QuestionQUESTION: Hi Sara,
I have a quick question regarding my first transvaginal ultrasound that I had
on October 27th. Basically it measured me at 8w1d with a CRL of 1.66
putting the due date at June 7th and date of conception at September 14th
I had a sexual encounter on September 5th (early morning of September 6th)
we used a condom. The first one broke right in the beginning of things when
he was not even close to ejaculation. He put a new one on and finished in that
(and I believed that he may have pulled out as well)
Thereafter, September 8th-the end of September I had unprotected sex with
my current boyfriend (with known dates of Sept 10, 11, 12 that we had
sex...this is known because we went on vacation). My question is, are
transvaginal ultrasounds pretty accurate in predicting the due date +/- days?
I have been doing a lot of research on crown rump length accuracy and
everything else, but I thought that I would ask you since you seem to be a
very reliable person when it comes to sonographs. I really just need to put my
mind at ease. I have even considered doing the prenatal paternity tests (CVS
and Amniocentesis), but I read that they are really not safe for the baby.
I'm almost positive that the first guy isn't the father since he did wear a
condom and I had a lot of unprotected sex after that, but I am just very
paranoid and I stress about everything.
I would really appreciate any response you may have
Thank you,
Christine
ANSWER: Hi Christine,
To have a tranvaginal ultrasound at 8 weeks 1 day would be considered very accurate for dating purposes. It depends on who you ask, but some doctors will say +/- 3 day difference and some will say +/- 3-5 days. In my experience, I would think a measurement at 8 weeks would be highly accurate to that day, since the baby is not really doing somersaults quite yet like we see at 12 weeks. At 8 weeks it is more a wiggling motion so less room for error.
Given your history, and the fact you know all your dates of sexual exposure, I would not worry because it seems highly unlikely you got pregnant from the Sept 5/6th encounter. The ultrasound would have to be off by about 8 days, which again would be extremely unlikely. In my opinion, I would not risk your baby for a prenatal paternity test because you are right, there is a risk of miscarriage with these procedures (a little higher risk with CVS), but those are options as well as after the baby is born (no risk) if you need to put your mind at 100% rest.
I would trust this; relax and enjoy the pregnancy!
Sincerely
Sara
---------- FOLLOW-UP ----------
QUESTION: Hi Sara,
Just wanted to ask you more more thing. I too have a feeling that it is pretty
accurate as well since I did have unprotected sex September 12, and 13th for
sure and I believe some days before that as well. I did want to ask you
though, do babies all tend to grow at the same rate up until a certain time? I
have heard that they do, but is that pretty accurate? Is an 8 week old fetus
quite a bit smaller than that of a 9 week old fetus?
AnswerHello,
Yes during the first trimester babies grow and develop at the same rate, unless there is a serious problem like a severe chromosomal defect, which is very uncommon. An 8 week fetus is smaller than a 9 week, etc. If I were to have separate images of a fetus from week 6 to week 12 I could tell just by looking at the picture what week the baby is in. They grow consistently until after the first trimester. In the second trimester there can be some variation, and in the third trimester there is even more room for variation in growth.
Hope this helps some!
