Overview of Gestational Age Assessment
Gestational age is essentially how far along a pregnancy is. Doctors use this information to plan when to do certain tests and evaluations on the baby and the mother. This can be checked at any point during pregnancy, and there are many ways to figure it out. Some methods are more precise than others, and using better methods for figuring out the gestational age can help doctors take care of pregnant patients more effectively.
Before technological advancements, doctors had to rely on collecting detailed information from the patient and carrying out physical check-ups to figure out the gestational age. One way was by finding out the date of the woman’s last menstrual period, which could be used in formulas to give an estimated delivery date and gestational age. Another was by measuring the height of the womb through a physical examination.
In modern times, ultrasound has become the more accurate way to figure out how far along a pregnancy is, especially in the early stages. Both transvaginal (which involves inserting the ultrasound probe into the vagina) and transabdominal (where the probe is moved over the belly) ultrasound exams can be used to get more precise measurements of gestational age. Transvaginal exams are especially useful in the first three months of pregnancy. Multiple different ultrasound measurements can be used to calculate gestational age.
Additionally, doctors can get an idea of gestational age by conducting physical and neurological assessments on the newborn baby. This involves looking at certain physical features and checking for certain reflexes that vary based on gestational age.
Anatomy and Physiology of Gestational Age Assessment
The uterus is an important organ located in the pelvic region of a woman’s body. Its primary role is to support the growth of a developing baby. About four weeks after conception, the uterus begins to grow, expanding approximately 1 cm each week.
Around 4.5 to 5 weeks into the pregnancy, a gestational sac or a small fluid-filled pouch forms in the uterus. This pouch is the first sign of early pregnancy. Between the 5th to 6th week of pregnancy, a structure known as the yolk sac develops. The yolk sac helps to nourish the developing baby and is usually present until about the 10th week of pregnancy.
By the time you reach 5.5 to 6 weeks into your pregnancy, doctors can detect a fetal pole with a beating heart as the baby starts to form. After this, the baby’s organs continue to develop and become more prominent.
During a pregnancy ultrasound, a scan of the pelvis can reveal various structures including the bladder, uterine wall, vaginal stripe, and rectum. To give you an idea, the bladder is usually positioned below and in front of the uterus. It is identified by its circular shape filled with a dark or black fluid (urine) and its size can change based on how much urine it’s holding.
The uterus has a thick wall that appears grey on an ultrasound and it has a dark or black center where a developing pregnancy can be spotted. You can differentiate between the uterus and the bladder by the thickness of their walls, with the uterine wall being significantly thicker.
The vaginal stripe, another structure, is located behind the bladder. The rectum, a tube where waste material is expelled from the body, is the furthest back and also appears circular on an ultrasound. It’s center can either be black or grey during the examination.
Why do People Need Gestational Age Assessment
It’s important for all pregnant women to know the gestational age of their pregnancy. This simply means knowing how many weeks along you are in your pregnancy. This calculation helps doctors to keep a close track of the health and development of both the mother and the baby throughout the pregnancy.
When a Person Should Avoid Gestational Age Assessment
There aren’t any hard rules that prevent a healthcare professional from figuring out how far along a woman’s pregnancy is. But the methods used to determine this can sometimes pose a problem for specific individuals. For example, a transvaginal ultrasound – a technique where a small device is inserted into the vagina to create pictures of a woman’s internal organs – might not be suited for everyone.
If a pregnant woman is experiencing vaginal bleeding due to a condition known as placenta previa, where the placenta partially or completely covers the lady’s cervix, this type of ultrasound exam should not be done. It’s also not recommended for someone whose water has broken too early – a situation referred to as the premature rupture of membranes. Additionally, if a woman does not want this exam, despite having all the information about it, it should not be done.
There’s also a method called a transabdominal ultrasound, where the ultrasound device is moved over the belly to get a view of the baby. This method doesn’t have any known restrictions. However, it wouldn’t be the best option for quality care and image capture if it is performed over an open wound.
Equipment used for Gestational Age Assessment
We use an ultrasound machine equipped with a special type of scanner, either a phased array or a curvilinear probe, for a procedure called the transabdominal approach. This approach involves examining your abdominal area using sound waves. For a procedure known as the transvaginal approach, where the inside of your vagina is examined, we use a different kind of scanner called an endocavitary probe.
Who is needed to perform Gestational Age Assessment?
If you’re pregnant, it’s important that a skilled ultrasonographer, a healthcare professional who uses ultrasound technology, figure out how far along you are (this is called your gestational age). This person should have received specific training either through hands-on practical sessions under an expert with ultrasound proficiency, attendance at educational courses or seminars, or through other ways of learning about ultrasound.
The person who performs your ultrasound examination should not only have been specifically trained to estimate gestational age, but they should also feel confident in making such a determination based on their past experiences and an honest assessment of their own level of skill and ability.
If you want a more accurate calculation of your gestational age, you should consider getting checked by a certified ultrasound technician. They are professionals with a high degree of training and expertise in conducting ultrasound evaluations.
Preparing for Gestational Age Assessment
Before an ultrasound is used to determine the age of a pregnancy, it’s important to explain the process to the person who is pregnant. They should understand what to expect, as well as the potential risks and benefits of this type of evaluation. It’s crucial that permission is given before starting the procedure.
If the ultrasound to be done is transvaginal (inside the vagina), it’s advised that someone else suitable is there too for the comfort of the patient. The wellbeing and comfort of the person who is pregnant should always be a top priority throughout the entire process.
How is Gestational Age Assessment performed
Prenatal techniques help to establish a baby’s development stage in the womb, also known as gestational age. There are several methods to do this.
Non-Sonographic Methods for Determining Gestational Age
* Naegele’s Rule: We first need to establish the date of your last menstrual period. From this date, we add one year and seven days, then subtract three months to give us your estimated delivery date. This allows us to approximate the age of your baby.
Uterine Size: As your pregnancy progresses, your womb, or uterus, increases in size to accommodate your growing baby. From around 12 weeks, your uterus becomes large enough to feel just above the pubic bone. At 16 weeks, we can feel the top part of your uterus (known as the fundus) halfway between your belly button and pubic bone. At 20 weeks, the fundus is level with the belly button. After this, the height from the pubic bone to the fundus in centimeters should match with how many weeks you have been pregnant.
Sonographic Methods for Determining Gestational Age
* First Trimester Dating: A sonogram, or ultrasound scan, provides the most accurate estimate of your baby’s age in the first 13 weeks and 6 days of your pregnancy. We can use both an internal (transvaginal) or external (transabdominal) ultrasound, but an internal scan often provides clearer views of the developing baby. Although we can see and measure the gestational sac and yolk sac (early signs of pregnancy) on an ultrasound, these don’t correlate well with gestational age. Instead, we measure the crown-rump length (CRL), which is the length of your baby from the top of their head to their bottom. This is the most accurate indicator of how old your baby is.
If we can’t determine your baby’s age in the first trimester, we can use other methods. We can measure their head diameter (biparietal diameter; BPD), head circumference (HC), femur length (FL), and the circumference of their abdomen (AC). All these techniques give us a good idea of your baby’s size and growth. Please note, while these techniques can tell us if your baby is growing normally, they should not change the estimated due date established during the first trimester.
If we get to the third trimester and have not been able to date your pregnancy accurately, we might notice certain features on an ultrasound that can give us clues about your baby’s age. For example, certain parts of your baby’s thigh bone (femur) and arm bone (humerus) start to solidify (ossify) at around 32–35 weeks and these changes can suggest that your baby’s lungs are maturing.
Postnatal Techniques
* Dubowitz Method: Using this method, we can date a newborn baby’s age based on their physical and neurological assessments, including muscle tone, certain movements, reflexes, abnormal signs, and behaviors. Each feature is given a score, and the total score indicates how mature your baby is, which helps us figure out their gestational age.
New Ballard Score: This scoring system gives us an even more accurate estimate of a newborn’s gestational age as early as 20 weeks. We look at features of a baby’s physical maturity, such as skin texture and tone, hair (lanugo), foot creases, breast tissue, eyes, ears, and genitals. We also consider certain movements and postures. These assessments are not only quicker, but they may also be less stressful for unwell babies.
Possible Complications of Gestational Age Assessment
To figure out how far along a pregnancy is, doctors use several methods before and after birth.
Before a baby is born, non-sound wave techniques include Naegele’s Rule (a calculation based on a woman’s last menstrual period) and examination of uterine size. Naegele’s Rule, however, assumes a 28-day menstrual cycle with fertilization on day 14, and this may not hold true for all women. Estimating the size of the uterus also varies based on factors like different body types or medical conditions like fibroids.
Sound-wave techniques (sonographic methods) are also used. The length from the baby’s head to the bottom of his or her torso (Crown-rump length – CRL) helps guess how far along the pregnancy is. But, this works better earlier in the pregnancy. The same goes for measuring the baby’s head (Biparietal Diameter – BPD), overall head circumference (HC), thigh bone length (Femur Length – FC) and stomach size (Abdominal Circumference – AC), which all become less accurate after 22 weeks into the pregnancy. Also, looking for centers for bone formation (ossification centers) in the baby can indicate how mature they are, but it doesn’t provide an exact age.
After the baby is born, doctors can also use the Dubowitz Method and New Ballard Score. Both of these tests look at the baby’s physical traits and abilities to estimate age, but they can be a bit tricky and could overestimate the baby’s age, especially in babies born earlier than expected.
What Else Should I Know About Gestational Age Assessment?
Early ultrasound scans are really helpful in confirming how far along a pregnancy is. They can be used along with the mother’s own account of her last menstrual period and a physical examination. Though ultrasounds can visualize the pregnancy at various stages, it’s important to know that they have their limitations and need to be used correctly. The sooner the precise gestational age is determined, the better it is for the healthcare and well-being of both the mother and the baby throughout the rest of the pregnancy.
