Wednesday, December 03, 2008

Childbirth and gravity

We all know how important gravity is. When we put a turtleneck on a baby, we want gravity to work with us, not against us. So we all hold our babies upside down over the shirt and let the baby fall through the neck opening, right?

Wrong, of course. Yet that is the principle that homebirth and "natural" childbirth advocates invoke when arguing that women should be upright in both the first and second stage of labor. They are absolutely certain, based on no evidence, that gravity provides a powerful and necessary aid to labor.

Consider this from Charlotte DeVries of Lamaze:
I gained a greater appreciation for gravity when, during my second pregnancy, our midwife listened to my tale of woe about a 36-hour labor and forceps delivery with our first (very big) baby and suggested I become a dedicated walker in the months ahead. "Three things," she said. "It's a positive way to move through your pregnancy, your body will be fitter for labor and birth, and you are cooperating with gravity and getting your baby ready to make its way out." She was right on all three counts for that pregnancy and for the one that followed a couple of years later on the other side of the country. For both births, the day I went into labor I did my regular brisk two-mile loop.

...[T]hose long walks can be a time to sort out the needs from the strengths, a time to get acquainted with yourself in a different way, to better listen to your body’s cues when it comes to dealing with the purposeful pain of labor, to grow to trust something as simple as gravity on your birth day.
Or how about this gobbledy gook from the Lamaze Care Practice #5?
Upright positions—such as standing, kneeling or squatting—take advantage of gravity to help your baby move down...

Respected childbirth educator and author Penny Simkin recommends a "standing supported squat" or "dangle" position, especially for women with a long second stage. In this position, the woman is supported under her arms, putting very little weight on her legs or feet. Her trunk becomes longer, providing more space for the baby to move. Simkin also points out that, in this position, the pelvis can move freely as the baby passes through it.
Why is it gobbledy gook? Because it's based on no data at all. "Natural" childbirth advocates simply made it up.

There are very few scientific papers on the subject and the ones that exist offer show no difference in outcomes. Consider Upright position during the first stage of labor: a randomised controlled trial:
The upright position during the first stage of labor did not contribute towards a shorter duration of labor; however, it proved to be a safe and well-accepted option for the women of this study.
"Natural" childbirth advocates argue that this is the way that women give birth in nature:
Until doctors began using forceps in the 17th century, women were rarely shown giving birth in supine positions (lying on the back). With the support and encouragement of family members and community midwives, laboring women used objects such as posts and ropes to gain leverage during pushing. They often used birthing supports or stools to help them squat, crouch, or kneel.
That's not true either.

According to Mobility and maternal position during childbirth in Tanzania:
...More women were mobile at home after the labour pains started than in the labour ward at each hospital. The greatest difference between mobility at home and in the labour ward was at the district hospital (27.6% compared to 4.5%). However, a surprising finding was the apparent restriction on movement prior to admission to the labour ward; across all hospitals, most women chose to rest with little movement when at home (51.6%), and just 15% said they were mobile at home. Another important finding is that 28.3% of all women who laboured in bed in the labour ward said they wanted to be mobile.
In other words, when left to their own wishes, more than half of all women did not want to be mobile in the early stages of labor, and more than 70% did not want to be mobile during active labor. So much for "listening" to your body.

We can go beyond the fact that the Lamaze recommendations are not evidenced based, and ask just what physics tells us about the relative contribution of gravity to childbirth. The uterus generates tremendous force with each contraction, and more force is applied with coached pushing, and by a woman holding her legs under the knees and pulling them back. The uterus supplies approximately 82 newtons (N) of force. Coach pushing (a Lamaze no-no) with legs adds 47 N and pulling the legs back adds 31 N of additional pushing force for a grand total of 160 N.

What would gravity add to the 82 N pushing force of the uterine contractions? For a 7 lb. baby, gravity would add 31 N. In other words, the benefit of gravity is far less than the benefit of coached pushing with legs pulled back. Not only is there no evidence that gravity has a beneficial effect on labor, there is no reason to think that the relatively small force of gravity would have much benefit.

This is yet another example, in the endless parade of examples, that "natural" childbirth professionals advocate practices that have no basis in scientific evidence, no basis in scientific reasoning, and are simply made up to appeal to the whims of "natural" childbirth advocates.

1 Old Comments:

I have no idea where all your negativity and opposition comes from, maybe from your medical training that insists that women have no idea how to give birth without the aid of drugs and obstectricians, but I can tell you now that of my 2 births so far, I would gladly chose undrugged, natural, mobile labour over the drug-induced, bed-ridden, monitored birth that resulted in giving birth to a grey floppy baby who appeared dead! Open your mind to the fact that medical intervention isn't the best option for the majority of women in low risk situations!

By Anonymous Amy semmens, at 2:22 AM