If you are reading this after your first trimester, you can probably stop; for the most part, miscarriage usually occurs in the first 10 weeks of pregnancy. The second trimester is truly a milestone, and couples can breathe a little more easily when they've reached this point. In fact, pregnancy loss after twelve weeks is almost always due to a rare catastrophic event or an even rarer genetic mishap that took a little longer to catch up.
Yet we all live our mortal lives at the mercy of the biological rules that govern survival. And, sometimes bad things happen: one such bad thing is miscarriage. Some say miscarriage is a good thing, assuring the health of our species. But couples aren't thinking about the survival of our species when they choose to have a child. No one thanks evolution for a miscarriage. In fact, miscarriages usually cause pain and anger. But such a complex creature as a human being is exceedingly special by the very nature of what it takes to build one.
Doctors love lawyer jokes (probably too much), but there is this joke that comes to mind:
Q: What do a sperm and a lawyer have in common?
A: They each have a one in 60 million chance of being a human being.
My brother, the lawyer, hates lawyer jokes. When he gives me that look, I remind him about the arithmetic involved: a 1 in 60,000,000 chance for him to have been conceived, and then another 1 in 60,000,000 to be the great guy that he is. He's one in three and a half quadrillion! The point is that each person is a unique individual that is the result of infinitesimal odds.
We don't consider these odds because we look around at everyone and see, well … everyone. But each and every person we encounter—those people in the elevator with us, in those partially obstructed seats at rock concerts, in line at the DMV, in the park with their kids—they've all made it through a process much more challenging than winning all the Grand Slams in a year. But not every entrant in the field gets to the finals. Even when there is conception (a long-shot event anyway), some further process in the nine-month plan to create a human being can go awry, and a pregnancy ends when this process is no longer compatible with life.
Why Miscarriage Happens
Miscarriage is nature's way of discarding a pregnancy that didn't proceed in a way compatible with life. Even though it may be mere "disposal," to prospective parents it is a real tragedy—hopes and dreams and a certain romantic vision of their child-to-be dashed before their broken hearts. But the fact remains that it does happen, and it happens for a reason.
The science of in vitro fertilization (IVF) has brought about advances in our knowledge of conception and survival of the zygote and subsequent embryo. We now know that there are many miscarriages that go undiagnosed, a fertilized egg unsuccessfully implanting or unable to do so because of severely distorted fusion of chromosomes. Since a lot of these miscarriages happen very early, even before implantation, a woman may not even miss a period. Such miscarriages are completely absorbed or fall away with what is seen as the routine menstrual flow. Taking this type of miscarriage into account, we're careful now to say that miscarriage happens in 20 percent of all diagnosed pregnancies. But total miscarriage risk is probably closer to 60 percent to 80 percent when the silent ones are considered.
At first the thought of such an increased miscarriage rate seems astonishing, but when one realizes how many things must go perfectly to make a baby, it's a wonder that it happens at all. "Miracle" is never a worn-out word for a baby.
As physicians, we obstetricians must treat the discarding aspect of miscarriage scientifically and the human tragedy aspect with compassion and understanding.
Miscarriage can happen for a number of reasons. Almost always it is because of some random genetic mismatch making the fetus unsuited to progressing all the way. Once again, we're at the mercy of the biological rules. It is nature's way of assuring a continuing healthy species.