pregnancy dating / u/s questions - Mothering Forums

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#1 of 11 Old 08-11-2006, 12:32 PM - Thread Starter
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I've got a couple related questions.... The first is re: gestational vs. fetal age... I know one of them starts from the first date of your last period, and the other starts from ovulation (gestational, fetal?). I also know that the number of weeks you are is the one that starts from your lmp, which is generally assumed to be two weeks before you ovulate. The thing is, I ovulated a week later (cd20). So according to the midwife, I am 6 weeks today based on my lmp date of 6/30. But it seems like actually I'm only just over 5 weeks, based on when I ovulated. Does that make sense to anyone??

The other question is about having an u/s to figure out how far along I really am. I have one scheduled for the 29th (which, according to the midwife would be my 9th week). I also have a follow up appointment for next Tuesday (8/15) to make sure the BV I had is all gone. What I'm wondering, and would really love, is if I could move the u/s up to the appt. on the 15th. Does anyone know if there is a minimum number of weeks that you have to be before they can date the baby with the u/s? I'd like to move it up partly for my peace of mind, and partly because dh could go to the sooner appt. and not the later, and if there's a chance that we could see the heart beating, I know he wouldn't want to miss it.

I hope this has made some sense &
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#2 of 11 Old 08-11-2006, 12:41 PM
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I can't remember, but you can call your doctor's office, and they can tell you right away.
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#3 of 11 Old 08-11-2006, 02:43 PM
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I'm not sure when the soonest is, but I was in a similar situation as you my last pregnancy. I ususally ovulate on CD23, not 14 like most people. The doctors had my due date set a week earlier than I knew it should be. I had to have an ultrasound at 7 weeks, because of spotting. It was early enough at that time to date, and since I was showing to be exactly a week behind they did go ahead and put my due date back a week.
As for the difference between gestational and fetal age...fetal age is the age from conception, gestational is the age from your LMP. So the fetal age will always be 2 (or 3 in my case) weeks behind the gestational. For example I'm considered 6 weeks right now, however the actual fetal age in only 4 weeks...does that make sense?
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#4 of 11 Old 08-11-2006, 02:50 PM
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Your u/s should show how many "real" weeks you are. My periods are so crazy that I can't ever go by my LMP.

The heart is beating at 4 weeks fetal age (from conception), so will be cutting it kinda close if you do the u/s in a couple of days. Is there any way that you could just reschedule it for another day that your dh could go?
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#5 of 11 Old 08-11-2006, 02:59 PM
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I just had an u/s today at 6w6d (from lmp - I O on day 15, so close enough) and the fetal age is considered ~5 weeks. I saw the heartbeat! It was so cool - just a little white blip on the screen. I went last week for an u/s at 5w5d, and all we saw was the gestatinal sac. My OB told me that he dosn't usually see much on u/s before 6.5 weeks, but he isn't a technition, so he doesn't do dating either.
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#6 of 11 Old 08-11-2006, 05:00 PM
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Yep, it makes perfect sense. On the cycle I conceived, I ovulated on Day 21, not Day 14, so I know I am five weeks pregnant not six like caregivers calculate. They come up with the gestational age by counting the days from your last period, which is only right if you have a perfect 28 day cycle and ovulate on Day 14.

I've been charting extensively and showed the OB/Gyn I visited my charts which included BBT, LH test strips, cervical mucus, intercourse dates and other information. I knew I ovulated on Day 21 but they didn't seem to give credence to my charts. After over two years of infertility, if I didn't know how to chart and know exactly when I was ovulating I wouldn't be pregnant.

As for ultrasound dating, I have read that they can tell within 5-7 days at around 8-9 weeks.

If you know when you ovulated and have charts, try convincing them... but be warned, many stick to the "conventional" dating methods. What sucks about it is that it could mean they want to induce you early because they think you are farther along than you really are. Hopefully an early ultrasound will clear that up. The birthing center that I am considering going to doesn't do an early ultrasound, but I hope they will listen to me when I tell them how far along I am.

Me (37) ~ DH (39) ~ DS (3) ~ TTC #2 since 4/10
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#7 of 11 Old 08-12-2006, 02:53 AM
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Im seriously considering lying about my last cycle just for this reason. I do NOT want to be pressured to induce because Im a week late by thier calender when I know Im not late, just on time! I can just tell them the first day of my lmc was ten days later than it was. What do you think?

~Me, mama to soapbox boy (1991), photo girl (1997), gadget girl (2003), jungle boy (2005), fan boy (2003) and twirly girl (2011). Twenty years of tree hugging, breastfeeding, cosleeping, unschooling, craziness
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#8 of 11 Old 08-12-2006, 09:39 AM
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Speaking of gestational and fetal age, when people (authors in books, MDCers who say which week they're in, etc...) say a certain week during pregnancy, are they more often than not talking about the gestational age?

I ask, b/c I've read in certain books that weeks 5-10 are the absolutely most crucial in a woman's pregnancy b/c that's when all the major organs are formed. I'm almost 6 weeks pregnant (gestational)....(I'm at ~26 DPO) and I'm curious as to if it's now that all the major organs are being formed...or if it's not for another 2 weeks or so.

Anyone know?
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#9 of 11 Old 08-12-2006, 10:51 AM
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Most books go by gestational age, so it should be now for you. I have a really good book called What To Expect When You're Expecting. It's nice because it give you both gestational and fetal age.
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#10 of 11 Old 08-12-2006, 01:32 PM
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I'm in the same exact situation. Even down to ovulating on cd 20! My lmp was 7/10 (maybe 7/11), but I ovulated on 7/30. So the charts say my due date is 4/17, but the baby is a week behind. I am going to tell my midwife to put my dd at 4/24 for that reason.

With my last baby, I have about 5 different due dates! I had my homebirth midwife, who I delivered with, but early on thought I might go with a midwife practice for financial reasons, and they changed the date from my lmp after I had an early u/s, then I had my own from dates, etc. and the baby was born on that very day that I calculated! Not that its an exact science or anything, but it was validating to prove to everyone that didn't listen to me, that I did know what I was talking about!
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#11 of 11 Old 08-13-2006, 07:24 PM
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I have thought about changing my dates before but you have to be careful. If you change it to much or plan on having ultrasounds than having your dates different from the tests can single a problem. Then you are stuck having lots of extra tests or being risked out of a homebirth because you dates don't match.

So it really just matters on your provider and how far you need to fudge your dates
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