Longer cycles = wrong due date? - Mothering Forums

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#1 of 18 Old 04-28-2007, 11:15 AM - Thread Starter
 
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I've been wondering this for awhile. Most medical professionals I talk to say "It doesn't really matter", but I don't know if I believe that.

If they calculate your due date based on a 28 day cycle, and you actually have a longer cycle, say 35 days, shouldn't your due date be a week later?

And if you had a longer cycle, and they gave you a due date based on a 28 day cycle, would you measure correctly?

Based on cycle length, my due date should be May 12th, not the 5th, but I am measuring to dates for May 5th, and have throughout the entire pregnancy.
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#2 of 18 Old 04-28-2007, 11:31 AM
 
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yeah, probably if you have longer cycles, you ovulate later (than day 14) and thus got pregnant later in your cycle, an are due later than if you had 28 day cycles, with ovulation on cd14..

as for measuring, it is not an exact science. i always measure bigger than how many weeks i am pregnant, especially in the late 2nd and into the 3rd trimester.

i would really advise going by a due date based on your ovulation rather than your last period, both for your own peace of mind and to avoid an unnecessary induction.

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#3 of 18 Old 04-28-2007, 12:05 PM
 
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i would really advise going by a due date based on your ovulation rather than your last period, both for your own peace of mind and to avoid an unnecessary induction.
Yes, the wheel they use in the office uses the first day of your last menstrual period. This assumes that you ovulate around day 14. For me the wheel is pretty accurate even though I have short cycles I do ovulate around day 14. But, if you don't ovulate on or around day 14 then it will be inaccurate.

I chart and I know a very accurate way to calculate your dd is to take the date of the first high temp, go back 7 days and then add 9 months. So for me, my first high temp was Sept 8, I go back 7 days to Sept 1 and then ahead 9 months to get a dd of June 1. If you know the day you ovulate (or the approximate date) you could do the same trick (minus 7 days plus 9 months) and then get a more accurate due date.

The wheel really drives me nuts, even though for me it has been basically right on with both pregnancies. The drs take it as gospel when they should know better.

hth,

Beth

Beth wife to Tom and mommy to Therese 11/4/04 Anna Mary 6/15/07 and Veronica 10/20/09
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#4 of 18 Old 04-28-2007, 12:48 PM
 
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yep i also had funky cycles when i got pregnant with this baby.....that's why i took the day i ovulated on, counted back 14 days and told my OB that was the day of my last period.....so their stupid wheel would give them the correct date and i saved myself a heated discussion!
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#5 of 18 Old 04-28-2007, 12:56 PM
 
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my due date keeps getting changed on me because of this. if i'd had a 28 day cycle i would be due july 24, but i didn't have a 28 day cycle. i concieved sometime after my first postpartum af, so i have no idea when i ovulated, just a strong feeling that it was definitley more than a 28 day cycle. they've set my due date by the baby's size, so it's now august 6, but that's impossible because dh was away that week... :
my midwife is very cool and says that if the baby comes early or late she'll change the due date on the way to the hospital so that i'm not classified as preemie or overdue and taken out of her care.
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#6 of 18 Old 04-28-2007, 01:06 PM
 
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This is the first baby I was adamant about my long cycles with. All 3 of my boys were "past dates" and induced. Sure enough when I had my first ultrasound at 7 weeks MY dates were on and their little spinner chart was off by almost 2 weeks. I had another ultrasound at 20 weeks and they bumped the date up to the 20th from the 23rd, I told my new doc I'm sticking with the 23rd and he's cool with it. So yes your cycle length very much can effect your due date.

Nic, loving mama to 5 with a SURPRISE 6th on the way.

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#7 of 18 Old 04-28-2007, 02:33 PM
 
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Originally Posted by Emma's_Mommy View Post
yep i also had funky cycles when i got pregnant with this baby.....that's why i took the day i ovulated on, counted back 14 days and told my OB that was the day of my last period.....so their stupid wheel would give them the correct date and i saved myself a heated discussion!


That's what I do for my doctor. It's not worth telling the truth on this little thing and getting the wrong date set in stone.

It's so sad that so many professionals think that women have no idea what is up with their bodies. I've had a doctor tell me there is no way I could know I was ovulating (he had no idea what fertility awareness was).

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#8 of 18 Old 04-28-2007, 03:29 PM
 
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Yeah if I were using an OB I'd lie about my LMP as well. I ovulated on day 26 when I conceived this baby (which actually is early for me...I have super long cycles!).

Since I'm homebirthing with mw's I trusted that they would truly understand a woman's cycles and charting so I told the truth. I gave them a copy of my chart and they totally understand they can't use their wheel accurately.

If I didn't know exactly when I conceived but knew I had long cycles I would just go into the doc and say I just couldn't remember my LMP date at all so that they would date only by early u/s which is going to be more accurate.

Rachel, mom to Jake (5/04) and Alexia (7/07) a surprise UC thanks to hypnobabies!
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#9 of 18 Old 04-28-2007, 03:53 PM
 
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I like how they say it "doesn't really matter" but then, when one goes a week or two past the LMP due date, you better believe it matters.

I have long cycles, about 36 days. With both pregnancies, I've had very supportive doctors and midwives, and we adjusted the due date based on my charting. My dd was born 5 days after my adjusted due date, so she would have been more than 2 weeks over if we hadn't done that. That would have involved a lot more testing, and maybe meant a hospital birth rather than home.
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#10 of 18 Old 04-28-2007, 06:44 PM
 
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yes, it does matter, yes you should adjust it, and uyes, the whole thing is ridiculous.
There is NO WAY to know how long any one specific pregnancy is SUPPOSED to last. Period. If you have a significant personal or family birthing history which has a certain trend, that is one trhing to go off of. 40 weeks is a guess, an estimate, an approximation.......there is absolutely NO EVIDENCE whatsoever that a pregnancyt SHOULD last 40 weeks, or that a 40 week pregnancy is better, healthier, etc.

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#11 of 18 Old 04-29-2007, 11:58 AM
 
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Obviously the most accurate way is to go by ovulation. If you don't know ovualation, and have cycles iwth varying lenghts..then an early u/s is the most accurate.

Just going on cycles length isn't really accurate, because cycle length changes at any time. You can have a 35 day cycles for months and months..and then suddenly have a 28 day cycle.

Plus, I read somewhere that you are more likely to concieve and have a viable prengancy with an earlier ovulation date (ie. day 14 instead of day 21, becaues the "older" the egg is before it is released, the more likely there are to be mutations or abnormalities, etc. So, it is quite possible that you got pregnant on the month you ovulated on day 14 instead of day 21 and if you hadn't gotten prengant you WOULD have had a 28 day cycles.

Plus, if there were other changes around the time of you last cycle, ie less stress, more stress, change in daylight (ie. daylight savings time, move to a new time zone,), you started taking vitamins or herbal supplaments, dietary changes, etc. ..those things can all affect ovulation date.

For months and months and months I ovulated EXACTLY on day 14...textbook..then 2 months ago, it was day 13 ( I believe that was because I started taking vitex that cycle and also daylight savings time occured) , and last O it was day 11. Not quite sure why the change...other than that I started supplamenting with b6 that cycle

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#12 of 18 Old 04-29-2007, 12:13 PM
 
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Quote:
Originally Posted by Emma's_Mommy View Post
yep i also had funky cycles when i got pregnant with this baby.....that's why i took the day i ovulated on, counted back 14 days and told my OB that was the day of my last period.....so their stupid wheel would give them the correct date and i saved myself a heated discussion!
Me too.

I ovulate on day 21-23, & I chart so I know when I got pg. I just lie about the lmp being 14 days before I O'd.

North Idaho rural living  mama to: 23 yo DD, 16 yo DS, 8 yo DS, 6 yo DS, 4 yr old DS, 2 yo DD, and 1 yo DS. And someone new coming this Christmas!
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#13 of 18 Old 04-29-2007, 12:56 PM
 
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When I got pg, my body was still normalizing itself after coming off BC pills 4 months earlier. So I didn't ovulate until day 41(!) of my cycle. I knew for sure because I was charting. This would have really messed up my due date if I had used my LMP date. My CNM had me get an u/s done at 11 weeks to comfirm my dates, and I was right! It felt so good to be right! So, yes, it totally makes a difference!

Wife to J. Mama to DD(3yo) & DS(1yo)
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#14 of 18 Old 04-29-2007, 03:02 PM
 
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My OB has always listened to me on what I thought my due date was since I chart. This little guy though I did actually ovulate on day 14, so that made it easier than the first 2 pregnancies. If she didn't, I'd probably adjust my LMP to not have to deal with it, but she does thankfully.

Mom to a 6 year old, a 3 year old, and a cuddly little newborn
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#15 of 18 Old 04-29-2007, 06:04 PM
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I was wondering the same thing. I usually have 35-40+ day cycles. I have no idea when I was ovulating and we were very surprised by the pregnancy (an awesome surprise!).

**here's what my midwife said***

I had an ultrasound at 14 weeks, and 20 weeks. I asked my midwife if there's any chance I could be due on a different date than the wheel and she said no because at 14 weeks, the baby's measurements are pretty accurate. She said at the 20 week you'll see more variation in size of babies, but at 14 weeks, I measured 14 weeks and she said that's what it is. Now, I know when I first saw her last month she said I measure small for how far along I am..

Going to see her tomorrow, so now I'm really curious.
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#16 of 18 Old 04-29-2007, 06:42 PM
 
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I also have super long menstrual cycles (40 days or more), but my ob-gyn was more than willing to listen to me when I told her that I charted, and around what time I *really* ovulated (more like 20 days past my last menstrual period than 14). So we first calculated a due date based on the 28 day cycle (lmp due date), and then calculated a due date based on the propable date of conception. When I had my first ultrasound, the baby measured spot on for the date of conception due date. And I felt briefly like a charting genius.

I'm really surprised that people have to lie to their OB to get them to agree to a more accurate due date...are most ob-gyns really that obtuse?!
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#17 of 18 Old 04-29-2007, 07:06 PM
 
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My cycle has no relation to my due date. I was 8 weeks when I first found out, according to the ultrasound my ob did a few weeks later. That is 20 days later than my cycle says I am. My ob is going by the 8 week us. Even though later USs show a baby a week above that count- I have big babies!

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#18 of 18 Old 04-29-2007, 09:22 PM
 
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I tend to have long cycles when I'm not on the pill, but I ovulate EARLY. I know this because the only time I could possibly have gotten pregnant was on about the 8th day after the beginning of my LMP - just a couple days after my period ended. Since I wasn't entirely sure about my LMP, they dated with an ultrasound and gave me a supposed LMP which is at least a week earlier than the real one.

This would also explain why my son was 7 lb 15 oz, with a full head of hair, long nails, and a good suck reflex, when he was born 2 1/2 weeks early.
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