QuestionQUESTION: I am trying to figure out whose child I am carrying. My LMP was on or around December 12, 2010, give or take. On December 18 & 28 of 2010, and also January 1, 2011 I was with partner #1. I took a pregnancy test on January 11 that came back negative. January 12 I slept with partner #2. I took another pregnancy test on January 15, which came up positive. On February 24 My first ultrasound said I was approximately 10w2d, two days less than what my LMP indicated, which was 10w4d. My question is, what are the chances of my pregnancy being with partner #1? Chances with partner #2? If I were pregnant by partner #1, would it not have shown up yet with the first pregnancy test taken on Jan 10? And also, how much of a window of error is there on an ultrasound done at this point in pregnancy? I realize the ultrasound would suggest partner #1, but can it be off by enough to allow the baby to be with partner #2? I know with these circumstances, a paternity test may be the only way to know for sure. I would just like your expert opinion on who you think is most likely the father. Any help is greatly appreciated. Thank you for your time!
ANSWER: Dear Callie,
A woman is generally fertile around 12-16 days before she expects her next period to start +/- 2 days. So, if you normally have 30 day cycles, you would be able to conceive on days 14-18, with the first day of your period being day one.
With your dates, you were certainly fertile on December 27-30, and more likely from December 25-January 2. So you most likely conceived during those days.
Since you were already near the end of your cycle on January 12, it is very unlikely that that is when you conceived.
On January 11, it was probably still too early for a positive result from the pregnancy test, but since the HCG levels rise very rapidly during the first month of pregnancy (HCG (Human chorionic gonadotropin) is the hormone that the home pregnancy tests look for) it was already positive on the 15th.
It wouldn't be possible for a pregnancy test to come back positive from a pregnancy that started 3 days before, so that is another reason that it's very unlikely that conception occurred on the 12th.
So to answer your questions in order:
It is probable that you are pregnant from partner #1.
It is very unlikely that your are pregnant from partner #2.
The first test on the 10th or 11th would not show up positive, only because it was still too early.
There is a small margin of error in early ultrasounds, but not enough that partner #2 would be the father.
That relationship happened too long after ovulation (release of an egg to the uterus) for you to have conceived then.
If your cycles are very long - around 40 days or so - the answer could be different. If so, I would suggest a paternity test to be sure.
I wish you the best of luck, and feel free to ask any other questions you may have about pregnancy.
Have a great day,
Sheva
---------- FOLLOW-UP ----------
QUESTION: Okay, so I just had another ultrasound yesterday, April 19th, which said I was 17w5d, which is slightly less than my ultrasound in February would indicate. I'm assuming that's normal as the pregnancy progresses for the dates to not match up exactly each time an ultrasound is done, and probably doesn't matter much. I guess my question now is: With the estimated gestation that I was given in February based on the ultrasound, and the one yesterday being relatively consistent with that date, and the fact that I got a positive on my pregnancy test 3 days after the act with partner #2, is it safe to say it's partner #1's baby? I know you said you were pretty certain it was his, but I wasn't sure if that's something that I can be positive of based on this information or not? Are there times in these situations that you can definitely rule out one of the men without a paternity test, or is that something that I'll have to do to know for sure in my case? Sorry to ask basically the same question as I did the first time. I just wasn't sure if it's something I should be able to be confident with (in assuming it's partner #1) or if I will need the paternity test. Thanks in advance, and thanks again for your speedy, informative reply last time!
AnswerDear Callie,
I still think, based on the previous calculations and the new ones, that partner #1 is the father.
However, if something important is riding on the knowledge one way or another, it would be a good idea to have a test done, if possible, to establish paternity 100%.
Good luck, and I hope everything goes well with your pregnancy,
Sheva
