Infertility/Fertility/Implantation bleeding



I am hoping with your experience in sonogram you will be able to clarify some questions. I will number the questions if you don't mind.

1. Abdominal ultra sounds accuracy at 9 week and 3 week. What is the max they can be out by when determining gestational age?

2. Is a 12 week 3 day ultrasound still accurate for dating?

Sept 09 2012
Oct 12 2012 ( 4 days late ) seemed normal just late. I was expecting in on the 9th

December 2012 abdominal ultra sound dated me 8 weeks 4 days
Jan 07 2013 abdominal ultra sounded dated me 12 weeks 3 days

Google is not my friend! After doing some reading I am in fear that Oct 12, 2012 period was implantation bleeding and not an actual period.

Would the ultrasound reflect differently if it was implantation bleeding? If so what would fetus size be? Would they use Sept 09 as my last period for dating proposes?

Thank you for your time."

Hello Cheryl from Canada,

The 8 week ultrasound has a +/- 3 day margin of error whereas the 12 wk has a +/- 14 day margin of error.

The dating for the ultrasound is based on calculation using the measurements and not the last menstrual period you give.  The LMP is used for comparison and the ultrasound date should match.  If it does not match, then a second ultrasound must be used to calculate and confirm the dating of the pregnancy.  Again, the 8 week ultrasound would be used as the most accurate dating scan and the estimated due date that derives from this ultrasound would be used as the due date.  From that point on, all ultrasounds will be dated based on that date.  I cannot give you specifics regarding fetal size as they can vary.

Good Luck,

Dr. Edward J. Ramirez, M.D., FACOG
Executive Medical Director
The Fertility and Gynecology Center
Monterey Bay IVF Program

Monterey, California, U.S.A.

for additional information check out my blog at check me out on twitter with me at @montereybayivf and facebook @montereybayivf.  Skype and internet comprehensive consultations now available via my website for those who want a more extensive evaluation that this site can accommodate  


All Answers

Answers by Expert:

Ask Experts


Edward Joseph Ramirez, MD, FACOG


I am a specialist in infertility and advanced gynecological care. I can answer questions about infertility, gynecology related ills, menopause...virtually anything that affects women's health. PLEASE tell me where you are writing from as I am always interested.


I have been practicing as an Ob/Gyn and Infertility Specialist for over 23 years. Gynecology, advanced laparoscopic surgery, basic infertility, IUI's, IVF, reproductive surgery, and ovulation induction are all areas of my expertise. I am Board Certified. I have been doing In Vitro Fertilization in my clinic for 19 years.

American College of OB/GYN, American Board of Obstetrics and Gynecology, American Society of Reproductive Medicine, California Medical Association, American Association of Gynecologic Laparoscopists, Fellow of The American College of Obstetricians & Gynecologists

American Journal of Obstetrics and Gynecology, Wall Street Journal, Monterey Herald, SERMO, Women's Health and Fertility Blog

Medical Degree from Stanford University, Residency at Tripler Army Medical Center, Reproductive Training at Pacific Fertility Center, San Francisco

©2017 All rights reserved.