I am 35 weeks and I count calories.
This is a bit of a long read but it can help you. Basically, you figure out the normal amount of calories your body needs to "maintain". In your 3rd trimester, you should be eating 500 calories in addition to that.
For me, at 5'5 and original weight of 123lbs (now 153lbs at 35 weeks), I eat about 2,500 calories per day. I've been gaining the proper amount of 1lb per week.
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First Step: Calculating Your Basal Metabolic Rate
Your basal metabolic rate (BMR) simply means the amount of energy used by your body during a 24-hour period if no activity is performed. In other words, if you're inactive for 24-hours straight, you'd still "burn" the amount of calories equivalent to your BMR.
Your BMR is a function of your size, sex, and age. It's also influenced by your metabolic status (hypo or hyperthyroid state for example). We can calculate BMR with the following formulas (by Harris-Benedict):
For Women
BMR = 655 + (9.6 x weight in kg) + (1.7 x height in cm) - (4.7 x age)
So for a 28 year old figure girl of 132lbs (60kg) at 5'6" (165cm) it comes up to:
BMR = 655 + (9.6 x 60kg) + (1.7 x 165cm) (4.7 x 2
BMR = 1380 calories per day
Second Step: Factoring in activity level
The amount of calories found using the Harris-Benedict formula is what your body burns every day, even if you do nothing all day. Obviously, the more active you are the more you'll burn fuel. So, energy expenditure will be increased when your activity level goes up.
To get an adequate estimation you need to multiply your BMR by an activity level factor:
1.0 Sedentary
1.2 Very light activity
1.4 Light activity
1.6 Moderate activity
1.8 High activity
2.0 Extreme activity
By sedentary we mean doing nothing all day (sleeping and watching TV).
By very light activity we mean doing nothing physical. Working a desk job or on a computer and not performing any type of physical activity during your day.
By light activity we mean having a non-physical job (desk, computer, etc.) but performing some sort of physical activity during the day (e.g. above average walking) but no hard training.
By moderate activity we mean having a non-physical job, performing some sort of physical activity during the day, and including a daily workout session in your routine. This is where most of you are at.
By high activity we mean either training plus a physical job or non-physical job and twice-a-day training sessions.
By extreme activity we mean a very physical job and daily hard training.
So if our 220 pound bodybuilder with a BMR of 2122 calories/day is moderately active, his daily energy expenditure is bumped up to 2122 x 1.6 = 3395 calories per day. This is the amount of food to consume to maintain present body weight.
Third Step: Adjusting caloric intake to your goal
*** +500 calories for 3rd trimester