confused about gestational age

[xsamx89x]

Im newly pregnant and had a scan the other day, i worked out before i had the scan that i should be 7 weeks and 4 days pregnant ( i worked this out by the date of the first day of my last period which was 7th of september) but at the scan i was told that i was only 6 weeks + 3.

I found out i was pregnant over 3 weeks ago as i did a test on the day i thought my period was due, so could a pregnancy test be positive at only 3 weeks pregnant? and how accurate is a scan??

My periods were as regular as clockwork until about the last 2 months, when it came earlier than expected. So confused!

 

[Samantha675]

I am not sure about that. I had a scan this morning and it was pretty much spot on with dating. From the FLP I am 11 weeks, the scan measured me at 10 weeks and 6 days. But I did find this:

Your healthcare provider will use hormone levels in your blood, the date of your last menstrual period and, in some cases, results from an ultrasound to generate an expected date of conception. However, many differences in each woman's cycle may hinder the accuracy of the conception date calculation. The viability of sperm varies as well, which means that intercourse three to five days prior to ovulation may result in conception. Ultrasound dating of conception is not reliable for determining paternity because the ultrasound can be off by at least 5-7 days in early pregnancy.

If a patient has good menstrual dates, and ultrasound measurements are within the expected variation, use the menstrual dates; if there are poor menstrual dates use the ultrasound gestational age. After 28 weeks there is a huge amount of variation in fetal size due to macrosomia and intrauterine growth restriction. With a certain LMP it is not a good idea to change the due date in the third trimester based on ultrasound measurements until the pregnancy has been fully evaluated.

 

[future mommy]

I had somewhat of the same issue. When I thought I was 8 weeks the scan said 7 weeks 3 days. I had a gut feeling to stick to my date as I am positive on the first day of my last cycle. When I went back at 10 weeks <----my date! The scan verified that I was right. The scan is not completely accurate in early pregnancy.

This is how the scan works. When they take a measurement from crown to rump, for example, at my 8 week the baby was 12MM. Well they take an average of however many number of women. They take the average date that women were at when the baby was 12MM. So everyone is not always average.

 

[Serene123]

I had a scan on Tuesday 23rd October and they told me I was 7wk+2. I started bleeding on Wednesday night so I had another scan on Thursday 25th October and they told me I was 8wk exactly. I don't think early scans are too reliable. If I go by the first day of my last period I should be 10wk+6 not 9wk+2 lol

 

[ColtonsMom]

your pregnancy test will come out positive on the day you are supposed to have your period.. some will work 5 days before your missed period.

And as for the doctor telling you you're only 6 weeks.. + he might be talking about how only the baby is.. technically you dont get "pregnant" until 1-2 weeks after your last period. So even though your last period was for example March 28th, you didn't actually get pregnant until around the 2nd weeks of June.