What are ultrasounds..?
Ultrasounds are sound waves which frequency is higher than what the human hear can detect. Ultrasounds are used in medicine for imaging or sonography since they are a non-invasive and safe method to capture size and structure of organs and tissues in real time tomographic images. Sonography allows the physician to see small internal details in structures and tissues without posing any risk to the patient’s heath since it does not use radiation .
Obstetric sonography is used in prenatal care to visualise fetuses. In this procedure the sonographer puts a handheld instrument on the surface of the belly pointing towards the uterus. The sound waves transmitted penetrate the uterus and bounce off the fetus or embryo allowing the device to detect the position, size, form and movements of your baby. The signal is converted to a real time image by the computer.
When do I have to do an ultrasound during pregnancy?
As with most things in pregnancy the amount of times you will have to perform an ultrasound varies from woman to woman. The times you should to get an ultrasound are the following:
- Early pregnancy. The first ultrasound is usually performed at 6 to 10 weeks to confirm the gestational date.
- The second ultrasound is done mid-pregnancy between 16 and 20 weeks. This is when you can learn the baby’s gender.
- During a procedure. If you perform a genetic diagnostics test (amniocentesis, nuchal translucency test or chorionic villus sampling) the doctor performing it will use ultrasound in order to do the procedure.
- Medical complications. If you have any medical complications (hypertension or diabetes) or an emergency (cramps and bleeding), you will have to perform ultrasounds more frequently.
Early pregnancy ultrasound
In this stage the ultrasound will be able to show:
- Less than 5 weeks. The pregnancy is not detectable by ultrasound; the technician can only see the thickened endometrium and an ovulation cyst. Which do not indicate for sure that you are pregnant.
- At 5 to 6 weeks. The gestation sac is small but detectable usually only by transvaginal ultrasound. It is too early to detect the embryo’s heartbeat in most cases. Your doctor can confirm the location of the yolk sac.
- At 6 to 7 weeks. The embryo measures 5 to 9mm and the heartbeat is detectable.
- At 8 to 11 weeks. The embryo can be seen by trans-abdominal ultrasound.
- At 10 to 11 weeks. The embryo is 3 to 4 centimetres long, has members and head formed and can move in the pregnancy sac.
Not all women need to have an ultrasound in this early part of the pregnancy. Your doctor may request this ultrasound for a number of reasons, including:
- Confirming your baby’s heartbeat.If you had vaginal bleeding during your first trimester your doctor will schedule an ultrasound to detect the baby’s heartbeat. If it is detectable you have 90% chance of not having a miscarriage.
- Date your pregnancy.Sometimes it is difficult to determine exactly the due date since there are women who do not remember their last menstrual period or that have irregular menstrual cycles. This ultrasound gives an estimate of the date of conception.
- Location of the embryo. If there are suspects of an ectopic pregnancy your doctor will order an ultrasound to check the position of the embryo in the uterus.
- Number of embryos.If you have undergone fertility treatments in order to conceive, have a family history of twins or a larger uterus than expected, your doctor may order an ultrasound to see the number of embryos.
- Risk of miscarriage. This ultrasound can be used to identify factors associated with risk of pregnancy loss, such as a slow heartbeat or pregnancy sac irregularities.
- Reproductive organs state.If you have a history of fibroids in the uterus or ovarian cysts your doctor can order the ultrasound to check the state of these organs.
Second trimester morphology ultrasound
The midterm ultrasound is usually performed between 18 and 20 weeks gestation. This ultrasound is part of routine pregnancy care and it can check the development of the baby. There are many parameters to be assessed during this ultrasound:
- The general anatomy of the baby. The ultrasound checks for all the structures that have already developed in your baby. By this time the fetus is fully formed, measures about 16.5 centimetres and weights 300 grams.
- Measurements of the baby. The ultrasound is used to measure the baby’s head, abdomen, legs, arms and between eye distance. This way the sonographer can tell if the baby is developing inside the normal parameters.
- Gestational age. By the measurements of the baby the gestational age can be calculated more precisely than before.
- The number of babies. In case you did not have an early pregnancy ultrasound.
- The baby’s heart rate. The baby’s heart rate should be between 120 to 180 beats per minute.
- The placenta placement. This ultrasound is used to check for placenta previa by assessing the position of your placenta relative to the cervix.
- The amniotic fluid volume. This is measured subjectively.
- The uterus and cervix. It is important to determine the cervix length if you have any risk factors. The anatomy of the uterus can also be assessed to check for the presence of fibroids.
- The gender of the baby. This ultrasound can also be used to determine the gender of the baby if the parents wish to know. Although, this is not always possible due to the baby positioning.
Third trimester ultrasound
This ultrasound is usually performed after 22-24 weeks gestation and is the last ultrasound during pregnancy if it proceeds normally. The sonographer will be able to assess at this point:
- The baby’s anatomy. All the parts of your baby’s body are observed and measured in this ultrasound to see their morphology.
- The baby’s position. Especially towards the end of the pregnancy it is important to check if your baby is correctly positioned to birth.
- The baby’s size. This ultrasound is used to check if your baby is growing normally by measuring length and estimating weight.
- Placement of the placenta. Especially if the previous ultrasound showed abnormalities or if you have symptoms of placenta previa.
- The general status of the baby. This ultrasound can reassure the doctor that the pregnancy is progressing well.
- The volume of amniotic fluid.
- The umbilical’s cord blood flow. These are known as Doppler studies and help to assess the baby’s health and help to decide if the baby has to be delivered early in the case of complications.
- Heart rate of the baby. The baby heart rate should be between 120 to 180 beats per minute.
- The uterus and cervix. If you have signs of premature labour it is important to check your cervix’s length and the uterine anatomy.