The gentlebirth.org website is provided courtesy of
Ronnie Falcao, LM MS, a homebirth midwife in Mountain View, CA

Evidence Basis for Exercise Recommendations

I'll establish a little credibility first:

My bachelor's degree (1973!) is in Physical Education with a concentration on Special Populations.  Today this is often called Adaptive PE.

When I moved to the US from Holland in the early 80's I was the prenatal exercise instructor for the city wide Recreation Program, called cleverly enough Expectercise. TM.  To further my education I took a post graduate in Physical Aspects of Childbearing with Elizabeth Noble PT.

For  more than 20 years.during which time I became certified as a childbirth educator with Informed Homebirth, labor assistant with ALACE,  Doula, CD(DONA) and sometime midwife ..I have continued to read and collect information about exercise.

Not much has changed in the recommendations mostly because there isn't an experimental group to systematically record exercise at higher performance levels.

One of the most "authoritative" books written on the subject back was edited by Raul Artal and Robert Wiswell back in the 80's.   I remember being terribly

disappointed after spending $40 to read 17 chapter by 23 authors to find so little concrete direction.  The  8th chapter on "Changes in Maternal Hemodynamics During Pregnancy" proclaimed a surprisingly narrow approach and bias to boot!  I still have my notes..

"Third, posture dominates the control of cardiac output late in pregnancy because of its influence on venous return," which sets the stage for emphatic recommendations later in the book that no pregnant woman should EVER do any exercise while supine. They state that "about 5% of women experience symptoms of supine hypotension" so presumably it s the fetus that is believed to suffer if women exercise while supine. Problem was.this was neither documented nor discussed in the book.

Nor was any mention made of this being the most prevalent position for birth!

The book included various experiments on maternal cardiovascular response to exercise, yet time and time again the authors would point out deficiencies in the experimental designs that prevented anything but cautious conclusions.  Many of the experiments that showed reduced fetal growth with severe exercise or chronic overwork (which in themselves are not equal in my book!) were conducted on animals.  The authors say "we believe that appropriate advice for healthy pregnant women who are accustomed to exercise is to limit the intensity of their exercise to that which causes their heart rate to rise to levels less than 70% of the age predicted maximum for durations of half an hour or less and with a frequency of three times weekly."  Oh yes they give a "prescription" all right..the problem is that they never discuss how this advice was derived!!!

Even after citing the flaws in nearly ALL the research on maternal exercise and the wide variation in finding.the authors conclude: "due to cardiovascular complications that may occur in pregnancy, the unsupervised exercise prescription should be limited to a maximum of 140 beats/min."

Again.we have a directive but without any evidence to support it!

The authors' concerns with fetal bradycardia was the motivation to limit exercise intensity but the only evidence they offered in "Fetal Response to Maternal Exercise" didn't substantiate their recommendation.  "In 82 recorded cases during exercise, fetal bradycrdia was observed in only 7 cases (incidence of 8.5%). Six of the 7 cases were normal patients and completed successfully their pregnancy."

"It is not clear whether brief periods of fetal bradycardia are common during maternal exercise and mechanism by which they are triggered can only be speculated upon."

Women exercise for other reasons than to elevate their heart rate and no consideration of the psychological aspects of either exercise or physical training is even mentioned in the studies they included.   Curiously enough there wasn't even a mention of endorphins!!

I would also point out that there are major cultural components to how exercise is perceived.  When I lived in Holland it was hardly considered aberrant for a 9 month pregnant woman to bicycle everywhere; doing her grocery shopping, transporting other children or attending her prenatal appointments with the midwife.. My midwives incidentally had  their office on the second floor of a walk up building. When I took formal tennis lessons my coach however  kept asking if it was a good idea! By contrast, when I moved to the US people were surprised (yet very supportive) of by my regular  participation in a doubles tennis tournaments during my pregnancy but I was  cautioned against bicycling!

When woman ask me how to calculate their target zone I give them the following information  explaining the lack of documentation to establish a firm criteria.

220 (which is considered the highest pulse) minus your age equals your safe maximum attainable heart rate (SHR). Multiply that number by the "appropriate" percentages of your SHR to get your target zone. So what is "appropriate"? The percentages cited are 60-70% for beginning exercisers and 70-75% for those who were fit before pregnancy.

A 20 year old woman gives easy numbers to demonstrate:

220 - 20 = 200

70%-75% of 200 = 140-150

A 40 year old woman would be

220 - 40 = 180

70%-75% of 180 = 124-134

Make sure you don't use your thumb! It too has a pulse and it is easy to get confused as to which you are counting.

So how do these number play out for you whether you are considered already fit or on the way to getting fit? Lets say you are 25. Your target zone as a beginning exerciser would be 116-136 Your target zone as an fit exerciser would be 136-146 The upper level of a beginning exerciser actually is the same as the lower level of a more experienced one.

At this point I'd fall back on the most general rule of thumb which would be whether you could talk while exercising. One sign of overworking aerobically is shortness of breath.

The International Childbirth Education Association (ICEA) has a written review for purchase on the Maternal Physical Activity Effects on the Fetus and Pregnancy Outcomes.

They address hyperthermia, uterine blood flow, metabolic substrate and waste product concentrations, increases in catecholamine levels, altered blood gases and pH, cardiovascular variables and increased uterine activity but conclude that "basically there is a scarcity of data with which to evaluate and make recommendations".

Group Aerobics Classes

One of the biggest detriments I perceive with this kind of group activity is the potential for the woman to move to the relentless beat of the music and the group rather than to heed messages from her own body.

With the nearly competitive nature of some aerobic classes the baby's needs sometimes aren't taken into consideration either.

It is rare to hear an instructor extol the virtues of "listen to your body . . . do what YOU need to do and at the speed you need to do it!"

I think this has huge implications for labor.  Rather than tune in to her own body. (and after all who has the direct line to the baby anyway?) she may be conditioned to  listening to the coaching and the voices prodding her to work faster, harder and without letting up!

What about her fluid consumption?  There have been studies that discuss the need to replace the fluids and there is some concern about raising the core body temperature of the mother. This might merit an internet search for updated recommendations.  Certainly fluids, combined with
jumping/stepping/moving and a growing uterus sets the stage for more frequent bathroom trips. Again, is the environment one that supports the mother taking the break she needs when her body asks for it?

Any of us who has been pregnant knows that babies respond to their environment and it is not usual for mothers to report that their baby's
respond to the music the mother is listening to.  Rarely do mothers report that they find the rock music of their aerobic classes soothing and I would
wonder about the effects on the baby if a woman was moving to this music many hours a week.  That said, 8 years ago I attended an aerobic instructor's birth in which she listened to the Rolling Stones on her Walkman while we listened to classical music with the father. She insisted it was the kind of energy she needed!