In 2002, the American College of Obstetricians and Gynecologists published exercise guidelines for pregnancy, which suggested that in the absence of medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women. However, these guidelines did not define ‘moderate intensity’ or the specific amount of weekly caloric expenditure from physical activity required. Recent research has determined that increasing physical activity energy expenditure to a minimum of 16 metabolic equivalent task (MET) hours per week, or preferably 28 MET hours per week, and increasing exercise intensity to ≥60% of heart rate reserve during pregnancy, reduces the risk of gestational diabetes mellitus and perhaps hypertensive disorders of pregnancy (i.e. gestational hypertension and pre-eclampsia) compared with less vigorous exercise. To achieve the target expenditure of 28 MET hours per week, one could walk at 3.2km per hour for 11.2 hours per week (2.5 METs, light intensity), or preferably exercise on a stationary bicycle for 4.7 hours per week (~6–7 METs, vigorous intensity). The more vigorous the exercise, the less total time of exercise is required per week, resulting in ≥60% reduction in total exercise time compared with light intensity exercise. Light muscle strengthening performed over the second and third trimester of pregnancy has minimal effects on a newborn infant’s body size and overall health. On the basis of this and other information, updated recommendations for exercise in pregnancy are suggested.

Exercise guidelines in pregnancy: new perspectives.

Available evidence supports the existence of both risks and benefits of aerobic conditioning during human pregnancy. During intensive exertion, maternal skeletal muscle and the fetus may compete for blood flow, oxygen delivery and essential fuel substrates. Hence, the most important hypothetical risks include acute fetal hypoxia, hyperthermia and malnutrition. If exercise is repeated on a chronic basis, teratogenic effects, fetal growth retardation or altered fetal development may result if maternal/fetal adaptive reserve is exceeded. A dose-response relationship for such effects has been demonstrated in laboratory animals, but specific findings may have limited applicability to voluntary exercise in pregnant women.

Prescription of aerobic exercise during pregnancy

Photoswitching of a homogeneous 1‐l discharge has been tested on a specially designed excimer laser by using either an x‐ray beam or a KrF laser beam as a photoionization source. With x rays, a 1.4‐J, 4×4‐cm2, XeCl laser beam has been obtained with 1.7% efficiency and an impedance‐matched 50‐ns pulse‐forming line directly connected to the electrodes. Since the output energy seems to rise monotonically as a function of electron–ion pair initial density, even better performances should be attainable with a more intense photoionization source.

Phototriggering of a 1-J excimer laser using either UV or x rays

This paper describes the laser performance of an X-ray preionized ten-liter volume, electron-avalanche discharge XeCl system, operated at dc charging voltages of up to 70 kV both with and without X-ray preionization. An output energy of more than 11J uniformly distributed over a (7×10) cm2 spot size was achieved using a multichannel spark-gap as the main discharge switch. The discharge was also successfully operated in the switchless mode, yielding a 4.8 J output energy and a 0.9% efficiency. The time-resolved gain measurements provided information on the laser discharge evolution.

Performance of a ten-liter electron avalanche-discharge XeCl laser device

Gestational diabetes mellitus is one of the major medical complications of pregnancy. Untreated, the mother and the unborn child may experience morbidity and fetal death may even occur. It is important to diagnose and treat all hyperglycaemia appearing during pregnancy. Ideally, a screening and diagnostic test that identified all women at risk for hyperglycaemia-associated complications would be employed in all pregnant women. Unfortunately, there is no such test available currently. The best alternative is to administer an oral glucose challenge test to all pregnant women and then apply the best strategies for interpretation. This article discusses the limitations of our present diagnostic tools and suggests an option for the clinician until the definitive test has been elucidated. In addition, this article outlines one dietary and management strategy that has been associated with an outcome of pregnancy that is similar to the outcome of pregnancies in healthy women. This strategy includes starting with a "euglycaemic" diet (comprising or =40% fat), which can then be individualised according to the patient's glucose levels. Appropriate exercise, such as arm ergometer training, may enhance the benefits of diet control. For patients who require insulin, if the fasting glucose level is >90 mg/dL or 5 mmol/L (whole blood capillary) then NPH insulin (insulin suspension isophane) should be given before bed, beginning with dosages of 0.2 U/kg/day. If the postprandial glucose level is elevated, pre-meal rapid-acting insulin should be prescribed, beginning with a dose of 1U per 10g of carbohydrates in the meal. If both the fasting and postprandial glucose levels are elevated, or if a woman's postprandial glucose levels can only be blunted if starvation ketosis occurs, a four-injections-per-day regimen should be prescribed. The latter can be based on combinations of NPH insulin and regular human insulin, timed to provide basal and meal-related insulin boluses. The total daily insulin dose for the four-injection regimen should be adjusted according to pregnant bodyweight and gestational week (0.7-1 U/kg/day); doses may need to be increased for the morbidly obese or when there is twin gestation. There is now some evidence that insulin lispro, other insulin analogues and oral antihyperglycaemic drugs may be beneficial in gestational diabetes, and more data on these agents are awaited with interest.

Achieving euglycaemia in women with gestational diabetes mellitus: current options for screening, diagnosis and treatment.

X rays with a mean energy of ∼50 keV produced by a flash x‐ray source have been used to preionize high‐pressure CO2 laser mixtures so as to obtain uniform glow discharges. The x‐ray exposure measured in the active volume was 1–2 mR/pulse with a pulse duration of 100 nsec (FWHM) which permitted specific energy inputs of up to 300 J/l atm. Glow discharges were obtained for a variety of pressures and gas mixtures including some which were helium‐free or in which helium was replaced by argon. Further, a realistic comparison of UV and x‐ray schemes was made under sealed‐off conditions. X‐ray preionization appears to be advantageous and the resulting discharges are shown to tolerate oxygen (up to 2.6%) better. Additives such as xenon or organic compounds were not necessary for obtaining uniform glow discharges.

X‐ray preionization of self‐sustained, transverse excitation CO2 laser discharges

Pulsed x rays with a dosage of 1–2 mrad/pulse at a mean energy of ∼50 keV are shown to be capable of initiating glow discharges in various gas mixtures up to and above atmospheric pressure. dc voltages (up to 32 kV) have been switched in this way to form glow discharges in CO2, N2, He, and their mixtures with the resulting generation of 10.6‐μm laser radiation when an appropriate cavity was used.

A. J. Alcock

Papers

X‐ray preionization of self‐sustained, transverse excitation CO2 laser discharges

X‐ray initiated high pressure glow discharges