For most expecting mothers, weight gain during pregnancy can be difficult to manage. In most cases, gaining any sort of weight is seen as a bad thing but when you are pregnant, gaining weight is a healthy and natural part of the process. The amount of weight you gain, however, can have a significant impact on the health of you and your baby, as well as the smoothness of the delivery and post-delivery recovery.
Extensive research has been done on pregnancies all over the world, and there are certain averages in terms of weight gain during pregnancy based on your BMI, lifestyle factors and your dietary preferences. 
What is Normal Weight Gain During Pregnancy?
There is no such thing as a “normal” amount of weight to gain while pregnant because every woman’s body is different. However, the common average for weight gain is between 20 and 35 pounds, but this is only for women who have a BMI that lies in the “normal” range. BMI stands for Body Mass Index and is a calculation based on your height and weight.
For women who lie in the normal range of BMI (18.5-25) should aim to gain 20-35 pounds during their pregnancy, provided they aren’t pregnant with twins. Overweight individuals, however, won’t need to gain as much weight during their pregnancy, and may only see an increase of 10-25 pounds. Underweight individuals, on the other hand, will need to gain more weight to compensate for the strain on their body, so weight gain of 30-45 pounds isn’t uncommon. 
The time at which you gain weight is also an important factor in the healthy development of the fetus and the outcome of delivery. Weight gain should differ depending on the specific trimesters of the pregnancy.
During the first trimester, when the fetus is at its smallest, it won’t need as many resources, so your weight gain will likely be limited to 3-4 pounds. In some cases, women report gaining almost no weight during the first three months of their pregnancy, typically when they are experiencing severe morning sickness. This can keep you “slim”, but it is important to ensure that your calorie intake is even and regular every day. 
This is when the growth of your baby will kick into high gear. Some doctors recommend an average weight gain of one pound per week throughout the second trimester. This goal may be slightly higher for women who didn’t gain weight during the first trimester, as a result of morning sickness. Basically, by the end of your second trimester, your weight gain should be between 12 and 16 pounds. 
In terms of weight gain during the third trimester, the one pound per week rule remains in place, but the mother’s weight often reduces during this period. Carrying around more weight makes every movement somewhere akin to a cardiovascular exercise, so burning calories will be at a premium during those final three months. The total weight gain in the third trimester rarely tops 10 pounds, as the body is preparing itself for delivery. 
Again, all of these numbers are closely dependent on your BMI and what your doctor’s recommendations are for your specific diet plan, based on your individual risk factors, medical history and the progression of your pregnancy. Regular monthly checkups are also an excellent way to make sure you are staying on track with healthy weight gain.
When to Gain Weight During Pregnancy?
Most women will notice weight gain beginning almost immediately in the pregnancy, as the fetus begins to grow and your hormones begin to shift. In fact, unexplained weight gain can often be the first sign that a woman is pregnant, particularly if her morning sickness is mild, or if she maintains a strict diet and weight. 
Once you realize you are pregnant, it is important that you consider your nutritional intake every single day. Many women think that eating for two means doubling your caloric intake, but that isn’t the case. The developing fetus, even when it is ready to be born, is very small and doesn’t require the same amount of calories and nutrients as a grown adult. Doubling your caloric intake would result in excessive weight gain during pregnancy, which can also be dangerous. 
Risks of Weight Gain During Pregnancy
While the fluctuation of weight during pregnancy may seem out of your control, there are specific dangers to gaining too much or too little weight while you are pregnant.
If you gain too much weight, it severely increases your risk of gestational hypertension and gestational diabetes, according to the NHS UK. Excess weight gain will also result in more stretch marks and a higher risk of developing diabetes after the pregnancy is over. Furthermore, with your body carrying an excess of weight during those nine months, it puts, even more, strain on the bones, joints, muscles, and metabolism if it is supporting more weight than it needs.  
If you gain too little weight during pregnancy, the outcomes are much more dangerous for your unborn baby. With a deficiency of nutrients, your child has a higher risk of birth defects, and if it is not developing normally, your risk for a pre-term birth or low birth weight is much greater. 
Clearly, the wisest choice is to follow the dietary guidelines of your doctor and maintain a moderate, but steady increase of weight throughout your pregnancy.
Is It Safe to Lose Weight When Pregnant?
Although it sounds counterintuitive, some women do lose weight during pregnancy, primarily if they were overweight at the beginning of the pregnancy, or are still recovering in terms of weight from a previous pregnancy.
A pregnancy diet is quite strict, and eating healthy sources of calories is an excellent way to change your lifestyle and set your baby up for a healthy start. For example, if you were 20 pounds overweight when you got pregnant, and then adopted a healthier diet with regular, mild physical activity, the result will be weight loss, even if you are supporting the development of your baby. 
The motivating push of having a child makes many women take up much healthier lifestyles during pregnancy that can carry over into their post-delivery life. While extreme weight loss during pregnancy is rare, a small reduction in weight, or maintaining a stable weight, is not unheard of. Keep your doctor apprised of all new diets or lifestyle activities you choose during your pregnancy, as each doctor’s recommendations for healthy weight during pregnancy will vary for different women.