Reaching the 31st week means you have now completed the first month of your third trimester and are entering the eighth month of your pregnancy. After the 30th week, your baby’s odds of surviving without any long-term complications are rising considerably every week . He would have around 95% chances of survival without any physical or mental anomalies if you were to give birth this week .
31 weeks pregnant: baby development
Internal organ development
The fetal lungs continue to mature and are now capable of functioning on their own; however, they would need external medical assistance in case of preterm deliveries . The kidneys and urinary tract are mature, with your baby passing about 2 cups of urine every day. The amniotic fluid is replaced by your body several times a day to eliminate the fetal waste materials .
These final weeks are vital for the fetal brain development with trillions of neuron connections forming, enabling your baby to use all the five senses . Brain scans performed around week 31 shows separate sleep cycles, indicating that your baby might already be dreaming about you . At eight months of gestational age, babies might even be capable of sensing emotions in the mother and those around her by hearing their voices .
With the growing fat layer taking over the job of keeping your baby warm in the womb, he is now shedding the lanugo hair (the downy hair keeping your baby warm until now); but, you might notice traces of it on his back and shoulders at birth . The developing fat layer is also filling out his body, giving him a plumper appearance.
Immune system development
The last stage of gestation is also crucial for the immune system development, preparing your baby for the outside world. However, he would need your colostrum and breast milk to boost his immunity for fighting infections and diseases immediately after birth .
Reproductive organ development
The 31st week is a milestone for reproductive development as this is the week when the testicles move into the scrotum through the groin. If you are having a girl, her clitoris has almost completed developing, awaiting to be covered by the still-growing vulva .
Sensory organ development
The relatively mature senses of vision and hearing, along with the developed neck and shoulder, allow your baby to turn his head in response to sound and light . He might even ‘jump’ (or make sudden jerky movements) in response to sudden loud noises or move rhythmically when you play some music he likes . Although his sense of smell is developed enough, he cannot smell anything yet as he is still submerged in fluid .
Fetal movements this week
Your baby’s increasing size is gradually limiting the space inside the uterus so he might not be able to kick and punch as much as he was until last week . The wake and sleep periods of your baby might also become more defined by this stage . You might also notice a rhythmic movement lasting for a few minutes at a time – these are probably fetal hiccups.
In many cases, the baby settles in the birth position (head-down) by the 31st week; however, it is also normal for babies to be in a breech (feet-down) or transverse (lying sideways) position as there is still time for them to rotate into a proper position .
How big is your baby?
The baby is just over 16 inches (40 cm) long , as big as a pineapple or a bunch of leeks, weighing about 3.3 pounds (1.5 kg) . He has almost reached the newborn length (19 inches to 21 inches)  and will be gaining more weight (about 1.7 to 1.9 pounds ) than growing in length in these last few weeks .
Twins at pregnancy week 31
The growth rate slows down a bit in twin pregnancies at this stage as the babies are now competing for nutrients to gain a healthy amount of weight before they are born  Although, they are as big as a baby in any singleton pregnancy at week 31.
31 weeks pregnant: weight gain, belly and body changes
The top of the uterus is now 4 inches above your bellybutton . You have probably gained around 3 to 4 pounds already in your third trimester, with the ideal range of weight gain being about a pound per week as your baby hits another growth spurt before birth .
You might notice your breasts leaking the thick, yellowish fluid colostrum as your body prepares for breastfeeding. However, it is completely normal if you do not have any such leakage. You will still be able to breastfeed your baby once he arrives .
31 weeks pregnant tests and ultrasound
31st week routine prenatal check up will include measuring your blood pressure to assess the risks of high BP and preeclampsia. Your doctor might also order a urine test to check for protein in the urine .
An ultrasound scan performed this week will show your baby moving his hands and feet and turning his head while also making different facial expressions. On a 3d ultrasound you can see your baby looking almost like how he is going to look at birth.
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Pregnancy week 31 signs and symptoms
- Braxton Hicks contractions 
- Feeling out of breath along with rib pain as the growing uterus puts pressure on your lungs and ribcage (however, it does not distress the baby in any way as he is getting his oxygen from the placenta) 
- Indigestion and heartburn 
- Gas, bloating and constipation
- Stretch marks 
- Itchy skin, especially around the abdomen, breasts and back
- Varicose veins and hemorrhoids 
- Insomnia and restless leg syndrome 
- Joint, hip and back pain 
- Round ligament pain
- Pelvic pain
- Tailbone pain
- Sciatica 
- Varicose veins and hemorrhoids (the latter is often associated with constipation and the strain of bowel movements apart from the increasing weight of your growing baby) 
- Clumsiness and pregnancy brain (mainly because of your changing hormone levels) 
- Emotional changes and depression
- Loss of appetite
- Swelling of the hands and feet (due to increased blood flow and fluid retention)
- Leg cramps 
- Numbness or a tingling sensation in your hands (carpal tunnel syndrome) 
- Linea nigra
When to call the doctor
- If you notice decreased fetal movement during a kick count (your baby should make 10 movements of any kind within 2 hours during his active periods) or any kind of change in his regular movement pattern 
- Contractions getting closer together over time along with throbbing lower back pain, pressure in the pelvic area, flu-like symptoms (diarrhea, vomiting), bleeding/spotting, pinkish mucus-like discharge or losing the mucus plug, leaking clear, thin fluid, and period-like cramping (might be signs of preterm labor) 
- Increased thirst, dry mouth and frequent urge to urinate accompanied by tiredness or dizziness, sudden blurred vision and recurring vaginal infections, such as yeast infection (might indicate gestational diabetes) 
- Pain or burning while urinating, dark or cloudy urine, thick white or yellowish jelly-like discharge, lower back pain (often around one of the kidneys) and nausea (might indicate UTI  or yeast infection )
- Sudden edema of the face and hands along with rapid weight gain, persistent headache, lightheadedness, shortness of breath, extreme fatigue, upper stomach pain and sudden vision changes (might indicate high blood pressure or preeclampsia) 
- Lots of straw colored or thin watery fluid discharge (might be leaking amniotic fluid)
- Unilateral swelling of the feet or one foot more swollen than the other (might indicate a blood clotting disorder)
Tips for a healthy pregnancy and baby
- Eating frequent small meals instead of three large ones to make it easier for your digestive tract to process the food in the limited space, preventing indigestion and heartburn 
- Including lots of iron rich foods, like leafy green vegetables, red meat, dry fruits, cereals and legumes, in your daily diet so your body has enough iron for both you and your baby (as your baby is storing iron that will help him grow even after birth) 
- Getting enough vitamin C (fresh fruits and fruit juices) as it helps in iron absorption
- Practicing breathing and relaxation techniques as your due date approaching 
- Taking a warm (not hot) bath with a little baking soda to manage hemorrhoids 
- Avoiding drinking water or fruit juices in between meals as they further minimize the space for solid food 
- Doing regular prenatal yoga or light exercises (e.g. swimming or going for short walks twice daily)
- http://pregnancy.familyeducation.com/pregnancy-day-by-day/third-trimester/36574.html [/ref]