The fact that you're here means you have been through or are currently in a similar situation. During pregnancy, your partner will change, as I'm sure most of you have already noticed by now. Coming home from work and opening that main door has become a game of potluck, you do not know what's on the other side of it. And I'm sure you have heard this from a lot of people but here it is- it's not her fault, it's the hormones! 
Hormones are chemicals our glands secrete into our body that get to control things, all kinds of things. When a woman becomes pregnant, these hormones go into hyper drive to create the perfect environment for the baby. And while they are at it, they also cause the following changes-
  1. Nausea and vomiting
    This is the earliest symptom of pregnancy. Hormonal changes of pregnancy are again responsible for it. It usually subsides by the 4th month. At times it may be prolonged due to which women will require to take medicines for many months.
    Word to the Husband 
    Remember the last time you had to take an antacid as you were having nausea and vomiting as a result of eating outside? Now imagine your wife having the same feeling for a period of 2-3 months.

  2. Pain
    'No pain, no gain.'  This age old saying is absolutely true for pregnancy. Whether delivery is normal or Cesarean some amount of pain will be experienced even with our newest medicines. She needs to undergo repeated blood tests, gynecological check ups, and has to get numerous vaccinations.
    Word to the Husband
    How many of us keep postponing health check ups, dental treatment for fear of pain?

  3. Change in Eating and Sleeping Habits
    When a woman gets married, she may enter a new realm of eating and cultural habits. What is eaten, the way it is cooked, eating time table, all may be entirely different from what she is used to since her birth. Add to that the increasing demands of pregnancy. She may experience craving for odd food items at times. Her sleeping habits may also change. Increasing abdominal girth makes it difficult for her to adopt a comfortable posture. Baby movements may keep her awake or wake her up frequently during sleep.
    All these things will overwhelm her.
    Word to the Husband 
    You can start by acknowledging the fact that she still keeps smiling despite all these changes. Get her one meal per day of her choice. The way she has always liked and share it with her. Make sure you do whatever you can to get her comfortable when she wants to sleep.

  4. Weight gain
    As pregnancy advances she is bound to gain weight. Growing fetus, placenta, uterus and many other factors are responsible for this. During each doctor visit, first thing that will be asked of her 'Have you gained weight?' Healthy weight gain is necessary for a healthy pregnancy. Then again it comes with its own discomforts. Feeling of bloating, backache, swelling in legs, all are part of the package. Even after delivery, returning to pre-pregnancy weight may not be easily achievable for many women.
    Word to the Husband 
    Empathy, sympathy and understanding will work for you. Accept the changes in her and help her do the same.

  5. Pregnancy Marks
    Pregnancy is going to leave its tell tale signs behind. Things like loss of hair will recover, pigmentation on face will also disappear with time and treatment. But stretch marks is the main concern. With our newer skin treatments it is possible that they appear less and can be made to go away to a certain extent. But even for a short period, her appearance and way of dressing may change.
    Word to the Husband
    Inner beauty and qualities of a person matter most in journey with your life partner. Tell her that she is the most beautiful woman that has walked in to your life at every opportunity that you get.

Put all this together & you’ve got someone who needs your help & support, however difficult it might be for you at times. So you’ll have to bite your lip, do a lot of agreeing & apologising, and keep telling yourself that she’s literally out of control. This is a hard time for her too. 
Things will get less confusing once you slowly learn to
 gauge her mood. 
Remember to always ask her what she needs.

Talk to her. Be with her. Support and love her.