If you want to understand the fickleness of pregnancy and the American laws that regulate it, one place to start would be a gas station in Iowa City, where a 31-year-old sat in the passenger seat of a gray Hyundai, making frantic calls. Her name was Stephanie Dworak, it was September 2021, and she was 20 weeks and five days pregnant. She’d already looked into the abortion clinics in her home state of Nebraska. For some of them, she was already too far along. Another one was booking three weeks out. She’d only started searching when she’d gotten a severe fetal diagnosis at 19 weeks; abortion was legal in Nebraska until 22. “They were very apologetic and just said that because of how far along I was, and their appointment availability, there was no way they’d be able to see me before I was at the 22-week mark,” she said.
That was what brought her and her husband Dave to Iowa City. The night before, they’d dropped off their 3-year-old with Dworak’s stepmom, a hair stylist, who’d taken the day off work to babysit. They’d both taken time off themselves. It would be a two-day procedure, so they’d booked a hotel. They’d left before dawn, driven 250 miles in time for their 8:30 a.m. appointment, and started yet another ultrasound — only to be told that, according to this scan, she was no longer eligible. “It read me as one week further along than every doctor in Omaha had,” she said. “So I was one day too far along for Iowa to do the procedure. I drove four hours to Iowa City and paid $250 for them to tell me, ‘Sorry, we can’t help you,’ and send me back to Omaha.’”
She’d screamed and cried. She’d begged them to do another ultrasound. She’d told them about the proteins in her urine, warning signs of pre-eclampsia. They were sorry, the staff said, there was nothing they could do. She and Dave stormed out. It felt weird to sit there panicking outside the clinic, in view of all the security cameras, trying to figure out their next move. Hence the gas station. After a few minutes of letting herself break down under the red Kum & Go sign, she was back on the phone, searching for an appointment in Minnesota or Colorado.
Gestational age is a measure we all use. We talk about it so much we hardly realize we’re talking about it at all. It’s written into laws and news reports, discussed from the NICU to the playground. A mom might say she gave birth at 36 weeks; a neonatologist might talk about the case of a 24-weeker. A law might limit abortion after 15 weeks; a journalist might write about a severe fetal diagnosis received at 19 weeks.
Those sentences make gestational age sound like a certainty, a fact, as incontrovertible as saying that today is Thursday. But that’s wishful thinking. Instead, gestational age is an estimate. Carefully thought out, obsessively researched, but an estimate all the same. “We have this fantasy that we can be exact about dating a pregnancy,” said Rosemary Reiss, co-director of obstetric ultrasound at Brigham and Women’s Hospital. “The only time it’s really true is when somebody has in vitro fertilization, and you know when the fertilized egg got into the uterus. Otherwise, the very best we can do is plus or minus five days.”
That margin of error is key. It’s a way of setting goalposts for our uncertainty. If you’re going to be even a little wrong about something, it’s best to know by how much you might be off — and that changes over the course of a pregnancy. It’s plus or minus five days early on, but plus or minus 10 by the trimester Dworak was in when she got to Iowa City. “The later you estimate gestational age, the more inaccurate your hypothesis is going to be,” explained Aris Papageorghiou, a professor of fetal medicine at Oxford. In other words, if a patient’s gotten a good estimate early on, go with that, and don’t redate the pregnancy. Certain state laws, though, don’t give doctors that liberty.
That day in Iowa City wasn’t the first time Dworak’s gestational age had been adjusted. When she first realized she was pregnant, her doctors in Omaha switched her from 8 weeks to 6 weeks and five days. That made sense. The initial number had emerged the traditional way, by starting the count from the first day of Dworak’s last period. The LMP, as OB-GYNs call it, is a proxy for a proxy: If all hormonal cycles proceeded like clockwork, then the LMP would be two weeks before ovulation, which would be around the time of fertilization. It’s a strange convention — “You’re two weeks pregnant before you even have sex,” said Papageorghiou — but the thinking is that you’re more likely to know when you started menstruating than to know when you were ovulating.
The trouble is, hormonal cycles don’t always proceed like clockwork. They might run on a slightly different schedule. They might be thrown off by anything from intense exercise to stress to medications. And not everyone remembers exactly when their last period started.
Dworak is a case in point. Hers was a wanted, planned pregnancy. She’d been tracking her periods on an app, and knew that her cycles hovered between 33 and 35 days. Of course a gestational age calculus built on a 28-day cycle was going to be off. Her doctors in Omaha were following the guidelines from the American College of Obstetricians and Gynecologists to a T: Confirm the LMP-based gestational age by taking measurements with an ultrasound, assume the fetus is an average size, then calculate about how far along the pregnancy ought to be — and if there’s a discrepancy of more than five days early on, go with the scan.
The ultrasound method is imperfect, too. It presupposes that all fetuses are an average size. As Papageorghiou put it, “That’s a fundamentally flawed assumption. It’s like saying, ‘My kid is this tall; how old is my kid?’” But some imperfect estimates are more imperfect than others.
At first, an embryo is hardly visible on an ultrasound, just a thickening on the wall of the yolk sac, surrounded by amniotic darkness. “We talk of it sometimes as being the diamond on the ring,” said Reiss, at Brigham and Women’s. Then, that thickening will expand outward, until it looks almost like a kidney bean — what had been a small, tasteful stone becoming ostentatious bling. Soon, it will start to look more recognizable.
At these early stages, the measurement to take is known as the crown-rump length, from the top of the head to the bottom of the butt. It’s possible to misread that distance, if you’re not careful, especially as the fetus begins to move. “It is about 13 weeks in this case,” Reiss said, pointing to a scan. “See how this baby is now arcing back a little bit here?” She switched to a different scan from the same appointment: “And here, it’s curling up? So that distance is not so fixed at this age.”
Eventually, with the fetus starting to scrunch up, the crown-rump length getting too big to fit onto one screen, sonographers move on to other measurements, like the diameter of the head, the abdominal circumference, and the femur length. As it did with the crown-rump length, the ultrasound machine itself plugs those numbers into a formula, to translate millimeters into weeks — and it’s possible that those algorithms might’ve contributed to Dworak’s gestational age whiplash in Iowa City. After all, as Katherine Grantz, a maternal-fetal medicine specialist at the National Institute of Child Health and Human Development put it, “That formula from 1984 was based on a pretty homogenous population. It was only several hundred women, and they were all white, from a single center in Texas.”
When she and her colleagues developed a new formula, based on a bigger, more diverse patient sample, they did shave off a few days from the margin of error later on in pregnancy. But they found that the old formula held up pretty well. Switching the formula could improve your margin of error a bit — but, for an individual, that was nowhere near the improvement you could make by simply using earlier ultrasounds to estimate gestational age.
It’s a question of biology. Every fetus starts out as a single cell, but could end up weighing 10 pounds or 3. The closer to term you get, the more that natural variation becomes visible. You might be looking for gestational age, and seeing a future career in the NBA.
There are cases in which someone didn’t have access to prenatal care and a late ultrasound is all you have. “You’re not sure if this a growth-restricted fetus or a well-grown fetus that’s poorly dated,” said Naima Joseph, a maternal-fetal medicine specialist at Beth Israel Deaconess Medical Center.
That wasn’t true for Dworak. She’d had seven previous ultrasounds, the earliest of which would have given the most accurate estimate. The clinic in Iowa just wasn’t able to use it.
“We are required to repeat an ultrasound for every abortion patient in Iowa. We would not have been able to use this patient’s records from Nebraska,” said Sarah Traxler, chief medical officer of Planned Parenthood North Central States. She couldn’t speak to Dworak’s case specifically, but explained why these situations arise in the health centers she supervises.
In a place like Minnesota, where the highest court has recognized the right to abortion under the state constitution, “we would have just used her gestational age from her providers in Nebraska,” she said.
“We were in an incredibly hostile state, and would not have — for potentially one singular patient — jeopardized our ability to care for every other patient that came to us.”
Sarah Traxler, chief medical officer of Planned Parenthood North Central States
But in a state with more byzantine restrictions, providers have to worry about legally protecting themselves, too. That means using the gestational age from their own in-house ultrasound, even if they know it may not be as accurate. That’s true in Iowa, and was true in South Dakota, when Traxler provided abortion care there, before Roe v. Wade was overturned and the state made the procedure illegal. “We were in an incredibly hostile state, and would not have — for potentially one singular patient — jeopardized our ability to care for every other patient that came to us.”
When Dworak told her story to a CNN reporter, right around the time of the overturn of Roe v. Wade, the episode in Iowa City didn’t make the final cut. The childcare, the 250-mile drive there, the $250, the devastating ultrasound, the crying and begging, the panic, the gas station, the 250-mile drive home — all of that was summarized in seven words: “After a desperate search across nearby states, the family settled on the Boulder Abortion Clinic in Colorado.”
Pointing this out is not meant as a critique of the CNN segment, but rather an acknowledgement about the complexity of pregnancy. There’s always some part of it that gets treated as flyover country. Even gestational age — that most basic fact of obstetrics — upon closer examination unfurls a dizzying array of possibilities. Legislation that treats it as a definite, knowable line is based on a fiction. Ignoring uncertainty only deepens the likelihood of inaccuracy.
It’s not so different from making exceptions for “the life of the mother.” When asked whether maternal-fetal medicine doctors were getting together to figure out which conditions officially count as deadly, Annie Dude, a North Carolina specialist in high-risk pregnancies, balked. “If you want to clear up what counts as a life-threatening condition, you would probably write a thousand-page textbook. It’s not something where I can just give you a list of 25 situations and be like, ‘These 25 things are what counts as life-threatening, and everything else is completely fine,’” she said. “I trained for 11 years to get my job. And I would have to talk to you for 11 years about all the situations that may arise that might constitute a life-threatening emergency. Because it’s not something that’s easy to spell out or clarify.”
There’s a similar nuance to every abortion, every pregnancy carried to term — each sentence a Russian Doll, a story nested within a story. In Dworak’s case, you could zero in on the thousands of dollars she and Dave spent to get this medical care. You could zero in on the fact that she’d spent over a decade working in food service — host, barista, Mexican restaurant, bakery — when needing to take this kind of time off would’ve meant losing her job. You could zero in on the six weeks of uncertainty, after they’d found out their fetus’ organs were growing in a sac outside of its body but before enough anatomy was visible to know the severity of the diagnosis.
You could zero in on how much she appreciated the Boulder Abortion Clinic’s care, how much she appreciated their relationship with a funeral home, so she didn’t have to find one willing to work with families who’ve had abortions. You could zero in on how much demand has risen for the Boulder Clinic’s services since Dobbs, how it is no longer able to see patients on short notice as it did Dworak. You could zero in on the way that Dworak had to call ahead, when she was sending the clinic cookies and cupcakes, so the staff wouldn’t mistake her package for a bomb threat.
The name the Dworaks had chosen was Oliver James. “James was my dad’s name, a little tribute there,” said Dworak. His ashes are displayed in their living room, along with his hand- and foot-prints.
That sort of experience can’t help but transform your thinking about pregnancy. “It is difficult, still, when I hear somebody announce that they’re having a kid,” Dave said. A friend or a coworker is standing there, thrilled — but his first reaction is fear, knowing just how much can go wrong. “There’s always that couple of seconds where I have to kind of work through my own feelings — and then move on to, ‘That’s awesome. Congratulations.’”
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This story is part of ongoing coverage of reproductive health care supported by a grant from the Commonwealth Fund.
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