Ultrasound and Pregnancy

Newly-expectant parents may feel apprehensive about their first pregnancy and have many questions regarding the development of their unborn child. The Obstetrician will inform them about the different stages of the pregnancy, as well as appropriate, and necessary, testing to monitor the progress of the pregnancy. For over 30 years, Ultrasound has been used as a valuable diagnostic tool for Obstetricians.

The different stages of pregnancy are broken down into trimesters, each filled with exciting changes and development:


Trimester One –      weeks 1 to 12

Trimester Two –      weeks 13 to 27

Trimester Three –   weeks 28 to 42


How is the ultrasound performed? The expectant mother may be asked to refrain from voiding before the ultrasound, causing a full bladder. This brings the bladder up, rather than lying flat, allowing for better view of other organs.

The expectant mother will be asked to change into a gown. After lying on an examination table, she will then be asked to move down the table until she is able to place her feet into stirrups, cup-shaped holders that are attached to the table. This will gently bend her knees and place her in position similar to a pelvic exam. The Obstetrician will then insert a small ultrasound probe into the vagina, obtaining ultrasound pictures across or through the vagina; hence, the name transvaginal.

The expectant mother may also have an ultrasound by placing the probe on the skin of the abdomen, rather than into the vagina. After she is lying on the table, gel is placed on the probe, which improves skin traction. The ultrasound probe is then moved around the abdominal area while the Ultrasound Tech seeks the best possible images of the unborn child.

The sex of the baby can be determined by the 20th week

During the ultrasound, the expectant parent (s) can view images of their unborn child for the first time on the television monitor, an emotional event. The Ultrasound Tech will instruct the parents that white and grey areas indicate tissue or bone, while darker areas indicate liquid such as amniotic fluid. The parents may even receive printed images of their unborn child to take home to family.


10 weeks

Why would ultrasound be performed at this stage? Ultrasound is typically performed before fourteen weeks of pregnancy to ensure the pregnancy is viable (alive) and correctly placed. If a pregnancy starts in the fallopian tubes, an ectopic pregnancy, this can cause the fallopian tube to rupture leading to life-threatening hemorrhage.

In addition, the Obstetrician verifies the pregnancy is a single child. If the ultrasound indicates multiple fetuses, special precautions will be taken during the pregnancy for both the mother and child (s).

Many times the expectant mother’s last menstrual period date is unknown. The Obstetrician is able to determine the estimated due date (EDD) at this time by measuring the length of the fetus from the top of the unborn child’s head to the rump, known as CRL, crown rump length measurement.

Ultrasound allows the Obstetrician to detect any abnormalities at this stage of development. From 11 to 14 weeks, by measuring the thickness of the skin located at the back of the neck (nuchal translucency measurement), the Obstetrician can calculate the risk of the unborn child having a chromosome abnormality.

How big is the unborn child? At this stage of pregnancy, the unborn child is only a few millimeters long. Although tiny, the organs have formed. Fingers and toes begin to separate and the tail disappears, while tooth buds begin to form in the mouth.


Eighteen weeks

Why would ultrasound be performed at this stage? The most common stage to have an ultrasound is between the 16th and 20th week of pregnancy. The Obstetrician will be able to clearly view the unborn child’s organ systems at this stage. This allows the organs to be examined to ensure the unborn child is growing and developing at a normal rate. If the expectant mother is overweight, this can cause the ultrasound to be a bit more difficult to view clearly. The child’s sex can also be determined at a 80-90% certainty rate. Earlier sex determination can be difficult if the unborn child is curled or turned.

The Obstetrician will also view the placenta and its position in the uterus. This ensures the placenta has attached higher up in the uterine wall, away from the cervix (opening).

How big is the unborn child? At this stage of development, the ultrasound will show much more detail. Along with the legs and arms, the unborn child’s brain, heart, kidneys, lungs and even spine is visible.  The unborn child’s ears will begin to protrude and hearing will develop, allowing sounds such as the mother’s heartbeat to be comforting. The unborn child’s eyes begin to form and soft bones begin to harden.


Thirty weeks

Why would ultrasound be performed at this stage? At this stage of the pregnancy, an ultrasound is performed so the unborn child’s growth can be documented.  It is important the unborn child is growing and developing at a normal rate. The Obstetrician estimates the unborn child’s growth by measuring the fetus, as well as comparing these measurements with previous ultrasounds.

Estimating an unborn child’s growth can be difficult. For some women, they may have a history of pregnancies that resulted in a smaller baby. For others, a serious medical condition could affect the unborn child’s growth such as pre-eclampsia. Pre-eclampsia can cause the expectant mother to have a high increase in her blood pressure as well as protein in her urine, due to kidney problems. For the mother, pre-eclampsia can affect kidneys, brain and liver. For the unborn child, pre-eclampsia can lead to complications such as premature birth, low birth weight and even stillbirth. Pre-eclampsia can lead to seizures, and is then referred to as eclampsia.

 In the United States, Eclampsia is the second leading cause of an expectant mother’s death  

Should the expectant mother begin to develop signs of pre-eclampsia, she and the unborn child will be closely monitored. The only ‘cure’ is to deliver the child, sometimes prematurely.

Ultrasound is also performed at this stage of pregnancy to view the umbilical cord. This is the connecting cord from the unborn child’s abdomen to the placenta, essentially the ‘life-line’ between the unborn child and mother. The umbilical cord is made up of three blood vessels- two that carry blood to the placenta and one larger vein that returns blood to the unborn child. This cord can grow up to 60 cm long. When the child is born, the umbilical cord is cut, which will then form the baby’s belly-button.

The ultrasound will allow the Obstetrician to view the umbilical cord, and its bloodstream, to see if it is functioning properly, transporting oxygen and nutrients to the unborn child. The placenta is also checked to verify it is in normal position, or if it is too close to the inside of the expectant mother’s cervix. This condition, known as placenta-praevia, can be very dangerous for both mother and unborn child.

Birth defects occur more often in pregnancies with placenta-praevia

It can cause the placenta to tear away from the uterine wall (placenta abrupio) severe bleeding during delivery, birth defects, as well as having to deliver the unborn baby early. Some cases of placenta-praevia are found only when the expectant mother experiences symptoms such as bleeding.

How big is the unborn child? The unborn child weighs about three pounds at this stage, hasand measures around fifteen inches long. The expectant mother may feel the baby hiccup. The unborn child can taste and see, and the toenails and fingernails have grown longer.

Ultrasound is an important diagnostic tool for the Obstetrician and is used to determine the unborn child’s age or sex, to monitor placement, development and heart rate, identify any abnormalities or developmental problems and monitor the expectant mother’s placenta, pelvis and amniotic fluids.

1 thought on “Ultrasound and Pregnancy”

  1. This issue is very important to me. I have an 8 year old who has sesorny issues, eating and sleeping problems and now as of last year is epileptic (benign rolandic epilepsy). Loud noises, sirens were of particular distress to her as a young child. We were living (sleeping) in a home with high EMF, plus I had two ultrasounds, same day at 6 months, the DR used a fetal doppler at 5,6,7, and 8 months and another test (not sure if it was ultrasound) at 9 months to confirm the baby was in the right position. They left me on the machine too long and I became extremely uncomfortable and had to call out for them to remove it. My daughter was born with a low apgar score and failed to gain weight till three weeks. I am a health nut and worked hard to have a healthy pregnancy. My first child was robust, healthy and had no problems, no ultrasounds. I was also 25 when she was born. This time at 42, and under the care of a regular doctor, rather than midwife, and I was cautious. I have suspected the effects of ultra sound, on my daughter’s behavior, sleep, appetite problems. I believe it is a contributor.

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