Early Pregnancy Ultrasound: What Are They Used for?
Unlike a few decades, now an early pregnancy ultrasound has become a reality and most of the times is very helpful when it comes to the health of the mother or baby.
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
- 1 How Does an Ultrasound Work?
- 2 What Are Ultrasounds Used for?
- 2.1 The Diagnosis & Confirmation of an Early Pregnancy
- 2.2 Vaginal Bleeding during Early Pregnancy
- 2.3 Determining the Gestational Age & Assessment the Fetal Size
- 2.4 Diagnosis of Fetal Malformations
- 2.5 Placental Location
- 2.6 Multiple Pregnancies
- 2.7 Polyhydramnios and Oligohidramnios
- 2.8 Other Measurements
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.
What Are Ultrasounds 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. – More info!
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.
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.
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.
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.
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.