QUESTION: Hello...If my lmp at the time was on 11/16/10 and I went in for an transvaginal ultrasound on 1/10/11 which dated me at 7weeks 6days...Does that mean I conceived on 11/30/10? How accurate are transvaginal ultrasounds? Also what does it mean when your lmp matches an ultrasound in my situation?(My periods are very irregular does that change anything) Thank you

ANSWER: Transvaginal ultrasound are accurate to within +/- 3 days at most, and typically to within +/- 1 day.  If your ultrasound dated you at 7 weeks, 6 days on 1/10/11, then you most likely conceived on 11/30/10.  When your ultrasound matches your LMP, it just means that you happened to ovulate at day 14 of your cycle that month.  With irregular periods, LMP is not typically accurate for calculating due dates because ovulation varies from cycle to cycle.  Since your ultrasound confirms your dates, it is safe to say that you conceived on 11/30/10.

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QUESTION: Thank you for answering me so if I had one partner on 11/22/10 with the pull out method and another on 11/27/10 with no pull out method, would I still have conceived on 11/30/10 with the 11/27/10 encounter? Thank you

Yes.  Conception most often occurs from intercourse in the 2-3 days prior to ovulation.  It takes the sperm some time to reach the egg, so when intercourse occurs a couple of days before ovulation, the sperm have time to travel toward it before the egg is released.


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Catherine Beier MS CBE


I can provide evidence-based information and current research findings concerning childbirth and pregnancy. My specializations include natural childbirth, pregnancy and birth interventions, fetal positioning, labor induction, choosing a care provider, midwives, homebirth, unassisted birth, natural pain relief, medications in pregnancy and birth, informed consent, understanding the risks and benefits of childbirth choices, doulas, waterbirth, childbirth methods, childbirth education classes, cesarean section, and VBAC.


I have been a childbirth educator, mother, author, public speaker, researcher, and birth advocate for the past 9 years. I am also the author of, a site dedicated to natural childbirth and pregnancy information. I publish evidence-based articles on pregnancy, childbirth, newborn care, and post-partum care. I'm also a mother of three children, two daughters and one son all born naturally.

My book, Birth Outside the Box, was published in 2007.

I hold a Master's degree in communication disorders with an emphasis in child development. I am also an independent childbirth educator.

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