Being the Eldest Daughter Might Have Set You Up for PCOS

When I was first diagnosed with PCOS (polycystic ovary syndrome), I thought of it as simply bad luck. I know it's fairly common and I was among the unlucky ones, but as I started joining online forums, talking to friends who shared the diagnosis, and reading more about it, I came across the odd realization that a majority of us are eldest daughters. Is this a coincidence? Is this just a particular instance in my social circle? There’s a known tendency for eldest daughters to overextend themselves in the care of others, and I’ve personally taken it up a notch by working in a draining nonprofit field that requires me to deal with trauma and emergencies on a daily basis. Many of my fellow PCOS-diagnosed eldest daughters were in similar situations, so is that it? What exactly is the correlation between being an eldest daughter and being diagnosed with PCOS? What exactly is the correlation between being an eldest daughter and being diagnosed with PCOS? I went looking for the data and details around that coincidence, and it turns out the internet already had a name for it, and a fully formed theory to go with it. “Eldest daughter syndrome” has become one of those phrases that spreads because it resonates with millions of women who recognize themselves in the description of a girl who is hyper-aware of other people’s needs before she was even conscious of her own habit to do so. It’s something one does so naturally and enough times that it becomes who you are. Caretaking and being empathetic for others inevitably puts your body under stress, and when done constantly for decades, it hardens into a personality and, the theory goes, eventually into a body that reflects it. While I do believe the theory is true, I also think there's a lot more to it. The behavioral patterns aren’t just a psychological matter; they are also a biological one which leaves us with consequences harder to shake off than just habits or overall behavior. That’s where PCOS comes in. You were shaped before you arrived In February 2024, a team led by UCLA anthropologist Molly Fox published the results of a 15-year study that followed 253 mothers and their children from pregnancy through adolescence. The researchers wanted to know something narrower than “eldest daughter syndrome.” They wanted to know whether a mother’s psychological distress during pregnancy could shape how quickly her child’s body matured. So they measured mothers’ stress, anxiety, and depression at five points across pregnancy, then tracked their children’s puberty for the next decade and a half, using saliva samples to measure the actual hormones involved. What they found was specific enough to set off alarms. Elevated prenatal distress predicted earlier adrenarche (that is, the early stage of puberty when the adrenal glands start producing hormones like DHEA-S, well before any visible sexual development) and higher DHEA-S levels overall. But only in daughters; and within daughters, the effect was strongest, by a wide margin, in the first-born. Sons showed nothing. The correlation held even after the researchers accounted for stress the child experienced after birth, meaning something about the pregnancy itself, not just the household or overall environment that followed it, appeared to be the culprit. The researchers’ own interpretation reaches for evolutionary biology: a mother under stress may be, in effect, recruiting her eldest daughter early, unknowingly priming her for social and caretaking maturity sooner, without necessarily accelerating reproductive puberty itself, so she’s available to help raise the siblings who come after her. And in their paper, they say so directly: this finding, they write, offers biological insight into the “eldest daughter syndrome” everyone’s been discussing online. This is not just a metaphor, but proof of what PCOS online forums have been noticing. How an early signal becomes a diagnosis For background, DHEA-S is an androgen, therefore one of the “male” hormones women produce in smaller amounts, and the same hormonal family implicated in PCOS, which, according to the World Health Organization , affects an estimated 8 to 13 percent of women of reproductive age worldwide and goes undiagnosed in as many as 70 percent of the women who have it. This is where things get interesting on a biological level. Early or exaggerated adrenarche (that is precisely the pattern Fox’s team found in first-born daughters of highly stressed mothers) is a recognized prepubertal risk marker for PCOS. A 2006 paper tracking girls with premature adrenarche into adolescence found the condition “can no longer be considered benign,” linking it to hyperinsulinemia and elevated androgen activity well before any ovarian symptoms appeared, and describing premature adrenarche as a potential forerunner of PCOS and metabolic syndrome. Meaning, PCOS may develop later in life, but the biological setup for it is already in place way before any ovarian symptom is felt. A more recent follow-up study out of Finland, which tracked young women with a history of premature adrenarche into their late teens, found meaningfully higher rates of hirsutism and lower levels of sex hormone–binding globulin, that is, the protein that keeps testosterone from running loose in the bloodstream. These results are considered higher in comparison to women without a history of premature adrenarche. The conclusion from these results is that our mechanism runs in one clear direction: adrenal androgen excess in childhood has a way of becoming ovarian androgen excess later on. Put plainly, what Fox’s study regards as an evolutionary trait goes hand in hand with the same early hormonal signature that may prime a first-born daughter to grow up socially faster. This is a documented risk pathway toward the exact condition so many eldest daughters report living with and what not always, but often, becomes PCOS. What the science doesn't say I want to be careful here, because it would be easy to overstate this into something more than it is. No study has measured PCOS diagnosis rates by birth order directly. Even if true, that specific data doesn’t exist yet. What does exist is a correlation worth noting: a hormonal marker (elevated DHEA-S via early adrenarche) that shows up disproportionately in first-born daughters of highly stressed mothers, and that same marker is independently established as a risk factor for PCOS. That’s a real scientific fact, but not the same as a straight line from “eldest daughter” to “PCOS diagnosis.” It’s also worth clarifying: the study is about first-born children who are girls, not “eldest daughter” in every sense the internet uses it, so a woman with two older brothers wasn’t part of this pattern. Which came first? Looking back to my time in utero, on one hand, my mother did not have a difficult pregnancy with me. My parents were financially stable, happy newlyweds, and I was a product of a fruitful honeymoon. There were no health or stress complications in sight. But there was a particular incident that did mark my time in utero. At six months of gestation, my uncle, my dad’s younger brother, unexpectedly died in his sleep. My mom often retells the story of receiving the call and rushing to the hospital to find my dad crumbling in tears in a chair outside the room where my uncle rested already dead. She ran to hug him and as he was seated, he wrapped his hands around my mom and cried with his face buried in the belly. At six months of gestation, babies already kick, and as a first-time mom, my mother was enjoying feeling those kicks, but after this fateful day there was no more kicking for a whole week. My mom worried that the shock and stress had killed me and decided not to say anything due to the already sad and stressful situation. And thankfully she eventually felt me move again. But now looking at Fox’s study, I do wonder if this was the moment in which my pre-born body and psyche felt my father’s tears, my mom’s stress, and prepared itself to come to care for others. I’ve often been told that my birth brought a lot of joy to this grieving family, and now I wonder if this was more internalized in me than the romantic family story gives credit to. The hormonal wiring was in place before birth, and being an eldest daughter is simply the pattern that makes it visible. So what came first, PCOS or being an eldest daughter? The UCLA research points to biology getting there first. The hormonal wiring was in place before birth, and being an eldest daughter is simply the pattern that makes it visible. That doesn't cancel out the lifestyle explanation. Stress still plays a part, but it was never the whole story, and knowing that changes things. It means that a diagnosis isn't a verdict on how well you managed your life. The pattern I kept noticing was real all along: eldest daughter after eldest daughter, the same diagnosis. It reaches women of every birth order, but eldest daughters are the ones statistically primed for it. If you're one of them, this isn't something you did, but it is something you can finally understand.