The 11–14 week ultrasound
Ideally it is done between the start of week 11 and the start of week 14 of pregnancy. The timing matters: in this window the baby is the right size for the measurements.
What is this examination for?
- To confirm that the pregnancy is viable and how many babies there are
- To establish the gestational age precisely
- To carry out risk screening for chromosomal differences
- To detect marked structural differences at an early stage
- To assess the risk of pre-eclampsia
Why does establishing the gestational age with this ultrasound matter? Because the baby's crown–rump length is the most reliable measurement for determining gestational age. The accuracy of all subsequent care and tests rests on it.
What is looked at?
Contrary to what is assumed, this is not just a "nuchal measurement". Many of the baby's structures are examined:
- Head and brain: the ossification and shape of the skull; the symmetry of the brain; the brain structures with regard to an opening in the spine (spina bifida).
- Face: the nasal bone, the eye sockets and the upper lip (with regard to cleft lip).
- Nuchal translucency: measured to determine risk with regard to chromosomal differences and heart abnormalities.
- Heart and chest: the rhythm, position and axis of the heart; its four chambers and the outflow of the main vessels.
- Abdomen: the presence of the stomach and the bladder; the site where the umbilical cord enters — this is where the temporary herniation that is normal at this stage is distinguished from a true opening in the abdominal wall.
- Arms and legs: the three segments of each are seen separately.
- Placenta and womb: if there has been a previous caesarean, the relation of the placenta to the scar is assessed.
A common misunderstanding about the nasal bone: in about 50–60% of babies with Down syndrome the nasal bone is not seen. This is an indicator of risk, not a diagnosis — its not being seen does not by itself mean a conclusion, and its being seen does not remove the risk altogether.
Why is Doppler used at this stage?
- In the baby: the flow in certain vessels going to the heart and at a heart valve is examined to assess markers of risk for chromosomal differences and heart defects.
- In the mother: the flow in the uterine arteries is measured; together with blood pressure and blood tests, a risk calculation for pre-eclampsia is made.
The 18–22 week ultrasound (the detailed scan)
This is the detailed anatomical examination carried out routinely between weeks 18 and 24 of pregnancy.
What is this examination for?
- To examine all the baby's organ systems in detail
- To take the baseline measurements for monitoring growth
- To assess the amount of amniotic fluid
- To establish the relation of the placenta to the cervix
What is looked at?
- Head and brain: the integrity, shape and bone density of the skull; the cavities of the brain, the cerebellum and the areas around it — with regard to enlargement of the brain cavities and differences in the posterior region.
- Face: the upper lip and palate (with regard to a cleft), the profile (for the structure of the jaw) and the symmetry of the eyes.
- Heart: its position, axis, rhythm and size; the four-chamber view, the outflow tracts and the vessel views — congenital heart disease is screened for with these images.
- Lungs and chest cavity.
- Abdomen: the position of the organs, the stomach, the gallbladder, the site where the umbilical cord enters and the appearance of the bowel.
- Kidneys and bladder: the presence of both kidneys and whether there is dilatation of the renal pelvis — if it is above a certain measurement, follow-up is needed.
- Spine: along its length and in cross-section, together with the integrity of the skin covering it. A particular appearance seen in the cerebellum is the strongest indirect sign of an open spinal defect.
- Arms and legs: the symmetry, length, position and movement of the bones.
- Placenta: its position and its distance from the cervix. In pregnant women who have had surgery on the womb, additional findings are looked for with regard to a problem of placental attachment.
Two notes to set expectations correctly:
- Counting fingers is not a required part of routine screening. The symmetry, length, position and movement of the arms and legs are assessed.
- If the placenta is closer than a certain distance to the cervix, a repeat look in the third trimester is recommended — this does not mean there is a problem at the time; the placenta can move upwards as the pregnancy progresses.
What else is measured
- The estimated weight of the baby is calculated from measurements of the head, abdomen and thigh.
- The amount of amniotic fluid is measured.
- In those at high risk of premature birth, the length of the cervix is measured.
Frequently Asked Questions
Is the 11–14 week ultrasound just the nuchal measurement?
No, that is a common misunderstanding. The nuchal translucency is only one of the values measured. This examination also looks at the head and brain, face, heart, abdominal organs, arms and legs and the placenta; it confirms that the pregnancy is viable and how many babies there are, establishes the gestational age and assesses the risk of pre-eclampsia.
Why is my gestational age determined by ultrasound?
Because the crown–rump length measured at this stage is the most reliable measurement for determining gestational age. The accuracy of all subsequent care and tests rests on this dating.
They said the nasal bone was not seen — what does that mean?
This is an indicator of risk, not a diagnosis. In about 50–60% of babies with Down syndrome the nasal bone is not seen — so its not being seen does not by itself mean a conclusion, and its being seen does not remove the risk altogether. The result is assessed together with the other findings and tests.
Why is Doppler done?
For two separate purposes: in the baby, the flow in certain vessels going to the heart and at a heart valve is examined to assess markers of risk for chromosomal differences and heart defects. In the mother, the flow in the uterine arteries is measured and, together with blood pressure and blood tests, a risk calculation for pre-eclampsia is made.
What is examined in the 18–22 week ultrasound?
All the baby's organ systems are examined in detail: head and brain, face, heart, lungs, abdominal organs, kidneys and bladder, spine, arms and legs. Growth measurements are also taken, the amount of amniotic fluid is assessed and the relation of the placenta to the cervix is established.
Were my baby's fingers counted?
Counting fingers is not a required part of routine screening. The symmetry, length, position and movement of the bones in the arms and legs are assessed. This is a point worth knowing so that expectations are set correctly.
They said my placenta is low — should I be worried?
If the placenta is closer than a certain distance to the cervix, a repeat look in the third trimester is recommended. This does not mean there is a problem at the time — the placenta can move upwards as the pregnancy progresses. If you have had surgery on the womb, additional findings are also looked for with regard to a problem of attachment.
They said there is dilatation in the baby's kidney?
Dilatation of the renal pelvis is one of the findings looked at in the detailed ultrasound. If it is above a certain measurement, follow-up is needed — in most cases it is managed by monitoring. Your doctor decides how often checks are needed according to the degree of the finding.
Sources
- ISUOG Practice Guidelines — Updated performance of the 11–14-week ultrasound scan. The timing and purposes of the examination, the structures measured, the anatomy examined and the place of Doppler.
- ISUOG Practice Guidelines — Routine mid-trimester fetal ultrasound examination. The scope of the detailed second-trimester scan, the measurements, the assessment of the organ systems and the position of the placenta.
The information on this page is based on the national and international guidelines listed above. The page is reviewed whenever those guidelines are updated.
Practice and Contact Details
The information on this page is general. Please speak to your doctor about your own situation.
- DoctorOp. Dr. Murat Alpay — Specialist in Obstetrics and Gynaecology
- AddressOp. Dr. Murat Alpay Practice, Tekelioğlu Cd. No:51 B Kat:2, Filo Apt., 07160 Muratpaşa / Antalya
- Telephone0505 351 77 88
- HoursMonday – Saturday 09:00 – 18:00 · Closed on Sunday