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I had unprotected sex with my collegue on 8,9&10 August 2014. Then had unprotected sex with my boyfriend on 17 August 2014. I had my first ultrasound on 8 October 2014 where they say that the foetus is 6 weeks 3 days old. I also had my gestation scan done currently whre they said that the gestation age is 26 weeks 3 days. I am totally confused as who is the father of the baby. My periods were also irregular. As i beleive i had my last period on 22 July 2014. Docs gave me due date as 13 May 2015. Please help.


Hi Guest,

Some things aren't making 100% sense.  Normally due dates are based on your LMP, even when using an ultrasound.

Your first ultrasound indicates a LMP of 24 August.Your second ultrasound (if using todays date) indicates 25 August for your LMP.

The problem is the due date doesn't match.  Both of the above would put the due date around 1 June.

Backtracking, using the due date to determine your last period, I get 6 August.

If we go by the ultrasound dates, you wouldn't have gotten pregnant - unless you had sex after 25 August.

If we go by the due date, you would have had sex with your colleague on days 2,3, and 4 and your boyfriend on day 11.  You normally would ovulate between about days 11 and 16 of your cycle.  Sperm can survive up to about 5 days.  It is UNLIKELY that your colleaque would be the father.  You would have been near PEAK FERTILITY when you had sex with your boyfriend and HE is the likely father.

Unfortunately you will likely need a DNA test to confirm paternity.  Irregular periods make these estimates a bit "challenging."

Hope it helps.  Good luck.



Thank you for the response. My periods were continuosly irregular since one year. So if i remember correctly my LMP was 26th July 2014. You said it right the ultrasound dates and due date does not really match!! But there is one big confusion. Let me explain it. As i told i had unprotected sex with my collegue on 8, 9 & 10 th August and with my boyfriend on 17th August. I saw slight spotting on 21st & 22nd August :( . I was assuming that i was having a period then. However the first dating scan on 8th Oct said that baby is 6 weeks & 3 days old giving me EDD at 28 May 2015. I had my gestation age determination done on 7th Feb 2015 which said that the baby is 26 weeks 3 days old and my EDD will be 13th May 2015. Hence dont understand if i had a period on in August or it was due to implantation. If it was due to implantation then i actually conceived in 8, 9 or 10 th August ?? But one more question does gestation age acutally mean the time from when the egg is fertilized or the time from when the egg is actually implanted in the uterus?? More confused now :(


Gestation or gestational age is usually considered to be 40 weeks from the 1st day of the women's last period. This is almost 2 weeks before you'd ovulate. Remember too, due dates are approximate.

OK, I had used today's date when calculating your 2nd ultrasound. Using the date of your 2nd ultrasound I calculate an LMP of 6 August which matches your due date. In that case then yes, the 21/22 spotting may have been implantation bleeding. This all points to your boyfriend being the father.

It makes more sense now. A DNA test can confirm.

Hope it helps.