In this Article
- What is CRL?
- Uses of Crown Rump Length Measurement
- What Does Crown Rump Length Indicate About Your Baby’s Health?
- Does It Determine the Gender of Baby?
- Crown Rump Length Chart
Regular check-ups, prenatal screening, and scans are essential during pregnancy. Tests used in dating the pregnancy, estimating gestational age, and looking for chromosomal abnormalities might be prescribed by your doctor so your pregnancy can progress smoothly. Estimation of the crown-rump length (CRL) of the fetus is one such scan. It is used in fetal ultrasound to estimate gestational age and monitor fetal growth, typically measured during the first trimester of pregnancy. It is also considered the most accurate measurement for determining gestational age in the first trimester of pregnancy, particularly between 7 and 13 weeks of gestation.
Also Read: Common Trimester Wise Tests during Pregnancy
What is CRL?
CRL is the length of the foetus, measured from the top of its head to its buttocks. This measurement is in centimetres and doesn’t consider the limbs or the yolk sac. Since CRL can be taken from about 6 to 7 weeks of pregnancy with an upper limit of 14 weeks, it is useful in calculating the foetus’s gestational age. The low biological variability at this stage of pregnancy makes it the most accurate estimation of your baby’s gestational age.
Once the gestational age is evident from the CRL, your doctor can provide an estimated delivery date. The earlier this scan is conducted, the more accurate it is. Note that the gestational age is different from the fertilisation age. Gestational age is calculated from the first day of your last menstrual period, whereas fertilisation age is typically two weeks less than the gestational age.
Uses of Crown Rump Length Measurement
Crown-rump length (CRL) has several important uses in obstetrics and gynaecology. These include:
1. Estimating gestational age
CRL is an accurate measure of gestational age during the first trimester of pregnancy, and is used to estimate the due date and monitor fetal development.
2. Monitoring fetal growth
CRL is also used to monitor fetal growth throughout pregnancy. Regular ultrasounds are performed to measure the crown-rump length and ensure that the fetus is growing properly.
3. Identifying abnormalities
CRL measurements can help identify abnormalities in fetal development. Deviations from the expected growth rate can be an early sign of a potential problem, prompting further testing and follow-up care.
4. Guiding delivery decisions
CRL measurements can also help guide decisions about delivery methods. For example, if the fetus is significantly larger or smaller than expected for its gestational age, a different delivery method (such as a C-section) may be recommended.
5. Evaluating multiple gestations
In cases of multiple gestations (such as twins or triplets), CRL measurements can help determine whether the fetuses are developing similarly. This information is used to monitor the health of the fetuses and plan delivery.
6. Determining fetal weight
CRL measurement can also be used to estimate fetal weight. Using mathematical formulas, the CRL measurement can predict fetal weight, which can be useful in determining appropriate delivery methods and planning for potential complications.
What Does Crown Rump Length Indicate About Your Baby’s Health?
The CRL scan assists your doctor in evaluating the well-being and development of your baby in the womb. An average baby measures about 51 cm tall and weighs around 3.5 kg at the time of birth. With this scan, it’s possible to find out your baby’s length and weight at different stages of your pregnancy. These are some issues that CRL helps to reveal:
- Presence of a heartbeat – If the CRL measurement is 7 mm or more, a transvaginal ultrasound can detect the foetus’ heartbeat. This type of ultrasound is conducted through the vagina instead of from outside which is how most ultrasounds are done.
- Miscarriage – A CRL can reveal the absence of a heartbeat and, in turn, a missed miscarriage. In such cases, the expecting mom doesn’t suffer from the usual symptoms of miscarriage like pain or bleeding. Also known as a silent miscarriage, the placenta keeps on producing the pregnancy hormone, leading the woman to believe that she is still pregnant.
- If your mean sac diameter (MSD) is less than 5 mm greater than the CRL measurement, a first-trimester miscarriage may be impending. This can occur in spite of detecting a normal heartbeat in your baby.
- CRL measurements that are on the lower side may also be indicative of chromosomal abnormalities such as Edwards Syndrome (trisomy 18), triploidy, or other growth-related problems.
- According to a study, there is a direct correlation between CRL measured before the 10th gestational week and birth weight. This is a one-of-a-kind study as other studies focus on the correlation between both factors only after the 10th week of gestation. A total of 632 ultrasound scans were performed on pregnant women who didn’t have any complications. The results indicated that there is a positive association between CRL in the early first trimester and the birth weight of the foetus. This can help to predict low birth weight (LBW) and ensure parents-to-be are emotionally prepared for premature delivery and newborn care.
Does It Determine the Gender of Baby?
Crown-rump length (CRL) is used in fetal ultrasound to estimate gestational age and monitor fetal growth. However, it is not a reliable method for determining the gender of a baby. Research has shown no significant difference in CRL measurements between male and female fetuses. While there are some claims that CRL can be used to predict gender based on the size of the fetal genital tubercle, these claims have not been supported by scientific evidence.
Instead, fetal gender is typically determined by ultrasound during the second trimester of pregnancy (between 18-22 weeks), when the genitalia are more developed and can be visualised on the ultrasound image. Even then, there is a small margin of error in gender determination, and ultrasound technicians may not always be able to determine the gender with certainty. Therefore, while CRL is a useful measurement in estimating gestational age and monitoring fetal growth, it is not a reliable method for determining the gender of a baby.
Crown Rump Length Chart
The CRL diagram was first presented by Robinson in 1975 and is, still, the primary reference for pregnancy dating as well as evaluation. Below, we provide a CRL chart for your reference.
|Gestational Age in Weeks||CRL (mm)||Mass|
|6 weeks||4 mm||< 1g|
|7 weeks||11 mm||< 1g|
|8 weeks||17 mm||1 g|
|9 weeks||23 mm||2 g|
|10 weeks||34 mm||4 g|
|11 weeks||44 mm||7 g|
|12 weeks||57 mm||14 g|
|13 weeks||68 mm||23 g|
|14 weeks||81 mm||43 g|
These are the approximate foetus measurements at different stages of pregnancy. Other factors, such as the mother’s age, smoking habits, and the amount of folic acid consumed, may influence crl in pregnancy.
Every baby is different and slight variations in growth and development are normal. Your doctor’s benchmark measurements may also differ from the CRL chart. After a CRL scan, make sure you have a chat with your gynaecologist about your baby’s progress and ask for a detailed report on the same.
1. Can the CRL measurement be incorrect?
Like all measurements, CRL can be incorrect in some cases. Factors such as fetal position, maternal obesity, and technical errors during the ultrasound, can affect the accuracy of the measurement. However, CRL is considered a highly accurate method for estimating gestational age in the first trimester of pregnancy.
2. What if CRL is lower than expected?
A lower-than-expected CRL measurement may indicate a problem with fetal growth. Further testing may be recommended to identify potential issues in such cases.
3. Is CRL smaller for females?
Scientifically, there is no significant difference in CRL measurements between male and female fetuses. However, gender can be accurately determined by ultrasound around 18-20 weeks gestation, where the genitals become visible on the ultrasound.
4. What is the normal range of CRL at 8 weeks?
At 8 weeks gestation, a normal range for CRL in pregnancy is typically between 16-24 mm. It is important to note that the range may vary depending on the accuracy of the measurement and the individual characteristics of the fetus and mother.
Also Read: Giving Birth To a Baby With Down’s Syndrome
Conclusions: Fetal gender may reliably be determined when CRL ≥ 60 mm (gestational age ≥ 12+2). Male gender may already be reliably determined when CRL ≥ 55 mm (gestational age ≥ 12+0). If CRL < 50 mm (gestational age < 11+4) the gender cannot be reliably predicted.What size should the CRL be at 12 weeks? ›
|Gestational age (weeks)||CRL (mm)||Known gender at birth (n)|
|12 to 12 + 3||55.4–62.5||135|
|12 + 4 to 12 + 6||62.6–67.9||194|
|13 to 13 + 6||68.0–83.9||226|
Conclusions: Fetal gender may reliably be determined when CRL ≥ 60 mm (gestational age ≥ 12+2). Male gender may already be reliably determined when CRL ≥ 55 mm (gestational age ≥ 12+0). If CRL < 50 mm (gestational age < 11+4) the gender cannot be reliably predicted.What is the average CRL at 7 weeks? ›
|CRL (mm)||GA (wks, days)||GA (days)|
At 6 weeks the baby measures approx. 4mm from head to bottom, this is called the crown – rump length or CRL and is the measurement we use to date your pregnancy in the first trimester.What is the CRL for Down syndrome? ›
Screening for Down's syndrome should be by combined screening when the CRL is between 45.0 and 84.0 mm. Where the CRL is greater than 84.0 mm, screening for Down's syndrome should be by maternal serum quadruple testing, performed after 14 weeks and two days.What CRL is used to diagnose miscarriage? ›
If the crown rump length (CRL) is > 7 mm and there is no embryonic cardiac activity, this is defined as a missed miscarriage, or. If the mean gestational sac diameter is > 25 mm and there is no yolk sac or embryonic pole, this is defined as an empty sac miscarriage.How to tell the difference between a boy and girl 12 week scan? ›
We can tell the sex of the baby at the 12 week scan by assessing the direction of the nub. This is something that can be identified on babies at this stage and if it points vertically then it is likely to be a boy. If it points horizontally then it is likely to be a girl.How does a girl 12 week scan compared to a boy? ›
The Difference between the Genders
Are you wondering how you can tell if it is a boy or a girl in a scan? The answer is simple, i.e., a boy's Nub will be pointing out in a different direction than a girl's Nub. If you are expecting a baby boy, the Nub will angle upwards.
Dating / Reassurance Scan
We will check the gestational age of your baby by measuring from the top of your baby's head to your baby's bottom. This is called the Crown Rump Length (CRL). This measurement can be used accurately up to 14 weeks gestation.
Between 50-55 mm, that is, 11+4 weeks to 12 weeks of gestation, the accuracy is about 75%, but jumps to 96% with a CRL of 55-60 mm. For male fetuses, in fact, it is 99% vs 93.5% in females at this time. As stated above, by 12+2 weeks, with a CRL of 60 mm or more, the accuracy is 100% for both sexes.What size should the CRL be at 8 weeks? ›
|Gestational Age (Weeks)||Sac Size (mm)||CRL (mm)|
|GA (weeks)||CRL (cm, mean ± SD) Males||Females|
|9||3.31 ± 0.36||3.31 ± 0.36|
|10||3.89 ± 0.56||3.85 ± 0.50|
|11||4.82 ± 0.77||4.76 ± 0.67|
|12||5.73 ± 0.90||5.57 ± 0.86|
Measurement of the crown–rump length (CRL) between 6 and 12 weeks is the most accurate dating parameter. CRL measurements of gestational age are accurate to within 3–5 days.What are normal values of CRL? ›
The distribution of the NT thickness for CRL has been reported in many studies. The median NT thicknesses has been reported to be 1.2-1.9 mm, 1.22-2.10 mm, and 1.19-1.73 mm for a CRL between 45 mm and 80 mm in Japan, Korea, and Brazil, respectively.What is the size of the fetus at 7 weeks in MM? ›
By 7 weeks, the embryo has grown to about 10mm long from head to bottom. This measurement is called the crown-rump length.What is the most accurate CRL? ›
Measurement of the crown–rump length (CRL) between 6 and 12 weeks is the most accurate dating parameter. CRL measurements of gestational age are accurate to within 3–5 days.What if CRL is smaller than gestational age? ›
Small crown-rump length
Between six and eight weeks of gestation, the crown-rump length is the measurement of the entire length of the embryo. Smaller than expected fetuses at this gestational age may mean there is a concern for miscarriage.
Experienced operators using TVS can visualise cardiac activity in an embryo whose crown‐rump length (CRL) is as small as 1.3 mm. However at CRL < 5 mm, up to one third of embryos will not have detectable heart activity on TVS.Can ultrasound detect miscarriage at 6 weeks? ›
In a study of asymptomatic women attending an early pregnancy ultrasound unit, the diagnosis of a miscarriage could not be made on initial ultrasound examination until 35 days from LMP and most miscarriages were diagnosed when the first assessment was between 63 and 85 days after the LMP.
From 6 weeks to 9 1/2 weeks gestational age, the fetal CRL grows at a rate of about 1 mm per day.What is gestational age with CRL? ›
The CRL is predictive of fetal age with an error of 3 days (90% confidence limits) from 7 to 10 weeks and of 5 days from 10 to 14 weeks' gestation. The CRL grows approximately 10 mm per week from weeks 8 to 12 and a simple rule to obtain GA is the following: GA (week) = CRL (cm) + 6.5.What abnormalities can be seen at 12 week scan? ›
As well as being a good marker for babies with Down's syndrome, an increased nuchal translucency measurement can also pick up other genetic conditions, such as Edwards' syndrome (where the baby has an extra copy of chromosome 18) and Patau's syndrome (an extra copy of chromosome 13), and some other structural problems, ...Can you see gender at 12 week ultrasound? ›
When Can You Use Ultrasound to Learn Baby's Sex? The accuracy of determining your baby's gender increases with how far along you are in the pregnancy. The accuracy can vary from 70.3% at 11 weeks to 98.7% at 12 weeks, and 100% at 13 weeks.Are 12 week gender scans accurate? ›
That is to say, reporting a male gender in the ultrasound imaging performed in the 11th or 12th weeks of pregnancy is likely to be 87.6% correct and reporting a female gender is likely to be 96.8% correct. Overall, ultrasound gender identification showed a high sensitivity, specificity, and accuracy [Table 3].Are girl fetuses smaller than boys? ›
Conclusions: Female fetuses grow considerably slower than male fetuses, and these differences are observed from early gestation. However, the female fetus is not merely a smaller version of the male fetus, but, rather, there is a sex-specific growth pattern for each of the individual fetal biometric indices.Are boy fetuses bigger than girls? ›
It is now clear that the growth of the male fetuses is greater than the female fetuses from very early stages of gestation. There appears to be a complex interaction between the placenta and fetal sex.Do boys and girls look different on ultrasound? ›
Ultrasound more reliable after 18 weeks
Until the 14th week of pregnancy, baby boys and girls look exactly the same on ultrasound. Beyond this point, noticeable anatomical differences in the genitals can show up on the scan.
Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18.What should be baby's heart rate at 12 weeks? ›
Your baby's little heart is racing away at about 110 to 160 beats per minute—that's probably twice as fast as yours (and totally normal, BTW).
The 12-week ultrasound is part of combined first trimester screening for chromosomal anomalies like Down syndrome. This screening process also includes a blood test. As part of the ultrasound scan, the ultrasonographer measures the fluid at the back of your baby's neck.How many cm is a 13 week fetus? ›
Your baby, or foetus, is around 7.4cm long, which is about the size of a peach. The weight is about 25g, which is as heavy as a toothbrush with toothpaste on it. Your baby's ovaries or testes are fully developed inside and final tweaks are being made on the outside. The baby is moving around.What does crown rump length indicate? ›
Crown rump length (CRL) is the length of the embryo or fetus from the top of its head to bottom of torso. It is the most accurate estimation of gestational age in early pregnancy, because there is little biological variability at that time.How many mm is 9 weeks pregnant? ›
At 9 weeks of pregnancy, your baby has grown to about 22mm long from head to bottom.How big is the baby at 10 weeks pregnant? ›
Your baby, or foetus, is now around 30mm long from head to bottom, which is about the size of a small apricot. The baby will be making jerky movements and baby's movement can be seen on a scan.What is the normal CRL at 9 weeks in CM? ›
Your baby when you're 9 weeks pregnant. Your baby is tiny but growing very quickly: The embryo is about 1.7 cm long, from head to tail. The head looks much more like a baby's head now, although it's big compared to the rest of the body.What is the normal baby size at 12 week scan? ›
Your baby, or foetus, is now 5.4cm long from head to bottom, which is about the size of a plum. The weight is about 18g, which is around the same as 3 grapes. The internal organs and muscles have been created. The heartbeat can be picked up on an ultrasound scan.What are normal measurements at 12 week ultrasound? ›
Normal NT measurements can vary and depends on which week you are in your pregnancy. In the majority of the case, you can consider a normal screening NT measurement at 12 weeks to be under 3.0 mm.What is the actual size of baby at 12 weeks ultrasound? ›
Your baby at 12 weeks.
Ultrasounds, for gender identification based on the sex organs of the baby, can be performed as early as the 14th week of pregnancy. The further you are in your pregnancy, the more accurate the gender prediction will be. Accuracy varies from 70.3% at 11 weeks to 98.7% at 12 and 100% at 13 weeks.What is the average CRL at 11 weeks? ›
|GA (weeks)||CRL (cm, mean ± SD) Males||Females|
|10||3.89 ± 0.56||3.85 ± 0.50|
|11||4.82 ± 0.77||4.76 ± 0.67|
|12||5.73 ± 0.90||5.57 ± 0.86|
|13||6.56 ± 0.97||6.10 ± 1.35|
Clinical Considerations in the First Trimester
Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14.
At 12 weeks pregnant, baby is as big as a plum. The average 12-week fetus is about 2.1 inches long and . 49 ounces.What should I look for on a 12 week ultrasound? ›
What screening tests are done via ultrasound at 12 weeks? At 12 weeks, your doctor can screen for Down syndrome, trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome). This is called nuchal translucency screening.What is a good fetal fraction at 12 weeks? ›
At 10–20 weeks of gestation (the most common time for NIPS), FF is ~10–15% (5, 7). During NIPS, maternal and fetal cell-free DNA is not separated, so it is imperative to understand FF to accurately interpret NIPS results.How accurate is gender at 12 week ultrasound? ›
That is to say, reporting a male gender in the ultrasound imaging performed in the 11th or 12th weeks of pregnancy is likely to be 87.6% correct and reporting a female gender is likely to be 96.8% correct. Overall, ultrasound gender identification showed a high sensitivity, specificity, and accuracy [Table 3].How accurate is 12 week scan for Down's syndrome? ›
Babies with Down's syndrome are more likely to have a small or absent nose bone, with a flat profile. They often have leakage across the tricuspid valve and reverse flow in the ductus venosus. So adding in these additional markers will take the average detection rate of the standard technique of 80% up to 95%.