One of the most feared exams during pregnancy, the morphological ultrasound reveals if the baby is developing well or if they have some malformation or chromosome issue, which is why it’s usually faced with certain anxiety by expecting mothers.
The exam is done during two phases of pregnancy: during the end of the first trimester and every two months after that, during the second trimester. But it is the first one that usually generates more anxiety, since it is capable of detecting even 60% of malformations and anomalies – and 90% of cases of Down syndrome.
Morphological ultrasound of the first trimester
Done between 11 weeks and 13 weeks and six days, the morphological ultrasound (USG) of the first trimester looks into whether or not the baby can develop Down syndrome, primarily, and other malformations. It needs to be done at this stage because it is at that point which doctors are able to measure nuchal translucency, or the diameter of the fetus’ neck. Higher numbers than expected can indicate the child might have Down syndrome.
But, this isn’t a final diagnosis, as there’s always a margin of error and it’s not rare for the exam to yield false positive results (around 5%). With that in mind, before you start worrying about the results, wait until you complete other necessary exams.
In this ultrasound, the doctor will also analyze the size of the nose bone, which can signal a chromosome alteration. The exam is used to check the flow of blood in the umbilical cord, the baby’s heartbeats, examine the mother’s pelvic floor and placenta, and to check if the baby’s development is going according to the estimated birth date )or to determine more closely the date of birth).
While it might be too early to tell, some doctors are able to indicate what the sex of the baby might be, by analyzing the angle of the baby’s early genital formation.
Second trimester ultrasounds
Between 18 and 24 weeks of pregnancy (especially after the 20th week), the morphological ultrasound is repeated. This way, with a bigger baby, it’s easier to determine up to 80% of abnormal conditions. The heart chamber, internal organs, bone structure, the head and the members are all examined. On the face, it is already possible to detect if the child has a cleft palate – which can happen, on average, to 1 in every 700 babies.
It is also during this exam that doctors check for evidence of spina bifida, which means the spine doesn’t fully close and, in more serious cases, a part of the medulla ends up exposed (called myelomeningocele). The good news is, it’s operable while the baby is still in utero and is one of the biggest advantages of the morphological ultrasound – detecting issues early on.
In this ultrasound, the chances of confirming the sex of the baby are huge – it’s hard for the genitalia to hide during the exam, but not entirely impossible. The ultrasound specialist will also give you a weight estimate, basing their measures off the baby’s head (cephalic circumference), the abdominal circumference and the size of the femur, the thigh bone.
The ultrasound also analyzes the position of the placenta, the volume of amniotic liquid, the umbilical cord and the mother’s uterine arteries.
How are the exams done?
In both cases, the pregnant woman will lay on their back, the doctor will apply a gel so they can better slide the probe and will analyze the baby for about 30 minutes to an hour. You can see the baby’s movements in real time, which is usually very exciting. If possible, take the grandparents along with you for these exams, as a way to include them in the pregnancy.
If it’s positive for a syndrome, what then?
The doctor might ask you for other exams. Two of them will be invasive and, therefore, are only done after a lot of discussion, as there’s a risk, even if of only 1%, of it triggering a spontaneous abortion: the amniocentesis, a procedure that involves removing amniotic fluid from the uterus with a needle, and chorionic villus biopsy, which analyzes a sample of the placenta.
But, there are non-invasive blood tests that can be completed at the 10-month mark and that can scout for Down (chromosome 21 trisomy), Edwards (chromosome 18 trisomy) and Patau (chromosome 13 trisomy) syndromes. Combined with the morphological ultrasound, these can reduce the chances of getting false positives.