There is no single number that fits everyone. Recommended weight gain ranges depend largely on your body weight before pregnancy and whether you are expecting one baby or more. People who start at a lower weight are generally advised to gain more, and those starting at a higher weight less.
Gain is usually slow in the first trimester and steadier afterward. Focusing on balanced nutrition and staying active matters more than hitting an exact weekly figure. Pregnancy is not the time for weight-loss dieting.
Very rapid weight gain, especially with sudden swelling, can sometimes be a sign of a problem like pre-eclampsia and should be reported. Your midwife or doctor can monitor your gain and advise what is healthy for your particular situation.