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  • Dr Tarangini V

Pregnancy Ultrasound, When and Why?

When do you get an ultrasound during pregnancy?

First-trimester screening: It can be performed during the 11th to 14th week of pregnancy. Ultrasonography helps assess the risk of Down's syndrome and certain other chromosomal abnormalities. What do you anticipate from the second-trimester ultrasound? The second ultrasound will take about 18-20 weeks. Ultrasonography, also known as an "anatomical scan," is done late in pregnancy to check the growth of important organs in the baby and the location of the placenta. In late pregnancy, within 34-36 weeks of gestation, an ultrasound scan of the fetus is performed using an abdominal sensor. At this stage of pregnancy, the fetus has fully developed all of its important organs and is in a period of rapid growth and maturity.

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What are the common birth defects detected during pregnancy?

One of the most common birth defects – affecting about 1 out of 100 pregnancies –entails a part of the baby that is often outside its body. It takes place when the umbilical cord has two blood vessels instead of three. It does warrant a cautious, detailed look at other structures in the fetus, but unlike some of the other birth defects, this is usually not concerning as long as it`s the only abnormality.

Congenital heart defects are not unusual. It`s difficult to predict them because we frequently see small holes inside the heart when an ultrasound is performed. Generally, these holes disappear by the time the baby is born.

Can ultrasound detect any abnormalities in the baby?

Prenatal ultrasound has proven to be suitable for prenatal diagnosis of chromosomal abnormalities. Thickened nasal folds, a sign of the first ultrasonography of Down's syndrome, were first reported in 1985. Since then, the markers identified by some ultrasonography have been described as being associated with Down's syndrome. Gene sonograms, including a complete search for signs of aneuploidy ultrasonography, are used to identify fetuses at high risk of aneuploidy and, normally, aneuploidy during pregnancy in the absence of ultrasound markers. Combining genetic ultrasonography with maternal serum screening may be the best way to assess the aneuploidy risk of women who wish for such an assessment in the second trimester.

Ultrasonography allows an ultrasound examiner to view rare illnesses.

The following are the rare illnesses-

Anencephaly, spina bifida, cleft lip, diaphragmatic hernia, gastroschisis, serious heart defect, bilateral renal agenesis.


Anencephaly - Anencephaly is a serious birth defect in which a baby is born without a part of the brain or skull. This is a type of neural tube defect (NTD). Anencephalic fetuses are correctly identified at 12-13 weeks gestation. Anencephaly occurs when there is no cranial vault. The first-trimester scan at 12-13 weeks enables reliable diagnosis and aggressive treatment of anencephaly.



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Ultrasound of anencephaly


Spina bifida - Spina bifida is a type of birth defect that occurs when the spine and spinal cord don`t form properly. It's a deformity of the neural tube. The neural tube is the structure in a growing embryo that eventually becomes the baby's brain, spinal cord, and the tissues that enclose them. Fetal ultrasound is the most precise method to diagnose spina bifida in your baby before delivery. Ultrasound can be performed during the 1st trimester (11 to 14 weeks) and second trimester (18 to 22 weeks). Spina bifida can be accurately diagnosed during a second-trimester ultrasound scan.

Cleft lip: A cleft lip is an opening or rift in the upper lip that occurs when the fetal facial structure is not completely closed. Babies with cleft lips may also have cleft palate (cleft palate). From around the 13th week of pregnancy, a cleft lip can be noticed by ultrasound. As the fetus continues to grow, it may be easier to accurately diagnose cleft lip. The Cleft palate that occurs alone is more difficult to detect with ultrasound.

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Ultrasound of Cleft Lip

Diaphragmatic hernia: Diaphragmatic hernia is a congenital defect in which the diaphragm (the large muscle that separates the chest and abdomen) is punctured. Abdominal organs (intestines, stomach, liver, etc.) can advance from the diaphragm holes into the baby's chest. Congenital diaphragmatic hernias can be detected by ultrasound as early as the 16th week of pregnancy. CDH is strongly suspected if the thoracic cavity of a developing fetus has abdominal organs such as the intestines and stomach.

Gastroschisis: Gastroschisis is a birth defect with a hole in the abdominal wall near the navel. The baby's intestines and sometimes other organs are outside the baby's body and come out of the holes. Gastroschisis is usually detected late in pregnancy using prenatal ultrasonography. Diagnosis is often made when prenatal ultrasonography is done 20 weeks before pregnancy. The diagnosis was already made at 12 weeks gestation using transvaginal ultrasonography.

Bilateral renal agenesis: Bilateral renal aplasia is the absence of both kidneys at birth. It is a hereditary disease characterized by fetal renal failure. This lack of kidneys causes a lack of amniotic fluid in pregnant women. Bilateral renal aplasia is usually detected during the 18th to 22nd week of gestation during normal prenatal ultrasonography. If you find that the kidneys of your baby are deficient due to low amniotic fluid, your doctor may recommend further tests such as MRI (Magnetic Resonance Imaging) to confirm the diagnosis.

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Serious heart defect: Congenital heart disease may first be suspected during regular ultrasound scans of the baby in the womb. Next, special ultrasonography called fetal echocardiography is done during about 18 to 22 weeks of pregnancy to confirm an accurate diagnosis.



 

References

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  2. Molina FS, Avgidou K, Kagan KO, Poggi S, Nicolaides KH. Cystic hygromas, nuchal edema, and nuchal translucency at 11-14 weeks of gestation. Obstet Gynecol. 2006 Mar;107(3):678-83.

  3. Sinkovskaya ES, Chaoui R, Karl K, Andreeva E, Zhuchenko l, Abuhamad AZ. Fetal cardiac axis and congenital heart defects in early gestation. Obstet Gynecol. 2015 Feb;125(2):453-60.

  4. Chasen ST, Kalish RB. Can early ultrasound reduce the gestational age at abortion for fetal anomalies? Contraception. 2013 Jan;87(1):63-6.

  5. Merz E, Bahlmann F, Weber G, et al. Three-dimensional ultrasonography in prenatal diagnosis. J Perinat Med. 1995;23:213–222.

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