Healthcare professionals recommend that most pregnant people have at least one ultrasound during the second trimester of pregnancy, between 18 and 22 weeks. You may have more ultrasound scans depending on your individual needs and risk factors.

An ultrasound scan is a procedure that uses sound waves to allow healthcare professionals to visualize the organs or tissue inside your body. This procedure is safe to use during pregnancy, as it doesn’t involve radiation and won’t affect the health of the baby.

The sonographer (ultrasound specialist) will typically spread some gel on your abdomen, then place the probe on top of it and slide it around to obtain the images they need. You typically need to have a full bladder for this procedure.

Sometimes, a transvaginal ultrasound may be necessary if the sonographer cannot get clear images, usually if the pregnancy is not very advanced. A transvaginal ultrasound involves introducing a probe inside the vagina to visualize the baby, uterus, and ovaries.

Your doctor may conduct an ultrasound scan during pregnancy for various reasons, typically to check on the health of the fetus and whether they’re developing and growing as expected.

Read on to learn more about how many ultrasound scans you might need during pregnancy, what’s part of your standard antenatal care, and what ultrasound results may reveal about the health of your baby.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant people have at least one ultrasound scan in their second trimester of pregnancy, between 18 and 22 weeks. This is a detailed scan of the baby, usually called the anomaly or the anatomy scan. During this scan, the sonographer or obstetrician will:

Anatomy scan

To detect any potential fetal irregularities or congenital anomalies, the sonographer will have a look at the baby’s:

  • Head, including skull and brain: This will help the sonographer identify whether the shape of the skull or any particular features of the brain are a sign of a certain condition. Some examples of conditions that can be identified include Turner syndrome, and trisomy syndromes 13, 18, and 21.
  • Face and neck: Early detection of certain facial irregularities can lead to the identification of certain fetal anomalies, such as cleft lip and palate. Neck masses can point to conditions such as lymphangioma, enlarged thyroid, or branchial cleft cyst.
  • Thorax: The sonographer will look at the shape of the thorax and ribs, as well as examine the lungs and heart function. They will assess the heart rate, location, and size of the heart, as well as look for any structural irregularities. They will try to get images of the four chambers of the heart and ensure they’re functioning as they should. Possible conditions they may be able to identify during their assessment include lung masses, a ventricular septal defect, or an abnormal chamber size.
  • Abdomen: Looking at the abdomen will help the sonographer visualise the stomach, kidneys, and adrenal glands. They will also check the bowels and liver. They should also be able to visualise the bladder after 15 weeks of gestation. The sonographer could identify conditions such as :
    • a ventral wall defect
    • dysplastic kidneys
    • infantile polycystic kidney disease
    • fetal bowel dilatation
    • echogenic bowel
  • Spine and limbs: The sonographer will check whether the baby has all extremities and that nothing looks unusual. They could identify conditions such as thanatophoric dysplasia or achondroplasia.

Some of the conditions identified during this scan could help healthcare professionals come up with an early diagnosis. An early diagnosis can then ensure prompt treatment is administered to the baby. Some conditions can be deadly and parents can therefore be prepared for how they may want to manage the pregnancy.

First trimester scan

The first trimester scan, or dating scan, would typically take place during the first trimester, between weeks 10 and 14 of gestation. This scan can help identify if you’re carrying more than one baby.

During this scan, healthcare professionals can usually date the pregnancy based on a measurement called the crown-rump length measurement. This is a useful measurement for dating the pregnancy during weeks 10 and 14, but may not be as effective later on, in the second trimester.

They may also check the position of the placenta and that the pregnancy is evolving as expected. At this stage, they may rule out other possible conditions, such as an ectopic pregnancy. With an ectopic pregnancy, the embryo has not implanted in the uterus, but somewhere else, such as the fallopian tubes.

An ectopic pregnancy can quickly become a medical emergency if the fallopian tubes rupture and needs immediate treatment.

Depending on your individual risk factors or complications, your doctor or obstetrician may request more scans. These scans will usually check:

  • fetal growth
  • placental position
  • fetal position
  • unexpected bleeding

Your doctor may want to check the location of your placenta in the third trimester, for example if during your second trimester scan they identified a low-lying placenta.

This usually migrates further up as the baby and the uterus grow bigger, but in some cases it may stay above the cervix, right above the baby’s exit. This is called placenta previa, and a C-section is usually necessary if you have this complication.

Your doctor might also want to check the baby is in the right position for the birth (head down), or that they’re growing as expected.

Other health conditions

A doctor may also order repeat ultrasounds for people diagnosed with gestational diabetes, preeclampsia, or other conditions that can affect the growth of the baby.

Fetal conditions can also affect the number of scans. Conditions such as fetal growth restriction or intra-uterine growth restriction can require follow-up scans more regularly or for repeat weekly fetal testing (NST).

High risk pregnancy

If your doctor deems your pregnancy high risk, you typically have additional ultrasounds to check on you and the baby. Risk factors during pregnancy include:

Currently, there are no risks associated with ultrasounds during pregnancy. Ultrasounds don’t harm the pregnant person or the baby.

However, healthcare professionals currently recommend that pregnant people have ultrasounds only for medical reasons and at the recommendation of their doctor.

People should have at least one or two ultrasound scans during pregnancy to accurately date the pregnancy and identify any conditions or irregularities that could cause complications with delivery or for the baby.

More ultrasound scans may be necessary to establish the position of the placenta or of the baby, and to ensure the baby is growing and developing as they should.

Your doctor or obstetrician will monitor your pregnancy and ensure you get the care you need.