Pregnancy Timeline: Understanding Early Development & Ultrasound Findings

Question
Hello I was really hoping that you could help with my question. May 13th was the first day of my lmp.  On June 22nd I had my first ultrasound, which showed the sac and yolk but no baby yet.  I was told I was 5 weeks and two days.  On June 22nd I took a blood test to measure levels and they were at 15,500, on the 29th the test was repeated and my levels had doubled.  On July 11th I had my second ultrasound where baby was seen and heart was beating and I was told I was only 6 weeks and 6 days.  I don't understand how 20 days later I'm only 1 week and 4 days further along.  If this helps you at all I had sex in May on the 19th, 22nd, 25th, and 31st. When did I concieve.  Thank you so very much for your time in this situation.

Answer
HI Eve,

congratulations!!!!

It sounds just fine. With a developing fetus there are variations how fast they can grow; usually the ultrasound measurements there are "averages", so one month the baby may measure on the larger side, the next month it may have slowed down. Also, an ultrasound is only as accurate as the person DOING the ultrasound. If they are off, even a tiny bit,  in calculating their measurements, then the ultrasound will have a different result...

I think what may have happened is, the first ultrasound may have slightly overestimated, and you could have been, say 5 weeks exactly.. then the 2nd ultrasound, it was underestimated, and you may have been measuring 7 weeks + etc.  Does this make sense?

And your doubling HcG levels are a good sign too.

here is how due dates are figured out: and remember, they are called "estimated" due dates or EDD but no one tells you this!

You take your first day of last period (May 13) and go back three months, (February) and add 7 days: February 20th.

So by your period and by the calendar, your due date is February 20th. However, if the baby is consistently measuring large or small, they will fiddle with your due date and adjust it accordingly.

You most likely conceived on the 22nd or the 25th, but these dates dont really make any difference in the due date, because it is calculated by the last period, not by individual days of conception. So technically, the first two weeks of your cycle when you are NOT pregnant are countes as part of the pregnancy!

So right now the baby is measuring a little small, but it will catch up. If/when you have a level II ultrasound you can get more detailed accurate measurements. This is usually done around 20 weeks.

good luck!!!!
andi