Effect of pregnancy on musculoskeletal health and gestational weight gain

Pregnancy: Pregnancy is accompanied by profound physiological changes.

• Menstrual cycle ceases for the duration of the pregnancy, which is approximately 40 weeks or 9 months. During that time estrogen and progesterone, which are rise continually.
• Gestation is traditionally divided into three phases or trimesters, each lasting about 3 months. During this time maternal health and behaviors can affect both fetal and maternal outcomes.

First trimester: Dedicated to the development of embryo. By 8 weeks embryonic development is complete and major organs and body systems are differentiated. The embryo is now a fetus. Facial features are evident and external genetalia can be observed. Most importantly,

By 8 weeks:

• Placenta is mature,
• the umbilical cord is functioning,
• the circulatory system is well established
• Placenta become the dominant source of estrogen and progesterone to sustain the pregnancy.

By 12 weeks:( @ the end of first trimester)

• the cardiovascular system is functioning,
• the liver is producing red blood cells
• Gastrointestinal & Musculoskeletal systems are developing
• @ 12 weeks the fetus weighs an average of 45g (1.6oz) and is approximately 8cm (3.15in) long.
• Maternal weight gain should be minimal during the first trimester.

"In response to increased fetal circulation, maternal blood volume and cardiac output(CO) begin to increase".

Second & Third trimester: Emphasis is on final development of major systems and relatively rapid growth of the fetus.

By the end of second trimester:

• At approximately 24 weeks
• Fetal movement are evident
• Heart rate can be ausculated
• Gastrointestinal system is intact with peristalis
• Oxygen and all nutrients are obtained through placenta,
• Insulin resistance increases continuously which allows glucose and amino acids to preferentially be used to support fetal growth.,
• The fetus now weighs approximately 780 g (27.51 oz or 1.72lb) and is 23 cm (9.06In) long

Reason for Dyspnea during pregnancy:

"Growth of the fetus and increased size of the uterus displace the diaphragm upward as much as  4 cm which limits diaphragmatic movement and reducing the functional residual capacity by approximately 5%, while at the same time oxygen consumption increases by as much as 15%".

Third trimester: 

• Gain in fat and lean mass
• Fetal adipose tissue increase subcutaneously  and at birth, Normal weight should average between 3000-3600 g, length should average 42-48 cm
• Due to increase in size maternal stress and by 40 weeks RMR has increased approximately 15%
• Oxygen consumption has increased by 30%
• Blood volume has increased by 50%
• Increased blood volume, increases maternal systolic and diastolic blood pressure. Respiratory rate and tidal volume are increased, and dyspnea on exertion becomes more common.

Effect of pregnancy on musculoskeletal health :  Pregnancy is accompanied by musculoskeletal problems that impact maternal health.

• Abdominal muscle stretch:The abdominal muscles are stretched severely and there is a shift in the center of gravity that further decreases the abdominal muscles provide.
• Increased force: An increase in maternal body weight can increase the force on knee and hip joints by as much as 100%.
• Weight gain: Weight gain is increased by fluid retention. During a normal pregnancy, women retain an additional 6500 ml of fluid
• Bone resorption decreased: By the third trimester bone resorption has also doubled, whereas the rate of bone formation has changed or decreased.
• Loss in Bone Mineral Density: For each pregnancy, overall losses in maternal BMD range from 1-2% in femoral neck to more than 3% at the spine.