Ultrasound in pregnancy – evaluation during first trimester

Technological advances achieved in the last years have contributed to increase the performance of ultrasound in pregnancy.

So, now it’s possible to evaluate and monitor the development from very early stages of the embryo.

By the end of the 4th week of pregnancy, the product of conception have attained a diameter of 2 to 3 mm and reached the threshold of detection by state-of-the-art transvaginal ultrasound transducers.

This is also the turning point for pregnancy test.

Modern home pregnancy tests, highly sensitive, become positive as a result of measurable quantity of human chorionic gonadotropin (hCG), a hormone produced by placenta, which now is in its very early forming stage (trophoblastic tissue).

During the first 8 weeks of pregnancy, so called "embryonic" stage, organogenesis takes place. Heart and other internal organs begin to form from this early stage of pregnancy.

Subsequently in the fetal stage (from 9th weeks until birth), the development focuses especially on fetus growth and organ maturation.

By performing two-dimensional ultrasound in pregnancy during the first trimester the aims are:

  • To confirm the existence and the viability of the embryo
  • Accurately to establish the age of pregnancy
  • To determine the number of embryos
  • For multiple pregnancies, that represents 2% of natural pregnancies and 10% of pregnancies after assisted human reproductive methods, to determine the number and location of gestational sacs and placentas
  • To evaluate maternal symptoms such as pain or bleeding

The association of the Doppler ultrasound examination makes possible to assess the development of the cardio-circulatory system and umbilical system by using an endovaginal transducer.

Umbilical cord has in its component:

  • 1 vein (carries oxygenated blood and nutrients, from placenta to fetus) and
  • 2 arteries (carry from fetus to placenta deoxygenated blood and “waste" products resulting from fetal metabolism)

It is possible to identify circulatory features characteristic for the first trimester obstetric pathology, with an important diagnostic and prognostic role.

For example: Defective embryonic implantation or abnormalities in implantation and placental development.

On the 6th  week of amenorrhea (lack of menstrual cycle), it is possible to visualize the embryo, of 3-5 mm in dimensions , having a curved shape the cephalic extremity more developed.

Also, Doppler ultrasound can localize and identify with certainty the fetal heartbeat, which by Bi-dimensional ultrasound can’t be achieved due to the small size of the embryo.

Thus it is possible to perform a differential diagnosis with a pregnancy stopped in evolution, in the first weeks. This may occur in 2% of cases.

The late onset of fetal heart beats or a frequency of less than 120 beats / minute at this age has generally negative prognostic significance, being more common in spontaneous abortions or Down syndrome.

During the 8th week of pregnancy the sketching of cartilaginous skeleton is identified and the buds for limbs are visualized as paddle like hands and feet, the genitals begin to develop but are not visible by ultrasound examination.

On weeks 9th and 10th, the fetal structures: head, trunk and limbs, as well as circulation in the main fetal arteries, are clearly highlighted.

From the 11th and 12th weeks of pregnancy we can identify the fetal structures, making it possible to perform a first morphological evaluation of the fetus, by ultrasound examination.

On this occasion, it can be identified first elements suggestive for some genetic diseases (e.g. chromosome abnormalities such as Down syndrome -Trisomia 21, Turner syndrome, Edwards syndrome- trisomy18, Patau syndrome- trisomy 13, cardiac malformations) characterized by structural malformations.

Fetal aspects which are evaluated in the first trimester by ultrasound:

  • The nuchal translucence, representing the thickness of the liquid collection located in the fetal neck region
  • The presence or absence of nasal bone
  • The maxillofacial angle
  • The appearance of blood flow through tricuspid valves from the heart, through venous duct in the fetal liver
  • The presence or absence of major fetal abnormalities at this age (congenital anomalies that can affect the central nervous system, heart, ventral wall, urinary tract, and skeleton)

Fetal findings by ultrasound in pregnancy are part of the first trimester combined screening test, which are done between weeks 11th  and 13th (plus 6 days) for the estimation of risk for some genetic diseases (chromosomal abnormalities).

For each pregnant an individual risk score is calculated based on the following parameters:

  • "double test screening" (identification in the venous blood of the two pregnancy hormones; PAPP-A acronym of Pregnancy-Associated Plasma Protein A and Beta free hCG- acronym of human Chorionic Gonadotropin)
  • the actual age of the pregnant woman
  • fetal heart rate (FHR) and
  • ultrasounds findings mentioned above

Calculation of individual risk does NOT allow for establishing a diagnosis of a chromosomal abnormality. It’s just give an estimation of the risk for such a condition.

The only possibility to set a diagnosis of a chromosomal abnormality is by performing 2 invasive tests:

  • Chorionic villus sampling, which usually is indicated to be performed between weeks 10th -14th or

  • Amniocentesis, in general can be perform between weeks 15th -18th

The decision to continue or not the investigations through one of the invasive method will be taken by you only after having a consultation with your obstetrician physician and, if possible with a genetics doctor.

Ultrasound in pregnancy can also provide other findings such as:

  • Fetal length (LCC)
  • Heart rate;
  • Bladder size;
  • Unique umbilical artery

Some structural defects may be due to genetic causes or sometimes as a result of an external factor action: drugs, toxic substance or some viral infection contacted during the early pregnancy. There are also situations in which no obvious cause can be detected.

If you want to watch what it looks like and what happens to your baby between weeks 8 and 11, click on below video:


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