Carried out since the 1970s, prenatal ultrasounds have become very important examinations in monitoring fetal development, not only for parents to discover their child, but above all to visualize possible anomalies and malformations.
What is the purpose of these Prenatal ultrasound scans?
3 mandatory ultrasounds are offered during pregnancy: in the first, second and third trimester. Other ultrasounds can be performed if necessary, in case of particular pathologies (bleeding, particular antecedents such as ectopic pregnancy, hypertension, confirmation of foetal abnormality…).
First quarter ultrasound
Usually performed at the end of the first trimester (between 11 and 13 weeks of amenorrhea), it is used to specify the date of fertilization, to detect multiple pregnancies and to ensure the viability of the fetus.
For parents, it is also the first visual contact with their child.
Even if the fetus is still very small, most of its organs are already present and this first ultrasound scan can detect several serious malformations.
The second quarter ultrasound
This second ultrasound, generally performed between 22 and 25 weeks of amenorrhea, is called a “morphological examination” because it allows the observation of all the organs of the fetus and the visualization of possible malformations.
It allows various measurements to be taken, such as those of the brain (biparietal diameter and cephalic perimeter), abdomen (diameter and perimeter) and femur (length), in order to evaluate fetal growth.
This examination also provides information on the mobility of the fetus, the amount of amniotic fluid and the position of the placenta.
In addition, through this ultrasound the parents can find out the sex of their child if they wish to do so.
The third quarter ultrasound
This last ultrasound, performed between 30 and 35 weeks of amenorrhea, allows the diagnosis of late morphological abnormalities (especially in the brain, heart and kidneys).
It also makes it possible to evaluate the mobility of the fetus, as well as its position and that of the placenta: these data can justify the choice of a caesarean delivery.
How are these Prenatal ultrasounds performed?
In most cases, the patient lies on her back and a gel, which allows good transmission of ultrasound, is spread on the skin of her abdomen. It should be noted that before an ultrasound, it is advisable to avoid putting moisturizing creams or milks on the body because this does not allow the ultrasound to pass through well.
The doctor then carries a probe on the patient’s belly that sends ultrasounds: these waves propagate in the tissues and are sent back by the fetus as an echo. This return signal is analyzed by computer and an image is transmitted live.
In some cases, for first trimester ultrasound, the doctor may have to insert the ultrasound probe into the pregnant woman’s vagina to better observe the fetus.
What about 3D ultrasound?
Recent advances in technology make it possible to view ultrasound images in 3D. This technique, which is beginning to be implemented in some hospitals, is of little medical interest, but offers parents a more realistic image of their baby.
Is it necessary to have a full bladder to do an Prenatal ultrasound?
It depends on the doctors: some ask to come with a full bladder, others do not.
A full bladder can give a better visualization of the uterus, especially in the first trimester, when the uterus is still small.
In all cases, it is important to follow the instructions given by the doctor.
Is ultrasound reliable in detecting 100% of abnormalities?
No, in Australia, fetal ultrasound can detect about 70 to 80% of malformations: thus 95% of cases of spina bifida (absence of closure of the nervous tube) can be detected, about 80% of trisomies, but only 50% of limb malformations.
Is Prenatal ultrasound dangerous for the foetus?
Ultrasound does not use radiation, unlike radiography or CT scan. It is therefore considered to be a technique with very little harm to the mother and her baby.
Moreover, the doctor does not stay on the same organ for long and goes through it very quickly as soon as he has checked all the parameters he is looking for, in order to limit exposure to ultrasound.