

  • The gestational age starts from the first day of your last period. You ovulate 2 weeks before your period normally comes. If you are on a 28 day cycle, you typically ovulate around day 14. Sperm in theory can hang out for 5 days before ovulation occurs and still fertilize the egg. And the egg can in theory be fertilized up to 2 days after ovulation. So whatever your normal cycle is and go back 19 days. Starting 19 days before your period is due til 12 days before your period is due is in theory your fertile period. If your periods are irregular that will not help so then you have to go by ultrasound. The problem is ultrasounds have a margin of error. Earlier ultrasounds are more accurate than later ones. Your ultrasound dating is less than a week apart and could just be margin of error or so. If you haven't done paternity testing which is the surefire way of knowing, then go with your first ultrasound dating and whenever you were 1 week 2 days til 2 weeks and 1 day would be your theoretical conception window. 
  • With only a three day window between partners, a paternity test is the only reliable way to know, especially since you don't know for sure your ovulation date.
    Me: late 30s | H: early 30s
    TTC #1 since April 2015
    RE Dx: Fibroids, surgery Jan 2016
    IUI #1 and #2, Nov/Dec 2016, BFN
    IVF March 2017: ER - 5R/3M/3F, 1 PGS normal
    Polyp removed May 2017
    FET May 2017 - BFP!
    Baby boy born 2/2/18

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