Ultrasound During Pregnancy

General Description

Ultrasound is the technique used to monitor the fetus or future baby during pregnancy, which is why it is also known as fetal ultrasound. A series of ultrasounds are scheduled during gestation to monitor both the growth and development of the embryo, as well as to determine if there are any abnormalities in the formation of its organs.

Prenatal diagnostic ultrasounds use sound waves to capture images of the fetus inside the womb. These tests are carried out at three key moments during pregnancy:

First Trimester Ultrasound: The first ultrasound is performed between weeks 11 and 14. It is typically an abdominal ultrasound to allow greater movement, although some specialists may prefer the transvaginal route to detect embryos at an earlier stage. This exam serves to:

• Confirm that the pregnancy is located in the uterus and rule out an ectopic pregnancy.
• Determine the number of embryos.
• Identify the heartbeat.
• Establish the size of the fetus by measuring the crown-to-rump length (distance between the crown and the coccyx).
• Study early indicators of risk for Down syndrome and other chromosomal abnormalities, such as increased nuchal translucency or the absence of the nasal bone.

Second Trimester Ultrasound: Performed between weeks 19 and 22. Known as the morphological ultrasound, this is a detailed exam that thoroughly observes the entire anatomy of the fetus, including complex organs like the heart and brain, to detect potential malformations.

Only transvaginal ultrasound is used if greater precision is needed, especially when an organ is positioned near the mother's vagina. It is also useful for checking if the cervix is shortening, which may signal a risk of preterm birth, or to locate the placenta if placenta previa is suspected.

Third Trimester Ultrasound: Performed between weeks 32 and 36. As with the second trimester, this ultrasound is performed vaginally only if placenta previa is suspected or if the cervix is shortening. It is a fetal growth ultrasound that checks:

• The size of the fetus.
• The heart rate.
• The condition of the umbilical cord.
• The maturity of the placenta.
• The amount of amniotic fluid.
• The length of the cervix.

The prenatal diagnostic ultrasound plan does not include Doppler ultrasound, but it is recommended if fetal growth delay is suspected, to rule out congenital heart diseaseHeart DiseaseHeart Disease , if the pregnancy is high-risk, or if the mother suffers from hypertension.

Routine fetal monitoring tests are performed using conventional ultrasounds (in two dimensions and grayscale). Three-dimensional or four-dimensional technology is only used if malformations are detected, as these allow for more detailed examination of the organs. These tests are also performed so parents can see the facial features of their future child before birth.

When Is It Indicated?

Fetal ultrasound is indicated in all pregnancies to ensure proper development of the embryo and to monitor the health of both the fetus and the mother.

How Is It Performed?

The pregnancy ultrasound is performed with the patient lying on her back on an examination table. After exposing the abdomen, a gel is applied to facilitate the reception of images, and a probe called a transducer is moved over the area where the uterus is located. This transducer emits sound waves and picks up the echoes that are produced when they hit the tissues. A computer converts the echo into an image.

If a transvaginal fetal ultrasound is chosen, the pregnant woman must lie on the gynecological examination table to facilitate the insertion of a smaller transducer into the vagina. To make the procedure easy and painless, a latex protector lubricated with gel is used.

Risks

Ultrasounds during pregnancy do not pose any risk to the health of the fetus or the mother.

What to Expect from a Fetal Ultrasound

It is generally not necessary to remove clothing during the procedure, except in cases where a transvaginal ultrasound is required. In those cases, it is necessary to remove underwear to lie on the gynecological table.

Since this is a special moment, the specialist will explain their observations as they make them, detailing each step. It is normal, especially in the first-trimester ultrasound, for the images to be hard to interpret with conventional ultrasound, so gynecologists are used to explaining where each organ is located and how to identify the future baby.

Pregnancy control ultrasounds typically last around 15 minutes, while the second-trimester morphological ultrasound may last up to half an hour. In neither case is hospitalization required, as they are performed on an outpatient basis.

The gel used for the procedure is easily removed and does not stain. As part of monitoring the fetus's development, it is common for the specialist to provide parents with a copy of the obtained images.

Specialties Requesting Pregnancy Ultrasound

These types of ultrasound controls are requested in the specialties of gynecology and obstetrics.