was your due date based on LMP accurate?

adrenalina19

hi ladies- so i had my first ultrasound today. according to my last menstrual period, i would be 8 weeks today. however, at the u/s, the baby measured at 6 weeks and 3 days. it has a heartbeat and the tech said everything looks good. i was very upset at first seeing that the baby is 10 days behind. however, based on my ovulation date (which i estimated to be last few days of june/first few days of july), the baby is right on track.

so basically, my question is this- how do people start counting the pregnancy on the first day of your last menstrual period, seeing how its basically impossible to get pregnant on that day??? wouldn't everyone be almost two weeks behind?

Daenaria

I bet the 6 week measurement doesn't include the first 2 weeks of your cycle when you aren't pregnant. Sounds like you are right on track! 

The baby is only 6 weeks old, but the pregnancy based on LMP is 8 weeks old - make sense? 

mcooper014

The only definite date you ever have is the day your period started (most women know this) you can never actually work out the day of actual conception because women don't usually know when they ovulate and sperm can live for up to 48 hours inside a woman's body.

Usually ovulation is 2 weeks after the 1st day of your period so when your period is due again if you are pregnant you are classed as being 4 weeks pregnant, ie 2 weeks from conception, 4 weeks from the start of your last period. Its all guess work really but the medical profession have to have a standard that they adhere to and this is it.

 

My due date (3/8/12) that I calculated based on my LMP was exactly the same as what the doctor calculated when I went for my first U/S because I am very regular in the # of days in my cycle each month.  If you aren't regular and your cycles are longer than normal it is likely that you are off in your calculation vs. what the Dr. saw on the U/S.

Sparkles01

I was about a week or so off.

lkm2006

Mine was spot on but it also was with DS. I don't chart but I have the textbook 28 day cycles. 

magel050485

Mine is not accurate because my LMP was 19 months ago.  However, you are not actually pregnant the first two weeks of pregnancy, those are freebies.  When they give you a length of pregnancy based off of an ultrasound they typically already have those two weeks built in so you would have actually ovulated closer to mid July.

How are you predicting your ovulation date?  Unless you are charting there is no way to know when you ovulated.  Every cycle can be different and very few women are textbook 28 day cycle/ovulate on CD 14.  You could have simply ovulated later this cycle.

CougFan

The u/s date is +/-4 days so there is tha margin of error to begin with. When using the LMP it is assumed you ovulated on day 14.

I have long , irregular cycles and ovulated closer to day 34 (I was charting and even that was wrong based on when we did the deed).

So if you weren't charting or using OPK and aren't positive you have 28 day cycles, the u/s is your best bet. 

5dogs

Unless you are charting (or using other methods like ultrasound/trigger with a RE), you have no idea when you actually ovulate. My ultrasound dating would have been off based off of LMP since I ovulate a few days later than CD14 - it was 100% accurate to my chart.

LitlePrety

mcooper014:

The only definite date you ever have is the day your period started (most women know this) you can never actually work out the day of actual conception because women don't usually know when they ovulate and sperm can live for up to 48 hours inside a woman's body.

Usually ovulation is 2 weeks after the 1st day of your period so when your period is due again if you are pregnant you are classed as being 4 weeks pregnant, ie 2 weeks from conception, 4 weeks from the start of your last period. Its all guess work really but the medical profession have to have a standard that they adhere to and this is it.

 

This.  Also, my due date was exactly right to the day.  But I had 28 day cycles.  I also knew I had to have ovulated on Day 14 because of when DH and I had sex (the night before).  So it was easy for me to figure out.   

PinkRoses53

My due date based on LMP is only 1 day off from my O date.  I only know this bc I was temping/charting and know for sure that I O'ed on CD14.  The month before, I had a 37 day cycle and O'ed on CD20, so that would have been a bit more off from LMP if I had gotten a BFP.

aeb20

When I went in for my first appt, according to my LMP I would have been a little over 8 weeks; however the ultrasound showed I was only 6 weeks and 5 days pregnant. I know that I have a longer cycle and I wasn't charting so I didn't really know when I had ovulated.

 

P.S.  How and when to start counting was all very confusing to me too! 

  

wittyschaffy

I could have written your post! My original edd was march 14 and we had our 1st u/s at what would have been 8.5 weeks and they said 6.5 weeks.  I panicked a little at first but when we looked at the calendar, their date was closer to when I likely ovulated.  (behind a couple days but that's ok). Nobody seemed concerned!