How you sit and use your body can affect the position of your baby in the uterus. While this does not matter so much during early pregnancy, later on, it can affect the position that the baby moves into the pelvis, prior to labor starting.
When you regularly sit in a slouching type of position and your pelvis rocks backward, this can encourage your baby to enter the pelvis in a "posterior" position as their back, the heaviest part of them is more likely to be positioned against your back. This can make having your baby harder and labor longer, as your baby will need to turn during labor to move down the birth canal (vaginal passage) the right way.
Midwives report there are more posterior babies born nowadays as compared to 20 or more years ago.
In the past, women used to spend a lot more time being upright and moving around than we tend to do now that we have many modern conveniences and cars to travel around in. They used to scrub floors and spend more time on their hands and knees than we need to now and this allowed more room for the baby to move around in and encouraged the baby to move into the right position in the pelvis. Their jobs were more labor-intensive than a lot of ours are now since the increased use of computers and modern appliances. It is when we spend a lot of time sitting during our day that the baby is encouraged to be in the posterior type of position. Crossing our legs can also cause our pelvis to tilt backward more and so discourage the baby from moving into the right position. Sitting in the car for long periods of time can also encourage a backward tilt position of your pelvis unless you consciously sit upright and with your pelvis slightly tilted forwards.
Midwives suggest using the hands and knees position during your pregnancy, especially in the later stages from 25 weeks onwards, but particularly the last 6 weeks, to encourage your baby to be in the right position for labor. When you are sitting, you should sit "on your sit bones", the two bony points under the cheeks of your bottom, rather than letting your pelvis rock backward so that you sit on your tailbone. This will help your pelvis to be in a forwards leaning position, which encourages your baby to move into the right position.
When you can, sit forwards slightly with your elbows on your knees or sit astride a chair. Sitting on the floor in either a cross-legged position or with your legs out will also assist your pelvis to be in the right position and will give you the chance to stretch your leg muscles so that you also become more flexible for labor.
Using these positions regularly during your pregnancy will help to give you the best chance of "optimally positioning your baby", prior to labor. If you are reading books and magazines, use this time to be on the floor for a while, either on your hands and knees for as long as comfortable, or sitting on the floor. Lying on your side is a better option when on the lounge, than sitting slumped and really relaxed back into the lounge chair. Also sitting on a low stool where you are in more of a supported squat type of position is also another way of getting your pelvis and back into the right position. If you place your feet flat on the floor this will also give you the opportunity for a calf stretch too and will help prepare you for having the supported squatting position as an option for during labor.
To prepare for having the modified squatting position as an option to use during labor, it is recommended that you practice this during the last 6 weeks of pregnancy. Sitting on a stool approximately 25 cm high with a cushion on it, with your back against the wall and your legs comfortably apart can be used to practice this position without going down into a very deep squat.
Sitting on a fitness ball is also a better option than sitting on a chair for long periods, providing you choose one at the right height for you so that your hips and knees are around 90 degrees when you are sitting upright. You can then lean forwards slightly while you are sitting on it, and move it around under you too, to allow you to change position slightly as needed, especially if you need to sit for any length of time. It again gives you the chance to stretch your calf muscles when you place your feet flat against the floor, and your inner thigh muscles if you have your legs comfortably apart. It is much harder to slouch when sitting on a ball. Balls are also available in many labor wards, and when you are used to using a ball it is easier to use it in different positions during labor. Resting over a ball while on your hands and knees is also another way of being in this position while being supported at the same time. This can even be a good position for practicing relaxation during your pregnancy.
When your labor starts you can continue to use these forwards leaning positions. If you are at home you could try leaning over a bench, kneeling on the floor and resting on the lounge, or being on your hands and knees. These positions will continue to encourage your baby to be or move into the right position during labor. Your partner can easily rub your back in these positions, which is another benefit of using them.
To find out more about "optimally positioning your baby for labor", and to help you understand this more fully, speak to your Midwife. Midwives are also able to advise you on how to try and encourage your baby to move from a posterior or breech position during the later stages of your pregnancy.