Further advice is given on pregnancy and travel by ACOG (2002). In-craft environmental conditions, such as low cabin humidity and changes in cabin pressure, coupled with the physiologic changes of pregnancy, do result in maternal adaptations, which could have transient effects on the fetus. Pregnant air travelers with medical problems that may be exacerbated by a hypoxic environment, but who must travel by air, should be prescribed supplemental oxygen during air travel. Pregnant women at significant risk for pre-term labor or with placental abnormalities should avoid air travel.