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When/how to date pregnancy??

491 Views 7 Replies 6 Participants Last post by  MaerynPearl
I'm nursing my 22m/o DS. Had two periods, 65 days apart. Found out on Wednesday that we're expecting #2!

I'm high risk. By the end of the pregnancy, knowing how far along I am will most definitely matter. It's highly likely that I will be on bedrest. There's a possibility I will have medical indications for induction - I know my OB will want to induce me at 38 weeks (he's said as much for high risk pregnancies - but this is better to me than the alternative OBs, as I'm comfortable saying no to an induction if I don't feel it's necessary). So, knowing how far along I am and what to expect, and balancing risks and benefits along the way will be important!

Anyway, I have no idea how far along I am. Well, I guess I have some idea. I've been tracking CM, but I don't think it was "accurate" because of nursing. I tracked when we had sex and when I tested (which has been at least weekly recently, but there's the possibility of a false negative, right?).

I have my first OB appointment (and this is not the OB that followed me for my first pregnancy) on Wednesday. I *think* I will be 5-6 weeks pregnant.

An u/s would be the best way to date the pregnancy, right? And would 5-6 weeks be a good time to do it?

Would anyone like to take a look at my chart and help me make sure my guesstimate of 4-5 weeks currently is accurate???

My current biggest fear is that we'll get to 37 weeks and things will be as crazy as they were in my first pregnancy, plus a toddler, plus some straw that broke the camel's back, and we'll be thinking induction. With DS, we couldn't do an amnio to check his lungs because of location of the placenta. Things calmed down and I was able to forego the induction and go into labor spontaneously...but if that's not the case with baby #2, I want to be sure we're not inducing at more like 35 weeks or something when we think I'm 37+.
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I'd be happy to double check your chart for you, but honestly, I wouldn't worry too much about it. If you're only about 6 weeks along, the U/S would only be off by a day or 2 either way, not anywhere close to 14 days.
If you have one at 5-6 weeks just be sure not to freak out by not finding a heartbeat. It is often too early in the 5th week and is not found until sometime in the 6th week. Likely, if they do not find one they will have you come in for another ultrasound to check progression.
I would get your dating u/s when you are 7-8 weeks (or when you think you are 7-8 weeks) it's the easiest to date then between 7-9 weeks as you can generally see a baby and heartbeat then and it's still early enough that it is pretty accurate. And then your doc isn't freaking you out if there isn't a heartbeat (at 5-6 weeks it can still be too early as that is right around when the heart starts beating).
If I am ok with not seeing a heartbeat, do you think it would be better to go ahead and get an ultrasound next week to date the pg? (I'll be 5-6 weeks and I think even if I got two false negatives I would be 7 weeks...)

My chart is here:

If it matters for sensitivity or error, I was using said they had 20 mIU/ml Sensitivity and a 99% accuracy rate. And that I could "test any time of day," but I generally tried to use FMU.

Thanks for the input!
If you have an appointment already, I don't see any reason to wait for the US. I got dated at 5 weeks (when I though I was 6w4d by LMP), and the US basically just showed a little DOT, so I wasn't freaked out, because there wasn't anything to really SEE that early, however, I think the measurements are pretty darn accurate early, so I figure the earlier, the more accurate.
My understanding is that dating ultrasounds are most accurate between 7 and 9 weeks because it is still very early, but the baby is big enough to actually measure crown to rump length, which can't really be measured well before that. The ultrasounds are most accurate for dating when crown to rump length can be measured.

From this website:

"The accuracy of ultrasound for dating a pregnancy depends on at what point during the pregnancy the ultrasound is taken. Pregnancy dating is most accurate during the first eighteen weeks of pregnancy. Measurement of the sac at five to seven weeks is not accurate. Measuring the crown-rump length gives an accuracy of plus or minus three days at seven weeks; this test can be used from the seventh to the fourteenth week. Between fourteen and twenty-six weeks, measurements of the biparietal diameter, the femur length and abdominal circumference are generally used. The accuracy is plus or minus seven to ten days. The accuracy further declines with advancing gestation age."
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Originally Posted by freistms View Post
My understanding is that dating ultrasounds are most accurate between 7 and 9 weeks because it is still very early, but the baby is big enough to actually measure crown to rump length, which can't really be measured well before that.
According to my U/S tech with DD its even better if you go in around 5 weeks and do not find a heartbeat then go in for a follow up... find a heartbeat AND are able to measure... that way you have a much closer idea of just how far along you are.
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