Twenty years ago, my twin sister Sarah signed us up for a twin research project out of the University of Chicago, our contribution to science. We were excited that, even as fraternal twins, we might have the opportunity to participate in the study. 

To get started, they sent us DNA kits to verify what kind of twins we were. Fraternal twins come from two separate eggs fertilized by two separate sperm. Therefore, their DNA is not identical. Basically, they are siblings born at the same time sharing about 50% of their DNA. We swabbed the inside of our cheeks and sent our genetic material through the mail. We weren’t expecting any news. When we were born, the doctor said we were fraternal twins, because there were two placentas. What we were hoping for was plane tickets to Chicago.

Three weeks later, we received letters telling us that we were monozygotic. Identical twins. Ninety-nine percent matching DNA. We were shocked.

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My 87-year-old father is hard of hearing, and while he went to the trouble of acquiring hearing aids, he has never worn them. This allowed the cardiologist to have a private conversation with me in the examination room as my father sat behind him on the paper-covered table, his legs dangling. 

“Why hasn’t your father seen a cardiologist in years? Since his bypass surgery? He’s in bad shape.”

“Because he was a grown man in charge of his own healthcare and now his daughters are,” I said calmly. 

“Oh.” The doctor sat back. “There’s a daughter in the next examining room doing the same thing, I guess.”

“It must be ‘take your father to cardiology day,’” I said.

The doctor walked us down the hall, ordered three ultrasounds for my father, to be performed right then, and left us in the waiting room. My father was impatient and wanted to leave; it was nearing mid-day. I assured him that this was the best way to get this done—all in one visit. Normally, it would take weeks to get an appointment and we’d have to go to another location. I don’t think he’d eaten yet, and it was a point of pride that he didn’t start drinking until noon. 

Following the ultrasounds on his carotid arteries, his heart, and his aorta, the doctor, looking agitated, took us in the hall and sat us down. He stood over us as he gave us the bad news. My father looked at him, then at me as I repeated loudly what the doctor said, nearly shouting. In this way I was the one who told my father he was in congestive heart failure, his arteries were nearly clogged, his aorta enlarged, compensating. In this way I told him he could have a stroke or heart attack at any moment.

After our conversation with the cardiologist, my father went down the hall to the restroom, and I went to the front desk to make an appointment for a stress test. When I finished, I waited by the closed bathroom door. After a few minutes, I caught my father’s blue t-shirt out of the corner of my eye and raced back toward the front desk. Somehow, I’d missed him. He was standing by the elevator with his phone in his hand.

“Dad,” I called.

“There you are,” he said, holding his phone for me to see. “I was just calling you.”

The phone’s screen displayed Sarah’s name. I’d spent nearly four hours with him, and he thought I was her.

I didn’t correct him.

“It’s not good,” he said.

“No, it’s not.” I hugged him. He stood like a stunned child who had been hit on the head by a ball right before the crying started. But he didn’t cry as I gave him a hug, and he didn’t hug me back.

When we arrived back at the apartment, my mother asked how it went. My father pointed his thumb at me and said, “Ask Sarah.”

“That’s not Sarah. That’s Susan.”

He glanced back at me and went to make his overdue whiskey.

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The truth is that identical twins can have separate placentas. The only way to know for certain if you are identical twins is a DNA test. Whether identical twins share a placenta depends on when the zygote splits. If it happens early, within days of fertilization, there are two placentas.

If it happens later, they share a placenta. 

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There are three stories told about Sarah and me that happened before our memories kicked in. The first is our birth story. The doctor delivered Sarah first because I was breech and had the umbilical cord around my neck. I was the smaller, some may say weaker, one. My aunt instructed my mother to name my sister Sarah after their mother, because she was more likely to survive. This aunt became my godmother. Apparently, in between our deliveries, the doctor left the room to deliver a baby boy next door. 

When we got the test results back stating we were identical, I still wanted to hold onto the placenta theory and thought perhaps with all the drama of our births, the doctor had miscounted placentas, adding one (perhaps from the boy next door) to our delivery room, because if we were identical there could only be one.

This is what the two of us had repeatedly informed people as they pointed and insisted that we were identical twins. We’d say in a condescending tone, “We are fra-ter-nal. It’s a medical fact. There were two placentas, so there’s no way we could be identical. Geez!”

Despite having the facts in our favor (or so we thought), strangers stared and compared as if we were wax figures in a museum instead of human beings looking back at them. Twins weren’t as common then as they are now. We were like mini celebrities. If an acquaintance found out I was a twin, I’d often hear, “How could you not tell me?” as if I’d kept my essential self from them. When Sarah and I were out in public, people asked if we were twins and beamed with pride that they were able to identify us. In conversation, people would inevitably ask if we’d ever traded places, switching seats in class or at the dinner table. No, we did not. They wanted to know if we’d tricked boyfriends or our husbands. Why would we do that? Why would we want to? Do you want to switch boyfriends with your sister or your best friend? Or, “Which one of you is the evil twin?” We were the stuff of movie premises and soap opera plot twists. Oh, the adventure, the intrigue, the manipulation!

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The cardiologist sent notes after my father’s stress test. He began by writing that he had a very extensive conversation with one of Mr. Barr’s daughters. This time it was my older sister Mary who took him for the test. He wrote about our father’s bypass surgery twenty-three years ago. Again, he brought up that my father had not been seeing a doctor or having regular workups. Most likely his bypasses were closed. They’d need to do a cardiac catheterization to see if something could be opened interventionally. Perhaps a defibrillator would benefit him. He should stop drinking. Go to rehab. The doctor ended by saying that the family should come into the office to discuss a plan.  

Despite the 250-word note, in which the doctor mentioned “sudden death” twice, my father wanted no part in a plan to undergo procedures or quit drinking.

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One in eight pregnancies begins as twins. Only one in ninety births results in twins. Earlier in the pregnancy, one of them suddenly disappears. 

Maybe this is why people are obsessed with twins: they have a sense of loss, something missing, someone missing. It’s more than fantasizing about a person who could easily step into their place, their job, their relationship to take over and give them a break from the mundane and let them live another life. I think they long for a twin, so they’d never feel alone. They’d be understood. They’d have someone created just for them. 

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Another story we’ve heard about us when we were babies was the time my mother decided we were old enough to be put into separate cribs instead of sharing one. She put our cribs on opposite sides of the room. After we were put to bed for the night, I stood up and flicked on the light switch. Sarah sat with her back against her crib and banged it again and again until the crib scooted (there were no wheels) across the room and was next to mine. By the time my mother arrived to investigate, we were asleep in our individual cribs, with our arms outstretched through the bars, holding hands in the light-filled room.

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Once the news of our DNA test results sunk in, Sarah refused to acknowledge we were identical twins. While she believes in science (she was not a flat earther), somehow, she didn’t believe in this. She said I could believe what I wanted, but we needed to agree to disagree.

My mother agreed with her. Science be damned. Even though the inaccuracy of our fraternal twinness was proven, my mother wasn’t giving up the two-placentas-equals-fraternal-twins story. Her response to the news: “Well, I don’t care what they say. I always raised you to be individuals.” 

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My father knows who my siblings are. And he used to know me, and I think for the most part, the difference between Sarah and me. It’s not that he called us by the wrong names sometimes, that happens to everyone. It’s that he has consistently called me Sarah since the death of my husband Peter to cancer eight years ago. My father seems to have forgotten me. There’s some strange mental gymnastics happening. Maybe the loss of his son-in-law was too much for him to bear. But they weren’t close. Or maybe his daughter losing her husband, his grandchildren losing their father was too much. But we’re not close. Somehow, in my father’s grief, I disappeared. Now there was one twin, and her name is Sarah.

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Mirror twins are identical twins, but less than 25% of identical twins are mirror twins. As the name suggests, they will be the mirror image of each other. One left-handed, the other right-handed. The swirls of hair on the top of their soft heads will turn in opposite directions. This is because the zygote splits after the egg has developed a left and a right side. Always they share a placenta because the zygote doesn’t split early enough for there to be two.

The other story. When Sarah and I were three or four years old, my mother took all the children shopping for Easter outfits. Traditionally, she dressed us (the twins, not the other siblings) in the same outfits for the holidays. But that year, standing in front of the dressing room mirror in identical dresses, Sarah said, “Okay, but this is the last time.” And so it was.

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Twenty years later, I wonder if Sarah regrets signing up for that twin study. The University of Chicago ghosted us. We were never flown out, never scrutinized with CAT scans or MRIs, or probed with needles or endless questionnaires. I tease her that she doesn’t want to be my identical twin. She says she loves being my twin. She says not to take it personally that she doesn’t want to be identical. How can I not? I’m the only one here.

To call ourselves identical opens us up to further scrutiny. I understand she doesn’t want to be stared at, but at the same time I want to be seen by her, by my family.

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Earlier this year, I visited my parents’ apartment with my daughter. While I was helping my mother get ready for bed, my father stood in the living room pulling pictures from the bookcase and telling my daughter about them. There was one of him holding a microphone. He told her about running karaoke at a few bars, how he’d sing a couple songs to the get the crowd going. My daughter enjoyed this rare moment of bonding. Next, he shared a photo Sarah had taken of the whole family at Christmas—my parents, all their children and spouses and grandchildren. My husband Peter was in the front sitting reclined on the floor.

“That’s Peter.” My father pointed to him. “He died too young. He was the best person you could know.” My daughter stared at him as he continued to gaze at the photograph, waiting for him to realize who it was he was talking to. He returned the photo and reached for another.

As we waited for the elevator on our way out, she cried as she told me what happened. I hugged her and she hugged me back. I apologized. I had tried not to take it personally that my father didn’t see me as Susan, but I had no idea that he’d detached my kids from me, from Peter, too. This was more upsetting to me, perhaps because I’d been accepting of my father’s behavior, letting it roll off my back, making light of it. But now seeing the hurt in my daughter, I was angry. How could he make her feel this way, and do it in such a way that denied her her own father?

I didn’t confront him. How can you confront someone who doesn’t know who you are?

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Twin research is so valuable because twins are born at the same time, the result of the same parents, and reared in the same environment. That’s a lot of controls to have in place when looking at nature versus nurture. Identical twins are even better with their matching DNA. However, in utero resources may not be evenly distributed, because of the positioning of the fetuses and the placenta(s) and/or the difference in the width and length of each umbilical cord. Their DNA is manifesting uniquely before their first breaths. 

When I tell our birth story, I tease Sarah that she put the umbilical cord around my neck, that she was trying to kill me. When she tells the story, she insists she’s the one who saved my life. She’s the hero. Our kids love these opposing narratives.

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When we first got the DNA results, Sarah’s and my children loved the idea of being genetically half siblings. The four of them were all born within four years of each other and spent a lot of time together when they were little, before soccer and crew and plays and performances filled their schedules. 

Through my husband’s many surgeries and treatments for cancer, Sarah often took the kids to her house so I could stay at the hospital with Peter. She cared for them as I cared for him. When he died, I took comfort in the thought that if anything happened to me, they’d have Sarah. Sarah who knew me the best, who loved them the best next to me. Sarah who could step in and take care.

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Recently, my sister Mary took our father to visit the bar he still owns but that other people are operating. She called right away to tell me of the visit. Our father was greeted as a returning hero, which made him very happy, she said. Everyone kept asking her if she was Susan, the one who wrote the novel, the one about South Philly. 

“No, no,” she said, “that’s my sister Susan.” 

Mary wanted me to know that he knew me at some point, because people at the bar knew me. It was very kind of her. 

One of the people who asked her if she was Susan was Sue, who had been bartending there for decades. She said when she met our father that’s the first thing he said to her, “I’ve got a daughter named Susan.” 

The one time my father called me was many years ago when the kids were little and Peter was healthy. He asked me to get down to the bar right away; he needed me to run it. I freaked out momentarily because I’d never bartended. My father had never asked anything of me.

Then, I said, “This is your daughter.”

“Not Sue the bartender?”

“No, Dad.”

He hung up.

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Twenty years ago, Sarah and I were in my kitchen with our mother discussing the DNA test news. Our mother told the old familiar tale. She and all four children (my little sister wasn’t born yet) were downtown shopping at Strawbridge’s for Easter outfits. Bored unless it was our turn, Sarah and I hid in the circular racks while my mother selected clothing for our brother and Mary. My mother always had at least one moment of sharp anxiety that we’d gone missing. Finally, our turn arrived. As always in this story my mother presented us with the identical dresses. Then my mother said, “…and Susan said, okay but this is the last time.”

I turned from the kitchen sink. “Who said that?”

“You,” she said. “It was you.”

Was this true? How could we have misremembered this story for so long? In the early stories of Sarah and me, it was always Sarah who expressed herself. She was the leader, and I was the follower. Sarah was the stronger one. Sarah spoke her mind. Sarah took control over the situation. I just switched on the light. I was in my twin’s shadow. My father used to call me tag-a-long.

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For a long time, I was convinced that my father thought he was never going to die, but he’s been letting go these past few years. Selling property. Handing over his finances to Mary. Taking care of our mother. He sold his car, done with driving. The truth is he is going to die sooner rather than later, and probably suddenly.

It’s not like we were close and I’m trying to get that back. I can count the times we were alone in conversation on one hand. It’s that I know now we will never have a conversation about our relationship. The possibility of us bonding, even briefly, is lost. For him, I no longer exist.

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Scientists call the twin that disappears early in pregnancy, the “vanishing twin.” They aren’t certain what happens. The vanishing twin is either assimilated into the other twin or absorbed into the parent.