ZocdocAnswersWhy do doctors add 2 weeks to UR ultrasound?

Question

Why do doctors add 2 weeks to UR ultrasound?

what do the extra days mean

Answer

I recommend that you discuss your concern further with your OB. I'm not entirely sure what your question is asking, but it sounds like you might be asking why obstetricians date your pregnancy back two weeks. This is simply a convention that doctors use when discussing the timeline of a pregnancy. In general it is very difficult to know exactly how old the fetus is, usually because people aren't exactly sure when they conceived and ultrasounds can only give you a general sense of how old the fetus is (ultrasonographers measure things like the length of the spine and the size of the head and plug that into a formula that estimates the age of the baby based on an average sense of how big a baby should be at a certain week gestation). The only thing that can be known for sure is when your last menstrual period was. The first day of your menstrual period is called 'Day 1' of your menstrual cycle, and ovulation typically occurs on day 14, which is the time a woman is most likely to conceive. All of which is to say that if a baby was conceived on day 14, the convention is to date the pregnancy back two weeks. That is why, for obstetricians, the duration of a pregnancy is 40 weeks, even though most pregnancies are not longer than 9 months. I hope that answers your question. If you have any further concerns or questions about your pregnancy make sure to bring it up with your OB, and make sure to go to all of your regularly scheduled visits to get all of the appropriate prenatal testing.

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