Sonar in Pregnancy – A Handy Tool
By Dimakatso Mphelo, Sonographer in Private Practice
What is ultrasound Imaging (sonar)?
Ultrasound imaging (sonar) involves the use of probe and ultrasound gel to expose the body organs to high-frequency sound waves to produce diagnostic image. It is a painless and non-invasive procedure that helps healthcare professional diagnose and treat a wide variety of medical conditions.
Ultrasound in pregnancy?
Sonar is done at different stages throughout pregnancy to tell us more about the pregnancy and about baby’s growth and development. InSouth Africa, most obstetricians/gynaecologists in private practices do a sonar with every visit, making it a routine part of their antenatal care. However, research shows that this does not necessarily improve pregnancy outcomes (and for that reason it is not routinely done as often in public sector clinics and hospitals).
Two sonars are definitely recommended in all pregnancies –a first trimester sonar, and another at around 20-24 weeks gestation.
In the first 16 weeks of pregnancy sonar is done to:
- Confirm whether the baby has a heart beat. If missed abortion has occurred, no heartbeat can be detected, sometimes even though the woman has not been experiencing any vaginal bleeding or other symptoms of a miscarriage. If the woman has had a miscarriage, the sonar will show whether it is complete, or if any parts of the baby or placenta are still implanted.
- Confirm the gestation (how far pregnant the mother is) and the due date. This is especially handy for women who are not completely sure when their last menstrual periods took place. A sonar done between 8 and 12 weeks is the most accurate tool for determining your due date, especially handy for women not sure of the dates of their last menstrual periods. A sonar done after 20 weeks is no longer considered accurate to determine a due date.
- Confirm the position in which the baby has implanted into the uterus. In an ectopic pregnancy, the baby has implanted outside of the uterus, for example in the fallopian tubes. This needs urgent medical attention.
- Confirm whether it is a singleton or multiple (twins, triplets, etc) pregnancy.
- Show the length and any abnormal shapes of the cervix. It can also show a cervix that is not closing properly, which may be a cause of repeated miscarriages.
- Measure the clear (transluscent) space in the tissue at the back of your developing baby’s neck. Babies with abnormalities like Down’s Syndrome tend to accumulate more fluid at the back of their necks in the first trimester. A larger measurement of this space may indicate the need for further tests to screen for abnormalities. It’s important to notice that the majority of babies referred for further testing shows no abnormalities whatsoever.
- Show any abnormalities in the pelvis that may cause complications in the pregnancy, for example tumors, cysts and fibroids.
In the second trimester of pregnancy it is recommended that all pregnant women receive sonar around 20-24 weeks gestation. This sonar is meant to:
- Assess organs like the heart, spine, intracranial structures, kidneys, limbs, etc.
- Placental position and appearance – a placenta that is implanted too low in the uterus (over the cervix) can cause complications as pregnancy progresses and when a woman goes into labour. This cannot be seen accurately on a sonar earlier in pregnancy.
- Shows whether all is fine with the umbilical cord.
- Shows if there is enough amniotic fluid. Shows baby’s gender, which can be seen from 16 weeks
In the third trimester:
- Assesment of growth and amniotic fluid, especially if there is suspicion of growth abnormalities by the health care provider or a midwife, including a baby too big or small for his/her dates.
- Fetal weight – it is important to know that these estimates are not always completely accurate towards the end of pregnancy, and should not be used to determine if a mother can give birth naturally.
- Umbilical artery blood flow assessment.
- Placental assessment, i.e. insufficiency, position and maturity.
- Fetal position, i.e. if the baby is in breech position or not.
3D and 4D sonars can be booked separately by parents with a sonographer. 3D sonar shows still pictures of your baby in three dimensions, while a 4D sonar shows moving pictures of your baby. You may see the shape of your baby’s face, or may see her yawn or suck her fingers. Some sonographers may even give you a DVD with your baby’s sonar on it. How much you can see on the sonar really depends on how baby is lying. If baby is facing your back, if you have a lot of tummy fat or if you don’t have much amniotic fluid it may be difficult to see baby’s face. Sometimes it may help to go for a walk, or to come back a few days later.
Not all parents like having a 4D scan, and may feel disappointed with what they see.These scans do not have significant medical value, and parents should never feel that it is something that they have to do. There is something to be said for some mystery, and for only finding out baby’s gender at birth. In the end, this remains a personal choice.