Summary:

1. Yoga practices can provide benefits in many symptoms associated with pregnancy. Main target symptoms can be nausea, vomiting, back pain, food aversions or cravings, constipation. Besides, yoga can also reduce generalized physical discomfort and stress.
2. Yoga practices can also help in reducing risk of miscarriage and increase chances of normal delivery.
3. The type of yoga practices change significantly during different trimesters of pregnancy due to physiological changes. 

Yoga during pregnancy can provide many benefits for both the mother and the developing fetus. It can help alleviate physical discomfort, reduce stress, improve sleep, and increase strength, flexibility, and balance. Considering the continuous physiological changes in the body, it would be important to choose a qualified prenatal yoga teacher who is knowledgeable about modifications and precautions to ensure a safe and effective practice.

Yoga for pregnancy is generally discussed based on the three trimesters of pregnancy. But many of the yoga practices will actually be more helpful if started before pregnancy itself. For example, for practices like vamana dhauti, desired benefit is obtained if the practice is learnt well in advance. Similarly practices to strengthen back muscles can be started from the beginning of pregnancy and will provide maximum benefit during the last trimester. Besides there are practices which help increase chances of normal delivery and are to be started much before delivery time. One important aspect while taking yoga practices during pregnancy is that there is a need to modify the majority of classical postures to make them safe and beneficial. 

The First Trimester (Week 1-12) – Major symptoms during the first trimester are: Nausea, vomiting, fatigue, breast tenderness, mood swings, spotting or light bleeding, constipation, food aversions or cravings, bloating, frequent urination, headaches, dizziness, back pain, increased hunger, shortness of breath, spotty skin, morning sickness, increase in basal body temperature, darkening of the areolas, increased discharge. Some of these symptoms can be reduced with the help of appropriate yoga practices. The following are some recommendations from our side for the first trimester of pregnancy:

1. Vamana dhauti: Vamana dhauti (a  yogic cleansing practice) can target the symptoms of nausea and vomiting. It helps in developing better control over the risky & uncontrolled force of persistent retching and vomiting. 
2. Pawan-muktasana: This set of practices will particularly be helpful to control the symptoms of bloating, constipation and increased frequency of urination. It also helps to stretch hips and lower back. 
3. Cat-Cow Stretch: This stretch helps to relieve tension in the lower back and promote flexibility in the spine. 
4. Mountain Pose: This pose strengthens the legs and improves posture, which can help to alleviate back pain. This can particularly be useful if practiced before pregnancy and may not be recommended during pregnancy. 
5. Seated Forward Bend: This pose helps to stretch the hamstrings and lower back, and is a great way to calm the mind and relieve stress.
6. Warrior Poses: These poses strengthen the legs and improve balance, and are a great way to build strength in preparation for childbirth.
7. Pranayama: Anuloma-viloma, brahmari and complete yogic breathing are our recommendations during pregnancy.  

The Second Trimester (Week 13-27) – The second trimester of pregnancy is a relatively symptom free period of the pregnancy and hence yoga practices proposed here are preparation for the third trimester and delivery. There is relief from morning sickness and energy levels are increased during the second trimester. Some minor symptoms observed during this trimester are bloating, constipation, heartburn, gas and indigestion, changes in appetite, shortness of breath, Braxton Hicks contractions, swelling of legs, feet, and ankles, mood swings and emotional changes, increase in vaginal discharge, changes in sexual desire, back pain, increased weight gain, stretching and tingling sensations in the uterus. Forward bends are gradually becoming difficult here. Separating the legs apart is one way to get into forward bends.

Here are some recommended yoga poses for the second trimester:

1. Sarala-bhujangasana, Cat-Cow pose, setubandhasana: These poses help to relieve lower back pain and improve flexibility.
2. Triangle Pose: This pose stretches the hips, hamstrings and spine, which can help to relieve back pain.
3. Butterfly practice, seated forward bends: This pose stretches the legs, hips and spine and can help to relieve lower back pain.
4. Pranayama: Pranayama practices remain the same as proposed for the first trimester.   
5. Chants & Meditation: Chants and meditation can have a potential role for calming down the mind which will have tremendous benefits for the fetus. In our opinion, this is the most beneficial component of yoga from a fetus perspective. These can be practiced throughout the pregnancy, though religious sensitivities are to be taken care of while implementing these practices.    

The Third Trimester (Week 28-40) – The third trimester of pregnancy is associated with many symptoms due to increasing size of the fetus. These include back pain, leg cramps, Braxton Hicks contractions, shortness of breath, increased fatigue, swelling of hands, feet and face, urinary frequency, heartburn and indigestion, difficulty sleeping, nasal congestion and headaches, increased vaginal discharge, itching and skin changes, hemorrhoids, constipation.

Yoga practices during this phase will target the symptoms and will also be a preparation for the delivery. Majority of practices from the first and second trimester are useful (except vamana dhauti) in the third trimester also, though intensity of practices may have to be reduced significantly. Forward bends are to be either avoided or done with legs apart. The following are some recommended yoga practices for the third trimester:

1. Asana: Cat-Cow Stretch, wide-legged forward bend, reclined butterfly, supported bridge pose. 
2. Pranayama: Pranayama practices remain virtually the same. Though changed lungs capacity may throw challenges during pranayama practices.
3. Support your body: The third trimester of the pregnancy is the time when you will need the props the most. Use props such as blocks, blankets, and straps to support your body and make poses more comfortable.
4. Keep your breathing steady: Focus on slow, deep breathing to help regulate your breathing and calm your mind. 
5. Chants & Meditation: These are particularly useful in the final trimester to overcome fear and keep mind calm. 

Precautions to be taken for yoga practices during pregnancy: 

There are many yoga practices which are either absolute contraindication or partial contraindication during pregnancy. Hence due care to be taken before taking initiative for yoga practice. The following yoga practices should be avoided during pregnancy:

1. Advanced and intense practices: Virtually all advanced yoga postures are absolutely contraindicated during pregnancy. For example: shirshasana, sarvangasana. Similarly intensity of a yoga session for pregnancy is to be kept mild to moderate.  
2. Twisting poses: Poses that involve twisting the torso, such as the Revolved Triangle Pose (Parivrtta Trikonasana), can compress the uterus and affect the growing fetus.
3. Deep backbends: Deep backbends, such as the Camel Pose (Ustrasana), can place too much pressure on the lower back, which can be especially uncomfortable during pregnancy. 
4. Deep forward bends: Deep forward bends, such as the Seated Forward Bend (Paschimottanasana), can cause discomfort or compression in the lower back and abdomen.
5. Supine and prone postures: During the last trimester of pregnancy, lying supine as well as prone is difficult for pregnant women and postures in these positions may not be feasible and many times these are unsafe too. 
6. Yoga forms: Some forms of yoga are not safe during pregnancy. Two major examples of such categories are power yoga and hot yoga. 
7. Support your body: Use props such as blocks, blankets, and straps to support your body and make poses more comfortable.
8. Keep your breathing steady: Focus on slow, deep breathing to help regulate your breathing and calm your mind.
9. Wear supportive clothing: Wear comfortable, stretchy clothing that provides support for your growing belly.
10. Stay hydrated: Drink plenty of water to keep your body hydrated and prevent overheating.
11. Take breaks: Take frequent breaks to rest, stretch, and walk around to prevent fatigue and swelling.

It is always important to listen to your body and adjust your practice according to your changing needs during pregnancy. It is also recommended to consult with a doctor or qualified prenatal yoga teacher to ensure the safety of you and your baby.