Hi Sarah,
I am a Women's health/Musculoskeletal physio who has started training through Birthlight. Over the years I have seen a number of women who have developed lateral hip pain around this stage. It often coincides with the significant change in lordosis as the belly really starts to show over 20 weeks and any pre-existing structural problems are exacerbated. She may not have had hip pain in the past but assymetry in the body can start to show as the centre of gravity is moved forwards and the weight of the growing baby changes the dynamics within and outside of the pelvis. A number of muscles attach to the lateral bone of the hip - the greater trochanter- including the gluteus medius, and a fluid filled sack called a bursa sit between the muscles to provide further cushioning. The gluteus medius has a prime role in stabilising the pelvis and is being challenged as the changing centre of gravity pulls the body forwards. Both the gluteus tendon and bursa can become inflammed and do not like to be compressed, particularly at night. This side lying position also places a lot of pressure through the sacroiliac joints so will also show up any issues there.
It is important that she is fully assessed by a Women's Health/pregnany Physio or Osteo specialising in musculoskeletal problems as an individualised approach is important and the earlier it is addressed, the better as women can often become quite fearful of pain worsening with the pregnancy and often these pains are dismissed as 'normal' part of being pregnant (which I don't agree with). If treated and managed well, this problem can easily go away. It is really important that she becomes aware of her posture in all positions. It is highly likely that she weight bears more on one side than the other (and contrary to logic, it is often the painful side that is taking more weight - hence getting sore) - whether it be in standing or sitting. It is also important that her shoulders are aligned over the pelvis as shifts in the upper back can lead to assymetry in the pelvis and hips. She can also have tight gluts and piriformis - again this needs to be assessed but often these stretches can be incorporated through yoga poses. I find that a combination of gentle hands on release work, postural advice, functional training of movements (ie sit- stand, standing, walking, lie to sit, stairs etc), awareness of breathwork and acupuncture works really well to clear the pain and get women back on track and appropriate yoga reinforces the alignment, patterns, breathwork and movement. It is also important that she learns to listen to her body.
What she is doing by day will affect the pressure by night. Is she wearing high heels or appropriate comfortable footwear? Is she carrying a toddler or heavy work back on one shoulder? Is she sitting with a twist at a desk etc. etc. Whilst you may not have time to go through all this in a yoga session if you have the chance it can be really helpful - people can often problem solve really well if you point them in the right direction. Awareness builds awareness and they become empowered that they can be in control of their symptoms and come out of the episode more aware of their bodies and strengthened. At night, it is important that her left hip and left waist is given some support. Often rolling a normal sized bath towel into thirds and placing it lengthways across the bed so that her her waist rests on it helps to square the body and takes the pressure of the lateral hip. Hugging a pillow also gives the upper body support, and having a pillow between the knees can help spread the weight so it isn't all on the lateral side of the hip (over the greater trochanter). Sometimes placing the pillow behind the back can also help so that she is 1/4 off supine (her back) and not directly over the hip if she will only sleep on her left side at this point in time.
I know this is sometime after the initial post but if she is still having issues, I hope this helps!
Good luck, Wendy