WHAT IS POSTURE?
Posture is the position in which you hold your body while standing, sitting, or lying down.
POSTURE DURING PREGNANCY
Due to the growing belly, heavier breasts and hormonal changes, the female body adjusts to the changes during the pregnancy also with a posture. The centre of gravity of pregnant women is displaced anteriorly and superiorly (forward and upward). Each pregnant woman adjusts differently to the change in her centre of gravity (for example, by leaning back, extending hips, or increasing the activity of the triceps surae, etc.).
Most people imagine pregnant women as having a large inward curve in their lower back, but while some research studies do show an increase in the lower back, others actually show the opposite.(1)(2)
POSTURE CAN HAVE AN IMPACT ON SEVERAL THINGS
Posture has a significant effect on breathing and optimal daily functional movement, such as squatting and bending. This is especially important in pregnant and postpartum women. Where the »wrong pattern« may lead to chronic pain in the neck, lumbar spine, shoulder pain,...
Posture also has a significant impact on the muscular system. This means that in some cases a woman may, due to an inappropriate posture, activate certain muscles more than the others.
Posture can also affect pelvic floor dysfunction. Studies have shown that upright sitting results in a better resting activity of the pelvic floor muscles compared to slouched sitting and that sitting unsupported (without backrest) requires more pelvic floor activity than sitting supported. (3)
Moreover, one large study observed pelvic floor activation during load when posture was changed. This load included maximum-effort coughing, Valsalva manoeuvre (holding breath) and maximum voluntary contraction. Under this load, women were shown to have better pelvic floor muscle activation when adopting their habitual posture« in comparison to eighter a hypo or hyperlordotic posture. (4) (A pelvic floor physiotherapist can perform an assessment and determine if a more neutral pelvic floor position improves your pelvic floor activation.)
However, there's no such thing as perfect posture. Have you tried to sit in »perfect posture« for more than 3 minutes or walk with a completely erect spine, ears above the shoulders? It's hard, isn't it?
OUR BODIES LOVE VARIABILITY
It's important to have the capability to use a good form in basic movement patterns. For example, You struggle to use a good form when you slouch. Your thoracic spine should have the capability of flexing and extending, along with the capability of going through the rotation at each segment. If eighter of these capacities don't work properly, your lumbar spine takes on much more workload than it should and »AUCH«, that's not good...
Slouching is normal. It's not about having our postural muscles »engaged« 24/7. It's about having those muscles strong, responsive and engaged when we need them to be!
Proper posture during pregnancy involves training your body to stand, walk, sit, and lie in positions where the least strain is placed on your back. The same can be applied in the postpartum period when lifting a baby.
 Swift, S. E. (2000, August). The distribution of pelvic organ support in a population of female subjects seen for routine gynecologic health care. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/10942459
 Nygaard, I., Barber, M. D., Burgio, K. L., Kenton, K., Meikle, S., Schaffer, J., . . . Pelvic Floor Disorders Network. (2008, September 17). Prevalence of symptomatic pelvic floor disorders in US women. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/18799443
 Sapsford, R. R., Richardson, C. A., & Stanton, W. R. (2006). Sitting posture affects pelvic floor muscle activity in parous women: An observational study. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/16942457
 Capson, A. C., Nashed, J., & Mclean, L. (2011, February). The role of lumbopelvic posture in pelvic floor muscle activation in continent women. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/20833070