How Accurate Is an Ultrasound at Six Weeks?

Many women don’t discover that they are pregnant until they are at least six weeks pregnant, even if they may suspect they may be pregnant before then. This is especially true if a pregnancy is unplanned. Women actively trying to conceive may be more “tuned in” to observe any signs of pregnancy. Often, these women will want confirmation as soon as possible and will schedule a pregnancy ultrasound before reaching six weeks. But understanding the accuracy of these early tests is essential before you go ahead and schedule an appointment.

Ultrasounds are commonly used diagnostic tools for many health conditions. Still, they are most often associated in people’s minds with pregnancy, and obstetricians rely on ultrasounds in their practices. Ultrasound is especially useful for determining the gestational age of a fetus and to monitor fetal health. The first ultrasound you have is the most accurate method for determining your baby’s expected due date and, as an extension, the age of your fetus. In most situations, it will help you determine a due date that is within a week of the actual delivery date.

Why Would an Ultrasound Predict a Different Due Date?

The “normal” gestational period for babies is 40 weeks. This is measured not from the time of conception but from the first day of the mother’s last period. In most cases, conception takes place about two weeks later, so a baby’s actual average gestational age is 38 weeks at birth. 

It is important to remember that this 40-week calculation is based on a woman having a “regular” menstrual period of roughly 28 days. In most cases, women ovulate about two weeks before their period starts, which is when conception is possible. Consequently, calculating based on the date of the period is pretty accurate. But for women with irregular periods, it may be difficult to calculate the actual due date based on the day her period started. Consequently, the due date computed based on an ultrasound may differ but will likely be more accurate.

At six weeks gestation, a fetus is less than a quarter of an inch, or about the size of a pea. Obtaining measurements can be challenging; even a slight error could produce an inaccurate due date.

Why Are Ultrasounds Performed?

An ultrasound is a non-invasive test that provides health practitioners with valuable information about a pregnancy. Ultrasounds have no adverse effects on either mothers or their babies and are preferred over other imaging methods. Depending upon the stage of the pregnancy, an ultrasound can be used to observe, detect, and measure different things.

The information obtained in early sonograms, such as those done at or before six weeks gestation, can help newly pregnant women make important decisions about their futures. Early sonograms are often used for the following diagnostic purposes:

  • To confirm a pregnancy
  • To identify an ectopic pregnancy
  • To measure the fetus
  • To determine if there are multiple fetuses
  • To establish a due date for pregnancy

How Are Ultrasounds Performed?

Pregnancy sonograms are performed either across the abdomen or transvaginally. During the test, a special gel is applied to a wand device called a transducer. The transducer emits high-frequency sound waves that reflect off the tissues in the uterus, and those sound wave reflections create images on the computer screen. At a six-week ultrasound, your sonographer will locate the fetus, verify whether the pregnancy is viable (i.e., that it is not an ectopic pregnancy), and take a crown-to-rump measurement to help ascertain the baby’s gestational age to calculate a due date.

Ultrasounds are essential tools that obstetricians use for confirming and monitoring a pregnancy. When performed at or around six weeks gestation, they can estimate the due date with considerable accuracy. Open Arms Real Choices Clinic offers compassionate, no-cost, or low-cost services throughout pregnancy, including limited obstetric ultrasounds.

If you suspect you are pregnant, contact Open Arms Real Choices Clinic in Hayden, Idaho, to schedule a pregnancy test. If your pregnancy is confirmed, we may be able to perform an ultrasound to ascertain its viability, calculate your due date, and discuss your options. If you have any concerns about the ultrasound process, please reach out to us for more information.

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