A heartbeat may not be visible during an ultrasound if the examination is performed early in pregnancy.
This would be prior to the development of cardiac activity.
These ultrasounds came in handy the next two pregnancies as well.
Earlier this week the American College of Obstetricians and Gynecologists (ACOG) met with the American Institute of Ultrasound in Medicine and the Society for Maternal-Fetal Medicine to set new guidelines for due date determination. James Goldberg, vice chair of ACOG’s committee on obstetric practice, stated, “Some studies suggest up to 40 percent of pregnancies would have dates changed based on [a] first trimester ultrasound.” This difference is because most women do not know the day they conceive and the 40 week rule-of-thumb is based on a 28 day cycle, which is not always a good guideline for women with irregular or longer cycles.
Due dates based on high-tech ultrasounds will help doctors in deciding things like when to induce or to administer steroids or other drugs in at-risk pregnancies.
You can calculate your due date by subtracting three months from the first day of your last menstrual period (LMP) and then add a week. A pregnancy is based on being 280 days long, which is 40 weeks (more like 10 months not 9! When we give you a due date we consider 37 to 42 weeks to be full-term, so even if your baby is born two weeks before your due date it is not considered premature.
The accuracy of using your LMP to date your pregnancy depends on having regular cycles and assumes you ovulated (released an egg) on day 14 of your cycle and conceived right away - none of which may be true.