When I was pregnant with my daughter, Faith, I did not intend to write a book about the experience. I did keep a journal to chronicle ongoing transformation of my own body: the wobbly looseness in my hip joints, the intense desire for avocados, the evolution of my belly button into a taut porthole the size of a silver dollar.

I also used my a journal to explore two aspects of my identity thrown in sharp relief by the fact of my expectant motherhood: my life as an adoptee and my life as a cancer survivor. I received obstetrical care at the same hospital where I had previously received cancer check-ups. Thus, to undergo my first prenatal sonogram, I lay down on a table where I had once been scanned for signs of tumor. Same room, different day.

Being adopted -- and never having had the chance to know my biological parents -- meant that I was about to have a blood relative for the first time in my life. Denied the story of my own birth, I was about to give birth. My adoption also meant that I couldn't answer any of the questions the genetic counselor had for me. Any Down syndrome in my family? Cystic fibrosis? Birth defects? I felt I was navigating the seas of prenatal genetic testing without a compass.

Ironically, it was during one of these tests -- amniocentesis -- that I decided to write a book on the environmental threats to fetal life. Amniocentesis involves the removal of an ounce of amniotic fluid from the womb of a pregnant woman. The liquid and the cells floating in it are then both subjected to analysis. The chemical composition of the liquid shows whether the baby is suffering from neural-tube disorder, such as spina bifida, while the chromosomal arrangements inside the cells reveals any genetic abnormalities. The results of my amnio were destined to turn out fine. "Unremarkable" was the word the nurse would use to describe them. (A more lovely adjective was never spoken.) What was remarkable, however, was how much this procedure made me aware not so much of my genetic past but of my present ecological surroundings. Going through an amniocentesis reminded me, in the most direct way, that women's bodies are the first environment for all of us.

After she pulled the needle out, the obstetrician allowed me to hold the still-warm sample in my hands. The of liquid inside the glass was pale gold -- like the color of a fine Chardonnay. I thought it the most beautiful thing I had ever seen.

"It's like amber," I sputtered. "It's like an amber jewel!" The obstetrician laughed as she took the vial from my hand to label it. "That's baby pee," she said. "We like it yellow. It's a sign of good kidney functioning." Then she told me to drink plenty of water to replace the fluid she had just removed.

Here's how I describe, in chapter four of Having Faith, the epiphany the resulted from this simple directive:

Drink plenty of water. Before it is baby pee, amniotic fluid is water. I drink water, and it becomes blood plasma, which suffuses through the amniotic sac and surrounds the baby -- who also drinks it. And what is it before that? Before it is drinking water, amniotic fluid is the creeks and rivers that fill reservoirs. It is the underground water that fills wells. And before it is creeks and rivers and groundwater, amniotic fluid is rain. When I hold in my hands a tube of my own amniotic fluid, I am holding a tube full of raindrops.... I am looking at rain falling on orange groves. I am looking at melon fields, potatoes in wet earth, frost on pasture grasses... Whatever is in the world's water is here in my hands.

One of the most common questions I'm asked about Having Faith is whether a book on toxic threats to infant development (human amniotic fluid turns out to contain traces of pesticide, dioxins, and PCBs, for example) will make for appealing reading for expectant mothers. I can only say that this is the kind of book that I wanted to find during my own pregnancy but could not. Being aware of environmental dangers to children's health seemed part of my new responsibility as an expectant mother -- in the same way that infant car-seat recalls and pediatric vaccination schedules were. And yet, oddly, most popular guidebooks on pregnancy encourage mothers-to-be not to dwell too much on environmental dangers that seem to exist outside their individual ability to control. As if women were not also political beings with a voice outside their own homes who could be a potent force of social change.