How Your Body Changes in Pregnancy: The Musculoskeletal System

In previous installments of this series, we have looked at how pregnancy changes the physiology of the respiratory system ,the circulatory system, the digestive system, the urinary system, blood clotting, the endocrine system, and acid-base balance. Today, we’ll discuss the musculoskeletal system in pregnancy. As pregnancy advances, the pelvis and spine are altered noticeably to adapt to the increasing size of the womb. This happens as you gain weight and the volume of your blood increases. All of this, plus the growth of the breasts, is connected with a change in your center of gravity that pushes you to lean backward as you stand and walk. Related to this, many pregnant women experience an increased of the lumbar lordosis (the forward-pointing curvature of the lower spine), kyphosis (rounding of the upper back), and cervical lordosis (curve of the neck). This goes with a flattening of the usual curve between the lumbar and thoracic parts of the spine. Related to all of this the shoulders are pushed in a posterior (backward) direction, while the pelvis tilts more anteriorly (toward the front). Even for several weeks after you deliver, this new shape of your body may persists.

Pregnancy causes changes in concentrations of the hormones estrogen, progesterone, and relaxin. This, in turn, causes changes in the metabolism of the protein collagen that is vital to the structure of bone and other connective tissue. The connective tissue becomes more flexible and stretches out more. This allows for the pubic symphysis (the ligamentous connection between the left and right sides of the pelvic bone and the sacroiliac joints (connection between the lower spine and pelvis to loosen up to facilitate passage of the baby through the birth canal. Loosening of ligaments, however, also makes you more vulnerable joint dislocations and other injuries. This loose state begins around 10 weeks into pregnancy and continues generally for about four to twelve weeks after delivery, but it can persist up to about six months after you give birth.

Meanwhile, as you approach delivery the power of certain muscles increases to help you push the baby out. These muscle include the hip abductors (muscles that pull each leg sideways, as when you straddle your legs), hip extensor muscles. Other muscles, such as those controlling the ankle also get stronger to support your changed walking style and increasing weight. As the uterus moves upward, your ribs get pushed sideways and your chest diameter may increase. Also, because of the growing womb, your anterior abdominal muscles stretch longer elongation, while the linea alba (the connective tissue between the two front rows of abdominals, is stretched wider.

Overall, your joints lose stability during pregnancy and the nervous system adjusts in an attempt to compensate by changing the style of how you move. As the changes evolve over the course of pregnancy, different muscle groups are recruited for motions differently from how they were recruited prior to the pregnancy.

Pregnancy elevates your risk for bone fractures. This is due to hormonal changes causing calcium to move from the mother, through the placenta, to the growing fetus, which can decrease the density of bine mineral content (pregnancy-induced osteoporosis). It’s also due to an increase in the tendency for you to fall, especially near the end of pregnancy, because of the changing body shape and balance.

Based on the fracture type, as well as the location, the healing time, severity, and possible complications of fractures varies considerably. A simple crack that does not go all the way through the bone is called a greenstick fracture. Such a fracture is much more common in bones of young people, especially children, compared with older people. A linear fracture is a fracture that running lengthwise along a bone, while a transverse fracture runs directly across the width of the bone. A fracture also can be oblique, meaning that it runs at an angle across the width of the bone. All of these types of fractures are called non-displaced fractures, meaning that there is no shifting between bone areas on each side of the crack.

Non-displaced fractures that are not in a joint are usually simpler to treat and tend to heal more quickly than fractures within a joint, meaning the region where across the ends of two bones come together. The joint includes ligaments and tendons and often an enclosed cavity containing fluid called synovial fluid. Usually, it is more difficult and takes longer to repair fractures with complex shapes, such as spiral shaped fractures. It is also more difficult to treat fractures in which parts of the bone are separated, when there is a comminuted fracture (the bone is splintered into many pieces). Additionally, any fracture within a joint takes longer and typically requires more intervention to heal.

Another way to classify fractures is based on whether or not they are compound, or open, meaning that fractured bone penetrates out through the skin. Fractures are also described as being reducible, or not. A reducible fracture is a fracture whose displaced bone parts can be returned to their correct place and stay in place, without surgery and hardware (such as plates and screws) to hold the parts in place.

Your doctor can diagnose a fracture with a simple X ray scan. Many people in western society fear ionizing radiation and its effects during pregnancy, but simple X ray scans expose you only to very tiny X ray doses. There is no danger whatsoever to you or your baby, even during the early period of pregnancy, and even when you have a fracture in the lower spin or hip, requiring X ray scanning directly through the womb pass through the womb. On the other hand, there is a real danger if fear of radiation –known as radiophobia—leads you to avoid having a fracture diagnosed. If you have a complicated fracture, requiring computed tomography (CT) scanning of the injured site, the X ray dosage is much higher compared with a simple X ray scan, which may possibly put an embryo, or fetus, at risk. In such cases, however, the risks connected with a complicated fracture will outweigh the risk from the radiation of CT.

The main treatment for a bone fracture is to reduce (to set) the fracture. This means moving the separated bone parts into correct alignment, if the fracture is displaced. If this cannot be done by manipulation from the outside, then surgery will be needed. In order to heal, one or more joints near a fracture that has been set must be immobilized with a splint or cast. More complicated fractures require surgery. Certain soft tissue injuries, without bone fractures, also may need surgical treatment. Such injuries may include certain dislocations, if they cannot be corrected through manipulation, certain really bad sprains (ligament injuries without dislocation), ligament tears, and cartilage injuries. Often surgical treatment can wait, but not in all cases.

You also will receive medication to combat pain and inflammation from musculoskeletal injuries. If you require surgery and/or if you have a compound fracture, you also will receive antibiotic medication to prevent or treat infection. Certain medications work against pain, but not inflammation; these are acetaminophen in the United States and paracetamol in several other countries. In contrast, non-steroidal anti-inflammatory drugs (NSAIDs) are effective against pain and inflammation. NSAIDs include ibuprofen and naproxen. NSAIDs, and related drugs called salicylates, are of concern during pregnancy, as they may be harmful to the embryo or fetus during early and late pregnancy. Stronger pain medications may be needed during and after surgery and during an external reduction (the orthopedic surgeon sets the fracture by manipulating the bone from the outside without surgery). The stronger pain relievers are in a group of drugs called opioids (narcotics). There is a concern that long-term use of these of opioids can cause birth defects, but research has failed to demonstrate a danger when the drugs are used just for a few days. During breastfeeding, there are various antibiotics are available that are considered safe for a nursing infant. On the other hand, opioids could be harmful during breastfeeding, so if you require these drugs you should use infant formula instead. Acetaminophen, paracetamol, and NSAIDs are considered to be breastfeeding safe.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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