First you need to know is that cloudy urine is not a sign of pregnancy. However, In pregnancy, your urine compositions will be increased, so that this condition appears more frequent than usual.
Harmless cloudy urine
During pregnancy, the body of pregnant woman is in a state of hyperactivity, so as to generate large amounts of waste products, including urea, uric acid, creatine and creatinine. These waste products are going to be cleared from the blood into the urine and precipitated from the urine. Part of the waste also comes from her fetus. Therefore, the increase in metabolic products in the urine is the reason for cloudy urine during pregnancy more common than usual.
Infectious cloudy urine
Pregnant women are vulnerable to suffering from acute pyelonephritis for slow urine flow, which is caused due to progesterone acting on the urinary tract and enlarged uterine tending to compress the right ureter.
Pyelonephritis is the inflammation of the kidney and its pelvis, which is one of UTIs and often seen in pregnant women as common causes of cloudy urine. In addition, pyelonephritis is a urinary tract infection connected to cloudy urine, bacteriuria and pyuria. That is different from all kinds of glomerular nephropathy including glomerulonephritis, which are with features of blood in urine no pain and protein in urine.