[Britishmum]

Any input on due dates welcome as I'm now thoroughly confused!

I miscarried my last baby at 14 weeks before Christmas. I have also been breastfeeding and tandem nursing for 4 years, so have had irregular cycles for some time.

So, after two seemingly normal periods starting 19th Feb and 13th March, I did a pregnancy test and got a positive. I went for what was supposed to be my ten week appt a few weeks ago and the midwife did an u/s (due to the previous loss as I was starting to stress) and thought the baby looked big for my dates.

So I went back yesterday for the technician to take a look, and he dated me not at the 13 weeks I'd thought, but at 18 1/2 !!

I can understand that what I thought was a normal period in March wasn't one, but the date he's given me means that I had to conceive around 24th - during the last days of my LMP.

I'm not too fussed about due dates, except that I have to plan dates for family to fly out from Europe to help out with my other children. Logically, it seems to me that he is overestimating the size of the baby (although he measured a ton of stuff it seemed) and my due date has to be a week or ten days later than November 16th if the first day of my LMP was 19th Feb. But the midwife seemed fairly sure that it was accurate.

Ideas anyone? Is it likely that he was that far out? Or does ebf mess up with your cycles enough that he could be right and I could have ovulated 5 days after the first day of my LMP.

Sorry if this is too much info or too confusing, but I have nobody much around here to help and can't imagine what I'll do if my family have gone home and I'm alone with two young children and a fast labour like last time .

 

[CarrieMF]

If you were still bleeding at the 5 days after your lmp I'd say no you weren't ovulating then.

With my last pregnancy we did a blood test 2 days after AF was late. It barely came up positive(25hcg). By that bt and when I know I O'd I was due March 30th. At my US at 18/19 weeks they estimated me to be due April 11th. At my 30week US they still said April 11th. At the 37week US they said April 18th. I never had a set edd my dr would not give me one. I was due between Mar 30th & April 11, just in case the bt was wrong(???) for the paperwork and testing he would put me down as April 11th. When she was born at what the US's said was 40 weeks(on April 10th) they realized that yes indeed she was 2 weeks overdue and I was due Mar 30th.

It is possible that for you the AF you had in Feb wasn't really an AF either. You may have O'd Feb 5th making you 18 weeks last week. If implantation was a few days later that would move you to 18 weeks this week.

 

[obnurse]

Just so you know, there is a HUGE difference on u/s of a 13 week fetus and 18 and 1/2... HUGE. People ovulate at all different times, 14 days into a cycle is a rough estimate... as is the ultrasound at this size for a due date. I wouldn't be so hung up on EXACTLY when you got pg... but you can be pretty sure that you are a heck of a lot closer to 18weeks rather than 13. Good luck!!

 

[doctorjen]

In the second trimester, ultrasound is considered to be accurate within 2 weeks plus or minus either way. Usually, the baby's measurements are compared to standard growth curves to give an estimated age. If all the measurements taken were within roughly the same range, this narrows the range of error a bit (For example, if the femur measured 14 weeks, and the head 19 weeks, you have a much wider range of error than if the femur measured 14 wks 3 days, and the head 14 wks 5 days.) The ultrasound tech might be able to give you your baby's measurements, and range of error for each.
Going with a standard plus or minus 2 weeks would give you an estimated time of conception from about Feb. 10 to March 9. This means your ovulation date could have been anywhere in there (with an LMP of Feb. 19, you'd guess ovulation was probably around March 4 roughly if you based it on a 28 day cycle.) Of course it's also possible that you ovulated more like second week of Feb., and that bleeding on Feb. 19 was actually implantation bleeding. Either way, you're probably much closer to 18 1/2 weeks than 13 weeks, but probably not exactly 18 1/2 weeks either.
Then of course throw in the fact that babies don't always pay attention to their "due dates" and you really have to do some guessing to estimate when to get family around. Mid November most likely? Plus maybe take into account how close to "due date" your other babies were born?
Gosh, after rereading I'm wondering is that helpful at all, or just more confusing?

 

[Britishmum]

Thanks all!!

It's useful to know there is a likelihood of plus or minus 2 weeks. I just know that the 18 1/2 is not really likely, it's either side of that. Once I throw into the mix that I've been two weeks late with both dds, then I really am just taking a gamble with when I have family come to help...

The main thing I"ve decided is to try to look at alternatives for help if I dont have anyone around when I actually do go into labour. That's my main concern, I've never bothered abuot due dates much before, but last time I had to do an emergency dash to the birthing centre leaving dds with my mum, so I need someone on call to get her quick if necessary.

Note to self - start being friendly and chatting to nice couple next door.....

 

[normajean]

Well there are a lot of different reasons you bleed during the month. Menstruation is only one of them. One or more of your "periods" may actually have been breakthrough bleeding (bleeding b/c all of the lining didn't slough off during your last period, and there's too much so it just falls off), or ovulatory bleeding. (Bleeding during ovulation.) Finally, many women still have a couple of "periods" after they find out they are pregnant. These periods are usually breakthrough bleeding.

If it were me, I would request another U/S after 20 weeks when fetal growth starts to be more predictable in speed, and before 28 weeks when meaurements are less accurate.

If they try to induce you based on a dd you aren't sure of, be sure they check the baby's lung development beforehand. My SIL was induced 2 weeks early b/c they thought her baby was going to be "too big" and she ended up with a 8.5 lb preemie who had to be in NICU b/c his lungs weren't ready.

 

[CarrieMF]

I agree with the checking lung maturity. I have a friend who's sil was induced at what they(the dr's) thought was 37 weeks because the baby was measuring too small. She was only 33weeks which is more what the sil thought. Baby's fine but those dr's really set themselves up for a major lawsuit.

 

[Britishmum]

Thanks! I hadnt thought about the induction issue.

I am very anti induction, which my midwife knows, and she didnt push it at all last time when I was 2 weeks overdue and had a 10lb 4oz baby. However, this makes me realise that I could easily (in their estimation) end up four weeks 'overdue', so I need to be prepared for this to become an issue. I was 2 weeks late with both my girls.

I will ask for another u/s in a few weeks. What's the most reliable window to get a more accurate date? I just feel that their estimation is off, by two weeks either side. But it's tough not knowing if I"m at 16 maybe or 20 weeks.

(But it does make me feel better about being into maternity clothes already LOL)

 

[doctorjen]

Actually, the most accurate time to use ultrsasound for dating purposes is in the first trimester. After that, the variations in normal fetal size get larger, so ultrasound becomes less and less accurate at dating the pregnancy as pregnancy progresses.

 

[Britishmum]

Doctorjen, you said "Of course it's also possible that you ovulated more like second week of Feb., and that bleeding on Feb. 19 was actually implantation bleeding."

This would make their estimation of 18 1/2 weeks more likely, but if the Feb bleeding was implantation, is it likely then that I'd have bled again for several days (normalish period length and timing for me at the moment) starting 13th March?

I know it's going to be guesswork at the moment, but I just want to get my head around how accurate or inaccurate this is likely to be.

 

[obnurse]

Just wanted to second the first trimester ultrasound post by doctorjen. The later you are the less accurate it is. Before 12 weeks, the growth of the baby is MUCH more predictable then after 12 weeks. Even by 18 some babies are bigger than others, throwing off dating. Good luck!

 

[doctorjen]

Again, just guessing, but it's possible that Feb. 19 is your lmp, and the bleeding in Mar. was implantation bleeding. Given that your babies tend to be big, that might fit. Sometimes, of course, people have bleeding in pregnancy that is never explained, so it's possible that's your case, too.
I don't know if you're going to be able to figure this one out for sure!

 

[Britishmum]

That makes most sense to me.........

I've decided that I need to get Thanksgiving week covered by family coming over, and then cultivate some friendships here so that I have people to call on if I dont have anyone here when I go into labour. Last time I had to dash to the birthing centre with the first contractions, so I need to know I have someone available for the girls if that happens again.

Of course, I could alter plans and go for a homebirth, but again, I'd need someone for the girls, and my house is small, so I can't work out how that would be easier. Althuogh it may well end up as a homebirth if things go as fast as last time and I have to call around for someone to come over for the kids......

Luckily my midwife is very respectful of my feelings about induction, but I will voice to her my doubts about their dates so that they don't get too hung up on their 'due date'. Given that I usually go to 42 weeks, this baby could end up being four or more weeks 'late' according to their calculations!