Third-trimester ultrasound By the third trimester, most pregnancies are identified by ultrasound imaging. For example, the heart can be seen in its entirety for the first time around week 16, and major blood vessels such as the aorta and pulmonary artery can be visualized for the first time around week 18. Because of this differentiation process, by the end of the second trimester many more internal organs can be seen on ultrasound images than at earlier stages. Second-trimester ultrasound By the second trimester, most embryos have reached the stage of gastrulation, when they start differentiating into various tissues including brain, spinal cord, skin, muscle, bone, heart, GI tract, liver, lungs, and reproductive organs. A gestational sac, on the other hand, can be observed as early as 4 1/2 weeks following your last period, and a fetal heartbeat can be found as early as 5 to 6 weeks (though this is not always the case). How soon can an ultrasound detect an embryo?įirst-trimester ultrasound Most practitioners will not do the first prenatal ultrasound until the patient is at least 6 weeks pregnant. The purpose of the ultrasound is to determine the presence of a fetal heartbeat and estimate how far along you are in your pregnancy. You may be given a mild sedative before the test to help you relax while keeping you awake enough to avoid falling asleep during the procedure. You may be asked to lie on a table with your legs open while the sonographer scans your abdomen.
These images are then viewed on a computer screen by the sonographer who performs the test, or by another physician or nurse who reviews the results after they have been recorded. An ultrasound technician will use sound waves to generate images of structures inside the body, including the uterus, ovaries, fallopian tubes, lungs, heart, liver, spleen, stomach, intestines, urinary tract, and reproductive organs. This ultrasound exam may detect the baby's heartbeat and determine the baby's age and due date.Īn ultrasound can also reveal other information about the health of the fetus and mother, such as whether there is growth restriction (the baby isn't getting enough food), abnormal brain development, limb differences (such as one arm or leg that is shorter than the other), problems with the heart, kidneys, or other organs. Preliminary ultrasound If you're unsure when you became pregnant, or if you've had a past miscarriage or ectopic pregnancy, your doctor or midwife may prescribe an ultrasound scan in the early stages of pregnancy, usually around 8–10 weeks.