Third trimester or growth ultrasound: when to do it and why?
What is the third trimester obstetric ultrasound and what is it for? How does it work and how much does it cost? Here is all the most important information about this exam!
The third trimester ultrasound is an examination that has the main purpose of evaluating the growth of the child . For this reason, it is also called growth , biometric or fetal well-being ultrasound .
Unlike dating and morphological ultrasound , it is not mandatory . Consequently, it is not offered to all expectant mothers, but only if the gynecologist or midwife deems it necessary.
Growth ultrasound: when is it performed and after how many weeks?
Fetal growth ultrasound is done in the third trimester and usually between the 28th and 32nd week of pregnancy .
Furthermore, in some cases, the examination can be repeated around the 36th week of pregnancy .
Growth ultrasound: what is it for?
Third trimester obstetric ultrasound allows you to:
- check the growth of the child and make an estimate of the weight
- observe and measure organs and systems
- check the fetal position
- identify any malformations not previously visible
- assess the location of the placenta (and whether there is placenta previa )
- check the amount of amniotic fluid
In particular, to evaluate fetal growth, some specific parameters are measured , such as:
- CC= head circumference
- CA= abdominal circumference
- BDP= biparietal diameter
- FL= length of the femur
- OL= length of the humerus
All these values are then compared with the appropriate reference tables .
Also during the third trimester ultrasound, the position of the baby inside the uterus is checked , which can be:
- cephalic , head down
- breech , head up
- crossbar , horizontally
- oblique , diagonally
Based on all this information, the gynecologist will determine the need for further investigations.
Furthermore, if the baby is not in cephalic presentation , he will evaluate whether to proceed with corrective maneuvers to allow a vaginal birth .
Growth ultrasound: how does it take place and how long does it last?
Usually, this examination is performed abdominally and is preceded by an interview with the gynecologist , who collects all the updated data on the future mother’s health (weight, vitamin supplements, eating habits, most recent tests, doubts and questions).
Typically the duration of the appointment is around 20-30 minutes, although it can vary a lot according to the individual situation.
Sometimes, in fact, it can be difficult to carry out the required measurements, because the child is growing and tends to move very often.
Furthermore, the presence of overweight or obesity , uterine fibroids , scars or other problems can make the examination more difficult and prolong its duration.
Growth ultrasound and flowmetry
In some cases, the third trimester ultrasound may be accompanied by another type of ultrasound examination, which is used to evaluate the amount and speed of blood flowing between the placenta and the baby .
This technique is called fetal flowmetry and is used to evaluate the functioning of the placenta and the degree of oxygenation of the fetus , for example if there is a suspicion of a growth delay.
It is important to underline that fetal flowmetry in the third trimester is not a routine examination and is performed only if the biometric control has shown a poor development or a stunted growth of the fetus .
Generally, in fact, in selected or at-risk cases , this type of ultrasound is already proposed in the second trimester , starting from the 16th week of pregnancy , and is then repeated periodically to monitor the well-being of the child.
Growth ultrasound: how much does it cost?
On the basis of the new LEA (Essential Levels of Assistance) of 2017 , obstetric growth ultrasound is not one of the tests offered free of charge during pregnancy through the National Health Service, unless specifically indicated.
The cost varies and, depending on the region and the structure in which the exam is performed, it can even reach 150 euros .
Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.
Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.