AMAB stands for “assigned male at birth” and AFAB stands for “assigned female at birth.” These terms describe the sex a doctor recorded on a person’s birth certificate based on their physical characteristics, typically the appearance of their external genitalia. The terms are widely used in healthcare, legal documents, and everyday conversation to distinguish between the sex someone was labeled with at birth and the gender identity they may later come to understand about themselves.
How Sex Gets Assigned at Birth
When a baby is born, a clinician looks at the newborn’s external genitalia and records the sex as male or female. This happens within moments of delivery and becomes the sex listed on the birth certificate. In most cases, that quick visual assessment lines up with the baby’s chromosomes, hormones, and internal anatomy. But sex is actually determined by a combination of factors: chromosomal pattern (XX or XY), the type of gonads present (ovaries or testes), the balance of circulating hormones, and the physical appearance of the genitalia.
These factors usually align, so the external check at birth is a reliable shorthand. But not always. Some babies are born with anatomy that doesn’t fit neatly into male or female categories, a natural variation known as being intersex. In those cases, a doctor still typically assigns a sex, sometimes based on incomplete information. This is one reason the language of “assigned” sex exists: it acknowledges that the label was given by someone else, based on external observation, rather than being an inherent fact about who that person is.
Sex Assigned at Birth vs. Gender Identity
Sex and gender refer to different things, though the two words have been used interchangeably for decades. Sex generally refers to biological attributes: chromosomes, hormones, reproductive organs. Gender refers to a person’s internal sense of who they are, along with the social roles and expectations a culture attaches to being a man, a woman, or neither.
For most people, their sex assigned at birth and their gender identity match. A person assigned female at birth who grows up identifying as a woman is cisgender. But for transgender and gender diverse people, the two don’t align. Someone who is AMAB may identify as a woman, nonbinary, or another gender entirely. Someone who is AFAB may identify as a man or as nonbinary. The terms AMAB and AFAB give people a way to reference the label they were given at birth without implying it defines their identity now.
Why These Terms Replaced “Biological Male” and “Biological Female”
Older language like “biological male” or “born female” implied that sex is a single, fixed characteristic. In reality, biological sex involves multiple components that don’t always agree with each other. A person can have XY chromosomes but develop female-typical anatomy due to hormone differences, for example. Researchers have increasingly pushed to use precise language: “sex” for biological attributes, “gender” for the social and psychological dimensions. The AMAB/AFAB framework fits that push because it describes one specific moment (what was recorded at birth) without making broader claims about a person’s biology or identity.
Major medical organizations have adopted this language. The World Professional Association for Transgender Health defines sex assigned at birth as “a person’s status as male, female, or intersex based on physical characteristics,” noting that it’s “usually assigned at birth based on appearance of the external genitalia.” The American College of Obstetricians and Gynecologists has committed to integrating language that reflects the broad spectrum of sex and gender identities into its clinical guidance and communications, moving beyond exclusively gendered terms.
Why It Matters for Healthcare
Your sex assigned at birth determines which organs you have, and that affects which health screenings you need, regardless of your gender identity. A transgender man (someone who is AFAB and identifies as male) may still have a cervix and need regular cervical cancer screening. Current guidelines recommend Pap tests starting at age 21, with HPV DNA testing added after age 30. Screening stops at 65 if results have been consistently normal. These recommendations apply to anyone with a cervix, not just people who identify as women.
This is why healthcare providers have started shifting toward organ-based language. Saying “people with a cervix” or “people with a prostate” instead of “women” or “men” ensures that transgender and nonbinary patients don’t fall through the cracks. Research shows that AFAB people in sexual and gender minority communities actually face a greater burden of cervical cancer compared to their cisgender, heterosexual counterparts, partly because they’re less likely to get screened when guidelines and outreach materials are framed in gendered terms that don’t feel relevant to them.
How These Terms Appear on Legal Documents
Birth certificates record the sex assigned at birth, and changing that marker later varies dramatically depending on where you live. In the United States, 13 states allow an “X” gender marker on birth certificates for people who don’t identify as male or female, and 20 states plus Washington, D.C., offer an “X” option on driver’s licenses. But the barriers to changing a birth certificate’s sex marker range widely. As of recent data, 11 states had the fewest barriers (no surgical requirement, no court order), 11 states had moderate barriers, and 29 states had the most restrictive policies, requiring proof of surgery, a court order, or not allowing changes at all.
This patchwork means that for many people, their birth certificate still reflects the sex they were assigned at birth even if their gender identity, their body, and every other document they carry say otherwise. AMAB and AFAB provide a neutral way to reference that original record without suggesting it’s the final word on who someone is.
Using the Terms Respectfully
AMAB and AFAB are descriptive labels, not identity labels. They’re useful when the context calls for it, like discussing medical history, filling out health forms, or explaining why someone’s birth certificate says one thing while they present differently. They’re not a substitute for someone’s actual gender identity. Calling a transgender woman “AMAB” as a way to avoid acknowledging her as a woman misuses the term. The point of the language is precision, not avoidance.
In everyday conversation, most people don’t need to know or reference someone’s sex assigned at birth. It comes up in medical settings, in legal paperwork, and in discussions about transgender experiences where the distinction between birth assignment and identity matters. When it does come up, these terms offer a straightforward, respectful way to talk about it.