Here are the issues as I see them:
- You read online that 25 millimeters is bigger than 8.5 weeks, but actually that is the normal ultrasound crown-rump length for about 9 weeks gestation.
- Ultrasound is accurate give or take one week in the first trimester, so it is normal to be 9 weeks size at 8.5 weeks. That is just within the error of the measurements.
- When an embryo is found to be substantially larger than it was supposed to be in the first trimester, it always means that the dates are wrong, and the pregnancy is farther along than expected, and is not a sign of a medical problem.
This question reminds me of the saying “a little bit of knowledge is dangerous.” Knowing the millimeter measurement, but not having the professional interpretation, combined with inaccurate information from the Internet led you down a path of anxiety that was totally unnecessary. I feel so bad for my patients when they come in having been hurt like this, from too much information and not enough professional guidance. Please talk to your doctor or midwife and let her go over the results of the ultrasound, so you can understand what it means for you and your baby-to-be. And next time, try to get the context and professional interpretation first, before you try to make sense of technical information and drive yourself crazy!