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Ultrasound In Pregnancy: The Third Eye

- 8 min read
written by Shield Connect

Most pregnant women in the industrialized world have had ultrasound tests at some point during their pregnancy, while the frequency and number of scans vary widely depending on countries and situations.

Since its beginning in healthcare, obstetric ultrasonography has played a key role in obstetrics. Most pregnant women in the industrialized world have had ultrasound tests at some point during their pregnancy, while the frequency and number of scans vary widely depending on countries and situations. Ultrasound has a wide range of uses in obstetrics, including screening, diagnosis, and foetal monitoring. The advantages of routine (screening) ultrasonography include determining gestational age, detecting multiple births, locating the placenta, assessing foetal wellness, and detecting prenatal defects. Furthermore, ultrasound is useful in the monitoring and management of high-risk pregnancies in order to decrease perinatal fatalities. Due to the procedure’s inability to create high-quality images, any suspected anomalies must be validated through additional diagnostic testing. Although the ultrasound scan is not accurate all the time, it has the advantages of being painless, non-invasive, and safe for both the mother and the unborn child. However the use of ultrasound possesses numerous ethical issues, particularly in respect to non-medical provisions and its use in sex-selective abortions and foetal reduction in multiple pregnancies .

Ultrasound during pregnancy

First trimester: In first trimester ultrasounds are used to check that the embryo is developing inside the womb, confirm the number of embryos, and calculate the gestational age and the baby’s due date throughout the first three months of pregnancy.

Second trimester: Ultrasound between weeks 18 and 20 is used to assess the development of foetal structures including the spine, limbs, brain, and internal organs, The placenta’s size and placement are also examined.

Third trimester: After 30 weeks, a third trimester ultrasound is used to ensure that the baby is still growing at a normal rate. The placenta is examined to ensure that it is not blocking the cervix.

On its most basic level, ultrasound imaging is used to assess a developing pregnancy for the following:

Confirm the Pregnancy

Gestational Age –A full-term pregnancy lasts 37 to 41 weeks. For numerous reasons, it is critical to confirm the gestational age of the developing foetus. To ensure appropriate development, the baby’s growth will be measured against well-established growth charts.

Check for Multiple Pregnancies (twins, triplets etc) – Pregnancy with multiple babies carries unique dangers that must be closely monitored. Complications include “twin to twin transfusion” and cervical incompetence must be addressed right once.

Problems with the Placenta – Pregnancy with multiple babies carries unique dangers that must be closely monitored. Complications include “twin to twin transfusion” and cervical incompetence must be addressed right once.

  • Placenta Previa – The placenta lies extremely low in the uterus, almost touching or completely covering the cervix. Early in pregnancy, it is usual for the placenta to be near to the cervix opening and to “move up” the uterine wall as the uterus grows with the baby. However, if it is still very low at the time of labour, it can cause catastrophic bleeding. An ultrasound can assist decide whether the scenario necessitates a caesarean section birth.
  • Vasa Previa – Blood arteries in babies cross or run near the cervix. Because they are not maintained by the umbilical cord or placental tissue, these arteries are vulnerable to rupture when the mother’s membranes burst. Patients with vasa previa may need to stay in the hospital for a lengthy time during their pregnancy and have a caesarean section.
  • Placenta Accreta – The placenta’s blood veins and other elements protrude too far into the uterine wall. Because the placenta generally detaches from the uterine wall after childbirth, this can be a concern. Part or all of the placenta stays securely attached in placenta accreta. This can result in a lot of blood loss once the baby is born.
  • Placenta Increta – is a condition in which the placenta invades the muscles of the uterus.
  • Placenta Percreta – is a condition in which the placenta grows through the uterine wall.

Monitor Fetal Position – It’s vital to identify the baby’s position (breech, transverse, cephalic, or ideal) during birth because it can change the delivery procedure.

Check for Congenital Anomalies – Many parents may want to know whether their child has any congenital or genetic issues so that they can either abort the pregnancy or prepare for the challenges that come with the situation.

Monitor Fetal Growth – If the baby’s growth falls short of expectations, it could indicate an issue with the placenta or a problem with the baby’s health. In either case, early action may be necessary to address the issue.

Monitor the Level of Amniotic Fluid – The foetus produces amniotic fluid, and too much or too little amniotic fluid can indicate pregnancy complications that may necessitate intervention.


Transabdominal ultrasound: Water allows sound waves to travel very easily. Around the 20th week of pregnancy, the majority of pregnant women get a transabdominal ultrasound. This test verifies that the baby is developing correctly and that the placenta is securely attached. The fetus’s heartbeat may be heard, and the movement of the foetus can be seen. The scan takes roughly 30 minutes on average.

Vaginal ultrasound: A transabdominal ultrasound may not be able to give clear enough images in some circumstances. The doctor or ultrasound technologist (sonographer) can see and measure the foetus with a vaginal ultrasound. You may even find out if you’re expecting twins or triplets. The doctor or sonographer can examine your vagina, placenta, cervix, fallopian tubes, uterus, and ovaries during this procedure. The scan takes roughly 30 minutes on average.

Other types of pregnancy tests

Amniocentesis: A thin needle is placed into the abdomen to extract amniotic fluid guided by ultrasonography, the needle is guided. The fluid sample contains cells, which are subsequently tested for chromosomal abnormalities in a laboratory. Amniocentesis has a one-in-250 chance of causing a miscarriage.

Chorionic villus sampling: A little sample of placenta is taken using a thin needle put via the abdomen or cervix with the use of ultrasonography. The chorionic villi are then examined for chromosomal abnormalities in the laboratory. The chance of miscarriage after chorionic villus sample is one in a hundred.

Ultrasound in Post Delivery

Ultrasound is occasionally used to diagnose issues that arise after the baby is delivered. It’s particularly helpful in determining the cause of a brain haemorrhage and performing an initial assessment of brain anatomy to see if there are any changes in the anatomy that could indicate a previous lesion.


During the second trimester, an ultrasound employs high-frequency sound waves to create an image of the developing baby, the mother’s placenta, and the uterus. An ultrasound can help with a variety of diagnostic tests, such as verifying the pregnancy and gestational age; testing for multiple pregnancies, congenital defects, and/or placental problems; monitoring foetal position, growth, and the level of amniotic fluid; and assisting in other procedures. Hence the technique can be addressed as a “THIRD EYE” for the practioners.


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    3. Gill Moncrieff et al., PLOS ONE 16(12): e0261096.
    4. Shaimaa Fadl et al., RadioGraphics 2017; 37:979–998.
    5. Nahlawi S, Gari N. Sonography Transvaginal Assessment, Protocols, And Interpretation. [Updated 2021 Jun 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022.
Dr Sayamstuti Pattanaik
Dr Sayamstuti Pattanaik


Consultant Obstetrician and Gynaecologist, Laparoscopic Surgeon and Infertility specialist Shanti Memorial Hospital, Rourkela, Odisha.


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