Mis-calculated due-dates?

Question

I took my positive pregnancy test around September 27th. When I went to my doctor on October 5th I was told that I was already about a month pregnant according to my last period which was irregular and lasted about 2 days in the begining of September. All of my periods have always been atleast 5 days long, so I guess he was giving or taking about 2 weeks because of my irregular period. Anyway, he gave me a due date of June 16th. When I had my first ultrasound on January 3rd I was told that I was about 3 weeks further along & my new due date was about May 20th. I have had a couple more ultrasounds since and they tell me that I'm due the Begining of May. Has anyone had any issues like this in their pregnancies? If so, what was your experience like and what ended up being your due date? I just want to know if I'm a month further along than I'm thinking or if I'm a month behind.

Answer 1

The bleeding you had that was 2 days was not a period as such, but breakthrough bleeding, which is very common. The ultra sound is the most accurate way of determing the delivery date but it is important to remember that pregnancies vary in length. Just as babies grow at different rates outside the womb, they grow at different rates inside as well. Full term babies can be born from 36 weeks to 42 weeks.
Either way, be prepared for delivery from 7th month and you shouldn't go far wrong.
I've had my babies at 37 weeks, 39 weeks, 40 weeks plus 4 days, and 42 weeks and all were healthy.
So good luck and relax!

Answer 2

The date your doctor gave you first was a guesstimate, based on the date of your last period and the average length of a pregnancy. Ideally, you would know the date of conception, which you could use to calculate due date. SInce your periods were irregular, the old calendar dating system is not probably the most accurate predictor. It never actually was, but it did at least give you a target date. Ultrasounds are much more accurate, although the dates derived earlier in pregnancy are usually most accurate. In the first trimester, developement day by day is pretty well documented, so it's a lot easier to date a pregnancy. They know when fingers and toes make an appearance, for instance, so if you don't see five little fingers or toes yet you know you are not that far along. After the first trimester, dating is done by calculating from the baby's size, based on an average size baby. If you are a little taller than average, or a little shorter than average, then your baby could be a little larger or smaller, and the dates would be slightly off- even as much as two or three weeks.
In the end, it's really not a big deal. The baby comes on the day the baby choses, not the day you pick. Even with accurate dates of conception, most babies do not arrive on the predicted due date. Only about 4% of all babies do. With my last baby, we also had dates in the air. The first prediction was early July, sometime around the 10th. The first ultrasound moved the date forward to the 20th, then to the 25th. I happen to be on the small side of the size scale, and my doctor was older and more experienced. He said he thought all the dates were wrong, and felt we were looking at the end of July, probably closer to the first week of August. My son made his appearance on August 6, full term at just over 7 pounds. So the first due date, based on a calendar, was almost a full month off. The earliest ultrasound made the best prediction, based on development stage, with a date of 25 July. If I were to make a prediction, I think I'd be more likely to go with the date from the first ultrasound, and just ask the OB what his/her gut feeling is. And of course, remember that no matter what date you pick, none of you has the final word.