6 Weeks Pregnant: Development of the Baby
The baby remains most susceptible to factors that can hamper normal growth between the 17th and 56th day of development .
Facial and Sensory Organ Development: Your baby still looks like a tiny tadpole ; but, this is the week when his cheeks, jaw, chin, nose and the limb buds start to form. The passages of the inner ear begin to develop during the sixth week . The forebrain develops a hollow stalk on each side and forms two small cups, which later become the eyeballs . Inside the cups, skin cells start turning into the lens and cornea.
Neural Tube Development: At the same time, the neural tube connecting the brain and spinal cord closes. The head end of this tube develops into the brain while the other end forms the spinal cord .
Internal Organ Development: The liver, lungs and kidneys are developing as well while the heart is the size of a poppy seed. Primitive RBCs start circulating through the embryo and chorionic villi. This is also the week when the pituitary gland and intestines begin to appear .
Limb Development: Limb buds begin to grow in order to form the arms and legs of your baby.
Umbilical Cord: Continues to grow while supplying your baby with oxygen and necessary nutrients.
Size of the Baby at Week 6 Pregnancy
Your baby is around 4 to 5 mm long during the sixth week . Babies at this stage of development are measured from the crown to rump (head to bottom), meaning the size does not include the developing legs .
What Happens in Your Body during Pregnancy Week 6?
The most common body changes include slight weight gain and fuller breasts and legs . Your clothes may get a bit tighter around the waist due to the weight gain. It is also normal for women having severe morning sickness (hyperemesis gravidarum) to lose some weight. A pelvic exam may show a larger uterus as your baby is growing steadily.
The high hCG levels increase the blood flow to the pelvic area so that your baby gets enough oxygen and nutrients. Like the earlier weeks, this causes your kidneys to work more efficiently, leading to the symptom of frequent urination. The pressure applied on your bladder by the growing uterus also contributes to this symptom . Some women may start showing at week 6 pregnancy as the size of the belly depends on a number of factors, including the baby’s position in the womb and the mother’s height, apart from the stage of pregnancy .
Ultrasound Scan during Pregnancy Week 6
Most expecting women get their first ultrasound scan during week 6 . The exam result shows the heart as a large bulge while there is another bump at the neural tube’s top end which will develop into the head and brain . You may even be able to see and hear the tiny heart beating (90-110 times per minute)  on a transvaginal ultrasound . Throughout the pregnancy, the heartbeat grows faster every day until it reaches about 175-180 beats per minute before lowering again and stabilizing at 120-160 beats a minute . However, there is nothing to worry about if your doctor cannot distinguish a heartbeat at week 6. In such cases, another scan should be done within 3 to 7 days .
The limb buds are also visible at this stage while the two small dimples on the sides of the head later develop into external ears. A transparent layer of skin covers the embryo by this time while there are thickenings marking the location of the eyes .
What are the Symptoms of Week 6 Pregnancy?
Apart from the regular early pregnancy symptoms, such as nausea and vomiting (morning sickness) , gas, indigestion, heartburn, bloating (usually due to high progesterone levels), period-like abdominal pain and cramping , lower back pain, lightheadedness, constipation/diarrhea, food cravings or aversions (accompanied by queasiness), increased sense of smell, headache and emotional symptoms (e.g. mood swings, depression), other symptoms may include:
- Frequent urination (as you are now urinating for both you and your baby while the growing uterus putting pressure on your bladder contributes to the symptom as well)
- Extreme exhaustion or fatigue (due to the additional work your body is managing to provide for your baby) 
- Light vaginal bleeding or spotting (may be accompanied by mild cramping) 
- Tender and sensitive breasts (as they are already preparing for breastfeeding) 
- Insomnia or trouble sleeping (often due to restless leg syndrome caused by the pregnancy hormones)
- Passing egg white cervical mucus 
- Groin pain (as your body gets used to being pregnant)
- Runny/stuffy nose due to high estrogen levels (rhinitis of pregnancy) 
- Excessive thirst and dry mouth (it may indicate gestational diabetes) 
- Hot flashes and chills
- Rectal pressure (due to the uterus stretching for accommodating the baby)
- Shortness of breath 
- Leg and joint pain (knee, hips, elbows) 
- Itching over your belly, breasts and thighs
- Mild to moderate pain under the ribs on one or both sides (rare)
- Yellow coloration of urine (due to your pre-natal vitamin, high hormone levels or dehydration)
However, it is completely normal to have few or no symptoms during the sixth week.
Women carrying twins or triplets may experience severe morning sickness than those carrying a single baby due to the higher pregnancy hormone levels .
When to Call the Doctor?
- Severe pelvic pain with or without vaginal bleeding
- Sharp lower abdominal or back pain on one or both sides (may indicate a kidney or urinary tract infection) 
- Heavy bleeding and passing blood clots
- Yellowish or brownish vaginal discharge
- Whitish/gray odd-smelling discharge or watery odorless clear/whitish vaginal discharge along with pain while urinating (may indicate some infection such as bacterial vaginosis and yeast infection) 
- Fever continuing for over 24-36 hours 
Tips for a Healthy Pregnancy and Baby
- Quitting smoking and drinking alcohol if you have not already 
- Following a healthy diet consisting of vegetables and fruits rich in folic acid and vitamin C
- Avoiding handling any toxins, insecticides and drugs 
- Informing the doctor about your pregnant prior to any medical procedures (e.g. x-ray)
- Doing light exercises regularly 
- Consulting your doctor regarding the risks of taking prescription anti-anxiety drugs (e.g. Xanax)
- http://americanpregnancy.org/gettingpregnant/PECervical-mucus.html [/ref]