Chest Changes During Pregnancy
The chest begins to expand during the first trimester of pregnancy, with significant changes occurring by the 20th week of gestation when mammary glands are sufficiently developed to produce components of milk. 1
Timeline of Chest Changes
- During the first trimester, the ductal system of the breast expands and branches out into the adipose tissue in response to increased estrogen levels 1
- Elevated estrogen causes a decrease in adipose tissue and promotes ductal proliferation and elongation in the breast tissue 1
- By the 20th week of gestation (mid-second trimester), mammary glands are sufficiently developed to produce components of milk due to prolactin stimulation 1
- In the third trimester, the areola darkens, breast size increases further, and Montgomery glands become more prominent 1
Physiological Mechanisms Behind Chest Changes
- Estrogen stimulates the pituitary gland leading to elevated levels of prolactin, which prepares the breast for milk production 1
- During pregnancy, milk production is initially inhibited by high estrogen and progesterone levels, with colostrum being produced instead 1
- After birth, estrogen and progesterone levels decrease rapidly, allowing for full milk production 1
Cardiovascular Changes Affecting the Chest
- Cardiac output increases by approximately 30-50% during pregnancy, with significant changes beginning in the first trimester 2, 3
- Heart rate increases by 15-20 beats per minute during pregnancy, particularly noticeable by the early second trimester 4
- Normal resting heart rate during early second trimester is typically between 80-95 beats per minute 4
- The heart undergoes significant remodeling in the first few weeks of pregnancy with end diastolic volume increasing 3
Respiratory Changes in the Chest
- During pregnancy, there is a reorganization of rib cage geometry in shape but not in volume 5
- Despite the growing uterus, there is no lung restriction (forced vital capacity remains at 101 ± 15% of predicted values) 5
- Breathing frequency and diaphragmatic contribution to tidal volume and inspiratory capacity increase throughout pregnancy 5
- Diaphragm thickness is maintained throughout pregnancy (1st trimester: 2.7 ± 0.8 mm, 3rd trimester: 2.5 ± 0.9 mm), indicating a conditioning effect to compensate for the effects of the growing uterus 5
Other Chest-Related Changes
- Pericardial effusion (fluid around the heart) becomes increasingly common as pregnancy progresses: 15.3% in the first trimester, 19.2% in the second trimester, and 44.2% in the third trimester 6
- Pericardial effusion is more common in primigravidas (69.2%) compared to multigravidas (35.9%) 6
- Pericardial effusion is also more common in women who gain more than 12 kg during pregnancy (67.7%) compared to those who gain less (34.3%) 6
Clinical Implications
- The American College of Obstetricians and Gynecologists notes that these chest changes are normal physiological adaptations to meet the increased metabolic demands of pregnancy 4
- Position changes can significantly affect heart rate and cardiac output during pregnancy - the left lateral position increases cardiac output compared to the supine position 4
- Avoiding the supine position after 20 weeks is recommended as it can cause inferior vena cava compression 4