You are about to finish the fourth month of your pregnancy and are probably enjoying the time more with your appetite back to normal and the morning sickness almost gone. However, there is nothing to worry about if you continue to experience the early pregnancy symptoms as each pregnancy is unique and each woman has a different experience carrying her child.
Baby development during week 21
Internal organ development
The overall growth rate slows down a bit from this week; but, the internal organs and systems continue to mature  as the baby keeps practicing swallowing, sucking and producing urine. Another major change this week is your baby’s bone marrow gradually taking over its job of producing blood cells from the liver and spleen . He is also gaining fat fast to stay warm, but he is yet to be as chubby as you are going to see him at birth .
Your baby is no more swallowing amniotic fluid just for working out his digestive system, but is also absorbing essential energy boosting nutrients from it to support his recent growth spurt. However, the placenta is still the principal source of the necessary nourishment .
Sensory organ development
He now has properly developed taste buds and can taste the amniotic fluid while practicing swallowing . The taste of your amniotic fluid varies every day according to what you eat. Recent researches have even showed that infants tend to prefer foods with the same taste as they were exposed to while in the womb .
The waxy vernix caseosa continues to protect the fetal skin as the baby soaks in the amniotic fluid, in addition to preventing any scratches and cuts as he starts growing fingernails . The eyelashes and eyebrows are developing fast, while the eyelids remain closed to prevent your baby from poking himself in the eyes .
Limb development and fetal movement
By the 21st week, his arms and legs are already in proportion, while the rapidly developing muscles and neuron-connections contribute to more coordinated baby movements . This, along with the growing size of your baby, makes those kicks and punches feel like real fetal movements rather than just quickening.
The fetal heartbeat continues to get stronger and louder every day as you can now easily listen to the thumping sound with a regular stethoscope .
How big is your baby this week?
Your baby has grown around 10.5 inches (26.67 cm) in length (from crown to ankle), weighing about 12.7 ounces (360 gm) , almost the size of a carrot . In a twin pregnancy, both babies are around 10 inches (25.4 cm) long at this stage .
21 weeks pregnant belly and body changes
The body changes from last week, such as the darkening skin (chloasma) , stretching muscles and ligaments due to the growing uterus, your shifting center of gravity and the relaxing joints continue into this week . Your belly keeps growing with your baby while you may notice that you have already added a few extra pounds . It is also completely normal to have your bellybutton sticking outward . You may also notice a yellowish fluid (colostrum) leaking from the nipples as your body prepares for breastfeeding .
21 weeks pregnant ultrasound
An ultrasound scan performed this week will help your doctor evaluate the growth and health of your baby. You can see your baby moving his arms and legs or sleeping in a cozy position in addition to finding out the gender in an ultrasound image .
Signs and symptoms of pregnancy week 21
- Indigestion and heartburn
- Gas, bloating and constipation 
- Joint, hip and back pain
- Braxton Hicks contractions 
- Stretch marks 
- Swelling of the hands and feet 
- Food cravings and pica 
- Emotional changes and depression
- Leg cramps
- Sleep disturbances or insomnia
- Frequent urination 
- Varicose veins 
- Bleeding gums
- Linea nigra (a dark line running down you abdomen) 
- Increased vaginal discharge
When to call the doctor?
- Pain and burning during urination along with lower back pain and yellowish jelly-like or cheesy-white vaginal discharge (might indicate a complication like UTI and kidney or yeast infection) 
- Bleeding or spotting along with symptoms like abdominal cramps, pelvic pressure or back ache (might indicate serious complications and even increased risk for a late miscarriage) 
- Severe itching without any rash or other apparent reason (might indicate obstetric cholestasis, a rare liver disorder) 
Severe persistent headaches, blurred vision, dizziness, heart palpitations, feeling out of breath, upper abdominal pain an sudden swelling of the hands and feet (might indicate high blood pressure) 
- Extreme tiredness with severe nausea, increased thirst, dry mouth and vision changes (might indicate gestational diabetes) 
- Severe morning sickness (nausea and vomiting) and/or diarrhea lasting for over 24 hours (increases the risk of dehydration)
- Lots of straw-colored or watery discharge (might indicate leaking amniotic fluid)
Tips for a healthy pregnancy
- Resting your feet frequently (for a few minutes each time) throughout the day to reduce the chances of swelling at night 
- Including plenty of calcium rich foods in your daily diet can reduce the symptom of leg cramps 
- Taking some of the extra weight off your back by elevating your feet slightly, whenever sitting down
- Following a diet including lots of fresh fruits, vegetables and whole grains, rich in protein as well as nutrients like folic acid, calcium, iron and vitamins C and D 
- Taking a warm (not hot) bath to reduce stress and relax the aching muscles 
- Avoiding handling your cat’s litter as it might infect you with toxoplasmosis, a harmful parasitic disease 
- Reading out loud from a children’s book can keep the baby calm, helping you bond with him as it enables him to recognize your voice after birth (some experts even suggest that the book you read to your baby now may remain his favorite for many years) 
- Following a regular prenatal yoga or light exercise routine
- http://www.babycenter.in/21-weeks-pregnant [/ref]