The Unsettling Ambiguity of Early Pregnancy

Part of the reason that viability is so difficult to determine comes down to arbitrary rules. For example, guidelines in the U.S. and the U.K. define one of the indicators of miscarriage as an empty gestational sac of different sizes—sixteen millimetres in the U.S. and twenty millimetres in the U.K. “This leaves a window of 4 millimetres—a huge margin when you consider the size of an embryo,” Clancy writes, “where US radiologists would diagnose miscarriage and UK radiologists would not.”

Medical practitioners typically determine early viability based on gestational age, which is normally calculated from the first day of a pregnant person’s last menstrual period. (According to this method, a fetus is “born” a couple of weeks before the sex or procedure that conceived it.) This measurement, known as the “last menstrual period” method, is highly inaccurate, because it assumes a standard twenty-eight-day cycle; women whose cycles are longer or shorter than four weeks routinely present embryos that can appear “too small” or “too big.” If the timing is off by a week or two, a healthy early pregnancy can seem as if it’s not progressing as it should.

One of the patients that Clancy interviews was given, at different times, two fetal-age estimates, which varied by four weeks. Based on the patient’s last period, her doctors estimated that she was about ten weeks pregnant, but, according to the size of the embryo, she was about six weeks pregnant. When the patient started bleeding, which can be normal in early pregnancy, her doctors didn’t know if this was a six-week pregnancy that was potentially viable or a ten-week pregnancy that she had miscarried. (After two weeks of uncertainty, she was diagnosed with a miscarriage, and continued to bleed for another six weeks.)

Four weeks is a very large margin of error. A person might be diagnosed with either a continuing pregnancy or a miscarriage, and that diagnosis would depend on where they live, which hospital they visit, and who their attending physician is. But much of pregnancy exists in what Clancy calls a “significant middle space” between viable and nonviable, which clinicians attempt to capture with the term intrauterine pregnancy of unknown viability, or I.P.U.V. The terminology can be applied to pregnancies without a yolk sac, or pregnancies with a yolk sac but no visible embryo, or pregnancies with an embryo but no detectable heartbeat—cases that might otherwise be diagnosed as miscarriages. Clancy cites one research report that found that, of about a thousand cases of I.P.U.V. gathered in the U.K., approximately one-fifth turned out to be viable pregnancies.

The category of I.P.U.V. is helpful because “unknown viability” is often a more honest description of a pregnancy’s early stages than either viable or nonviable. But the uncertainty that comes with an I.P.U.V. diagnosis also intensifies the state of limbo that so often comes with the experience of miscarriage, during which most people, Clancy writes, have “no idea whether to hope or to begin to grieve.”

This waiting is not just a part of miscarriage. All pregnancies involve significant waiting: waiting for a heartbeat; waiting for an embryo to pass multiple stages, from successful implantation to placental approval; waiting for various test results at eight weeks, twelve weeks, sixteen weeks; or waiting for nothing in particular but hoping for the best.

This is part of what makes an online pregnancy announcement so strange: it implies that the experience of “finding out” is a singular moment. Many things can happen between peeing on a stick and having a baby, and confirming a pregnancy is not so much an experience of “finding out” as it is a process of ruling out all other possibilities, gradually homing in on a most likely outcome. “Life is a movie, not a picture,” is the way Clancy’s own doctor put it.

A lot of early miscarriages happen as part of a natural process of discarding “errors.” Sometimes the body defines these errors without us even knowing: with chemical pregnancies, a person is pregnant—that is, they have successfully completed gamete fusion and embryo implantation—and they miscarry around the same time that they expect their period. If they weren’t looking for it, they would never know they were pregnant.