Crown-rump length
Encyclopedia
Crown-rump length is the measurement of the length of human embryo
s and fetus
es from the top of the head (crown) to the bottom of the buttocks (rump). It is typically determined from ultrasound imagery
and can be used to estimate gestational age
.
inside the uterus
of the mother usually in a curved posture resembling the letter C. The measurement can actually vary slightly if the fetus is temporarily stretching (straightening) its body. The measurement needs to be in the natural state with an unstretched body which is actually C shaped. The measurement of CRL is useful in determining the gestational age
(menstrual age starting from the first day of the last menstrual period) and thus the expected date of delivery (EDD). Different babies do grow at different rates and thus the gestational age is an approximation. Recent evidence has indicated that CRL growth (and thus the approximation of gestational age) may be influenced by maternal factors such as age, smoking, and folic acid intake. Early in pregnancy
it is accurate within +/- 4 days but later in pregnancy due to different growth rates, the accuracy is less. In that situation, other parameters can be used in addition to CRL. The length of the umbilical cord
is approximately equal to the CRL throughout pregnancy.
Gestational age is not the same as fertilization age. It takes about 14 days from the first day of the last menstrual period for conception to take place and thus for the conceptus
to form. The age from this point in time (conception) is called the fertilization age and is thus 2 weeks shorter than the gestational age. Thus a 6 week gestational age would be a 4 week fertilization age. Some authorities however casually interchange these terms and the reader is advised to be cautious. An average gestational period (duration of pregnancy from the first day of the last menstrual period up to delivery) is 280 days. Thus if all months were of 31 days, it would be 9 months and 1 day.
The following formula is an approximation:
Gestational age [weeks of pregnancy] = crown-rump length (cm) + 6.5
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s and fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es from the top of the head (crown) to the bottom of the buttocks (rump). It is typically determined from ultrasound imagery
Obstetric ultrasonography
Obstetric sonography is the application of medical ultrasonography to obstetrics, in which sonography is used to visualize the embryo or foetus in its mother's uterus...
and can be used to estimate gestational age
Gestational age
Gestational age relates to the age of an embryo or fetus . There is some ambiguity in how it is defined:*In embryology, gestational age is the time elapsed since conception. This interval is also termed fertilisation age....
.
Measuring
The embryo and fetus float in the amniotic fluidAmniotic fluid
Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amniotic sac of a pregnant woman.- Development of amniotic fluid :...
inside the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
of the mother usually in a curved posture resembling the letter C. The measurement can actually vary slightly if the fetus is temporarily stretching (straightening) its body. The measurement needs to be in the natural state with an unstretched body which is actually C shaped. The measurement of CRL is useful in determining the gestational age
Gestational age
Gestational age relates to the age of an embryo or fetus . There is some ambiguity in how it is defined:*In embryology, gestational age is the time elapsed since conception. This interval is also termed fertilisation age....
(menstrual age starting from the first day of the last menstrual period) and thus the expected date of delivery (EDD). Different babies do grow at different rates and thus the gestational age is an approximation. Recent evidence has indicated that CRL growth (and thus the approximation of gestational age) may be influenced by maternal factors such as age, smoking, and folic acid intake. Early in pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
it is accurate within +/- 4 days but later in pregnancy due to different growth rates, the accuracy is less. In that situation, other parameters can be used in addition to CRL. The length of the umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
is approximately equal to the CRL throughout pregnancy.
Gestational age is not the same as fertilization age. It takes about 14 days from the first day of the last menstrual period for conception to take place and thus for the conceptus
Conceptus
Conceptus denotes the embryo and its adnexa or associated membranes . The conceptus includes all structures that develop from the zygote, both embryonic and extraembryonic...
to form. The age from this point in time (conception) is called the fertilization age and is thus 2 weeks shorter than the gestational age. Thus a 6 week gestational age would be a 4 week fertilization age. Some authorities however casually interchange these terms and the reader is advised to be cautious. An average gestational period (duration of pregnancy from the first day of the last menstrual period up to delivery) is 280 days. Thus if all months were of 31 days, it would be 9 months and 1 day.
Typical measurements
| Age | CRL (cm) |
|---|---|
| 6.1 Weeks: | 0.4 cm |
| 7.2 Weeks: | 1.0 cm |
| 8.0 Weeks: | 1.6 cm |
| 9.2 Weeks: | 2.5 cm |
| 9.9 Weeks: | 3.0 cm |
| 10.9 Weeks: | 4.0 cm |
| 12.1 Weeks: | 5.5 cm |
| 13.2 Weeks: | 7.0 cm |
| 14.0 Weeks: | 8.0 cm |
The following formula is an approximation:
Gestational age [weeks of pregnancy] = crown-rump length (cm) + 6.5