Is the ultrasound more accurate than due date calculator?

Kymbirleigh · January 2011

The first day of my last period was Sept. 11... Going by all the due date calculators, my due date should be around June 18.... But my ultrasound shows that I'm about a week behind that (I know it isn't much difference...). I'm just wondering which is more accurate, the ultrasound or an ovulation chart and due date calculator???

In the past I've never really had a normal cycle without the assistance of birth control. And I'm wondering if when we conceived if I had slid back into my old abnormal cycles... Otherwise, I really just can't figure out how my conception date is three weeks after my period.... Anyone else have abnormal cycles with similar issues?

normajeane6126 · January 2011

Unless you were charting and know exactly when you ovulated, u/s is MUCH more accurate than a random online due date calculator.

Lisa Frank · January 2011

Early ultrasounds are always the most accurate at dating a pregnancy.

Sounds like you ovulated a little late, which isn't really that "abnormal."

deskok · January 2011

The ultrasound is more accurate then the ovulation chart. I have a longer cycle then most. So my due date was supposed to be on June 12th, but the ultrasound showed that I am due on the 20th. So every woman ovulates differently, and not many give birth on their due date anyways.

Tomkat8403 · January 2011

An u/s measures the embryo, uterine lining thickness, sac...all of that...to jusde the age of the embryo.

Online due date calculators are just a shot in the dark based on a normal 28 day cycle.

So yes, an ultrasound is about 1,000 more accurate. Unless of course you were charting and KNOW your ovulation date. if they were mismatched in that case, then an ultrasound measuring the baby behind might indicate a problem.

Kymbirleigh · January 2011

Thanks everyone! I feel much more confident now knowing that the ultrasound is more accurate. I was charting, and I kept noticing my period was slipping later and later than what it should have been... And while Iw as charting, I just had it based on the average 28 day cycle, which for all I know, mine is actually longer (which seems to be the case) So I believe I was sliding back into my old habits when we conceived!

kimbo1216 · January 2011

I COMPLETELY understand what you are feeling. You are lucky though. They only pushed you back a week. I was pushed back 2 weeks. According to my period, my due date should be May 23. So when I went in for my first sonogram at 9 weeks, I was told I only measured at 7 weeks. This was devastating to my mindset (which NO ONE understood why). I thought I was only 3 weeks away from that glorious 2nd trimester marker, instead I was 5. It was tough wrapping my mind around that.

What was even more frustrating was that when I went for my NT screening at 12 weeks, I measured at 13 weeks. Furthermore, according to when I think we actually conceived, I think my due date is May 27th. They refuse to change it from June 7th. So, I have convinced myself I will deliver early.

All you can do is try not to worry, just relax, and go with it. They baby will come when the baby is ready no matter what due date they give us.

rrcraz7 · January 2011

Unless you were charting and know exactly when you ovulated then the u/s is more accurate. Ultrasounds can be +/- 5 or so days though. It's hard to get an accurate head to rump measurement because of how they can curl up and stretch out.

For me, if going by last period I'd be due March 20th. I'm really due April 12. Id go by what the u/s said.

rrcraz7 · January 2011

Kymbirleigh:

Thanks everyone! I feel much more confident now knowing that the ultrasound is more accurate. I was charting, and I kept noticing my period was slipping later and later than what it should have been... And while Iw as charting, I just had it based on the average 28 day cycle, which for all I know, mine is actually longer (which seems to be the case) So I believe I was sliding back into my old habits when we conceived!

Just an FYI, by charting they do not mean counting the days of your cycle and keeping track each month. Charting means taking your basal body temp every morning and charting it to see a temp shift, which will tell you what day you ovulated.

spokenfor1583 · January 2011

I would definitely go based off of the u/s because that is more than likely bound to be the most accurate.

Kymbirleigh · January 2011

kimbo1216:
I COMPLETELY understand what you are feeling. You are lucky though. They only pushed you back a week. I was pushed back 2 weeks. According to my period, my due date should be May 23. So when I went in for my first sonogram at 9 weeks, I was told I only measured at 7 weeks. This was devastating to my mindset (which NO ONE understood why). I thought I was only 3 weeks away from that glorious 2nd trimester marker, instead I was 5. It was tough wrapping my mind around that.
What was even more frustrating was that when I went for my NT screening at 12 weeks, I measured at 13 weeks. Furthermore, according to when I think we actually conceived, I think my due date is May 27th. They refuse to change it from June 7th. So, I have convinced myself I will deliver early.
All you can do is try not to worry, just relax, and go with it. They baby will come when the baby is ready no matter what due date they give us.

I know what you mean! Even just that one week of being pushed back, I was like dang, now I've got another week tacked on! Smile

luvdv8 · January 2011

rrcraz7:
Unless you were charting and know exactly when you ovulated then the u/s is more accurate. Ultrasounds can be +/- 5 or so days though. It's hard to get an accurate head to rump measurement because of how they can curl up and stretch out.

For me, if going by last period I'd be due March 20th. I'm really due April 12. Id go by what the u/s said.

An early dating/viability u/s is much more accurate than +/- 5 days- at that stage growth, uterine lining, etc is pretty methodical. The fertility clinic I was at said that (because they know the date of ovulation and implantation for all their clients and can compare the results of the u/s with what they know 100%) they're never off more than a day or two in a u/s before 12 weeks.

luvdv8 · January 2011

Double Post

rrcraz7 · January 2011

luvdv8:
rrcraz7:

Unless you were charting and know exactly when you ovulated then the u/s is more accurate. Ultrasounds can be +/- 5 or so days though. It's hard to get an accurate head to rump measurement because of how they can curl up and stretch out.

For me, if going by last period I'd be due March 20th. I'm really due April 12. Id go by what the u/s said.

An early dating/viability u/s is much more accurate than +/- 5 days- at that stage growth, uterine lining, etc is pretty methodical. The fertility clinic I was at said that (because they know the date of ovulation and implantation for all their clients and can compare the results of the u/s with what they know 100%) they're never off more than a day or two in a u/s before 12 weeks.

Interesting. I was with an RE and my due date is based on my ovulation date. I had weekly u/s from 4w through 14 weeks. My 7 week measured 4 days ahead. If I remember correctly only 2 of the u/s actually measured me right on my due date.

rrcraz7 · January 2011

luvdv8:
rrcraz7:

Unless you were charting and know exactly when you ovulated then the u/s is more accurate. Ultrasounds can be +/- 5 or so days though. It's hard to get an accurate head to rump measurement because of how they can curl up and stretch out.

For me, if going by last period I'd be due March 20th. I'm really due April 12. Id go by what the u/s said.

An early dating/viability u/s is much more accurate than +/- 5 days- at that stage growth, uterine lining, etc is pretty methodical. The fertility clinic I was at said that (because they know the date of ovulation and implantation for all their clients and can compare the results of the u/s with what they know 100%) they're never off more than a day or two in a u/s before 12 weeks.

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