After his wife lost four pregnancies, Jon Cohen set out to look for the facts.

After my wife, Shannon, had her third miscarriage, the best specialist we could find told us that she had a 3 per cent chance of ever carrying a baby to term.

Shannon was 39 at the time, and the doctor explained that first-trimester miscarriages become more common after women pass age 35 and enter what medical science indelicately refers to as "advanced maternal age."

Exhausted from the emotional roller coaster of repeated losses and satisfied that we had had one child, who then was 8, we decided to quit what had become an aggressive programme of trying to get pregnant.

When Shannon became pregnant again at 41 and lost that embryo, it seemed to seal our fate. But then a few months later, she became pregnant yet again — and this one went to term without a hitch.

Our son, Ryan, was born on August 6, 2000.

Ryan's arrival made it clear to me that there was much that Shannon and I, and our doctors, didn't know.

I began studying the subject. Much of what I learned flatly contradicted the "facts" given by the experts who had advised us.

Learning more

One of the first things I learned was that miscarriage is far more common than we had been led to believe.

An authoritative study published more than 15 years ago in the New England Journal of Medicine found that 31 per cent of pregnancies result in miscarriage.

The study determined pregnancy by testing the women's urine for human chorionic gonadotropin (hCG), a hormone that gushes from placental cells at implantation.

First, the study looked at relatively young, healthy women — 95 per cent of the participants were 35 or younger.

Several studies have shown that miscarriage indeed does happen more frequently in women after the age of 35.

Second, miscarriage can happen after conception but before the embryo implants on the uterine wall. But no test can detect those pre-implantation losses.

Given all of this, many experts believe, the true miscarriage rate is at least one out of every two conceptions.

Learning this left me with the sense, for the first time, that Shannon and I were not freaks.

Soon I found an eye-opening study that all but mocked the 3 per cent odds we were given of carrying a baby to term.

Researchers at St Mary's Hospital in London, which runs the world's largest miscarriage clinic, closely followed 201 women, each of whom had had at least three losses and had become pregnant again.

The doctors had not discovered any underlying causes for their losses. Nearly 70 per cent of these women carried their pregnancies to term without any interventions, save for the expert care they received at this clinic.

About half of all pregnancy losses are due to chromosomal abnormalities, and these losses, like Shannon's, typically occur within the first trimester.

But chromosomal abnormalities in miscarried pregnancies, it turns out, often are actually good news for couples.

If a woman miscarries an embryo that has too many or too few chromosomes, then everything typically is working right: She is becoming pregnant, but losing a baby that has virtually no chance of surviving.

Why weren't we offered this so-called "karyotype" test to determine if Shannon's miscarriages were due to chromosomal mayhem? I have no idea.

I soon became fascinated by the fundamental biology driving the chromosomal blunders involved with so many miscarriages.

Why are they so common, and why do they increase as a woman ages? I found an elegant, startling answer.

Getting to the root

A girl makes all the eggs that she will carry for life while she is still a foetus. Those eggs carry 46 chromosomes.

A human has 46 chromosomes, so the egg must throw away half its genetic cargo when it meets a sperm, which shows up to the fallopian boudoir with the requisite 23 chromosomes of its own. But the egg tosses those extra chromosomes overboard at conception.

So when an egg meets a sperm, the egg is decades old. As an egg ages, the mechanism that separates chromosomes becomes wobbly and inefficient, sometimes mistakenly tossing out, say, 22 or 24 chromosomes instead of 23.

Both of those scenarios lead to embryos that almost always miscarry. It further raised my eyebrows to learn that, technically, it's not age driving miscarriage but the woman's proximity to menopause.

The female foetus makes about 7 million eggs and they begin to self-destruct even before birth.

A female will ovulate only about 400 to 500 eggs during her reproductive years, so the system has a huge oversupply built in.

Once only about 1,000 eggs remain, a woman enters menopause. Given that women go through menopause at anywhere from 40 to 60 years old, each woman thus has her own unique biological clock.

Ultimately, then, each woman has her own miscarriage clock: The closer her ovaries come to having 1,000 eggs in the pool, the more likely she will have an abnormal embryo and a loss.

Besides chromosomal abnormalities, women miscarry because they have immune responses that disrupt implantation, blood-clotting problems, physical abnormalities with the uterus or cervix, or hormonal imbalances.

When Shannon and I were trying to navigate the stormy seas of miscarriage, no one sat us down and explained the knowns and unknowns.

She never received a test for antiphospholipid antibodies, even though a proven intervention exists for that particular problem, which affects roughly 15 per cent of women who recurrently miscarry.

All of this speaks to a deeper truth about miscarriage that I only came to realise after we had our second child: Miscarriage is a sub-sub-specialty that doesn't attract the attention, funding or research talent that it deserves.

— Los Angeles Times-Washington Post News Service