Obstetric screening ultrasounds: the key exams of the first and second trimester of pregnancy
Obstetric screening ultrasounds are among the most important appointments during pregnancy. Besides giving parents-to-be the thrill of seeing their baby, they are essential tools for assessing the baby's development and monitoring the wellbeing of the pregnancy.
Among all scheduled ultrasounds, those of the first trimester and the second trimester play a particularly important role, because they provide precious information about the baby's growth, the placenta and any anomalies that may require further investigation.
The first-trimester screening ultrasound
The first-trimester ultrasound is generally performed between week 11 and week 13 + 6 days of pregnancy.
At this stage the baby has already completed the first developmental milestones and the exam provides a great deal of information about the pregnancy.
During the scan the gynecologist assesses:
- The baby's viability.
- The number of fetuses.
- The gestational age and the estimated due date.
- The development of the main anatomical structures already visible.
- The position of the placenta.
- The amount of amniotic fluid.
In this same period it is also possible to carry out screening for chromosomal anomalies, which includes the measurement of nuchal translucency and, when indicated, additional maternal blood tests or the fetal DNA test on maternal blood.
It is important to remember that these are screening tests: they estimate the risk of certain chromosomal anomalies, but do not provide a definitive diagnosis.
Why is the first-trimester ultrasound important?
This exam is the first major check-up of the pregnancy and helps plan the following months in the best possible way.
- It confirms the baby's healthy early development.
- It allows precise dating of the pregnancy.
- It identifies twin pregnancies early.
- It assesses certain ultrasound markers associated with the risk of chromosomal anomalies.
The second-trimester anomaly scan
The second-trimester ultrasound, also known as the anomaly (morphology) scan, is generally performed between week 19 and week 21 of pregnancy.
It is considered one of the most complete exams of the whole pregnancy, because it provides a detailed view of the baby's anatomy.
During the exam the following are assessed:
- Brain and nervous system.
- Face and upper lip.
- Heart and great vessels.
- Spine.
- Lungs.
- Stomach, bowel, kidneys and bladder.
- Arms and legs.
- Fetal growth.
- Placenta, umbilical cord and amniotic fluid.
When conditions allow, it is often possible to find out the baby's sex too, if the parents wish to know.
What is the purpose of the anomaly scan?
The main goal is to check that the baby's anatomical development is proceeding normally and to identify any congenital anomalies that may benefit from further investigation or specialist care during pregnancy and after birth.
It is important to know that no ultrasound can rule out all possible anomalies with absolute certainty. Some conditions may not yet be evident, or may not be identifiable with the diagnostic tools available.
How are obstetric ultrasounds performed?
Both exams are performed with an ultrasound probe gently placed on the mother's abdomen.
- They do not use radiation.
- They are non-invasive.
- They are painless.
- They allow the baby's movements to be observed in real time.
The duration may vary depending on the baby's position, image quality and the characteristics of the pregnancy, but generally takes between 20 and 40 minutes.
How to prepare for the exam?
Obstetric ultrasounds do not require any complex preparation.
- Bring all your pregnancy records with you.
- Wear comfortable clothes.
- Follow any instructions given by your gynecologist before the appointment.
Fasting is generally not required.
Frequently asked questions
Are obstetric ultrasounds safe?
Yes. Ultrasound scans use sound waves and are safe for both mother and baby when performed according to clinical indications.
If the ultrasound is normal, does it mean the baby is certainly healthy?
A normal ultrasound is very reassuring, but no exam can rule out with absolute certainty every possible congenital or genetic anomaly.
Is it always possible to see the baby well?
Not always. The baby's position, the amount of amniotic fluid or other factors may make it necessary to complete the exam at a later time.
Can the ultrasound reveal the baby's sex?
In most cases the baby's sex can be identified during the second-trimester anomaly scan, if the baby's position allows it.
A prevention pathway throughout the whole pregnancy
The first- and second-trimester screening ultrasounds are key moments of obstetric care. They make it possible to monitor the baby's development, assess the wellbeing of the pregnancy and schedule further diagnostic investigations when needed.
Attending regular check-ups and following the recommended exam schedule means living your pregnancy with greater awareness, peace of mind and attention to the health of both mother and baby.