It is normal to gain some weight during pregnancy as a result of the hormonal and other changes occurring in your body. But, gaining too much or too little weight can be harmful for you and your baby . So, it is essential to know the healthy weight gain levels and how to achieve them. The recommended amount of weight to be gained during pregnancy varies from one woman to another depending mainly on their BMI (body mass index) before pregnancy. According to a pregnancy myth, if the extra calories tend to accumulate only in the belly area you are having a boy, while gaining all around the middle means it is a girl .
Weight gain is not an early sign of pregnancy as it often does not become evident before the second trimester.
It is erroneously believed that you are eating for two (you and your baby) when you are pregnant. Recent researches show that a pregnant woman needs only 300 additional calories (around 500 in twin pregnancy ) in a day, which can be acquired from an extra bowl of cereal or half a sandwich . So, it is not advisable to tuck in sugary treats and calorie-rich foods that make you gain weight without providing any additional nutritional value.
When the weight gain is centered on your belly area, it is baby weight. Experiencing weight gain in the hips, thighs and legs can indicate the presence of excess weight .
IOM or The Institute of Medicine published revised guidelines regarding the appropriate amount of weight gain during pregnancy based on WHO’s (the World Health Organization) body mass index (BMI) chart.
Recommended Weight gain 
|Underweight (BMI below 18.5)||28 to 40 pounds (13 to 18 kg)|
|Normal Weight (BMI between 18.5 and 24.9)||25 to 35 pounds (11.5 to 16 kg)|
|Overweight (BMI between 25 and 29)||15 to 25 pounds (7 to 11.5 kg)|
|Obese (BMI over 30)||11 to 20 pounds (5 to 9 kg)|
Recommended Weight Gain 
|Normal Weight||37 to 54 pounds (17 to 25 kg)|
|Overweight||31 to 50 pounds (14 to 23 kg)|
|Obese||25 to 42 pounds (11 to 19 kg)|
A pregnant woman typically starts gaining weight later during the first trimester (mainly retained water) , although the weight gain remains minimal at this early stage. There is generally little or no increase in weight during the first month (as the baby is still just a tiny ball of cells), while women suffering from severe morning sickness may even lose weight during the initial months.
Most mothers gain the highest amount of weight in the second trimester (eating habits in this period materially influence the baby’s birth weight) , while considerable weight gain occurs during the third trimester as well. However, it may slow down during the last month  due to various reasons (not being able to eat much or having an active baby).
Most women tend to start putting on weight earlier in second pregnancies while the total amount of weight-gain may be higher as well.
This is how the extra pounds are expected to be distributed throughout a healthy singleton pregnancy :
|BMI||First Trimester (total weight gain)||Second and Third Trimesters/Week|
|Underweight||1 to 4 pounds||1 to 1.3 pounds|
|Normal Weight||1 to 4 pounds||0.8 to 1 pound|
|Overweight||1 to 2 pounds||0.5 to 0.7 pound|
|Obese||0 to 1 pound||0.4 to 0.6 pound|
Pregnancy Weight Gain Breakdown Chart
Here is how the extra weight adds up in pregnancy :
|Amniotic fluid||2 pounds|
|Fat and Protein||7 pounds|
|Retained water||4 pounds|
It might be a difficult task to control the weight gain while pregnant. But it is vital to keep the body weight within the ideal range to avoid complications such as sleep apnea , preeclampsia (high blood pressure), gestational diabetes, back and leg pain, macrosomia (big baby) and c-section delivery . It is never advisable to adopt any weight-loss diets while carrying as crash and low-calorie diets can lead to malnutrition. The following guidelines can help you gain the minimum weight so that you can go back to your pre-pregnancy weight shortly after delivery.
Prenatal vitamins contain essential nutrients like folic acid that does not add any additional calories to your diet. So, taking the vitamins does not contribute to gaining excess weight.
The above two symptoms might indicate complications like preeclampsia and gestational diabetes . Babies born to mothers suffering from gestational diabetes often gain more weight and are larger than normal, requiring a c-section delivery .