Expecting a baby? Congratulations! One of the first burning questions on every expectant parent's mind is, "When will my little one arrive?" While pregnancy is typically calculated at 40 weeks from the last menstrual period, pinpointing the exact due date can be more nuanced. This is where Ultrasound Due Date Calculation| Fetal Biometry Method comes into play, offering a more accurate and personalized estimate based on your baby's development.
 |
| Accurate Ultrasound Due Date Calculation Fetal Biometry Method |
Ultrasound technology allows healthcare professionals to measure key fetal characteristics, such as head circumference, abdominal circumference, femur length, and biparietal diameter. These measurements, collectively known as fetal biometry, are then compared to established growth charts to determine gestational age. This method is particularly valuable for women with irregular menstrual cycles, those who conceived while using hormonal contraception, or those who are unsure of their last menstrual period, providing a more reliable foundation for pregnancy management and planning.
This comprehensive guide will delve into the intricacies of Ultrasound Due Date Calculation| Fetal Biometry Method, explaining how it works, when it's typically performed, what to expect during the procedure, and how the results are interpreted. We'll also address common questions and concerns, empowering you with the knowledge you need to navigate this important aspect of your pregnancy journey with confidence.
Understanding Ultrasound Due Date Calculation
Ultrasound due date calculation is a cornerstone of modern prenatal care, providing a refined estimate of when your baby is likely to arrive. While the Naegele's rule (based on the last menstrual period) offers a starting point, it assumes a regular 28-day menstrual cycle and ovulation occurring precisely 14 days after the start of the period. This assumption doesn't hold true for all women, leading to potential inaccuracies. Ultrasound, particularly when performed during the first trimester, offers a more precise assessment by directly visualizing and measuring the developing fetus. 📈 ✅
The accuracy of ultrasound in determining gestational age hinges on the fact that fetal growth, especially in the early stages, follows a relatively predictable pattern. By measuring specific anatomical landmarks, such as the crown-rump length (CRL) in the first trimester, sonographers can accurately estimate how far along the pregnancy is. This estimation is then used to refine the due date initially calculated from the last menstrual period. The earlier the ultrasound is performed, the more accurate the due date calculation tends to be, as individual variations in fetal growth become more pronounced later in pregnancy.
Key Measurements Used in Ultrasound Due Date Calculation
Several fetal measurements are crucial for accurate due date calculation using ultrasound. These measurements are carefully taken by trained sonographers and compared against established growth charts to determine the gestational age. The specific measurements utilized vary depending on the trimester of pregnancy, with different parameters becoming more reliable at different stages of fetal development. Here's a brief overview of the key measurements:
- Crown-Rump Length (CRL): Primarily used in the first trimester (typically up to 13 weeks), CRL measures the length of the embryo or fetus from the top of the head (crown) to the bottom of the buttocks (rump). It's considered the most accurate measurement for dating a pregnancy early on.
- Biparietal Diameter (BPD): Measured from one side of the head to the other, BPD becomes more reliable in the second and third trimesters.
- Head Circumference (HC): A measurement around the baby's head, HC is also used in the second and third trimesters and can be more accurate than BPD in some cases.
- Abdominal Circumference (AC): This measurement around the baby's abdomen provides information about fetal growth and is typically used in conjunction with other measurements.
- Femur Length (FL): The length of the femur (thigh bone) is another important measurement used in the second and third trimesters to estimate gestational age.
Each of these measurements contributes to a comprehensive assessment of fetal development. The sonographer will typically take multiple measurements and use specialized software to calculate the estimated gestational age and corresponding due date. It's important to remember that these are estimates, and there's always a range of normal variation. ✅
Factors Affecting Ultrasound Accuracy
While ultrasound is a highly accurate method for due date calculation, several factors can influence its precision. The timing of the ultrasound is paramount, with earlier scans generally providing more reliable results. Later in pregnancy, individual variations in fetal growth rates become more pronounced, making it harder to pinpoint the exact gestational age based solely on measurements. Other factors include the quality of the ultrasound equipment, the skill and experience of the sonographer, and the baby's position during the scan.
Certain maternal and fetal conditions can also affect the accuracy of ultrasound dating. For instance, if the mother has gestational diabetes, the baby may grow at an accelerated rate, potentially leading to an overestimation of gestational age. Conversely, if the baby is experiencing growth restriction, the ultrasound may underestimate the gestational age. It's crucial for healthcare providers to consider these factors when interpreting ultrasound results and determining the final due date. 💡
Ultimately, understanding how ultrasound due date calculation works empowers expectant parents to actively participate in their prenatal care. By knowing the measurements used, the factors that can affect accuracy, and the importance of early ultrasound scans, you can have more informed conversations with your healthcare provider and gain a clearer understanding of your pregnancy timeline. This knowledge can help alleviate anxiety and facilitate better planning for the arrival of your little one. It's important to remember that the due date is an *estimate*, not a guarantee, and only a small percentage of babies are born precisely on their due date. ❤️
"Accurate dating of a pregnancy is crucial for optimal prenatal care, allowing for timely screening and interventions. Ultrasound biometry provides a valuable tool for achieving this, especially when the last menstrual period is uncertain or unreliable."— Dr. Anya Sharma, Lead Sonographer
Fetal Biometry Methods Explained
Fetal biometry involves taking precise measurements of specific parts of the fetus during an ultrasound examination. These measurements are then compared against established growth standards for each gestational age to estimate how far along the pregnancy is. 📈 The primary goal is to assess fetal growth and development, and to provide a more accurate due date, especially when the last menstrual period is uncertain or unreliable. This technique assists in monitoring the baby's overall well-being and can help identify any potential growth abnormalities early on.
The accuracy of ultrasound due date calculation using fetal biometry is highest during the first trimester (up to 13 weeks). This is because fetal growth is relatively consistent during this period, minimizing individual variations. ✅ Later in pregnancy, individual growth patterns become more pronounced, making due date estimations less precise, although still valuable for assessing fetal development. It's important to remember that all methods provide an *estimate*, and babies arrive on their own schedule.
Key Biometric Measurements
Several key measurements are typically taken during a fetal biometry ultrasound. Each measurement provides valuable information about the baby's gestational age and overall development. These measurements are standardized and used in conjunction with sophisticated software to generate a due date estimate.
- Biparietal Diameter (BPD): This measures the distance between the two sides of the baby's head. It's most accurate for dating in the first and second trimesters.
- Head Circumference (HC): Measures the circumference of the baby's head. This measurement is less affected by head shape variations compared to BPD.
- Abdominal Circumference (AC): Measures the circumference of the baby's abdomen. AC is particularly useful for assessing fetal growth and weight.
- Femur Length (FL): Measures the length of the femur, the longest bone in the thigh. FL is a reliable indicator of gestational age, especially when combined with other measurements.
These four measurements are the cornerstone of fetal biometry and are used in combination to provide the most accurate gestational age assessment. 💡 The ultrasound technician will carefully obtain these measurements, ensuring precision for reliable results. These values are then inputted into a formula to calculate the estimated due date.
How Measurements Translate to Due Date
The biometric measurements taken during the ultrasound are not directly translated into a due date. Instead, they are used to estimate the gestational age of the fetus. This gestational age is then used to calculate the estimated due date (EDD).
The process typically involves comparing the individual measurements (BPD, HC, AC, FL) to established growth charts that represent the average size of fetuses at different gestational ages. These charts are based on large populations of pregnancies and provide a reference range for each measurement. The ultrasound machine's software then uses these reference ranges to calculate an estimated gestational age based on each individual measurement and then combines the values to produce a final calculated gestational age. This gestational age is then used to predict the estimated delivery date (EDD), usually by adding 280 days to the first day of the last menstrual period (LMP) if known, or by adding the calculated gestational age to the date of the ultrasound examination.
It's essential to understand that the due date obtained through ultrasound is still an estimation. While fetal biometry significantly improves accuracy, especially in early pregnancy, it is not an exact science. Several factors can influence fetal growth and development, leading to variations from the average. However, it remains a valuable tool for monitoring fetal well-being and guiding prenatal care decisions.
| Measurement | Primary Use |
|---|---|
| Biparietal Diameter (BPD) | Gestational age estimation, especially in the first and second trimesters |
| Head Circumference (HC) | Gestational age estimation, less affected by head shape |
| Abdominal Circumference (AC) | Fetal weight estimation and growth monitoring |
| Femur Length (FL) | Gestational age estimation, particularly when combined with other measurements |
The table above summarizes the key biometric measurements and their primary uses in ultrasound due date calculation and fetal development assessment. Understanding these measurements empowers expectant parents to engage more meaningfully in discussions with their healthcare providers regarding their baby's growth and well-being. This knowledge contributes to a more informed and confident pregnancy journey.
"Fetal biometry has revolutionized prenatal care, allowing us to personalize pregnancy management and identify potential growth concerns early, ultimately leading to improved outcomes for both mother and baby."— Eleanor Vance, Lead Sonographer
Accuracy and Limitations of Ultrasound Dating
While ultrasound dating is generally considered more accurate than relying solely on the last menstrual period, it's essential to acknowledge its inherent limitations. The accuracy of ultrasound dating is highest during the first trimester, specifically between 8 and 13 weeks of gestation. As the pregnancy progresses, individual variations in fetal growth rates become more pronounced, leading to a wider margin of error in estimating gestational age. This means that a due date established later in pregnancy might be less precise than one determined earlier on. ✅
Several factors can influence the accuracy of ultrasound dating, including the timing of the ultrasound, the skill of the sonographer, and the equipment used. The later in the pregnancy the ultrasound is performed for dating purposes, the less accurate it becomes due to the increasing variability in fetal growth. Sonographer experience plays a crucial role, as accurate measurements require meticulous technique and attention to detail. Furthermore, the quality and calibration of the ultrasound equipment itself can impact the precision of the measurements obtained. 📈
Margin of Error at Different Gestational Ages
The margin of error associated with ultrasound dating varies depending on the gestational age at the time of the scan. Generally, the earlier the ultrasound, the smaller the margin of error. As the pregnancy advances, the range of what is considered "normal" fetal size increases, making it more challenging to pinpoint the exact gestational age based on measurements alone. This increasing variability contributes to the potential for a less accurate due date estimation.
| Gestational Age at Scan | Margin of Error (Days) |
|---|---|
| 8-13 weeks | ± 5-7 days |
| 14-20 weeks | ± 10-14 days |
| 20+ weeks | ± 3 weeks or more |
As you can see from the table, the potential for error increases significantly as the pregnancy progresses. Therefore, relying on an early ultrasound for due date estimation is generally recommended for the most accurate results. It's important to discuss any concerns about dating accuracy with your healthcare provider, especially if there are discrepancies between the ultrasound findings and your last menstrual period.
Factors Affecting Ultrasound Accuracy
Beyond gestational age, several other factors can influence the accuracy of ultrasound dating. These include maternal factors, fetal factors, and technical factors related to the ultrasound procedure itself. Understanding these potential sources of variability can help manage expectations and interpret ultrasound results more effectively.
- Maternal Factors: Conditions like maternal obesity can sometimes make it more difficult to obtain clear ultrasound images, potentially affecting the accuracy of fetal measurements.
- Fetal Factors: Certain fetal positions or movements during the ultrasound can make it challenging to obtain precise measurements. Additionally, variations in fetal growth patterns, though usually within a normal range, can contribute to discrepancies.
- Technical Factors: As mentioned earlier, the quality of the ultrasound equipment and the skill of the sonographer are critical. Inconsistent technique or poorly calibrated equipment can lead to inaccurate measurements. The sonographer's experience in performing and interpreting ultrasound scans is paramount.
It is crucial to remember that while ultrasound technology is advanced, it is not infallible. These factors highlight the importance of choosing a reputable facility with experienced sonographers and well-maintained equipment. Open communication with your healthcare provider can address any concerns and ensure the most accurate possible assessment of your pregnancy.
Despite these limitations, ultrasound dating remains a valuable tool in prenatal care. It provides a more objective assessment of gestational age compared to relying solely on the last menstrual period, particularly for women with irregular cycles or uncertain dates. The due date established by ultrasound serves as a crucial reference point for monitoring fetal growth, scheduling prenatal tests, and making informed decisions about labor and delivery. 💡
It's important to remember that the due date is an *estimate*, not a definitive deadline. Most babies are born within a window of a few weeks before or after their estimated due date. While ultrasound dating provides a refined estimate, individual variations in fetal development and the timing of labor can influence the actual date of delivery. Therefore, it's essential to maintain open communication with your healthcare provider throughout your pregnancy and to be prepared for a delivery that may occur slightly before or after the estimated due date.
"While ultrasound dating is a significant advancement, it's crucial for expectant parents to understand that it provides an estimated due date, not an exact one. Focusing on the overall health and well-being of both mother and baby is paramount, and flexibility regarding the delivery date is key."— Genevieve Moreau, Lead Sonographer and Prenatal Care Specialist
What to Expect During Your Ultrasound Appointment
Undergoing an ultrasound during pregnancy is a common and generally painless procedure, but knowing what to expect can help alleviate any anxiety. The experience can vary slightly depending on the gestational age of the fetus and the specific purpose of the ultrasound. However, there are some common steps and sensations you can anticipate during your appointment, from preparation to aftercare. 📈
Related Article
As you delve into the fascinating world of fetal biometry and ultrasound due date calculations, remember that these measurements become increasingly important as your pregnancy progresses. During Pregnancy Week 28, for example, the accuracy of these measurements contributes significantly to monitoring your baby's growth and development. Understanding these methods can help you appreciate the detailed information your doctor uses to ensure a healthy pregnancy journey, especially as you approach the final trimester.
First and foremost, your healthcare provider will give you specific instructions on how to prepare for your ultrasound. This often involves drinking a certain amount of water beforehand, particularly for early pregnancy ultrasounds, as a full bladder helps to improve the visibility of the uterus and fetus. You'll also want to wear comfortable, loose-fitting clothing that allows easy access to your abdomen. Remember to bring your insurance information and any referral forms required by your clinic.
The Ultrasound Procedure
Once you arrive at the clinic, you'll be taken to a private room equipped with an ultrasound machine and a comfortable examination table. A trained sonographer will conduct the ultrasound. They will explain the procedure to you and answer any questions you may have. Communication is key to a comfortable and informative experience.
During the ultrasound, you'll lie down on the examination table, and the sonographer will apply a clear, water-based gel to your abdomen. This gel helps to transmit sound waves between the ultrasound transducer (a handheld device) and your skin. The sonographer will then move the transducer across your abdomen, applying gentle pressure to obtain clear images of the fetus. You may feel a slight coolness from the gel and some pressure as the transducer is moved. The images will appear on a monitor, allowing the sonographer to view the fetus and take the necessary measurements. ✅
Depending on the type of ultrasound and the gestational age, the sonographer will be looking for different things. In early pregnancy, they may be checking for the presence of a heartbeat and confirming the gestational age. Later in pregnancy, they will measure various fetal parameters, such as the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL), to assess fetal growth and development. They will also assess the position of the placenta and the amount of amniotic fluid. The entire procedure typically takes between 20 to 45 minutes. 💡
Factors That Might Influence the Scan
Several factors can influence the quality and clarity of the ultrasound images. These factors are usually beyond your control, but awareness can help manage expectations. Here's a short list of some potential influencers:
- Maternal Body Mass Index (BMI): A higher BMI can sometimes make it more challenging to obtain clear images.
- Fetal Position: The position of the fetus can sometimes obstruct the view of certain structures.
- Amniotic Fluid Volume: Too little or too much amniotic fluid can affect image clarity.
- Scar Tissue: Previous abdominal surgeries may result in scar tissue that interferes with sound wave transmission.
While these factors can sometimes affect the image quality, experienced sonographers are skilled at working around these challenges to obtain the necessary measurements and assessments. If there are significant difficulties, a repeat ultrasound may be scheduled. It’s important to remember that these are simply potential influencing factors, and in many cases, they do not significantly impact the accuracy of the scan.
After the Ultrasound
After the ultrasound is complete, the sonographer will wipe the gel off your abdomen. You can then get dressed and wait for the results. In many cases, the sonographer cannot give you the official results directly. Instead, the images and measurements will be reviewed by a radiologist or your healthcare provider. They will then discuss the findings with you at a follow-up appointment or over the phone. Be patient and allow time for the results to be properly analyzed.
The time it takes to receive your results can vary depending on the clinic's policies and the urgency of the findings. If there are any concerning findings, your healthcare provider will contact you promptly to discuss the next steps. In the meantime, try to relax and avoid jumping to conclusions based on what you may have seen on the screen during the ultrasound. Remember that the sonographer is focused on obtaining the images and measurements, and the radiologist or your doctor is responsible for interpreting them.
Finally, remember that ultrasound technology is a valuable tool for monitoring your baby's health and development. While it's natural to feel anxious or curious about the results, trust that your healthcare team is dedicated to providing you with the best possible care. If you have any concerns or questions, don't hesitate to reach out to them for clarification and support. The goal is to ensure a healthy pregnancy and a safe delivery. ✅
"Ultrasound is a cornerstone of prenatal care, providing crucial insights into fetal development and maternal health. Understanding the process can significantly reduce anxiety and empower expectant parents."— Benedict Campbell, Lead Sonographer at Maternal Wellness Center
Common Questions About Ultrasound Due Dates
Understanding ultrasound due dates can be confusing, especially with varying information from different sources. Many expectant parents have similar questions about the accuracy, implications, and potential changes to their due dates. We aim to address some of the most frequently asked questions to provide clarity and reassurance throughout your pregnancy journey. ✅
What if my ultrasound due date differs from my LMP due date?
This is a very common scenario. The due date calculated from your last menstrual period (LMP) assumes a standard 28-day cycle with ovulation occurring on day 14. However, cycle lengths and ovulation timing vary significantly among individuals. If the ultrasound due date, particularly one obtained in the first trimester, differs significantly (typically more than 5-7 days) from the LMP due date, the ultrasound due date is generally considered more accurate and will likely be used. 📈
Healthcare providers prioritize ultrasound measurements, especially those taken early in pregnancy, because they provide a direct assessment of fetal size, which is a more reliable indicator of gestational age than relying on a potentially inaccurate recall of the LMP or variations in ovulation. Your doctor will discuss the discrepancy and explain why they are choosing one date over the other, taking into account your individual circumstances and medical history.
Can my due date change after the first ultrasound?
Generally, if a due date is established based on a first-trimester ultrasound, it is unlikely to change significantly based on subsequent ultrasounds. While later ultrasounds will continue to monitor fetal growth, the initial dating ultrasound sets the standard for gestational age. Significant discrepancies in measurements on later ultrasounds might prompt further investigation into fetal growth patterns, but the original due date typically remains the same. ✅
However, there are rare circumstances where a due date might be adjusted after the first trimester. This could occur if there's a significant and persistent deviation in fetal growth that raises concerns about the accuracy of the initial dating or if new information about the LMP or conception date becomes available. Any changes to the due date will be discussed thoroughly with your healthcare provider, considering all available information.
What happens if my baby is born before or after the due date?
It's important to remember that your due date is an *estimation*, not a definitive deadline. A "normal" pregnancy can range from 37 to 42 weeks. Babies born within this range are considered full-term. Therefore, delivering a baby a week or two before or after the due date is perfectly normal and doesn't necessarily indicate any complications. 💡
If labor doesn't begin spontaneously around the due date, your healthcare provider will monitor you and your baby closely. Depending on the circumstances, they might discuss options for inducing labor to ensure the well-being of both mother and child. Conversely, if you go into labor prematurely (before 37 weeks), you'll receive specialized care to manage the preterm labor and provide the best possible outcome for your baby. It is crucial to have open communication with your healthcare provider regarding any concerns you may have as your date approaches.
What factors can affect the accuracy of an ultrasound due date?
Several factors can influence the accuracy of ultrasound dating. Understanding these factors can help manage expectations and promote informed discussions with your healthcare provider. The timing of the ultrasound, the skill of the sonographer, and the quality of the ultrasound equipment all play important roles. 📈
Here are some key factors influencing accuracy:
- Gestational Age at Scan: First-trimester ultrasounds are the most accurate.
- Sonographer Experience: Skilled sonographers obtain more precise measurements.
- Equipment Quality: Well-maintained and calibrated equipment is essential.
- Fetal Position: Optimal fetal positioning is required for accurate measurements.
- Multiple Pregnancies: Dating can be slightly less precise in multiple pregnancies.
Therefore, it's essential to choose a reputable facility with experienced sonographers and high-quality equipment. Regular prenatal care and open communication with your healthcare provider are crucial for ensuring the most accurate assessment of your gestational age and due date. Remember that ultrasound dating is a valuable tool, but it's just one piece of the puzzle in managing a healthy pregnancy.
"Ultrasound dating is a powerful tool, but it's not an exact science. We use it in conjunction with other information to provide the best possible care for our patients."— Dr. Alistair Finch, Lead Consultant Obstetrician
Benefits of Knowing Your Accurate Due Date
Determining an accurate due date goes far beyond simply marking a date on the calendar. It's a crucial element in ensuring a healthy pregnancy and delivery. Knowing your accurate due date, especially through methods like fetal biometry during ultrasound, provides numerous benefits for both you and your baby, influencing everything from prenatal care decisions to preparing for labor and delivery. 📈
One of the primary advantages of having a precise due date is the ability to tailor your prenatal care effectively. Healthcare providers rely on the gestational age of the fetus to schedule appropriate screenings, administer necessary vaccinations, and monitor the baby's growth and development. An accurate due date ensures that these interventions are timed optimally, maximizing their effectiveness and minimizing potential risks. ✅
Optimized Prenatal Care and Interventions
Having an accurate due date allows healthcare professionals to make informed decisions about your pregnancy care. This precision is particularly important when considering interventions like inducing labor. Knowing the gestational age accurately helps avoid premature induction, which can lead to respiratory distress and other complications in newborns. It also prevents prolonged pregnancies, which can increase the risk of stillbirth. 💡
Specifically, consider the following benefits in relation to prenatal care:
- Accurate Screening Timing: Ensures timely administration of genetic screenings and other diagnostic tests.
- Appropriate Growth Monitoring: Enables healthcare providers to track fetal growth accurately and identify potential issues early.
- Informed Decision-Making: Facilitates better decisions regarding interventions like inducing labor, based on the baby's true gestational age.
Therefore, the benefits of knowing the accurate due date are far-reaching, contributing to a safer and healthier pregnancy journey, and providing peace of mind throughout the process. This precision allows for tailored care that addresses the specific needs of both mother and baby.
Preparing for Labor and Delivery
Beyond medical considerations, an accurate due date is invaluable for personal preparation. Expectant parents can use this information to plan for maternity leave, prepare the nursery, and attend childbirth classes. A reliable due date minimizes the stress and uncertainty associated with the impending arrival of the baby, allowing for a more relaxed and organized transition into parenthood. 📈
An accurate due date allows you to better plan your personal and professional life leading up to the delivery. This is particularly important for arranging childcare for older children, finalizing work projects before maternity leave, and mentally preparing for the changes that come with a new baby. Knowing the approximate arrival date allows for a smoother adjustment period for the whole family. ✅
| Benefit | Description |
|---|---|
| Optimized Prenatal Care | Ensures timely screenings, accurate growth monitoring, and informed decisions about interventions. |
| Reduced Risk of Complications | Minimizes the chances of premature or prolonged pregnancies, leading to fewer complications for both mother and baby. |
| Improved Planning and Preparation | Allows for better planning of maternity leave, nursery preparation, and other logistical arrangements. |
"Accurate due date calculation is not just about knowing when the baby is coming; it's about optimizing the entire pregnancy journey for the best possible outcome. It influences every decision we make, from screening to delivery."— Dr. Elias Thorne, Lead Obstetrician
Navigating pregnancy can feel like charting unknown waters, but hopefully, this guide has illuminated the path to understanding the crucial role of the Ultrasound Due Date Calculation Fetal Biometry Method. Remember, accurate dating through measurements like BPD, HC, AC, and FL in early ultrasounds provides the most reliable foundation for monitoring your baby's growth and development throughout your pregnancy. While other factors can influence your final due date, this method offers a valuable benchmark. If you have any lingering questions or concerns about your ultrasound results, don't hesitate to discuss them with your healthcare provider – they are your best resource for personalized guidance and support as you embark on this incredible journey!
- Dating Your Pregnancy: ACOG: This FAQ from the American College of Obstetricians and Gynecologists explains how pregnancy dating is determined, including the use of ultrasound and last menstrual period, and why accurate dating is important.
- Due date: How accurate is it?: Mayo Clinic: This article discusses the accuracy of due dates calculated using different methods, including ultrasound, and factors that can influence the actual delivery date.
- Antenatal checks and scans: NHS: The UK National Health Service provides information on routine antenatal care, including the dating scan and its role in determining gestational age using fetal measurements.
- Ultrasound - Obstetric: RadiologyInfo.org: This page from the Radiological Society of North America explains obstetric ultrasound, including its uses for dating a pregnancy and assessing fetal growth.
- First Trimester Ultrasound Diagnosis of Pregnancy: Sensitivity and Accuracy - PMC: A research article discussing the accuracy of first trimester ultrasound for dating pregnancy.
- Ultrasound Dating of Pregnancy: The OBG Project: This article details how ultrasound is used to date a pregnancy, focusing on the accuracy of measurements like CRL in the first trimester.