Ultrasound

In gynaecology, ultrasound is not one examination among many but the central one. It answers the question of whether there is a pregnancy and how the baby is doing, just as it answers the question of why bleeding is too heavy or whether a coil is sitting correctly. This page explains what is scanned at this practice, how it works, what becomes visible – and what does not.

How ultrasound works

The probe sends out sound waves too high for the ear to hear and receives what comes back from the boundaries between tissues. From the travel time and the strength of the echo the machine calculates an image. Different tissues reflect to different degrees – fluid hardly at all, which is why it appears black; bone almost completely, which is why it appears white with a shadow behind it.

No radiation is involved. That is the most important difference from X-rays and computed tomography, and the reason ultrasound is the method of choice in pregnancy. No harmful effect is known at the energy densities used in diagnosis – even after decades of widespread use.

The price for that is a limitation worth knowing: ultrasound does not pass through air or through bone. A bowel full of gas hides whatever lies behind it. That is why image quality is not the same in every woman, and why this examination depends more than others on who carries it out.

The two routes

Transvaginal ultrasound

In gynaecology, transvaginal ultrasound is the standard examination. A slim probe is inserted into the vagina and therefore lies immediately against the uterus and ovaries. Because no fat and no abdominal wall lie in between, a high frequency can be used – and high frequency means fine resolution.

What that means in practice: a gestational sac is visible from about the fifth week of pregnancy, a heartbeat from the sixth. The lining of the womb can be measured to the millimetre, a polyp of a few millimetres identified, a follicle in the ovary followed as it matures.

The examination is carried out with an empty bladder and is as a rule painless. The probe is considerably slimmer than a speculum. If it is your first time, you are told beforehand what will happen – and it can be stopped at any point.

In young girls, in women who have not yet had intercourse, and whenever the vaginal route is not wanted for whatever reason, the scan is done through the abdominal wall. It tells you less, but is sufficient for many questions. That decision is yours, not the examination’s.

Abdominal ultrasound

Scanning through the abdominal wall is used from the second trimester onwards, once the uterus is large enough, and also in young girls and in women for whom the vaginal route is not an option. Here a full bladder helps: it pushes the bowel aside and serves as an acoustic window.

The depth of penetration is greater, the resolution lower. In pregnancy that is no disadvantage, because what has to be assessed has grown correspondingly larger.

Ultrasound in pregnancy

In Austria the Eltern-Kind-Pass provides for four ultrasound examinations – since 1 October 2026; before that there were three. Each has its own question to answer: they are not the same examination four times at different points.

The first ultrasound achieves something that is not possible later: it dates the pregnancy. In the first trimester the crown-rump length is almost the same in all babies – differences in growth arise only later. That is why the due date determined here is accurate to about five days, and why it applies from then on, even if later measurements show a larger or smaller baby. How that affects your appointments is worked out by the due date calculator.

The anomaly scan is the most detailed examination of the whole pregnancy. Every organ is gone through individually, the heart in several planes. Allow 45 minutes and more. It is also the appointment at which the sex can be determined reliably – if you want to know; say so beforehand if you do not.

The third ultrasound answers the questions from which the birth plan emerges: is the baby growing as expected? Is there enough amniotic fluid? Is the baby head down? And where is the placenta – if it lies over the cervix, a vaginal birth is not possible.

The fourth ultrasound is new: since October 2026 the programme provides for a further examination shortly before the birth, between 35+0 and 38+0. It answers the question that matters at that point – how the baby is lying, how it has grown, whether the amniotic fluid volume is right and whether anything speaks against the planned mode of birth.

When these windows fall in your pregnancy is worked out by the maternity passport planner, which also exports them to your calendar.

What ultrasound in pregnancy cannot do

This limit deserves to be named as clearly as the possibilities. A normal anomaly scan does not mean the baby is healthy. It means the structures that could be examined looked normal.

Chromosomal disorders are visible on ultrasound only where they cause visible features – with trisomy 21 that is the case in about half of cases. Metabolic and inherited diseases are not visible at all. Some heart defects escape even a careful examination. And image quality depends on factors nobody can influence: how the baby is lying, the amount of amniotic fluid, the abdominal wall.

For specific questions about chromosomal disorders there are other routes: nuchal translucency measurement from 11+0, the non-invasive prenatal test from maternal blood from 10+0, and, where there is a concrete suspicion, amniocentesis. Before each of these steps stands the same question, and it is harder than the question of which test: what should follow from the result?

Estimating weight also has a limit that is regularly underestimated. It rests on formulae using three measurements and has a margin of about ten to fifteen per cent in either direction. At an estimated weight of 3,500 grams that means a range of roughly 3,000 to 4,000 grams. Anyone who takes that number as a fact is making decisions on a basis that does not support them.

3D and 4D ultrasound

In three-dimensional ultrasound, many section images are computed into a surface view; 4D means that this view moves. For parents it is often the moment when an examination turns into a face.

Medically the technique brings genuine added value for particular questions – in assessing cleft lip and palate, or malformations of the limbs or spine. It is no substitute for the standard examination: the decisive findings are made on the ordinary two-dimensional image.

The pictures come out best between the 26th and 30th week – before that the baby lacks subcutaneous fat, later it becomes too cramped. Whether a good view is achieved depends on how the baby is lying and on the amount of amniotic fluid, and cannot be forced. An appointment without a usable picture does happen.

Ultrasound outside pregnancy

In gynaecological screening, transvaginal ultrasound is a fixed part of every annual check-up. The size and shape of the uterus, the thickness and structure of the lining and both ovaries are assessed.

Typical questions:

• Heavy or prolonged bleeding. Fibroids, polyps and adenomyosis can be distinguished on ultrasound – and that distinction decides the treatment.
• Bleeding between periods and bleeding after the menopause. Here the thickness of the lining is the most important measurement. Bleeding after the menopause always needs investigating.
• Lower abdominal pain. Cysts, infection of the ovaries and signs of endometriosis.
• Trying to conceive. Following follicle growth and assessing the lining across the cycle, along with the question of polycystic ovary syndrome.
• Checking the position of a coil. Four to six weeks after insertion and annually thereafter – see IUD & coils.
• Assessment of the breast alongside examination by hand, particularly with dense glandular tissue, in which mammography tells you less.

For cycle assessment the timing is decisive: the lining looks different on day five of the cycle than on day twenty. Say what it is about when you make the appointment, so that it falls at the right time – the ovulation calculator helps you judge your own cycle for that.

Doppler: making blood flow visible

Besides the ordinary image, the machine can also display movement. The technique makes use of the fact that sound reflected from something moving changes its frequency – the effect that makes a passing ambulance sound higher and then lower. Red and blue areas of colour in the image show whether blood is flowing towards the probe or away from it.

In pregnancy Doppler is used where there are questions about the baby’s supply: with growth restriction, with high blood pressure in the mother, with suspected pre-eclampsia or with multiple pregnancy. Resistance is measured in the uterine arteries, in the umbilical artery and in an artery in the baby’s brain. From the relationship between these values it can be estimated whether the placenta is doing enough.

Outside pregnancy Doppler helps in assessing ovarian cysts and fibroids: a nodule with a rich blood supply is judged differently from a bloodless one. And where torsion of an ovary is suspected, the question of blood flow is the decisive one, because how urgent surgery is depends on it.

What a finding says – and what it does not

Ultrasound findings are often read as a final verdict, although they describe a snapshot. Three examples that regularly cause worry at the practice, and mostly do not justify any.

“A cyst on the ovary.” The great majority of all ovarian cysts are functional: a follicle that has grown larger than usual, or a corpus luteum that has enclosed fluid. Such cysts disappear by themselves within one or two cycles. That is why the usual consequence is not “operate” but “let us look again in six weeks” – and mostly there is nothing left to see.

“A fibroid.” Fibroids are benign muscle nodules of the uterus and are extremely common in women over thirty. They need treatment only if they cause symptoms – heavy bleeding, pressure on the bladder or bowel, pain – or if they distort the cavity of the uterus and thereby affect a pregnancy or a coil. A fibroid found by chance, causing no symptoms, is watched rather than treated.

“Thickened lining.” What counts as thickened depends entirely on the day of the cycle and the stage of life. Twelve millimetres is normal shortly before a bleed, and not after the menopause. A finding without the day of the cycle is therefore hard to judge – and one reason why findings from different places are not readily comparable.

So bring ultrasound reports from elsewhere in the original, not as a memory of what was said. With this examination, comparability over time is half of what it tells you.

How an ultrasound appointment works

Hardly any preparation is needed. For transvaginal ultrasound the bladder should be empty, for abdominal ultrasound full. No particular clothing and no fasting are required.

The examination itself takes five to forty minutes depending on the question. The gel feels cool; nothing more happens. During the examination measurements are taken and documented; pauses in which nothing is said are normal and not a sign of a finding. If you become uneasy in those moments: ask. An answer is always possible.

At this practice the ultrasound is part of the examination and is not charged separately – the fees are on the page Fees.

You take the printouts and pictures with you. In pregnancy the measurements are also entered in the Eltern-Kind-Pass; that entry is the authoritative one, because every subsequent carer and the maternity hospital read it. So bring the passport to every appointment – one left at home means values have to be taken again or hunted down.

How safe ultrasound is

On current knowledge, diagnostic ultrasound in pregnancy is harmless. There is no ionising radiation, and harmful effects have not been demonstrated at the energies used – neither in animal experiments nor in large follow-up studies of children scanned before birth.

Even so, the professional principle is to scan for as short a time as necessary and to keep the power as low as the question allows. Doppler, which displays blood flow, puts more energy into the tissue than the ordinary image and is therefore used in a targeted way and not for entertainment.

For the same reason the specialist societies advise against purely commercial “baby television” offers, in which scanning goes on at length with no medical question and no medical report. A 3D picture within a regular examination is something different from half an hour of entertainment scanning.

The second objection to such offers weighs more heavily than the first. Whoever scans without providing a medical report may see something abnormal – and may neither interpret nor communicate it. Conversely, the parents are left with the impression of an examination that was none: a lovely picture of the face says nothing about the heart. Both misunderstandings occur in practice, and both cause more worry than the picture brings joy.

If you would like a keepsake picture, you get one at this practice within the regular examination – provided the baby is lying in a way that allows it; that cannot be promised. In return, somebody is looking at the same time who can judge what there is to see.

Where to go from here

Whether for screening, cycle assessment, fertility or antenatal care – at this practice ultrasound is part of practically every examination. Make an appointment. Which examination is due when is shown by the screening planner and the maternity passport planner.