This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
Weight gain in pregnancy is related to all except : 
Select and explain. 
A. Ethnicity, B. Smoking, C. Socioeconomic status, D. Preconceptional weight
B: Smoking
Answer: B: Smoking 
Explanation: Total weight gain in singleton pregnancy averages 11kg. It is distributed to 1 kg in first trimester and 5 kg each in second and third trimester. Total weight gain at term is distributed as reproductive weight gain 6 kg (fetus,placenta,liquor,uterus,breasts,accumulation of fat and protein) and net maternal weight gain of 6 kg ( increase in blood volume and extracellular fluid). Ideally weight gain in pregnancy depend on pre-pregnant BMI(20-26 is 11-16kg, >29 is 7kg, <19 is 18kg) Reference: Dutta Textbook of Obstetrics 7th edition page 50