Unlike the equation used to calculate your BMI (body mass index), the process of putting on kilograms is not an exact science (if only it were that easy - punch in the numbers, gain just the right number of kg, at just the right rate!). Your rate of weight gain will depend on a variety of factors, such as your metabolism, your activity level, and genetics.

More on metabolism

If you have a fast metabolism (count your blessings!) or you're very physically active (good for you!), you may gain weight more slowly (and will consequently need to eat more calories) than someone who puts on weight by just looking at a pint of ice-cream, or who leads a very sedentary lifestyle.

That said, there are some general guidelines, and these, too, depend on your BMI.

Here, some approximations:

- If your BMI is less than 18.5, plan to gain 2kg in the first trimester and 13-18kg total during your pregnancy (roughly a pound a week).

- If your BMI is between 18.5 and 25 (average weight), aim to put on about 1.5kg during the first trimester and plan to gain around 11-16kg total.

- If you're overweight (your BMI is between 26 and 29), gain 1kg during the first three months and between 7kg and 11kg total before your baby is born (less than a pound a week).

- If your BMI is 30 or more, you should gain around 5-9kg total and talk to your doctor about managing your weight gain.

Remember, not all weeks yield the same poundage, and you'll want to make sure you're gaining at the right time, and neither gaining too much weight during pregnancy nor too little weight during pregnancy.

* This article is just a guide. You should still consult your doctor to ensure your weight gain is healthy for your pregnancy.