Pregnancy week 17
8 Jan. 2026
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Pregnant at Week 17? In this exciting phase, your baby is developing rapidly. Here’s everything you need to know about growth, ultrasounds, and how your body is changing.
From the second trimester, measurements of what is known as BPD (measurement of part of the head) and FL (femur length) can be used as starting measurements for dating. This means that you determine how far along the pregnancy is by measuring the size of the foetus’s head and femur.
Up to week 22 of pregnancy, the starting point is that all foetuses grow the same amount and maintain the same size in the same week of pregnancy. What differs is when in each week the growth occurs. After the 22nd week of pregnancy begins, you can see that the weight starts to vary more from baby to baby.
By this time you should have been given an appointment for an ultrasound. It is usually carried out between weeks 18–20 and is called a routine anomaly ultrasound, which is offered to all pregnant women in the UK..
During the anomaly ultrasound, a sonographer checks, what the organs and extremities (arms and legs) look like. This examination is focused on the organs and anatomy. The heart and the vessels are examined. However, it is the small organs that are examined and assessed/measured. If everything cannot be seen and measured, a follow-up appointment is booked in to get a complete ultrasound examination.
The sonographer also looks at the placenta, where it is positioned in the uterus and how many vessels there are in the umbilical cord. If you have a low-lying placenta, you may need to check its position again later in your pregnancy. In some cases, the placenta can cover the entrance to the uterus, but often the placenta moves upwards as the baby and uterus grow.
The vessels in the umbilical cord are in most cases three in number and consist of veins and arteries. The anomaly ultrasound aims to detect any abnormalities and to see if the vessels in the umbilical cord are normally composed. If, for example, a vessel is missing, there may be reason to investigate further to see if it is connected to some other abnormality in development or organ formation.
The ultrasound can also see if there are benign muscle knots in the uterus (so-called fibroids). A fibroid may be known from a previous ultrasound and has often confirmed where it is growing and how big the fibroid is. The fibroid will then be followed up during the pregnancy to see if there is a risk that it would somehow be an obstacle to vaginal birth. In this case, you plan for the birth together with an obstetrician.
The size of your child and the growth of the myoma are also monitored depending on the medical planning made by the doctor at the beginning of the pregnancy. If a myoma is discovered during pregnancy, an assessment is made by a doctor depending on its size and where it is growing.
If the myoma is discovered a bit into the pregnancy, an assessment is made by the doctor depending on its size and where it grows. It is not uncommon for fibroids to grow in size during pregnancy, however it is less common for them to cause problems during pregnancy.
Pregnant women with fibroids are assessed individually and different hospital trusts have different guidelines for this.
In week 17, the foetus’ nails develop and hair begins to grow. The skin is reddish and wrinkled, but still partially transparent. Subcutaneous fat begins to be stored, which helps the baby keep warm after it is born. At the same time, vernix begins to form and is placed as a protective layer on the outside of the baby’s skin. The earlier the baby is born, the more vernix remains on the skin at birth.
The bones of the foetus become harder and the nervous system becomes more well-coordinated. During the upcoming ultrasound, the development of the foetus will be seen by the fact that it moves with more synchronised movements. It is not certain that you will feel the foetus moving, but many women associate foetal movements with bowel movements. Therefore, it can be difficult to feel the differences at this stage.
Despite the fact that the foetus is surrounded by amniotic fluid which dampens the sound level, this week the foetus may react to sudden sounds near the abdomen. Don’t startle the foetus unnecessarily, but as you get closer to the end of your pregnancy, you may be able to feel them startle if a sudden noise occurs near you. Cool huh?
Many women associate foetal movements with tingling bubbles and bowel movements, especially if you are expecting your first child.
Even if you’re not exerting yourself, it’s normal to feel short of breath. This is because your heart is pumping around a larger amount of blood than usual. While your belly continues to grow, you may also feel a new type of fatigue or pain in your pelvis, back, groin and/or hips. Some of this pain may be pelvic pain, which is known as pelvic girdle pain.
This pain can occur when your pelvic joints soften, which is done with the help of a hormone called relaxin. Relaxin is secreted to widen the pelvis and make it more mobile before birth, so that the baby can pass through smoothly. If you experience this pain, you should talk to your midwife, physiotherapist or doctor.
If you notice fatigue or pain in your back, it is probably because the muscles have not been exercised in the same way in relation to constantly carrying a growing baby. It is also easy to get a more arched back or for your posture to be affected during pregnancy. A tip here is to do mobility exercises and to exercise the muscles in your bottom, legs, back and torso to strengthen them and relieve the pain.
If you haven’t already purchased maternity clothes, now might be the time to do so. For some, it takes time before this need becomes apparent, and for others it happened a long time ago. Remember that it will vary from person to person as to how the abdomen and the rest of the body will react to pregnancy!
Your choice of maternity clothes can feel small compared to what you are used to. It can feel sad to spend money on maternity clothes when you know that the clothes will only be used for a short period… But something many people don’t think about is that a lot of the clothes can still be used after giving birth! This is because it can be nice to wear clothes that are not too tight. High-cut maternity trousers can be particularly comfortable to wear after giving birth, as can bras that are designed for breastfeeding and have a small extra tab at the back where you fasten the bra, allowing its circumference to increase as your belly grows, which can eventually bulge as high as the underwire of the bra.
Dresses, sweaters and shirts with buttons that are not tight work great both during pregnancy and if you plan to breastfeed after giving birth.
You can also swap with friends in your area, ask around in different communities if anyone wants to resell their maternity clothes or buy regular clothes but go up a size! Some people find building up their maternity wardrobe super fun and others not at all. Customise it according to your likes and needs.
Tip! If your regular trousers fit but are starting to get a little tight at the waist, you can use a hair tie to hold the button and opening together while giving you more space to breathe. If you wear a larger sweater, then this gap will not be visible and you can wait a while longer to get maternity trousers.
This ultrasound is called an anomaly ultrasound and is something that all pregnant women in the UK are offered.
At the ultrasound, you can find out the gender of your baby, if you want. Talk to your partner before the ultrasound about whether you want to know the gender or if you want to wait until the birth and have it as a surprise!
If the gender of your baby is clear, the sonographer can tell you, but in some cases the baby is in a position where it is not possible to see! Checking the sex via ultrasound is not 100% foolproof, but in most cases a sonographer can usually see what your little one is hiding in there.
Being the one not carrying the baby may seem abstract, but seeing your baby during an ultrasound is much more real for many people. Nevertheless, the feeling that life is going on as usual often still persists until your baby is born, which is not so strange because, as a partner, you do not experience all the changes in your body.
