Your baby is now the size of a banana in length, measuring six and a half (6.5) inches from crown to rump (or ten  inches from head to heel) and weighing about ten and a half (10.5) ounces. You are in your fifth month of pregnancy.
During week 20 of pregnancy, your baby begins the next phase of growth and development. Over the next twenty or so weeks, your baby will pack on the pounds and the inches. The kidneys, which now take on a familiar bean shape, are in place in the abdomen. If your baby is a girl, her ovaries are in place on either side of her uterus. If your baby is a boy, his testes are moving into place in his scrotum. The rest of the internal organs will also soon move into their proper positions. The intestines also continue to produce meconium, which is comprised of the intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water that your baby produces and swallows. Your baby will pass this meconium in the first few dirty diapers, although some babies pass their meconium in the womb or during birth.
Your health care provider may recommend a second trimester ultrasound around week 20 of pregnancy (although you do not need to consent because routine ultrasounds are not necessary for normal, low-risk pregnancies). Your baby may move away from the pressure or sound of the ultrasound. During week 20 of pregnancies, your baby can hear the sounds of the womb environment, which include your heartbeat, digestive sounds, and voice and other external noises. Some babies will even startle and jump at loud and unexpected sounds. Your baby continues to move and wiggle, although the kicking and punching will slow down a little over the next few months a space becomes limited inside the womb for your ever-growing baby.
During week 20 of pregnancy, your uterus is about level with your belly button, which may begin to protrude now. On average, you should have gained about ten pounds by the halfway point of your pregnancy. From now until you give birth, you can expect to gain between one to two pounds per week for a total weight gain of twenty-five to thirty-five pounds. Make sure that you are eating a healthy and well-balanced diet. Make especially sure to get enough iron in your diet; low iron levels during pregnancy are linked an increased risk of preterm birth and an increased risk of low birth weight.
Also be sure to drink plenty of water or other healthy liquids. As the smooth muscles in the urinary tract relax during the second half of pregnancy, you are at an increased risk for bladder infections. Also try leaning forward on the toilet when you use the bathroom to empty all of the urine from your bladder. Other symptoms during week 20 of pregnancy include increased hunger, increased sweating, more difficulty breathing, snoring, increased vaginal discharge (leukorrhea), headaches, faintness or dizziness, leg cramps, and slightly swollen ankles and feet.
Disclaimer: The information provided in this article is not meant to replace the professional medical advice of your health care provider.
20 weeks pregnant: http://www.babyzone.com/pregnancy-week-by-week/20-weeks-pregnant_70790
Curtis, Glade B. & Judith Schuler. 2011. Your pregnancy week by week. 7th edn. Philadelphia: Running Press.
Stone, Joanne & Keith Eddleman, eds. 2003. The pregnancy bible: Your complete guide to pregnancy and early parenthood. Willowdale, Ontario: Firefly Books.
Your pregnancy: 20 weeks: http://www.babycenter.com/6_your-pregnancy-20-weeks_1109.bc
Your pregnancy week by week: Weeks 17-20: http://www.webmd.com/baby/guide/your-pregnancy-week-by-week-weeks-17-20
3-D Ultrasound of 20 Week Fetus: http://commons.wikimedia.org/wiki/File:3dultrasound_20_weeks.jpg
Baby Bump at 20 Weeks: http://commons.wikimedia.org/wiki/File:Myllissa_20_weeks.jpg