How Early Can a Baby Be Seen on an Ultrasound?

In obstetrics, an ultrasound is a medical procedure that is used by doctors foremost to determine the health of a baby. During an ultrasound, a device called transducer sends out high frequency sound waves. These waves reflect off the baby and are transformed into images on a screen. During the ultrasound, a woman and doctor can see the baby, placenta and amniotic sac.

Significance

• While ultrasounds are usually given between the 18th and 20th weeks of pregnancy, some physicians will perform them earlier than this. They may do this to find out the number of babies that are present, the health of the fetus, the presence of an ectopic pregnancy and the mother's due date.

Early Detection

• The earliest that a fetus can be seen is four to five weeks into the pregnancy, when it is possible to see the gestational sac. This structure is the first that doctors can look at on an ultrasound to determine whether a woman is pregnant, and it can be seen before the actual embryo can. Between the fifth and sixth weeks, the yolk sac, which is contained within the gestational sac, can be seen. The yolk sac is what provides nourishment to the embryo in the early stages of pregnancy.

Baby's Heartbeat

• At about six weeks, the embryo and the heartbeat can be detected. During an ultrasound at this stage, doctors are able to start to look at the health of the embryo and the possibility of its survival. If the baby's heartbeat falls below a certain range, 90 beats per minute, the woman is considered at high risk for miscarriage. The normal range for a baby during this time is between 90 and 110 bmp.

Determining Age

• During an ultrasound performed during the first six to seven weeks, the doctor can also determine the age of the fetus and the due date. This has to do with the length of the baby at the time, or the crown-to-rump length. During this ultrasound, the baby should be in a curved structure with the head and a tail-like structure at different end. At six weeks, the length should be 0.4 mm, and at seven weeks, it should be about 1 mm.

Seeing Clearly

• During the eighth week of pregnancy, it is possible to see the fetus in clear detail because it has grown and developed and its heartbeat has become stronger. According to Sophia Levis in her article "How Early Can a Pregnancy Be Seen in an Ultrasound," a doctor is likely able to see more during an ultrasound done at eight weeks because the gestational sac carrying the baby is so small. It is during the eighth week that the baby begins its transformation from an embryo to a fetus. An embryo refers to the form that a baby takes from the time it is conceived until eight weeks into the pregnancy, when it goes from a single cell to a one-inch organism. A fetus refers to the growing baby as it changes into a human being with a functioning heart, lungs and a brain. By eight weeks into the pregnancy, the baby's heartbeat should be stronger, at around 140 to 170 bmp, and easily detectable.

Detecting Defects

• Earlier ultrasounds, during the first trimester, can be helpful to physicians because they can help to show whether a baby has birth defects before the regularly performed ultrasound during the 20th week. An ultrasound that is done during the first trimester can help to show birth defects such as spina bifida, cleft and lip palates, Achondroplasia, Down Syndrome and other conditions that would affect the appearance and health of the baby. These are generally found through targeted ultrasounds, which look for structural abnormalities or soft markers that show if a baby could have a health problem.