The embryo is approximately 1.3mm from the crown of the head to the rump but is very difficult to see and measure at this stage using ultrasound.
Week 17 of pregnancy (Days 119-125)
Your baby and the umbilical cord are experiencing a growth spurt this week. Your baby's sex can now be accurately detected on an ultrasound scan.
Your Baby
The fetus now typically measures between 11.4cm and 12.7cm long (from crown to rump) and weighs around 100g. This increase in length and weight is larger than in previous weeks due to a growth spurt that is well underway. This growth spurt not only applies to the fetus, but also to the umbilical cord, which is thickening and growing stronger too. As well as a growth spurt, the fetus also experiences an energy burst – becoming more active over the coming weeks. This week could be the time that you feel the first movements of the fetus, although many women, particularly if it is their first pregnancy, do not feel fetal movement at this stage.
The skeleton, which is largely formed of cartilage at the moment, will start to harden during the course of this week and myelin (a protective coating) is forming around the spinal cord. Body fat is also beginning to develop. This will eventually help to maintain a constant body temperature. The brain now controls heart rate, irregular heartbeats are now rare and heart rate is usually between 140 and 150 beats per minute – twice the rate of an adult female.
Your Body and Symptoms
You may find that your weight gain is now sufficient to affect your centre of gravity – making you feel off-balance. If you are struggling with your balance, it may be a good idea to avoid wearing high-heeled shoes. It is also around this time that many women begin to need to wear maternity clothes.
Although an increased need to urinate is a perfectly normal part of pregnancy, caused by a combination of increased hormone levels and the physical effects of the uterus pressing down on the bladder, you should look out for additional urine-related symptoms such as a burning sensation during urination. This could be an indicator that you have cystitis or a urinary tract infection (UTI). If you have any concerns, you should seek the advice of a health care professional.
You may also continue to, or start to experience a thin, milky vaginal discharge called leukorrhea. This is both normal and functional as it helps to keep the birth canal free from infection. You may be experiencing occasional dizziness or faintness. There are many possible causes for this, including hormonal increases and fatigue, however headaches and dizziness may also be the result of dehydration. Drinking plenty of fluids and avoiding diuretics such as caffeine can help with this.
Due to a combination of increased levels of progesterone causing blood vessels to dilate and a higher metabolic rate causing more body heat to be generated, many women suffer from hot flushes during pregnancy. Avoiding triggers such as alcohol, spicy foods and coffee may help to reduce hot flushes.
Symptoms to Watch Out For
Vaginal bleeding is not normal at this stage. Some mild abdominal pain and backache is normal. Vaginal discharge should be of consistent milky colour and volume. If it should be pink or more voluminous you should see a medical professional. This is particularly true if you have had a previous late miscarriage, operation on your cervix or short cervix. This is also important if you are carrying more than one baby.
Your Care on the NHS
The midwife will be able to provide you with advice. The NHS will not routinely be able to offer you an ultrasound scan at this time.
Private Care Available
General midwifery and medical advice is available in private clinics for which you do not require a referral letter. An ultrasound scan, called a reassurance scan at this stage can check the size and normality of the baby. It can also determine the sex of the baby quite accurately. If you are concerned about your cervix becoming short or have other concerns about your cervix then an ultrasound scan of your cervix can be reassuring. This gives a better assessment when performed through the vagina (you can request a female sonographer).
Explore other weeks
Week 5 of pregnancy (Days 35-41)
Week 6 of pregnancy (Days 42-48)
Facial features continue to develop during this week, with tiny pits forming where the ears will eventually be. Nostril openings begin to appear along with dark spots where your baby’s eyes will be.
Week 7 of pregnancy (Days 49-55)
This week your baby experiences a huge growth spurt. Your baby's heartbeat will be visible on a viability ultrasound scan.
Explore other tests
Early Pregnancy Scan
From 6-11 weeks of pregnancy.
Panorama NIPT
From 9 weeks of pregnancy.
Non-Invasive Prenatal Test (NIPT)
From 10 weeks of pregnancy