From the Guidelines
Pregnancy does affect pulmonary function test values, with changes in respiratory parameters occurring due to the growing uterus and hormonal influences. During pregnancy, several respiratory parameters change as the growing uterus elevates the diaphragm and hormonal changes affect the respiratory system. Tidal volume increases by about 30-40%, while residual volume and functional residual capacity decrease by approximately 20-25% [no direct evidence from 1 or 1]. Total lung capacity decreases slightly by 4-5% [no direct evidence from 1 or 1]. Despite these changes, forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) remain relatively stable, with the FEV1/FVC ratio staying normal [no direct evidence from 1 or 1]. Oxygen consumption increases by about 20-30% to meet the metabolic demands of pregnancy [no direct evidence from 1 or 1]. These physiological adaptations occur primarily due to mechanical pressure from the enlarging uterus pushing upward on the diaphragm and hormonal influences, particularly progesterone, which acts as a respiratory stimulant [no direct evidence from 1 or 1]. The provided evidence from 1 and 1 does not directly discuss the physiological changes occurring in pregnancy, but they do outline the management of reproduction and pregnancy in women with airways diseases. When interpreting pulmonary function tests in pregnant women, clinicians should consider these normal physiological adaptations rather than mistaking them for pathological conditions. Key points to consider include:
- Changes in respiratory parameters due to the growing uterus and hormonal influences
- Increased tidal volume and decreased residual volume and functional residual capacity
- Stable FEV1 and FVC with a normal FEV1/FVC ratio
- Increased oxygen consumption to meet the metabolic demands of pregnancy
- Consideration of normal physiological adaptations when interpreting pulmonary function tests in pregnant women.
From the Research
Changes in Pulmonary Function Test Values During Pregnancy
- Pregnancy causes many visible and invisible changes in the human body, including alterations in respiratory physiology 2.
- Studies have shown that pulmonary function test values, such as forced vital capacity (FVC), forced expiratory volume in one second (FEV1), peak expiratory flow rate (PEFR), and maximum ventilation volume (MVV), are significantly decreased in pregnant women compared to non-pregnant women 2, 3.
- The decrease in pulmonary function test values is more pronounced as pregnancy progresses from the first to the third trimester 3.
- However, some studies have reported an increase in FVC and peak expiratory flow (PEF) during pregnancy, particularly after 14-16 weeks of gestation 4.
- The changes in pulmonary function test values during pregnancy may be influenced by factors such as parity, with nulliparous women having lower FVC% values than parous women 4.
- Despite the changes in pulmonary function test values, patients with many lung diseases can tolerate pregnancy well, except for those with pulmonary hypertension or chronic respiratory insufficiency from parenchymal or neuromuscular disease 5.
Key Findings
- Significant decrease in FVC, FEV1, PEFR, and MVV in pregnant women compared to non-pregnant women 2, 3.
- Increase in FVC and PEF during pregnancy, particularly after 14-16 weeks of gestation 4.
- Nulliparous women have lower FVC% values than parous women 4.
- Patients with lung diseases can tolerate pregnancy well, except for those with pulmonary hypertension or chronic respiratory insufficiency from parenchymal or neuromuscular disease 5.
Pulmonary Function Test Parameters
- FVC: decreased in pregnant women compared to non-pregnant women 2, 3, but increases after 14-16 weeks of gestation 4.
- FEV1: decreased in pregnant women compared to non-pregnant women 2, 3.
- PEFR: decreased in pregnant women compared to non-pregnant women 2, 3, but increases during pregnancy 4.
- MVV: decreased in pregnant women compared to non-pregnant women 2.