The womb is moving further out of the pelvic area during this week, and your waist will shrink as the uterus continues to move into the abdomen.
Although this is the 18th week of pregnancy, it may not be exactly 18 weeks since you conceived. Most people do not not exactly when conception took place, so we count from "day 1," which is the first day of your last menstruation.
This MNT Knowledge Center feature is part of a series of articles on pregnancy. It provides a summary of each stage of pregnancy, what to expect, and insights into how your baby is developing.
Take a look at the other articles in the series:
- First trimester: Fertilization, implantation, week 5, week 6, week 7, week 8, week 9, week 10, week 11, week 12.
- Second trimester: Week 13, week 14, week 15, week 16, week 17.
Your pregnancy may be starting to show at 17 weeks.
One of the most noticeable symptoms at this stage of pregnancy is a feeling of dizziness and lightheadedness on standing up too quickly.
The uterus can push against an artery and slow the flow of blood. This means that when a woman around week 18 of pregnancy sits upright or stands up quickly, the rush of blood can cause a dizzy sensation. The uterus also demands a large volume of blood to support the fetus, which can cause occasional feelings of lightheadedness.
However, your body produces extra blood during pregnancy to compensate for this. To help support the increased blood volume, make sure you consume foods rich in iron and drink lots of fluids.
You may also feel aches or pains in the back, as the growing fetus and uterus might have caused you to shift your center of gravity forward and place stress on the spine.
You may not notice much weight gain yet, as most weight is put on after 20 weeks. The amount gained is usually between 22 and 28 pounds during pregnancy, but it depends on what your BMI was at the beginning.
Hormones will be preparing your hips for delivery by making them looser. This can also affect other joints, and the combination of this and the extra body weight can have an impact on the comfort of your back.
The fetus now weighs around 8 to 9 ounces (oz) and measures roughly 9 inches from crown to rump. They are about the size of a dollar bill.
The fetus will now have learned to yawn and hiccup, and you may even be able to feel the hiccupping motion.
Female fetuses will be developing their own uterus and fallopian tubes, and male fetuses may have visible external genitalia at this stage of pregnancy, although this can be difficult to see.
Myelin, the protective covering found on nerve cells, is now forming as the fetus' nervous system develops.
Things to do
Between 18 and 20 weeks of pregnancy, you will be called in for your third prenatal visit.
Screening blood tests may be carried out to check for chromosomal or anatomic abnormalities. If a screening blood test results positive, you will likely have further testing to confirm whether your baby is affected.
A maternal serum alpha-fetoprotein screening (MSAFP) is screening blood test used to evaluate the baby's risk of neural tube defects, such as spina bifida, and abdominal wall defects. This tests the levels of alpha-fetoprotein (AFP) and helps the physician estimate the likelihood of an abnormality.
If you are feeling anxious about the screening tests, remember that these are not diagnostic tests and are only meant to be an indication that diagnostic tests are needed. Keep in mind that some people decline a screening after discussing all of the options with their doctor.
A fetal anatomy scan may also be carried out between weeks 18 and 21 of pregnancy. This is a detailed ultrasound scan of the fetal brain, heart, bones, face, spinal cord, and abdomen, and it provides imaging of physical deformities, although it will not find every problem.
It will look for:
- open spina bifida
- cleft lip
- a diaphragmatic hernia
- serious abnormalities of the heart
- lethal skeletal dysplasia
- trisomy 13, 18 and 21
- bilateral renal agenesis
- the sex of the fetus
The technician carrying out the ultrasound, or sonographer, will apply gel to your abdomen to create good contact between the probe of the ultrasound device and the fetus. The image of your fetus will appear on a screen.
You are welcome to bring a partner or friend along for emotional support.
As with earlier weeks, you will soon find out that there are many lifestyle modifications which need to be made during pregnancy and even after delivery.
During pregnancy, look after yourself and the baby. Avoid alcohol, smoking, and all other toxic or illicit substances during this time. Discuss any prescribed medications with your healthcare provider to make sure that they are safe to use while pregnant.
Make sure you eat a healthy diet and take vitamin supplements if necessary.
Staying physically active throughout pregnancy is vital for both your own health and that of the fetus. However, by the 18th week, your body shape will be starting to change, and you may find that maintaining a healthy routine is becoming difficult.
However, there are ways to stay active while keeping discomfort to a minimum. The key thing to have in mind is avoiding overexertion or exhaustion. You should be able to hold a conversation while exercising during pregnancy. If you find yourself becoming out of breath, it is likely that you are exercising too hard. Light exercise can still be beneficial for both mother and infant.
It is best to avoid strenuous exercise during pregnancy if this was not already part of your lifestyle before becoming pregnant. Any aerobic exercise program, such as swimming, cycling, or even walking, should be limited to 15 minutes for three sessions per week.
This can then be gradually increased to four 30-minute weekly sessions.
Here are some tips to help you get as much benefit from exercise during pregnancy as possible:
- Warm up before every session and cool down when finished.
- Avoid working out in hot weather.
- Try to partake in physical activity every day, even if that only means going on a half-hour walk.
- Make sure you stay hydrated by drinking plenty of water and fluids.
- If taking an exercise class, confirm that the instructor is fully qualified and aware of the stage of your pregnancy.
- Swimming can provide great benefits during pregnancy, as the water can support your weight. Aquanatal classes may be on offer at your local swimming facility.
- Take extreme caution with, or avoid completely, exercises that pose a risk of falling, such as skiing, horseriding, or gymnastics. Falling can cause damage to the fetus.
Avoid exercises that involve lying flat on your back for long periods of time, contact sports, or spending long times diving in deep water or exercising at high altitudes.
Refer any questions about your pregnancy to your healthcare provider.
Call your doctor if you are experiencing symptoms of vaginal bleeding or passage of tissue, leaking vaginal fluid, feeling faint or dizzy, low blood pressure, rectal pressure, shoulder pain and severe pelvic pain or cramping.