Ultrasounds During Pregnancy: What Information Do They Provide?

· May 2, 2019
During pregnancy, several ultrasounds must be done. In this article, discover what information they provide.

Ultrasounds during pregnancy are one of the quintessential medical tests that control the fetus’ evolution and growth. Ultrasounds are used to visualize internal structures.

Obstetric ultrasounds provide information about female sexual organs (uterus, fallopian tubes, and ovaries), neighboring structures (bladder) and, of course, in the case of pregnancy, the fetus and its environment (gestational sac, amniotic fluid, umbilical cord…).

They’re noninvasive tests that don’t hurt and pose no risk to the soon-to-be-mother and her baby. During pregnancy, usually three ultrasounds are done. One is carried out during each trimester and they each provide different information.

First trimester ultrasound

It’s usually done at 12 weeks of pregnancy (between 11 to 13 weeks) and provides essential information:

  • Number of embryos. This indicates whether the pregnancy is multiple or regular.
  • Presence of fetal heartbeat. A heartbeat can be detected approximately from the 6th week of pregnancy.
  • Gestational age and length of the embryo. Makes it possible to verify if the calculated pregnancy weeks are accurate.
  • Embryo morphology. It verifies if the fetus is developing properly.
  • A nuchal scan is used to detect cardiovascular anomalies in a fetus.
  • It checks the uterus and ovaries. 

This ultrasound is one of the most exciting ones for the mother, as it confirms pregnancy when an embryo is detected.

A pregnant woman smiling during an ultrasound.

Second trimester ultrasound

It’s usually done at 20 weeks of pregnancy (between 18 to 21 weeks). It’s also known as morphology ultrasound, since its main objective is to assess the proper development of the fetal organs and systems. This ultrasound makes it possible to detect fetal anomalies and marker chromosomes.

Here are some of the main functions of this ultrasound:

  • Confirms the number of fetuses and their viability.
  • Explores the placenta (location, characteristics, blood vessels in the umbilical cord…).
  • Detects the amount of amniotic fluid present.
  • Studies fetal growth according to different parameters: measurements of the head, abdomen, and femur.
  • Extensively studies fetal anatomy; which is why this ultrasound is the longest.
  • Allows the parents to discover the sex of the baby.
  • Checks the uterus and ovaries.

During this ultrasound, the parents can learn the sex of the baby, although many prefer to stay in the dark until the baby is born.

Third trimester ultrasound

This ultrasound is usually done between 32 to 36 weeks of pregnancy. Here are its main functions:

  • Measures fetal viability and the fetus’ position in the uterus.
  • Analyzes fetal growth against the measurements of the second trimester ultrasound. These measurements are very important in cases of intrauterine growth restriction (IUGR) or fetal macrosomia.
  • Locates the placenta.
  • Calculates the volume of amniotic fluid (normal quantity, polyhydramnios, or oligohydramnios).
  • If necessary, it studies placental blood circulation (Doppler ultrasound).

These are the minimum recommended ultrasounds that allow antenatal monitoring. However, if any alteration is detected in fetal growth, amniotic fluid, or the placenta, it may be necessary to carry out more ultrasounds.

Ultrasounds during pregnancy, along with blood tests, allow specialists to detect any anomaly. It’s very important to follow your doctor’s recommendations and consult them if you have any questions.

Other ultrasounds during pregnancy

A pregnant woman getting an ultrasound.

  • Fetal Doppler ultrasound. It makes it possible to assess the blood flow between the placenta and the baby. If any alteration is detected, more comprehensive studies will be required.
  • Uterine artery Doppler ultrasound. This test studies the resistance of maternal uterine artery blood flow. This level can be altered in cases of intrauterine growth restriction (IUGR) or hypertension during pregnancy (preeclampsia).
  • Fetal neurosonography. The fetus’ brain and spinal cord are studied in this test. It’s recommended in very specific cases.
  • Cervical‐length measurement. This ultrasound is performed vaginally to estimate the length of the cervix. It’s indicated in women with a history of preterm birth (before 37 weeks of pregnancy).
  • 4D and 5D ultrasounds. They provide clear images of fetal internal anatomy. Parents usually decide to get them done to be able to see their baby much more clearly.
  • Castán Mateo, S., Tobajas, JJ. (2013). Obstetricia para matronas: guía práctica. Madrid: Médica Panamericana.
  • Espinilla Sanz, B., Tomé Blanco, E., Sadornil Vicario, M., Albillos Alonso, L. (2016). Manual de obstetricia para matronas. 2nd ed. Valladolid: DIFÁCIL.