31 weeks pregnant.

Your baby is continuing to grow each week that you remain pregnant. Your baby's crown-to-rump length is nearly 11.2 inches and total length is approximately 18 inches. Your baby weighs approximately 3.5 pounds at this point. Your uterus is about 4.4 inches above your bellybutton and continues to get larger. An average weight gain at this point is between 21 and 27 pounds. The weight that you gain is made up of your baby, placenta, blood supply, uterus, breasts, fat, water storage and amniotic fluid.

Because the ligaments and muscles supporting the small of your back relax and loosen in order to get ready for childbirth, your back may be aching from now on. There is usually nothing that can be done to prevent backaches, only to make them more comfortable. Many women get heartburn during these last few weeks of pregnancy because the oversized uterus leaves less room for the stomach and the contents within the stomach. Eating smaller, more frequent meals can help relieve the discomforts of heartburn.

This week marks an incredible milestone in your baby's lung development. Before now, the air sacs and branches in your baby's lungs were present but not functional. The lungs were not able to inflate properly. However, now there is surfactant being produced in your baby's lungs. Surfactant prevents your baby's lungs from collapsing outside of the uterus and the baby is able to take in air and breathe properly. The fetal ear is almost completely developed both inside and out. Your baby can hear your voice and other familiar sounds that she will recognize after birth. Your baby is putting on white fat under the skin and the skin's color is pink instead of red at this point. Your baby's fingernails have grown to the end of her fingers and she may scratch herself while she is in the womb.