Ultrasound During Pregnancy: How Does It Work & What Is Used For?

Ultrasounds used in obstetrics and gynecology consist in investigations using ultrasounds performed during pregnancy. From their introduction at the end of 1950s until our times when 3D (4D) ultrasounds are now available in most hospitals and private clinics, ultrasonography has become a very useful diagnostic instrument in obstetrics.

Ultrasound During Pregnancy

In our times, ultrasounds are considered a sure method of examination of the fetus, harmless, precise and with low costs. In time, it has become an indispensable obstetric tool, representing an important role in prenatal care of every pregnant woman.

Table of Contents

How Does an Ultrasound Work?

The equipments used in our times are known as being devices that reproduce images in real time through which the fetus can be seen on a monitor. The devices use waves of high frequency, between 3.5 MHz and 7 MHz (3.5 and 7 millions frames per second) for this type of ultrasound. The waves are emitted by a transducer which is placed in contact with the mother`s abdomen and moves across the belly to reproduce (similar to the light from a torch) the image of every part of the uterus. Repetitive rays of ultrasonic scan the fetus in “thin slices” which are then reflected back to the same transducer.

The information obtained from different reflections is recomposed in an image which appears on the monitor (a sonogram or ultrasonogram). The movements, such as the fetal heart beats or any abnormalities, can be obtained and measured with precision based on the images displayed on the monitor. These measurements represent the base of the gestational age`s evaluation, but also of the size and growth of the fetus.

For the procedures performed in early pregnancy is requested, usually, for the bladder to be full, which might represent a small discomfort. Also, the gel applied on the belly with the role of “leading” the waves emitted by the transabdominal probe can be perceived as wet and cold. However, ultrasounds used in the process of examination itself don`t create any kind of discomfort.

The images recorded on the ultrasound`s monitor represent the first pictures of the baby. You`ll have the opportunity to keep these images, as each ultrasound is accompanied by printed images for the future parents. More than this, morphological ultrasounds can be recorded on a DVD, which is also offered to the parents.

How Does a 3D Ultrasound Work?

3D ultrasounds offer us three-dimensional images (length, width, height) of what we want to examine. They use the same type of ultrasounds as 2D ultrasounds (two-dimensional), but reflected in more angles. The ultrasound transducer scans a series of images, fine slices of the subject, and the computer process these images and present them as a three-dimensional image. The operator obtains images by utilizing computer commands which otherwise wouldn`t be able to display with the 2D ultrasound.

3D ultrasounds are particularly involved in the prenatal examination of mothers and not only: the 3D models of any commercial product are more advanced than their less actual “relatives.” 3D ultrasounds require special ultrasound transducers and specialized software to gather and reproduce 3D images, the time of reply shrinking from a few minutes to a few fractions of seconds when ultra-advanced devices are concerned.

A 3D image with a good resolution is often impressive for parents. From 3D images can be extracted 2D scans. The volumetric measures are more precise with 3D examinations, and both doctors and parents can appreciate more a certain abnormality or its absence. This way is possible to create a special psychological connection between the parent and future baby.

There are lots of studies regarding the undisputed utility of a 3D ultrasound, while the diagnosis of congenital abnormalities gets more attention. It was already proved that congenital defects that are more difficult to detect by ultrasound, such as spina bifida, cleft palate and polydactyly can be demonstrated more clearly by 3D ultrasounds. Other features that are more subtle, such as ears that are positioned a bit below, facial dysmorphia or congenital club foot (varus equine) can be evaluated more easily, which makes the diagnosis of chromosomal abnormalities a lot more efficient. It`s the same thing in the case of cardiac malformations. However, there are also limitations of the method: the undisputed utility of the sonogram depends by the demonstrated abilities of the doctor, the amount of amniotic fluid around the fetus, the fetal position, the degree of obesity of the pregnant woman, so there isn`t always a guarantee of a satisfying image.

3D ultrasounds are superior types of examination to 2D ultrasounds, and are more and more used in the last few years. These ultrasounds use advanced equipment capable to offer a series of images of superior quality (photographic) of the fetus.

The investigation is superior in the evaluation of congenital abnormalities, such as spina bifida or cleft palate, but it isn`t performed as a routine examination because a 3D ultrasound cost is expensive. This type of ultrasounds is available in some university hospitals and private clinics, the investigation being quite costly. – Learn more!

A lot of times parents choose these types of ultrasounds because of the clear 3D ultrasound images that they offer, having a great emotional impact on the parents. Even though from the morphologic point of view a 3D ultrasound can offer false information, lots of parents choose them for the reason described above.

How Much Is a 3D Ultrasound?

If you would be interested in having 3D ultrasound images at home with you, take a look in the yellow book or online and check what type of business they provide. Generally speaking, the expenses are between $100 – $300, depending on the chosen packages. Some businesses offer promotions on special days, such as “Tuesdays All Packages for as Low as $99.” You can also call them to check if you can get a special discount.

What Is a 4D Ultrasound?

Recently, 4D ultrasounds appeared on the market (length, width, height and time) or 3D dynamic ultrasounds, making possible to see the fetal movements before he was born, which contributed at the increase in popularity of this methods for parents. It`s known to have a strong catalyst effect of building a special relationship between the mother and baby even before birth. 4D ultrasounds are recommended between 26 and 32 weeks of pregnancy to ensure an excellent quality of the displayed images as the animated facial movements are the best represented during this period.

A lot of doctors don`t consider 3D and 4D ultrasounds mandatory for prenatal examination in detriment of the conventional 2D ultrasounds, but even recommend to parents to consider them additional instruments, such as a  Doppler ultrasound. Lots of diagnoses will still be put based on the 2D evaluation of pregnancy. 3D ultrasounds seem to have an increased potential in research and the study of embryology.

What Is Ultrasound Used for?

There are many reasons for which an ultrasound is used. Here are the most important ones.

The Diagnosis & Confirmation of an Early Pregnancy

The gestational age can be evaluated starting with 4 ½ weeks of pregnancy, while the Yolk sac is visible from the 5th week. The embryo can be seen and measured from 5 ½ weeks of pregnancy. Also, ultrasounds can confirm with precision the presence of pregnancy in the interior of the uterine cavity or in its exterior.

Vaginal Bleeding during Early Pregnancy

The viability of the fetus can be questioned in the presence of bleeding during early pregnancy. The heart rate can be visible and detectable by the Doppler ultrasound at 6 weeks of pregnancy, and can be measured since the 7th gestational week. If all these are present, then in proportion of 95% we deal with an evolving pregnancy. Miscarriages and anembryonic pregnancies (an embryo implanted on the uterine wall, but which no longer develops) indicate typical images of a dyform gestational sac with the absence of the fetal pole (a group of fetal cells separated by the Yolk sac) and of heart rate.

The fetal heart rate tends to vary depending on the gestational age in early pregnancy. A normal fetal heart rate at 6 weeks of pregnancy is of around 90 to 110bpm (beats per minute), and at 9 weeks of 140 to 170bpm. A heart rate under 90bpm at 5 to 8 weeks is associated with a high risk of miscarriage.

Lots of women don`t ovulate during the 14th day of menstrual cycle, so the results of the first ultrasound must be interpreted with caution. The diagnosis of miscarriage should be placed after a series of ultrasounds which indicate the lack of the gestational sac. For instance, if the ultrasound can discover an embryo of 7mm, but not a constant heart rate, then we can deal with a diagnosis of miscarriage. In such cases, the gynecologist will recommend a new ultrasound at 7 to 10 days for avoiding any errors.

The moment when a woman gets a positive pregnancy result can be useful in establishing a probable conception date. For example, a positive result at 3 weeks can indicate a pregnancy which has a gestational age of 7 weeks. – More details!

An ultrasound is indispensable in the presence of bleeding during the first trimester of pregnancy when diagnosing ectopic or moral pregnancies (the development of abnormal tissue in the uterus due to genetic error when the egg was penetrated by sperm).

Determining the Gestational Age & Assessment the Fetal Size

Fetal measurements reflect the gestational age of the fetus, especially during the early stages of pregnancy. At patients who aren`t able to reveal with precision the date of the last menstrual cycle, these measurements need to be made as early as possible as soon as a positive pregnancy result was obtained for establishing a correct gestational age. In the last months of pregnancy, measuring the body parameters of the fetus will allow the assessment of the development and size of the fetus, being useful in case of intrauterine growth restriction (intrauterine growth retardation or IUGR).

These measurements are:

  • Crown-rump length determination (CRL): meaning the crown-rump length. The measurement can be performed between weeks 7 and 13, offering a very precise estimation of the gestational age, the precision margin being of 3 to 4 days from the last menstrual cycle. It should be mentioned that if it was established a probable due date based on this measurement, this date shouldn`t be changed later by another ultrasound. For example, if at an ultrasound made with 6 to 8 weeks later it`s noticed that the due date should be postponed, the date specified by the previous measurement shouldn`t be changed, but rather the doctor should interpret it in the idea that the fetus doesn`t grow in the rhythm that he should.
  • Biparietal diameter (BPD): It represents the diameter from the 2 extremities of the head. The measure is performed after week 13 of pregnancy and it varies from 2.4cm at 13 weeks to 9.5cm at term. Babies of same age can have different biparietal diameters, that`s why the measurement performed in early pregnancy is uncertain. The measurement of the biparietal diameter should be performed as soon as it`s relevant, meaning week 13.
  • Femur length (FL): Measures the longest bone of the body and reflects the longitudinal growth of the fetus, being just as useful as biparietal diameter. It increases from 1.5cm at 14 weeks of pregnancy to 7.8cm at term. Just as biparietal diameter, the measurement should be performed as soon as it becomes relevant (at week 14).
  • Abdominal circumference (AC): The only important measurement that is made during the last months of pregnancy reflects most the fetus`s size and weight than the gestational age. Successive measurements are useful in monitoring the fetus`s development, that`s why the method of measuring the abdominal circumference shouldn`t be used as a method of indicating the gestational age.

The fetus`s weight at different gestational ages can be estimated with big precision using polynomial equations containing BPD, FL and AC, using a computer software and charts of growth that are already available. For instance, a biparietal diameter of 9cm with an abdominal circumference of 30cm indicates a weight of the fetus of 2.85kg.

Diagnosis of Fetal Malformations

Lots of the fetus`s structural abnormalities can be diagnosed by ultrasound even since the beginning of the second trimester of pregnancy. These may include hydrocephalus, anencephaly, myelomeningocele, achondroplasia (the most common form of dwarfism), spina bifida, exomfalus (umbilical hernia). The equipments of latest generation can also diagnose cleft palate or congenital cardiac abnormalities even since the first half of pregnancy.

An ultrasound examination of chromosomal abnormalities during the first trimester of pregnancy is indispensable, such as the absence of nasal bone and an increased nuchal translucency (the area behind the neck) are, at present, common measurements for determining Down syndrome. Also, ultrasound can also be used as support for other prenatal diagnostic procedures such as amniocentesis, chorionic villus sampling (CVS) or cordocentesis. – Read this!

Placental Location

Ultrasound is indispensable in locating the placenta and determining its inferior margins for diagnosing or excluding a placenta previa. The measurement can be used for detecting placental abnormalities, gestational diabetes, Hydrops fetalis (severe swelling caused by an accumulation of liquid in the uterine cavity), Rh isoimmunization and severe intrauterine growth restriction.

Multiple Pregnancies

In this case, ultrasound is invaluable in establishing the fetal presence, the number of fetuses, the evaluation of retardation and fetal abnormalities and presence of placenta previa.

Polyhydramnios and Oligohidramnios

The amniotic liquid in large or small quantities can be detected easily by ultrasound. Both cases can cause adverse effects to the fetus and, in both cases, the ultrasound examination must be made with great care to eliminate the possibilities of intrauterine growth restriction and congenital fetal abnormalities such as intestinal  atresia, hydrops fetalis or rental dysplasia.

Other Measurements

Ultrasounds are successfully used in:

  • Establishing the baby`s sex (starting with the week 16);
  • Confirmation of intrauterine death;
  • Confirmation of the fetus`s presence in exceptional cases;
  • Evaluating fetal movements, tone and breathing;
  • Diagnosing uterine and pelvic abnormalities: ovarian cysts, fibrosis.

How Many Ultrasounds Are Done during Pregnancy?

There isn`t an exact number of ultrasounds that a pregnant woman needs to do. An additional ultrasound is indicated whenever an anomaly of the pregnancy is suspected. In reality, the first ultrasound is recommended at 7 weeks for confirming the pregnancy, excluding an ectopic pregnancy, confirming the presence of cardiac activity and establishing the pregnancy`s age and due date.

The second ultrasound is performed between 20 and 22 weeks of pregnancy to check the presence of possible fetal abnormalities, as the fetus is big enough for a careful evaluation of fetal anatomy. That`s why it`s also named a morphological ultrasound. The multiple pregnancy is also evaluated accurately now, as well as the baby`s growth parameters, the placenta`s position and the baby`s sex.

Lots of centers perform an ultrasound between weeks 11 and 14 to measure the nuchal translucency and the presence of fetal nasal bone which helps in diagnosing the Down syndrome. A new ultrasound can be recommended during the 32nd week or even later for determining the position of the fetus, his weight, the rhythm of growth, as well as the position and weight of the placenta. Some doctors perform a last ultrasound during the 39th – 40th weeks of pregnancy to check the quantity of amniotic liquid, weight and cardiac rhythm of the fetus. The total number of ultrasounds depends on the pregnancy health; if at an ultrasound were detected certain abnormalities, than the pregnancy requires an additional evaluation. – More info!

Which Is the Pregnancy`s Minimum Age when an Ultrasound Can Be Done?

In case of pregnancy, ultrasound is the only method that can visualize the fetus without adverse effects and without limiting the number of examinations.

The intrauterine evolution knows 2 stages:

  • Embryonic stage – up to 10 weeks of pregnancy
  • Fetal stage – from 10 weeks of pregnancy.

Ultrasounds can be performed:

  • In the embryonic stage – when their main purpose is to confirm the pregnancy, their position (intrauterine or ectopic), viability (demonstrated through the presence of tonus and heart beats, usually around 5 weeks of gestation through the endovaginal examination).
  • In the fetal stage – when the ultrasound is performed transabdominal and the main purpose is to detect abnormalities.

Does Ultrasound Have Side Effects?

There were numerous studies made that tried to demonstrate the effect of ultrasounds on embryo or fetus while developing. Studies from the last 35 years have shown the fact that an ultrasound doesn`t have adverse effects on the development of the fetus or that there would be a harmful cumulative effect after multiple exposures to ultrasound.

There are some smaller studies which suggested that ultrasound can increase the risk of health problems for the fetus: low birth weight, issues of communication and hearing or clumsiness. However, there isn`t enough evidence to prove it.

Do Ultrasounds Detect Certain Fetal Abnormalities?

A routine ultrasound shouldn`t scare a pregnant woman because in most cases this doesn`t identify major abnormalities offering guarantee for a healthy baby. Still, in some situations it can be detected some congenital anomalies, malformations or functional abnormalities more or less serious.

Not any fetal abnormality is synonym with a compromised pregnancy, lots of the health problems of the fetus being able to be treated even from the gestational period.

Some cardiac anomalies can be partially corrected through endoscopic surgeries. Cardiac arrhythmias (rhythm disorders) can be successfully treated by administrating some antiarrhythmic drugs. Some congenital abnormalities of the urinary tract can be corrected surgically. – Click here!

An ultrasound is very important because if it detects certain fetal health problems that can be corrected prenatal, it can offer the necessary monitoring of the fetus until birth when the newborn will be able to receive the specialized medical treatment.

Ultrasounds offer the possibility of interrupting a compromised pregnancy (severe congenital malformations with a bad prognosis after birth) which protects the pregnant woman from a major psychological trauma.

Image courtesy of americanpregnancy.org

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