Pregnancy is one of the most important times in life to really be focusing on your nutritional needs. There’s that old saying that pregnant woman should be “eating for two”. This couldn't be further from the truth, especially during the first two trimesters. 
During the first trimester when morning sickness usually takes place you might find that you struggle to keep anything down or have severe food aversions. Making sure you are taking your prenatal supplement during this time is very important as this when a lot of very important fetal developments are taking place, and you might not be able to be getting enough nutrients from your diet if you are suffering from morning sickness. 
During the first trimester there is no need to increase calorie intake, just focus on eating a healthy well balanced diet. 
During the second trimester the morning sickness has subsided and you may feel like you can keep food down again, this in itself will give you more energy. The food aversions might still be there though. There is still no need to increase your calorie intake during this time, but make sure you are eating a wide variety of fruit and veg and getting in good quality protein sources along with your prenatal vitamin. 
The third trimester is when you need to increase you calorie intake - but it’s still nowhere near “eating for two”. You only need to increase your intake by 200-300 calories which is equivalent to a couple slices of toast with butter. Although I would suggest to increase these calories with more nutritionally dense foods if possible. During the third trimester with your baby taking up more space you might find it hard to eat 3 main meals a day so I would suggest trying to eat 5-6 smaller meals spreading your calories out through the day. 
The ‘4th trimester’ as it’s often referred to is the first 12weeks after having a baby. Whilst it’s often not talked about or given the same attention as the first 3 trimesters, there are many changes still going on in the mothers body as it recovers from growing a baby for 9months. During this time the mother will most likely be breastfeeding, so will be needing about an extra 500calories a day along with an increased water intake to help keep up milk supply. I would recommend taking a post natal supplement during this time to support nutrient intake for the mother and the baby through the breastmilk. Now that the baby is born you can enjoy your unpasteurised dairy and sushi, but coffee and alcohol intake should still be very limited as they can pass through breast milk.