On a Thursday morning, two months before my 40th birthday, the test strip on my ovulation predictor kit registered a bright blue. That meant that the upcoming Saturday would be the likeliest time for conception. Unfortunately, while running a few days earlier, I'd taken a spill. Besides severely scraping both knees, shoulders and arms, I'd somehow managed to break my nose, which I was scheduled to have reset that very afternoon. Ordinarily, the worst would have been over when my nose was audibly snapped back into place. But given the timing, there was a need for further damage control.

I perfunctorily nodded my assent when the doctor informed me that my nose could not be touched for two weeks and that I must sleep in a reclining chair for that period of time. But I adamantly drew the line when he proposed a precautionary round of two medications that I knew were contraindicated for pregnancy.

Relieved at having narrowly averted a derailment of my urgent agenda, I drove home, the throbbing in my nose increasing as the anesthetic wore off. Later, surveying the damage in the bathroom mirror, I snapped at my husband when he suggested that with all my injuries perhaps we'd best just skip this month. It was only when a friend joked that she'd like to be a fly on the wall during the weekend baby-making session -- with the prospective mother mercifully free of zygote-imperiling pharmaceuticals but racked with pain from knee to untouchable nose -- that I realized how obsessed I'd become on the eve of my 40th birthday. That ovulation kit was a dangerous technology in the hands of a woman who had hit the snooze-control button on her biological clock once too often.

Some women use the conventional wisdom that there is no good time to have a baby to justify taking the plunge sooner rather than later. Not me. When my life took a turn for the interesting in my mid-30s, the time I'd penciled in for starting a family, I simply rescheduled it -- indefinitely.

When 39 tapped me on the shoulder -- 40 was the absolute deadline I'd set for myself -- I dutifully cleared my desk and joined the ranks of women whose ambivalence about motherhood magically resolves at the moment that an alternative turns into a last chance. Now we would go after it with a vengeance. And were we systematic -- not only in our attempts to get pregnant but, once that mission was achieved, in flawlessly navigating the perfect gestation.

The last time I had taken the pulse of this group, we were in our early 30s -- many of us between marriages, others fearful of growing old alone -- and consumed with the day-to-day Sturm und Drang of relationships with men whose emotional baggage often exceeded the customary allowance. Curiously, though, upon entering our mid-30s, we either promptly met the perfect man or laid down our swords with our longtime partners in combat. At 35-plus, we were no longer talking on the phone about dating strategies; now we exchanged information about amniocentesis and laparoscopy.

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It made sense that we would pursue our now-urgent tasks with the savvy that 30-odd years of practiced consumerism had imbued us with. Whoever invented that ovulation predictor kit knew well the end-users: What could be more alluring to a woman in a hurry to get pregnant than an efficient little test that provided her with a daily read-out of precisely what was going on in her body? I, for one, was completely taken with it. One week each month, our kitchen turned into an ersatz laboratory, papered with charts, bar graphs and historical comparisons. So preoccupied was I with the day-to-day progress of what I visualized to be this game of human pinball that I would find myself casually dropping the day's results into conversations with friends -- male or female.

"It looked pretty blue today, John."

"So why are you still at work?"

We who are responsible for raising the average age of first motherhood are a difficult group -- and not just because, nursing our Perriers, we're no longer any fun at parties. We've got a lot to be nervous about, not the least of which is the specter of infertility and the serious medical risks often attendant to deferred pregnancy. Mostly, however, many of us are worried because our trust in the medical profession has been significantly eroded; the doctor is no longer the authority figure he was for our mothers. A woman whose mother unquestioningly took the DES that her doctor recommended to prevent miscarriage and now surveys the deleterious effects of that miracle drug on her own reproductive system is understandably wary.

Fortunately, we'd had years of experience in preparing ourselves for new undertakings: How much more difficult could getting educated for motherhood be than, say, buying a major appliance? The goal was certainly the same: to make the most enlightened choices after having first evaluated the available data. Obviously, there were studies out there. If we were sufficiently informed, at a minimum we'd be able to ask the pertinent questions and make our own educated choices. As soon as my pregnancy was confirmed, I got serious.

A sophisticated consumer always begins by scanning the available literature. I discovered that the bookstore pregnancy inventories tended to fall into two categories: the ubiquitous bromides, for women (usually under 30) who believe that all they have to do to pop out a baby is follow the doctor's advice and pick colors for the nursery; and the more elusive hard-facts books, for the woman who believes that growing a baby requires her full participation and unblinking vigilance, lest she fall asleep at the wheel and irresponsibly allow nature to take its course unguided. Or worse, be forced to rely on her doctor.

Naturally, we older future mothers prefer the latter source. When a shoot-from-the-hip book was discovered, its information -- though often far from reassuring, even frightening -- was passed among us, like urgent gossip.

Of course, sometimes the use, or misuse, that we made of the hard-facts books was the best argument for the bromides. One friend, Lisa, suffered from allergies so severe that in the early weeks of her pregnancy she took an antihistamine. Unfortunately, that was before she had read about the detrimental effects such medications could have on the developing fetus. Certain that she'd done irreparable harm to her unborn, Lisa kicked prenatal lay research up to a new level when she stormed the stacks of the local medical school library and read for herself the antihistamine studies. It took a phone call from her husband to the author of one of those studies -- pleading with him to please let him put his wife on the phone so that he could assure her that a single antihistamine could do no irreversible damage -- to calm her down.

Another friend, Zini -- a Californian by birth and lifestyle, and a former gynecological nurse-practitioner -- had apparently spent much of her time in obstetrical practice contemplating the perfect pregnancy and concluded that having a baby was something best left to the mother's instincts. As the rest of us watched enviously, she bypassed the medical profession and placed herself under the care of a midwife. She then designed her own prenatal diet, declined amniocentesis and finalized plans for a home birth before setting off for eight weeks in Morocco -- during her fifth month and the height of the flu season.

Hers was a textbook pregnancy, up until delivery. Although Zini's worst-case scenario must have included the possibility of a hospital rather than home birth, she certainly never expected an emergency room C-section, though that's what she got.

A persistent and discomfiting counterpoint to the search for an enlightened, fail-proof pregnancy was always the attitudes of women of our mothers' generation. Lottie, one of these, laughed when I described my daily debate over the propriety of a morning cup of coffee. "I'd just relax about all of that," she'd say. "When I was pregnant, the medical thinking was that it was best to gain very little weight, so my friends and I drank pots of coffee and smoked dozens of cigarettes every day -- just to keep from eating. We were clueless that any of that was bad, but we seemed to do OK." I had to admit that Lottie's grown daughters -- one a doctor, the other a lawyer -- seemed none the worse for mom's prenatal transgressions.

The news that Margaret, 36, had an amnio and tested positive for Down's syndrome sent tremors through our group: Margaret was one of our best-informed. What could have caused this hideous malfunctioning of a natural process that had been so carefully guided? After all, what was the point of all this intensive information-gathering if so much still lay beyond our control? Then, too, if it was possible to have a healthy baby on caffeine and cigarettes and a defective one without them, why bother?

All of these maddening contradictions pointed up the futility of trying to influence an essentially uncontrollable outcome. Maybe I'd gotten carried away with the placental checklist I'd custom-designed to ensure my own perfect baby: holding my breath while filling the car with gas or in a room with someone who was sick; forcing myself to account for the nutritional value of every bite of food, to the point that eating became a mechanical, joyless chore. Waiting for a headache to wear off rather than take a chance on the Tylenol that my doctor assured me was perfectly safe. Thank God no one, except my husband, had seen me sitting in front of my computer wrapped in a dental-office lead apron.

What was I doing? Probably looking for the same kind of predictability in pregnancy that the ovulation kit purported to offer for conception. What I had neglected to factor in was the stress that would necessarily accompany such a bid for quality control. Having a healthy baby, it turns out, was not that much like picking the best fridge. It gradually dawned on me that the best thing I could do for my offspring would be to give him a relaxed, if older and wiser, mother. So I loosened my grip. And had a cup of coffee.