You are now well into your second trimester with the risks of early pregnancy complications considerably low, while your body is coming in better terms with being pregnant. You may already have started wearing maternity clothing as your baby continues to grow in size.
Baby development at 16th week of pregnancy
Bone and muscle development
The backbone and the muscles in your baby’s back are gradually gaining strength, enabling him to straighten his head . The cartilaginous skeleton has already begun turning into bone, but the ossification process will finish only after birth so the bones remain flexible at the time of delivery .
At the same time, development of the facial muscles continues with your baby practicing swallowing, sucking  and making various facial expressions (however, he cannot control them at the moment).
Sensory organ development
Your baby can now move his eyes a little from side-to-side; however, the eyelids are still fused shut . The hearing also continues to develop with the growth of tiny bones in the baby’s ears, enabling him to hear your voice when you speak or sing . The skin remains transparent enough for you to see his developing blood vessels. Fat begins developing underneath the skin which will later act as insulation for the fetus .
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Internal organ development
The circulatory system, lungs and urinary tract are fully developed with your baby practicing to inhale and exhale the amniotic fluid that is protecting her within the amniotic sac . His body is now pumping around 25 qt. of blood every day , while the sweat glands are also growing in place .
The development of the umbilical cord is now complete with two arteries and a vein, protected by the jelly-like substance (Wharton’s jelly) covering the cord . The production of meconium, which will later be the first bowel movement of your baby after birth, also begins around this time in the fetal intestinal tract .
How big is the baby at pregnancy week 16
He is now almost as big as an avocado, being around 4.6 inches (11.68 cm) long, weighing 3.5 oz (100 gm) .
Fetal movements at pregnancy week 16
As you must already know, the baby has started to move his arms and legs by now. In most cases, the mother cannot feel these movements before the 20th week as the baby is still too small, nestled within the cushion provide by the placenta and amniotic fluid . However, you may start feeling a slight fluttering, often referred to as ‘quickening’  in your uterus around this week. Women having a placenta lying closer to the back of the uterus are more likely to feel these movements earlier than those with their placenta near the front uterine wall . Women carrying their second child generally recognize the fetal movements earlier than first time mothers .
Pregnancy week 16 fundal height
This week, the uterus is located between your pubic bone and navel, with the fundal height (the distance between the top of the uterus and the top of your pubic bone) being around 16 cm .
Changes in your body during 16th week of pregnancy
So, the biggest change this week is the baby bump which is now large enough for others to notice. The round ligaments have already started to thicken and stretch to support the growing uterus. So, it is normal for you to feel occasional sharp pulls in your abdominal muscles and ligaments, especially when you make any sudden movements.
The production of colostrum, the first fluid produced by the breasts in preparation for breastfeeding, may start this week . Due to this, some women may notice their nipples leaking a thick yellowish fluid during the 16th-17th week.
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16 weeks pregnant ultrasound
An ultrasound scan performed this week will show your baby’s facial features to be more defined  with prominent nose, forehead, lips and the eyes close together in their proper place. The external genital organs are already developed; so, your sonographer might be able to detect the gender at this stage, depending on the position of the baby within the womb . Major physical defects can also be detected at this stage through ultrasound.
Your doctor will also use a Doppler device to check the fetal heartbeat and assess your baby’s health. According to old midwives’ tales, fetal heart rate over 140/min means you are having a girl while heart rate below 140/min indicates it is a boy. However, there is no scientific evidence for this theory .
Signs and symptoms of pregnancy week 16
Most of the early pregnancy signs are probably gone by now, but there is nothing to worry about if you still have a few lingering signs of morning sickness, dry mouth, insomnia and loss of appetite. These are likely to be more severe in twin pregnancies due to the comparatively higher estrogen and progesterone levels . Other common week 16 symptoms are:
- Hip and back pain 
- Joint and muscle aches
- Round ligament pain 
- Enlarging breasts
- Visible veins, especially on the abdomen, chest and breasts (due to the increased blood flow) 
- Forgetfulness (pregnancy brain) 
- Breathlessness (due to the growing uterus putting pressure on the diaphragm, allowing less space for your lungs to function) 
- Braxton Hicks contractions 
- Weight gain 
- Indigestion and heartburn
- Gas and flatulence
- Itchy, dry and sensitive eyes (due to the pregnancy hormones or certain allergies) 
- Emotional changes or mood swings
- Nails and hair growing faster (because of the high pregnancy hormone levels) 
- Bleeding gums and nosebleeds
- Sinus, cold and flu-like symptoms 
- Increased vaginal discharge 
- dry itchy skin with or without rashes, especially around the expanding belly
When to call the doctor
- Although it is normal to feel some aches and pains in your pelvic area, abdomen and back, you should watch out for the following warning signs:
- Severe or constant abdominal cramping along with bleeding or spotting 
- Severe nausea with excessive vomiting and/or diarrhea continuing for over 24 hours
- Extreme fatigue with constant headache, palpitations, dizziness, upper right abdominal pain and vision changes (might indicate high blood pressure or preeclampsia) 
- Having symptoms like burning pain during urination, kidney or lower back pain, fever or odorless white discharge (might indicate a kidney  or yeast infection )
Tips for a healthy pregnancy and baby
- Drinking lots fluids to flush your system and avoid dehydration
- Considering getting the flu vaccine if you are pregnant in the flu season (June-September) 
- Using a sunscreen lotion that protects against both UVA and UVB rays so the symptom of skin darkening does not get worse due to sun exposure
- Following a light pregnancy-safe exercise routine or joining prenatal yoga classes (avoid those involving lying on your back or standing for long periods as it reduces blood flow to the fetus) 
- Using an eye drop for relieving your dry, itchy eyes (make sure to consult your doctor to know what eye drops are safe in pregnancy) 
- Taking your prenatal vitamins and following a diet rich in nutrients like vitamin C and folic acid
- Practicing sleeping on your left side as it improves your blood circulation which can lower the risk of developing edema and varicose veins 
- Going for all your routine checkups and screening tests (the doctor may also recommend certain blood and urine tests in case of high risk pregnancies)
- http://www.babycentre.co.uk/a758/guide-to-exercising-in-pregnancy [/ref]