Due date pushed back a week? What?

[Anonymous]

Newly pregnant again and saw my OB today. I thought my math was correct regarding my due date. I mean, I know when I had sex, so how can I be more than a week off? I thought I was due December 6 but the u/s tech says I'm due December 15. I don't get it. Can someone explain this to me?

[Anonymous]

They are basing their date on the measurements / size of the embryo (if it's X mm long, that translates to a certain gestational age which you use to deduce due date). I'm assuming they also probably pulled out one of those wheels that says "if your date of last menstrual is X, you're due Y". Hopefully they lead to about the same date.

Just because you had sex on a specific day doesn't mean you conceived that day. You can conceive up to 5-7 days after sex (because the sperm can linger that long).

The due date doesnt mean much of anything except when you get to 24 weeks (fetus is considered viable at that point, just in case you go into early labor) and 42 weeks when most doctors will induce if you havent gone into labor.

[Anonymous]

A later due date is not necessarily a bad thing. I actually pushed for a later due date my second pregnancy because I didn't want any chance of my due date being too early and having induction recommended before I was really 42 or more weeks.

My understanding is that those ultrasounds can be off by 3-5 days, even early on. So it's possible that your "real" due date is sometime between the due date you calculated based on the day you had sex, and the date calculated on the U/S.

[Anonymous]

According to my OB and the radiologist, the early sonograms are actually the most accurate due date predictors. I had a few sonograms during my first trimester and each one measured five days earlier than what I had calculated. As a result, my OB bumped my due date up.

[Anonymous]

Anonymous wrote:According to my OB and the radiologist, the early sonograms are actually the most accurate due date predictors. I had a few sonograms during my first trimester and each one measured five days earlier than what I had calculated. As a result, my OB bumped my due date up.

This is my understanding as well. Which is why most OBs won't change your due date based on later sonograms (I guess some still do though). If your 6 -7 week "dating/viability" scan shows your fetus a week younger than you expected, then chances are, you just ovulated late or something. I also agree that - while hard in some ways - having a later due date (that is more accurate) is a good thing, especially if you don't want to be induced...

[Anonymous]

Also, the day you had sex may not be the same day you ovulated. Sperm can live in the body for quite some time. I got pregnant 4 days after we had sex and was very surprised to learn that we had indeed gotten pregnant... so was hubby. My first OB appointment, the sono was 5 days after I thought the due date was, then at my 12 week sono, it was exactly where I thought it should be based on my ovulation.

[Anonymous]

OP, for both my pregnancies, the OB has moved my due date back. The first time it was a week. For my current pregnancy, it was almost two weeks. I actually prefer the later due date because it lowers the chances of an induction. The only thing it really affects is genetic testing. Otherwise, I believe there is a range of measurements that are considered "normal" for any particular week in a pregnancy.

Oh, and baby #1 came 15 days early. So much for moving the due date a week later!

[Anonymous]

According to my OB and the radiologist, the early sonograms are actually the most accurate due date predictors.

This is correct. Early on, the embryo develops rapidly with certain features appearing within pretty specific time frames, so that is the most accurate time to date the pregnancy, based on what is visualized on the ultrasound and the measurements. So, for instance, it would be much easier (for someone who knows what they're looking at) to distinguish a 5-week embryo from a 6-week embryo than it would be to try to distinguish a 28-wk fetus from a 29-wk fetus.

Also, while the sperm *can* live up to 5 days (I have never heard 7 days), that is under "ideal" circumstances and is not all that common; most of them live for 2-3 days. The majority of pregnancies are the result of sex within about 2-3 days before ovulation and the day of ovulation. If you happen to know exactly when you ovulated, that would be more accurate for you as the egg only lives a maximum of 24 hrs (most begin degrading about 12 hrs after ovulation), so the egg must be fertilized within that 24 hr window or pregnancy won't occur. You're more likely to get pregnant from having sex BEFORE ovulation rather than the same day as ovulation, so it's probably safe to assume you got pregnant at least a day after the day you had sex, and very possibly a couple of days after.

[Anonymous]

And at the end of the day, remember that a full-term pregnancy is anywhere from 38-42 weeks. So unless the date your OB gives you is WAY off from what you thought, it's all still in the window.

I knew when we had sex (aka conceived), but I don't have a standard 28 day cycle. The OB actually moved my due date up about 3 days. And I then delivered 14 days late, with a very average sized baby, who would have been quite small had she been born on the OB's due date.

[Anonymous]

What timing of this post! I just had this happen to me TODAY! Like you, OP, I knew exactly what days we could have possibily conceived (ie, when we had sex) and figured out my due date accordingly (rather than using the first day of my last period as the indicator). So I was very surprised when my OB just gave me a due date of an entire week later than what I thought. As she explained to me, the day we had intercourse is not necessarily the day we "conceived" - she said it can be several days, up to 5 days, later in fact. News to me! Anyway, just wanted to share because I got the same shock today as you did. I'm happy though... the later the better in my opinion. I don't want to be induced!

[Anonymous]

My situation is a little different. My OB actually moved the date UP from when I thought it would be. I was faithfully charting, so I know exactly when we had sex and when I ovulated (based on temp rise) so I am pretty flummoxed as to how I could be about a week farther along than I expected. Is it possible to just have a faster-growing fetus? Or is my chart misleading me? I really wouldn't care all that much, except with an earlier due date I'm afraid I'll be urged to induce if I go way past. Especially considering I'm due a week before Christmas...

[Anonymous]

was this your 1st ultrasound for this pregnancy? was there a reason for it at ~12 weeks?

Early ultrasounds are most accurate for dating. My dr sent me for a ultrasound to confirm dating as I was measuring off from the "scientific" 1st day of my LMP which was not a surprise to me as my cycles were irregular. When I went for my ultrasound they moved my EDD a little more than a week. I am greatful they did this as I would not want to get late into pregnancy and them being concerned / wanting to induce if I was going past an incorrect due date.

[Anonymous]

12:35 here. This was my first ultrasound. Based on LMP I would have been 7w5d. Measurements put me at 8w3d. Based on my chart, I ovulated on day 13 or 14, so it just seems odd.

[Anonymous]

My midwife and I worked together to come up with the latest possible due date. This was important to me because I wanted to avoid induction. I appreciated that my midwife was willing to work with me and consider all the evidence (my own knowledge of my cycle, early ultrasounds, date of last period, etc.). I trusted my own information and knowledge just as much as I trusted an early ultrasound and appreciated that she did too. It felt good to come up with a due date together that we both felt was feasible and reasonable. In the end, as others have mentioned, it's just an estimate, but it does sometimes have important implications for one's care, so I think it's important to be thoughtful about making sure it is as accurate as possible. I didn't feel as stressed about it this time because my midwife seemed comfortable with my pregnancy continuing to 42 weeks or even a bit further, but with my first pregnancy, I felt much more frustrated that the date seemed too early and was worried about unnecessary induction.

[Anonymous]

New poster here. I got an u/s and measured 8 weeks, 6 days; I thought I was 2 days later than that -- 8 weeks, 4 days, based on OPKs. I wonder if I caught the tail end of the OPK.

Also -- is it possible that if an embryo implants faster (since there's a range of implantation time), it can grow faster???