Table 1.

Studies that measured DL_CO in pregnant women.

Study	Number and type of pregnant women	Number of diffusing capacity tests done per subject per session	Conclusion of the study
McAuliffe et al. (2003)	112 (sea level) and 192 (4300m) healthy subjects from Peru	2 tests per session. 1 session total (cross-sectional study)	DLCO measured in women living at altitude versus without altitude in the first, second, and third trimester compared to non-pregnant controls. DLCO was higher at altitude and DLCO decreased by about 15% by the third trimester.
McAuliffe et al. (2002)	68 women with twin pregnancies and 140 women with singleton pregnancies (all healthy)	2 tests per session. 1 session total (cross-sectional study)	To compare the differences in lung function between women with twin or singleton pregnancies, various lung function tests were performed. DLCO did not change between the first and the third trimester in women with either twin or singleton pregnancies. DLCO was 10% lower compared to non-pregnant women.
Milne et al. (1977)	21 healthy subjects	2 tests per session; 9 sessions total	DLCO was measured at 8 different time points during pregnancy and 3–5 months post-partum. DLCO decreased by 16% by the third trimester. [Hb] was lowest at 20–23 weeks gestation.
Lehmann (1975)	23 healthy subjects; 8 of those reporting spontaneous reported dyspnea with pregnancy	About 2 tests per session. 5 sessions total	DLCO was measured at 12, 24, 32, and 36 weeks of gestation, and 12 weeks post-partum. Women with dyspnea in early pregnancy (12th week gestation) had a 10% decrease in DLCO. Non-dyspneic women did not show a decrease in DLCO by the 12th week.
Norregaard et al. (1989)	39 healthy subjects; (10 in each trimester and 9 post-partum)	2 series of repeated measurements (seated and supine). So 4 tests in total per session. 5 sessions in total	Lung function and postural changes with pregnancy (first, second, and third trimester), and about 2–4 weeks post-partum. DLCO decreased by about 15% by the third trimester, regardless if the measurement was done in the sitting or supine position. No change in DLCO between sitting and supine.
Gazioglu et al. (1970)	24 subjects; 8 healthy, 8 valvular heart disease, 8 chronic pulmonary disease	At least 2 times per session. 4 sessions total	DLCO, DM, Vc were measured at 10, 24, and 36 weeks gestation, and 10 weeks post-partum. In normal subjects, DLCO and Dm equally decrease by 14% by 36 weeks gestation. No change in Vc. In those with emphysema, DLCO and Vc increased by 36 wks gestation with no change in DM. Those with pulmonary sarcoidosis had no change in DLCO, DM, or Vc.
Garcia-Rio et al. (1996)	23 subjects; 11 healthy with dyspnea, 12 healthy asymptomatic	At least 2 times per session. 4 sessions total	DLCO was measured 12, 24, 36 weeks gestation, and 16 weeks post-partum. DLCO was not altered during pregnancy in either the non-dyspneic or dyspneic group. There was no difference in DLCO in either group. The increase in dyspnea in pregnant women could be due to an excessive increase in sensitivity to CO2 or hypoxia.
Boggess et al. (1995)	9 subjects; interstitial and restrictive lung disease	About 2 times per session. 1 session total	3 women had DLCOs ≤ 40% predicted; 6 women ≥44% predicted in the first trimester. All women had vital capacity’s ≤84% predicted. There was an association between DLCO and vital capacity (r2 = 0.63). Mean birth weight was (50th percentile) was not different between those with the most severe restrictive lung disease or the least severe restrictive lung disease. Restrictive lung disease can be tolerated in pregnancy. Exercise intolerance was common and patients may require early supplemental oxygen, DLCO < 50% better predicted the need for oxygen supplementation than did vital capacity < 1.5 L.

All diffusion testing was accomplished with the single-breath DL_CO technique. No study reported adverse outcomes on mothers or their babies before or after birth.