Human Studies Offer Real Answers
O’Hagan claims that her work using rabbits is necessary because “[f]or ethical and technical reasons, it is difficult to directly investigate the uterine blood flow response to exercise in pregnant women.” But this claim is demonstrably false. A literature review using the National Institutes of Health’s (NIH) PubMed database confirms that uterine blood flow has been measured in women during clinical studies. In fact, many studies specifically measure the effects of exercise on uterine blood flow in women; in other words, O’Hagan’s justification for her rabbit studies is based on a false premise.
When physicians investigate uterine blood flow in women, they use a noninvasive technology called Doppler ultrasound, which bounces sound waves off moving blood cells to measure the speed of blood flow. Doppler is easy, effective, and completely safe and painless. There is no reason for using rabbits in painful experiments.
The results of more than 20 years of clinical studies of pregnant women show that moderate exercise is safe and beneficial during pregnancy. Women show little if any change in uterine blood flow, and there is no significant change to fetal blood flow. Therefore, even if O’Hagan’s study were applicable to humans—which it is not—it would only reproduce data already available.
The following is a partial list of studies that support our findings:
- Kennelly MM, Geary M, McCaffrey N, McLoughlin P, Staines A, McKenna P. Exercise-related changes in umbilical and uterine artery waveforms as assessed by Doppler ultrasound scans. American Journal of Obstetrics and Gynecology 2002 Sep;187(3):661-6. This study of 22 women investigates the same topic as O’Hagan and concludes, “The modest change in the uterine artery pulsatility index … indicate[d] that a single bout of maximum symptom-limited exercise does not have immediate adverse fetal or maternal cardiovascular effects.
- Bonnin P, Bazzi-Grossin C, Ciraru-Vigneron N, Bailliart O, Kendra AW, Savin E, Ravina JH, Martineaud JP. Evidence of fetal cerebral vasodilatation induced by submaximal maternal dynamic exercise in human pregnancy. Journal of Perinatal Medicine 1997;25(1):63-70. This study of 14 women states, “We conclude that submaximal maternal exercise at 80 percent of [theoretical maximal heart rate] does not significantly alter uterine perfusion,” and states that “uterine resistance indices did not change.”
- Erkkola RU, Pirhonen JP, Kivijarvi AK. Flow velocity waveforms in uterine and umbilical arteries during submaximal bicycle exercise in normal pregnancy. Obstetrics & Gynecology 1992 Apr;79(4):611-5. This study used Doppler ultrasound in a protocol remarkably similar to O’Hagan’s rabbit study. Eight healthy pregnant women exercised at varying work loads (70, 83, and 92 percent of maximum heart rate) and had their blood flow measured. It was found that although uterine blood flow decreased slightly, no change was made in umbilical blood flow to the fetus.
- Asakura H, Nakai A, Yamaguchi M, Koshino T, Araki T. Ultrasonographic blood flow velocimetry in maternal and umbilical arteries during maternal exercise. Nippon Sanka Fujinka Gakkai Zasshi 1994 Apr;46(4):308-14.
This Japanese study of 21 women found no significant change in uterine blood flow after aerobic dancing at 65 percent maximal heart rate. - Steegers EA, Buunk G, Binkhorst RA, Jongsma HW, Wijn PF, Hein PR. The influence of maternal exercise on the uteroplacental vascular bed resistance and the fetal heart rate during normal pregnancy. European Journal of Obstetrics, Gynaecology and Reproductive Biology 1988 Jan;27(1):21-6. This study of 20 women concluded, “No significant change was found in the uterine blood flow velocity waveform post-exercise, as expressed by the pulsatility index, suggesting absence of change in the uterine vascular bed resistance.”
- Vaha-Eskeli K, Pirhonen J, Seppanen A, Erkkola R. Doppler flow measurement of uterine and umbilical arteries in heat stress during late pregnancy. American Journal of Perinatology 1991 Nov;8(6):385-9.
This study of 17 women used Doppler to show that moderate thermal stress is not dangerous to a healthy fetus. - Moore DH, Jarrett JC II, Bendick PJ. Exercise-induced changes in uterine artery blood flow, as measured by Doppler ultrasound, in pregnant subjects. American Journal of Perinatology 1988 Apr;5(2):94-7. This study concludes, “[N]onexhaustive maternal exercise does not compromise uterine artery blood flow in healthy, low-risk pregnant subjects.”
- Pijpers L, Wladimiroff JW, McGhie J. Effect of short-term maternal exercise on maternal and fetal cardiovascular dynamics. British Journal of Obstetric and Gynaecology 1984 Nov; 91(11):1081-6. This study of 28 women found: “Mean blood flow velocity in the fetal descending aorta as measured by pulsed Doppler unltrasound and fetal heart rate did not show any significant changes. These data indicate that there are no cardiovascular signs of fetal stress immediately after moderate short-term maternal exercise.”
- Veille JC. Maternal and fetal cardiovascular response to exercise during pregnancy. Seminars in Perinatology 1996 Aug;20(4):250-62. This review confidently states, “With the two-dimensional Doppler echocardiogram and M-mode echocardiogram, one can study maternal and fetal cardiovascular physiology during rest and exercise.” The review concludes that moderate exercise is clearly safe for healthy women and concludes, “Further studies are needed to determine if less active pregnant subjects, women with chronic hypertensive disorders, women with sickle cell anemia, or women with insulin-dependent diabetes adapt to exercise as well as their ‘normal’ counterparts.”
Clinical research into exercise and pregnancy has offered clear answers for most women and now should address the needs of special populations, including women with hypertension disorders. Unfortunately, by the NHLBI’s own admission, “There are few obstetrician/gynecologists trained in rigorous clinical research and even fewer formal training programs.”
