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Childbirth/conception date.


I went to my ultrasound on 7/29/13 the doctor told me my due date is 3/12/14. and that I'm 7 weeks and 5 days pregnant. I don't always have my periods around the same time. I'm not sure if that matters or not. I was told to count back 40 weeks. but when I do a conception calculator on the computer it says I conceived on 6/19/2013 that wouldn't make me 7 weeks and 5 days along. Please help, When did I conceive?

Counting back 40 weeks gives you the likely first day of your last period (if you have regular cycles).  Counting back 38 weeks gives you your likely conception date. Conception usually occurs two weeks after your period begins.

In your case, you most likely conceived on 6-19-13 which would have made you 7 weeks, 5 days pregnant on the 29th.

Pregnancy length is calculated as 40 weeks from the first day of your last period, not from the date you conceived.

The reason why the calculators seem to be off is because you're trying to calculate pregnancy length from conception which isn't correct.


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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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