Pregnancy Ultrasound Report: AFI, EFW and Placenta Words
A pregnancy scan report is full of short codes, and most of them describe a snapshot, not a verdict. AFI, EFW, placenta position and presentation can all shift as the weeks pass, which is why a worrying word at 20 weeks is often just the picture of that day.
Quick facts
- EDD: the estimated due date, set from the scan or your last period.
- AFI: a measure of the fluid around the baby.
- EFW: the estimated fetal weight, with a margin of error.
- Placenta and presentation: where the placenta sits and which way the baby faces. Both can change.
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What is an ultrasound scan in pregnancy checking?
The NHS explains that ultrasound uses sound waves, not radiation, and in pregnancy it checks a baby’s development. Different scans have different jobs: early dating, a mid-pregnancy anatomy scan, and growth scans later. The mid-pregnancy scan looks at the baby’s bones, heart, brain, spinal cord, face, kidneys and tummy, along with growth and blood flow in the uterus. If the baby is not in a good position for clear pictures, the NHS says you may be asked to walk or have something to eat and come back, or be offered another appointment, before 23 weeks.
What do EDD and gestational age mean on the report?
Gestational age is how many weeks and days along the pregnancy is. EDD is the estimated due date. Early scans measure the baby and can date a pregnancy more closely than a remembered last period, which is why doctors may adjust the EDD. Later scans measure many babies who are simply bigger or smaller by nature, so they are poor at re-dating. Ask which date your doctor is using and stick to that one.
What are AFI and oligohydramnios?
AFI is the amniotic fluid index, a way of estimating the fluid surrounding the baby from several pockets measured on the scan. Low fluid is called oligohydramnios, and extra fluid is polyhydramnios. A single reading on the edge of the lab range is often repeated. The cut-offs are set by the unit, so use the numbers on your report and let your obstetrician interpret them with your baby’s growth and your symptoms.
How do EFW and the growth percentile work?
EFW is an estimate of the baby’s weight calculated from head, abdomen and thigh bone measurements. The percentile tells where the baby sits compared with others of the same age. Healthy babies fall all along the range. A late-pregnancy estimate can be off by a meaningful margin, so one number is never a promise about birth weight. What doctors look at is the pattern across several scans.
Insider tip: ask for the trend, not the number
Ask your doctor, “Is the growth curve following its line across scans?” and request that the previous scan values be shown beside the new one. Presentation can still change until late in pregnancy, so a breech baby or low placenta at 20 weeks is often just a snapshot.
What do placenta position words mean?
| Word | Plain meaning |
|---|---|
| Anterior | Placenta on the front wall, nearer your tummy; kicks may feel softer |
| Posterior | Placenta on the back wall; kicks are often felt earlier |
| Fundal | Placenta at the top of the womb |
| Low-lying | Placenta near the cervix; usually rechecked later in pregnancy |
A low-lying placenta is the phrase that frightens most. The placenta may end up higher as the womb grows, but your obstetrician decides when to rescan. The key warning sign is bleeding, which needs urgent care.
What is presentation: cephalic or breech?
Cephalic means head down, breech means bottom or feet first. Babies turn a lot in mid-pregnancy, so the position at a 20-week scan says little about the position at birth. Your care team checks it again later.
What is cervical length?
Some units measure the length of the cervix, the neck of the womb. A short cervix may prompt closer follow-up. It is a risk marker, so ask your doctor what it means for you.
What should you do with the report?
- Look for the EDD and the scan date, then note which dating your doctor follows.
- Circle each word you cannot explain and ask in plain language.
- Ask which findings need a repeat scan and when.
- Keep every report to compare. Related guides: the NT scan report and the double marker test.
- Know the sugar test too: the pregnancy OGTT.
You notice vaginal bleeding, fluid leaking, a clear drop in your baby’s movements, severe headache, vision changes, or sudden swelling. Scan reports describe pictures, and a normal-looking report never cancels these symptoms. For counting movements see baby kick counts and when to call. Never start, stop or change a medicine because of a report. Your doctor decides.
You can browse more guides in Lab Reports Decoded.
Frequently asked questions about pregnancy scan reports
What is a normal AFI range?
Units set their own cut-offs, so use the range printed on your report. A reading near the edge is often repeated rather than acted on at once, and your obstetrician interprets it with your growth scans.
What does a low-lying placenta mean?
It means the placenta sits low in the womb near the cervix on that day. It is usually rescanned later because the placenta’s relative position can change. Report any vaginal bleeding to your care team at once.
What does EFW percentile mean?
It places your baby’s estimated weight against other babies of the same age. A wide range is healthy. Doctors watch whether growth follows its own line across scans.
What does breech presentation mean in a report?
It means the baby’s bottom or feet are lowest at the time of the scan. Babies often turn, so earlier in pregnancy it is rarely final. Your team will check again later.
What does an anterior placenta mean?
It means the placenta is on the front wall of the womb. It is a common, ordinary position, though you may feel kicks less clearly early on.
Is EDD by scan or by LMP more accurate?
Early scans usually date a pregnancy more closely than a remembered last period. Later scans are poor at re-dating. Ask which date your doctor follows.
What is oligohydramnios?
It means lower than expected amniotic fluid. Causes and management vary, so your obstetrician decides the next steps after repeat measurements and checks on the baby.
What do the words on a pregnancy scan report mean?
Most are measurements or locations: fluid (AFI), weight estimate (EFW), placenta position, and head-down or breech. This page defines the common ones, and your doctor can explain any other.
Can a growth scan be wrong?
Yes. Estimated weight has a margin of error, larger late in pregnancy. That is why doctors rely on a series of scans.
Do all pregnancy scans need a full bladder?
Not all. The NHS says some scans need you to drink water beforehand, and the clinic will tell you if yours does.