Ultrasound scans use the ability of sound waves to pass through tissues and rebound on them depending on their density. The ultrasound then turns that bounce of sound or echo into an image that allows the specialist to make a diagnosis.
Ultrasounds are completely innocuous and will not harm the mother or the fetus in any case, since they lack the ionizing effect of X-rays.
Types of ultrasounds and how they are done
There are two types of ultrasounds:
- Abdominal: exceptionally done during the first trimester, but always in the second and third. The woman lies on her back and a gel that facilitates the transmission of ultrasound is spread on her abdomen. An ultrasound probe is in charge of obtaining and transmitting the images to a screen.
- A full bladder is recommended for it improves the quality of the image.
- Transvaginal: most indicated for the first trimester. The woman is placed in a gynecological position and a probe protected by a latex sheath covered with gel is inserted in the vagina.
- It does not require preparation and is more effective if the woman has an empty bladder.
The first-trimester ultrasound is becoming more important as more new technologies allow to diagnose possible alterations early and accurately. The route of choice is transvaginal, although it can sometimes an abdominal ultrasound may follow.
Objectives of the first-trimester ultrasound
In the first place, although they represent only 1% of the cases, we seek to rule out ectopic pregnancy, since this type of pregnancy outside the uterus is not viable.
A first-trimester also allows to determine the gestational age through the measurement of the embryonic length from the crown to the rump. The measurement used to establish this data is the cephalocaudal trend.
The vitality of the embryo will also be examined, evaluating the heart rate with a vaginal ultrasound from the sixth week or abdominal from the seventh week.
Multiple pregnancies can be detected as well as if the embryos share or not placenta or amniotic bag.
The patient’s uterus and ovaries will also be checked.
Finally, signs of chromosomal alterations can be screened by ultrasound. This technique studies, among other variables, the translucency or nuchal fold of the fetus, that is, it analyzes the fluid that all embryos have behind the nape of the neck. If the thickness exceeds 3 mm, then it is considered pathological, as well as the presence or absence of the nasal bone. These findings will force us to perform other diagnostic tests such as corial biopsy or amniocentesis to rule out chromosomal alterations, of which the most frequent is Down syndrome.
In addition to the ultrasound data, maternal age and biochemical markers – the plasma protein associated with pregnancy (PAPP-A) and the free fraction of the β-chorionic gonadotropin (free β-HCG), which are hormones associated with functioning, will screened.
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